Correctly determining the spatial distribution of steel corrosion within a structural member is critical for estimating the remaining service life of deteriorating reinforced concrete (RC) structures. While X-ray technology serves as a nondestructive inspection method, existing challenges persist, particularly in semi-automated corrosion boundary detection. This paper describes a deep learning-based semantic segmentation framework to autonomously detect X-ray images associated with RC, facilitating the visualization of nonuniform steel corrosion distribution. X-ray images were collected from a comprehensive experiment using RC specimens with various structural details by two accelerated corrosion methods. Four deep learning models were constructed, trained, and compared based on the database containing the original X-ray images and the corresponding pixel-level labels. The results demonstrate that the proposed autonomous detection method can segment uncorroded steel at a very high level of global accuracy without time-consuming work, outperforming traditional methods in terms of both accuracy and efficiency.

2011年東北地方太平洋沖地震の津波被害を受け，緊急避難先として津波避難タワーが建設されている．設置場所の検討時には最大規模の津波が想定されるが，地震断層の動きの評価に伴う不確定性により津波到達の予測時間は確率的に変動するため，その想定が安全側の解を与えるとは限らない．本研究では，ハザード評価，脆弱性評価，あるいは人の避難行動における不確定性を考慮した確率論的リスク算定のアプローチにより津波人的被害者の予測手順を提示し，それに基づき防災予算の制約下で避難タワーの設置場所を決定する手法を提案する．ケーススタディでは，南海トラフ地震の影響域に提案手法を適用し，津波ハザード評価手法の違いが避難タワーの配置に及ぼす影響を考察した．

Field investigations after recent large earthquakes have confirmed that several structures were severely damaged and collapsed not only by the earthquake, but also by the subsequent tsunami, landslide, or fault displacement. Effect of material degradation due to chloride attack on structural performance should be considered when structures are located in a harsh environment. In addition, climate change has produced typhoons and hurricanes with extreme intensity in recent years. Sea-level rise could cause severe storm surges and tsunamis, and global warming is accelerating the deterioration of structures. When structures are exposed to these different types of hazards, it can be difficult to ensure their safety and additional performance indicators such as risk and resilience are needed. Several lessons were learned about the importance of investigating individual structures from the perspective of ensuring network functionality. A probabilistic life-cycle framework for quantifying the loss of functionality of road networks including bridges is needed. A risk-based decision-making approach at the network level is required to identify the dominant hazard and the vulnerable structures that require strengthening and retrofitting. After a catastrophic event, the functionality of transportation networks can be significantly degraded, resulting in catastrophic economic impacts. To quantify the promptness of recovery, it has become common to use the concept of resilience. In addition, the economic, environmental, and social impacts of disaster waste management systems need to be examined in terms of sustainability. Consequences related to resilience and sustainability need to be investigated and implemented in the risk assessment of road networks under multiple hazards. Life-cycle design and assessment methodologies can incorporate risk, resilience, sustainability and multiple hazards, learning from the lessons of past disasters. This keynote paper provides an overview of measures to ensure the functionality of individual and spatially distributed structures under multiple hazards from the perspectives of reliability, risk, resilience and sustainability.

A novel analytical model is proposed to improve the accuracy of predicting the mechanical response of a strand with asymmetrically broken wires. This model incorporates a new approach to compute the contact force between the broken wire and the duct. When there is more than one asymmetrically broken wire, the previous method cannot handle this situation due to the large deflection of the center wire near the breaking end. This deflection results in a significant contact force between the center and broken wires. The omission of this force in the previous method leads to unrealistic solutions for two or three asymmetrically broken wires. This paper addresses the issue appropriately. The calculated results have been compared with those from a previous experiment, demonstrating satisfactory agreement. Furthermore, the proposed analytical model has been adopted to predict the mechanical behavior of the broken wire in multi-strand scenarios relevant to a prestressed concrete bridge. The contact force between strands is accurately calculated. The findings indicate that the axial force of the asymmetrically broken wire in multi-strands can recover after a short distance from the broken end. This recovery is attributed to the confinement effect of the other strands.

This paper aims to investigate shear performance and develop an equation for shear strength assessment of centrifugal forming hollow circular steel fiber reinforced concrete (HSFRC) piles in a practical manufacturing condition. The centrifugal forming was optimized using concrete mixes with different steel fibers. The shear performance and size effect of HSFRC and conventional hollow circular reinforced concrete (HRC) piles with/without stirrups were investigated. Results of X-ray visualization show that, after centrifugal forming, steel fibers were evenly distributed and reoriented in the circumferential direction of the piles, effectively enhancing shear performance. Even with a low steel fiber content of 0.5%, HSFRC piles achieve equivalent shear performance and less brittle behavior compared to HRC piles with shear reinforcement ratios of 0.27%. This implies that higher steel fiber contents can potentially be used to replace stirrups for a flexural failure. SFRC remarkably inhibited the size effect of HSFRC piles. Moreover, a proposed equation considering fiber orientation can better predict the shear strength of centrifugal forming HSFRC piles compared to existing equations.

To estimate the connectivity of a road network, it is crucial to evaluate the correlation of hazard intensities among individual bridge locations since the probability of multiple bridges being damaged simultaneously depends on the degree of this correlation. However, research on connectivity assessment of bridge networks considering spatial correlations associated with flood intensities is scarce in the literature. When quantifying the spatial correlation of flood intensities, modeling based on the stream distance rather than the Euclidean distance is required, taking into account that river flow is restricted only within the stream network. To achieve this purpose, a novel methodology is proposed to evaluate the spatial correlation of a stream network based on a geostatistical linear model and stream network covariance models. In addition, this study considers the spatial correlation of seismic hazard intensity. With the proposed method, it is possible to identify which bridges play an important role in ensuring the connectivity of the road network under multiple hazards, i.e. flood and seismic. As an illustrative example, the proposed method is applied to a hypothetical bridge network in Kumamoto Prefecture, Japan. The results demonstrate that improved network connectivity can be achieved by implementing a relevant retrofitting strategy for important bridges.

Sustainability considerations throughout the entire pavement life-cycle in the decision-making process under uncertainty are needed to achieve optimal pavement management from the perspective of the economy, environment, and society. A novel sustainability-informed management optimization of asphalt pavement is presented in this study. First, a deep neural network (DNN) model is trained using the Long-Term Pavement Performance (LTPP) database to learn the nonlinear and complex relationships among multiple performance indicators of asphalt pavement (i.e., the international roughness index (IRI), rut depth, and alligator and transverse cracking) and their associated parameters (i.e., the climate, traffic, and pavement structure and properties). Based on the multiple time-dependent limit-state functions incorporating the uncertainties associated with these parameters, the DNN model prediction, and the IRI measurement, Monte Carlo simulation is conducted to estimate the system failure probability of asphalt pavement. Finally, a genetic algorithm-based tri-objective optimization is utilized to find the optimal maintenance and rehabilitation actions that reduce the extent of detrimental economic, environmental, and social consequences during the pavement's life-cycle. The capabilities of the proposed approach are illustrated using LTPP asphalt pavement sections in Pennsylvania and Florida, USA.

Bridges and pavements are two major infrastructure components of a transportation network providing mobility of freight and commodities for economic vitality and access to a range of users as social benefits. However, the lack of a comprehensive infrastructure management system incorporating bridges and pavements inhibits accurate performance prediction, optimal maintenance actions, and the associated use of shrinking budgets. This paper presents an integrated probabilistic life-cycle connectivity framework for the performance analysis of transportation networks containing bridges and asphalt pavements by considering flexural and shear failure modes for prestressed concrete and steel bridges and four failure modes, including international roughness index, rut depth, alligator cracking, and transverse cracking, for asphalt pavements. In this framework, neural network-based deep learning models are used to assess the probabilistic performance of transportation networks and to provide guidance for the associated maintenance strategies. An existing transportation network consisting of bridges and asphalt pavement segments is selected to investigate its life-cycle connectivity reliability and component importance using the matrix-based system reliability method. Results show that the consideration of asphalt pavement failure probability has a significant effect on the probability of transportation network connectivity.

Chloride-induced corrosion of tensile rebars in reinforced concrete (RC) structures causes cracking in the concrete surface along corroded rebars. The width of these cracks could provide valuable information for estimating the amount of steel weight loss inside concrete beams. However, an experimental investigation revealed that the distribution of cracks in RC beams with multiple rebars was affected not only by pressure from the corrosion expansion of the corresponding rebar but also from that of adjacent rebars. This leads to a highly complex nonlinear relationship between crack width and amount of steel corrosion. In this study, a novel combined experimental-machine learning approach is developed to estimate steel corrosion distributions in RC beams. This procedure applies generative adversarial networks (GANs) to consider the effects of spatially correlated rebar corrosion in transverse and longitudinal directions. A pix2pix network is trained by the distributions of a dataset of steel weight loss that is generated based on random field theory with the statistical parameters identified using the experimental evidence and the distributions of a dataset of corrosion crack widths constructed using finite element (FE) analysis. Subsequently, the probability density function (PDF) of the flexural capacity for corroded RC beams is obtained using Monte Carlo-based FE analysis. A case study investigating the effect of the distributions of observed crack widths on the PDF of the flexural capacity for aging RC beams with spatially correlated rebar corrosion in transverse and longitudinal directions is presented.

The immense impacts of tsunamis can inflict substantial damage on coastal infrastructure systems during their lifetime and lead to considerable economic loss. However, with the increasing intensity and variability of sea-level rise due to climate change, evaluations of the life-cycle tsunami risk associated with cumulative loss have become increasingly complex since tsunami hazards are time-dependent. In addition, the number of earthquake events and the corresponding arrival times are substantially uncertain. Therefore, an accurate life-cycle tsunami risk assessment methodology should be established to appropriately develop disaster mitigation measures. This paper provides a novel life-cycle risk assessment of building portfolios subjected to tsunami hazards under non-stationary sea-level rise effects due to climate change. The cumulative loss of a building portfolio is evaluated through a compound renewal process based on earthquake interarrival time uncertainties and time-dependent risk. The earthquake interarrival times are modeled using a non-Poisson process based on historical data. Tsunami hazard curves that consider the effects of sea-level rise, estimated based on climate models, are obtained with tsunami propagation analysis. The time-variant annual risk is estimated based on reliability and building unit loss. Finally, a numerical procedure is proposed to estimate the life-cycle tsunami risk of building portfolios. An illustrative example is provided by applying the framework to several municipalities in the Kochi Prefecture of Japan to assess the effects of climate change on the life-cycle tsunami risk.

Repairing corroded flexural-deficient reinforced concrete (RC) structures using a hybrid scheme with stainless steel (SS) rebars and carbon-fiber-reinforced polymer (CFRP) sheets revealed excellent structural performance and contributes to lower maintenance costs in the remaining service life of the repaired structure. However, although cutting the bottom arm of stirrups in a hybrid repair method could affect the structural performance of shear-critical RC beams since this effect was not investigated in the past research. In this paper, structural performance of a group of shear-deficient RC beams repaired using the hybrid method is investigated experimentally to examine the effect of cutting the bottom arm of stirrup on the shear capacity of the repaired beams. The test variables included the longitudinal reinforcement types (i.e. carbon and SS), shear reinforcement configurations, and CFRP sheet wrapping schemes. Experimental results demonstrate that cutting the bottom arm of stirrup for replacing the corroded tensile rebar could significantly reduce the shear capacity of the retrofitted beams. Therefore, strengthening using CFRP sheet is needed to restore the shear performance of the retrofitted beams. Test results revealed that complete wrapping of CFRP sheet is effective to overcome the shear deficiency due to cutting the bottom arm of stirrup in the shear-critical RC beams. In addition, the effectiveness of CFRP sheet wrapping schemes on shear performance of SS-RC beams is approximately identical with that of CS-RC beams. Finally, a design methodology to repair the corroded RC bridge using hybrid method is developed and presented based on bending and shear tests.

A methodology for determining the optimal countermeasure for bridges subjected to ground motion and tsunami is proposed. Seismic and tsunami fragility curves of a bridge pier and bearing are developed considering the effects of seismic damage prior to tsunami action. The structural vulnerabilities against horizontal and vertical forces are investigated separately in this paper. Seismic and tsunami hazard curves are obtained assuming the occurrence of an earthquake. Uncertainties associated with fault movement, hazard intensity and structural vulnerability are considered based on Monte Carlo simulation. The expected recovery time of bridges (i.e. risk) is estimated based on the failure probabilities of bridge piers and bearings, and used to determine the optimal countermeasure for bridges. As an illustrative example, the proposed methodology is applied to bridges which would be affected by the anticipated Nankai Trough earthquake.

The colossal impact of tsunamis has been responsible for a significant loss to coastal infrastructure world-wide. However, due to the sea-level rise effects, the life-cycle risk assessment associated with the cumulative loss becomes intractable since hazards due to tsunami are time-dependent. A more accurate life-cycle tsunami risk assessment is needed to enhance the disaster preparedness of coastal communities. This paper presents a framework for life-cycle risk assessment of coastal residential buildings subjected to tsunami under sea-level rise effects. Earthquake occurrences are predicted probabilistically using a Poisson process based on historical data. Time-variant sea-level rise hazard assessment is carried out based on various climate models considering the uncertainties of emission scenarios. Monte Carlo simulation-based tsunami hazard assessment is performed to estimate the tsunami hazard curves considering sea-level rise effects. With the fragility curve of building structures developed from historical tsunami damage data, the tsunami risk of coastal building is estimated based on tsunami hazard considering sea-level rise effects, fragility curve, and the unit loss of individual buildings. An illustrative example is presented by applying the proposed framework to several municipalities in Kochi Prefecture of Japan. The effects of sea-level rise and earthquake occurrence on the life-cycle risk are discussed.

Asphalt pavement should be represented as a series system of limit state functions associated with the international roughness index, rut depth, alligator cracking, and transverse cracking. Traditional regression-based prediction models are too simplified to account for the relationship between pavement performance and the operating conditions associated with climate, traffic, pavement structure and property parameters. In this study, a deep learning model based on bidirectional long short-term memory neural networks is trained using the long-term pavement performance database to learn the nonlinear and complex relationship between four performance indicators and their associated parameters. Based on multiple time-variant limit-state functions incorporating the uncertainties associated with these parameters, deep learning model prediction, and international roughness index measurement, Monte Carlo simulation is conducted to estimate the system reliability of the asphalt pavement. In an illustrative example, the effects of different parameters on the life-cycle system reliability are investigated based on two pavement sections.

The devastating consequences of tsunamis on coastal infrastructure have highlighted the urgent need for effective disaster risk reduction strategies. To mitigate tsunami disasters, the insurance industry plays a vital role in implementing risk transfer measures by providing financial protection against asset damage. However, the current research on catastrophe insurance policies for coastal infrastructure lacks consideration of climate change effects. It is essential to take into account the non-stationary effects of sea-level rise to develop long-term tsunami disaster mitigation measures and promote socioeconomic resilience in coastal communities. This paper aims to provide an insurance portfolio optimization framework for coastal residential buildings subjected to tsunamis considering non-stationary sea-level rise effects based on a stochastic simulation approach. A spatiotemporal probabilistic sea-level rise hazard assessment is carried out by utilizing available climate models and considering several emission scenarios. Tsunami propagation analyses under various sea-level rise cases are performed to evaluate the time-variant tsunami hazard curves based on Monte Carlo simulation. A life cycle-based stochastic insurance claim model associated with the cumulative loss of building assets is developed based on a non-stationary compound renewal process. Finally, a sample average approximation method is leveraged to estimate the optimum basic insurance premium rate by maximizing the insurer’s profit under a cost-constrained insurance purchase decision of homeowners. As a case study, the proposed framework is applied to multiple municipalities situated in the tsunami-prone region of Kochi Prefecture, Japan. Sea-level rise substantially decreases the maximum profits of tsunami insurers and increases the premium rate and ruin probability.

Structural performance of RC members is significantly affected by localized corrosion on steel reinforcement. It is essential to study the effect of spatial steel corrosion on their structural performance assessment. Artificial chloride environment (ACE) method is regarded as an appropriate accelerated-corrosion technique for inducing steel corrosion similar to that under natural conditions. However, it is time-consuming. Researchers prefer to use the galvanostatic (GS) method by adjusting the current density. Nevertheless, applying different current densities causes a substantial difference in steel corrosion and structural behavior of RC members. This paper aims to investigate the spatial growth in steel corrosion and structural behavior of RC beams corroded by using the ACE method. Experimental results are compared to those associated with the GS method. Finite element analysis considering spatial steel corrosion is employed to simulate the structural performance of RC beams. Recommendations on suitable current densities to be used in a laboratory test are provided.

Infrastructure systems, such as bridges, are a driver for the economic growth and sustainable development of countries. Similarly, the development of operation and maintenance strategies for infrastructure systems may aim at optimal management using Key Performance Indicators (KPIs) such as reliability, redundancy, availability, safety, economy, environmental performance and resilience. Recent research and development projects, such as COST TU1406, highlight that infrastructure managers make decisions based on a mix of qualitative and quantitative data from various sources paired with models of various levels of complexity as well as expert judgement. Similarly, recent state-of-the-art academia reports on a variety of different decision-making models applicable to the optimal management of infrastructure systems may be used. Within IABSE Commission 5 on Existing Structures, Task Group 5.4 has performed a survey on implemented decision-making models among 23 infrastructure managers from 20 countries. It highlights some similarities in relation to KPIs, condition rating and limit state checks. This has stimulated the standardisation of decision making. The application of risk-based methods, performance prediction and intervention modelling are somewhat more scattered and may call for further research and development as well as training. The need to bridge the gap between implemented decision-making models and research is of paramount importance.

This paper presents a model-based probabilistic structural identification that uses the deflection of prestressed concrete bridges (PSCBs) as observational information to perform Bayesian inference on the state variables associated with creep, structural rigidity, dead loads, shrinkage and prestress. The creep development is modeled as a stochastic process, and the structural rigidity is modeled as a stochastic field using the Karhunen–Loève transform. By incorporating the stochastic process/field into the inference frame, detailed information on structural states can be extracted. Considering the high dimension of the state variables, their posterior distributions are derived by the Hamiltonian Markov chain Monte Carlo (HMCMC) algorithm. As an illustrative example, two sets of deflection measurement of a case bridge are used to update the state variables in a sequential manner. Bayesian inference can calibrate the state variables, while the uncertainties associated with the state variables can be reduced. A K-means analysis can reveal the typical modes in the joint posterior distribution of the state variables, corresponding to the typical failure modes in the attributive analysis of the excessive deflection. The updated state variables are used in the probabilistic condition assessment associated with the deflection evolution.

To enhance the seismic resilience of reinforced concrete (RC) bridge piers, a novel friction pendulum system was developed. It consisted of a friction pendulum and a spherical sliding surface that were constructed from conventional steel and concrete. In comparison to commercial isolators, the complex spherical shape was realised using a three-dimensional printer to fabricate an acrylic glass mold, which allowed a significant cost savings in production. The system was distinguished by stable oscillation and a significant reduction in response accelerations on the flat surface. The inclined part acted as a restoring force that limited the residual displacement. However, these properties were confirmed experimentally using only small specimens. To characterise the fundamental properties of the system, a bidirectional shaking table test was performed in this study to investigate the size effect on the seismic performance of the proposed system. The test results demonstrate that the excellent performance in reducing the response acceleration and residual displacement is independent of the specimen size. In addition to the dependency of the friction coefficient on the sliding velocity and axial pressure, the impact force was observed to increase with the superstructure weight. Furthermore, a simplified method for estimating the maximum and residual displacements of the proposed system is presented.

The time-dependent deflection data collected by a structural health monitoring (SHM) system contains information indicating the damage accumulation of prestressed concrete bridges (PSCBs). However, for this information to be used, the results must be fully translated into reliable metrics. Model-based structural identification (SI) targeting the time-dependent deflection of PSCBs is affected by time-dependent material behavior such as creep and shrinkage as well as the unknown path of structural deterioration, which should be considered in a stochastic volatility model (SVM). This paper presents an inference framework for an SVM conditioned on the time-dependent deflection of PSCBs. In this framework, the augmented state space includes the full ranges of the unobserved state variables affecting the time-dependent deflection of PSCBs, namely, structural rigidity, creep, shrinkage, prestress level and dead load level, along with the volatility parameters associated with the deterioration path of structural rigidity, which is modeled via the Wiener process. Exploiting the latent structure of the SVM, a cyclic Markov chain Monte Carlo (MCMC) sampler is proposed to draw samples from the joint posterior distribution of the unobserved state variables and volatility parameters. In an illustrative example, two-year continuous deflection monitoring data of an existing bridge are utilized as the target information for inference. The updated model can indicate the accumulated damage of the case bridge over the monitoring period. The proposed SI framework is able to support accurate probabilistic analysis of the time-dependent deflection of PSCB.

Tsunami-induced disasters present a significant threat to coastal communities. Under the effects of sea-level rise due to climate change, tsunami occurrence frequency and intensities would increase in a nonstationary manner due to the long-term progressive trend in the variability in sea level. Therefore, the reliability of coastal infrastructure systems affected by tsunami hazard will diminish over time. A procedure for hazard assessment that integrates tsunamis occurring at random times with evolving sea-level rise should be established. This paper presents a novel framework for the time-variant assessment of tsunami hazard considering the effects of nonstationary sea-level rise due to climate change based on a non-Poisson stochastic renewal process. A time-variant probabilistic sea-level rise is modeled by utilizing various climate models and existing data reported in several studies. The conditional tsunami hazard curves considering sea-level rise are estimated by performing tsunami propagation analyses under different sea-level rise cases and by Monte Carlo simulation, considering the uncertainties associated with earthquake fault movements. Finally, the new concept of time-variant tsunami hazard assessment considering the nonstationary effects of sea-level rise is developed according to a non-Poisson stochastic renewal process. An illustrative example is provided by applying the proposed framework to several municipalities in the Kochi Prefecture of Japan that are subjected to the anticipated Nankai-Tonankai earthquake. The effects of sea-level rise on time-variant tsunami hazard under Poisson and non-Poisson processes of earthquake occurrence are discussed.

Many bridges would be washed away due to giant tsunamis caused by the anticipated Nankai Trough earthquake. The accelerated bridge construction (ABC) concept should be applied to temporary bridge construction to save on-site construction time and help roads reopen immediately after the event. In this paper, a temporary bridge using precast reinforced concrete (RC) blocks with connections composed of steel shear keys and carbon fiber-reinforced polymer (CFRP) sheets is proposed. The proposed bridge facilitates rapid recovery from natural disasters and accordingly enhances disaster resilience. Bending and shear tests are conducted to investigate the effects of the proposed connection on the structural performance of beams. The experimental results indicate that the connection with an adequate CFRP sheet length provides sufficient flexural capacity for temporary bridges and does not negatively affect the shear capacity. Moreover, a 3D finite-element (FE) model is applied to simulate the bending tests. The FE model provides good agreement with the experimental results and can be applied to design the structural details of full-scale RC blocks.

To develop disaster mitigation measures in earthquake-prone regions, it is essential to evaluate the deterioration of bridge network functionality considering the damage to individual bridges. This paper presents a novel framework for probabilistic connectivity assessment of bridge networks under seismic hazard considering the spatial correlation of ground motion-induced damage. In the proposed methodology, the connectivity is quantified as the probability that a path does not exist between origin-destination pairs after a seismic event. As an illustrative example, an hypothetical bridge network in Owase City, Japan, affected by the anticipated Nankai Trough earthquake is analyzed. The effects of the spatial correlation of ground motion-induced damage on the road network are investigated. By applying the proposed method, the probabilistic connectivity in the analyzed road network can be easily estimated. The connectivity depends strongly on the seismic hazard and the spatial correlation associated with the damage state of bridges in the network.

The changing climate with resulting more extreme weather events will likely impact infrastructure assets and services. This phenomenon can present direct threats to the assets as well as significant indirect effects for those relying on the services those assets deliver. Such threats are path-dependent and place-specific, as they strongly depend on current and future climate variability, location, asset design life, function and condition. One key question is how climate change is likely to increase both the probability and magnitude of extreme weather events under different scenarios of climate change. To address this issue, this paper investigates selected effects of climate change and their consequences on structural performance, in the context of evolving loading scenarios in three different continental regions: Europe, North America, and Asia. The aim is to investigate some main place-specific changes of the exposure in terms of intensity/frequency of extreme events as well as the associated challenges, considering some recent activities of members of the IABSE TG6.1. Climate change can significantly affect built infrastructure and the society by increasing the occurrence and magnitude of extreme events and increasing potential losses. Therefore, specific relationships relating hazard levels and structural vulnerability to climate change effects should be determined.

This article presents a novel system reliability-based framework for multi-objective optimisation of preventive maintenance (PM) management of in-service asphalt pavement. To accurately predict the international roughness index (IRI) sequence of pavement sections, a long short-term memory (LSTM) neural network that considers the spatiotemporal correlations between IRI sequences is trained with data retrieved from the long-term pavement performance (LTPP) program. Based on time-dependent limit-state functions (LSFs) incorporating the uncertainty associated with LSTM neural network prediction and the observational error involved in IRI measurement, Monte Carlo simulation (MCS) with importance sampling (IS) is adopted to calculate the reliability of pavement sections. Pavement sections located in New Mexico and Montana are selected as illustrative examples. Tri-objective optimisation processes are investigated by maximising user benefits (i.e. improved system reliability) and agency benefits (i.e. extended service life) while minimising the associated life-cycle cost (LCC) (i.e. user and agency costs) with multi-objective genetic algorithms (GAs). The obtained Pareto solution sets may assist decision-makers in the selection of well-balanced solutions to identify the optimal timing for applying PM treatments to in-service asphalt pavement.

Design and assessment of structures have been geared towards addressing the most dominant hazard at the location of interest. In general, single hazard approaches underestimate risk. Therefore, the possibility of structures experiencing multiple independent or interacting hazards of different types during their lifetime needs to be considered. The design methodology of bridges must shift towards a more comprehensive approach of addressing multiple hazards to ensure adequate performance under different mechanical and environmental stressors. Quantification of the reliability and risk associated with damage to individual bridges under multiple hazards can help in prioritizing retrofit activities for bridges in a network. Significant advances have been accomplished in the field of earthquake engineering. However, there is a need to promote further research for developing concepts and methods in order to design resilient bridges and assess the resilience of existing bridges and bridge networks in a life-cycle context. Resilience emphasizes the impact of infrastructure damage, failure and societal recovery under extreme hazards with a low probability of occurrence and high consequences. An infrastructure system needs to include resilient and adaptive capabilities for ensuring its long-term performance. This keynote paper provides an overview of life-cycle design and assessment methodologies of bridges under multiple hazards with an emphasis on earthquake and continuous deterioration. Several important performance indicators such as risk and resilience necessary to be implemented into the practical design and assessment are introduced. Finally, the concepts and methods presented are illustrated in case studies on bridge networks under seismic and corrosion hazards.

The galvanostatic method has been widely used for accelerating the corrosion of reinforcing bars in concrete to complete test studies within a reasonable timeframe. However, which level of current density induces characteristics of steel corrosion spatial variability and the associated structural performance of corroded reinforced concrete (RC) beams that are similar to those observed under natural conditions remains unknown. In this paper, comprehensive experimental research is conducted to compare the characteristics of spatial growth in steel weight loss and crack width and the structural behavior of corroded RC beams by two corrosion-accelerated methods (i.e. galvanostatic method at six current densities and artificial chloride environment method). The effects of these corrosion acceleration methods on Gumbel’s location and scale distribution parameters and the associated yield load capacity of corroded RC beams are investigated using Monte Carlo-based two-dimensional finite element analysis. Finally, a suitable current density is recommended to better simulate the steel corrosion distribution and the associated yield load capacity of RC beams in comparison to those observed under an artificial chloride environment.

Sea-level rise due to climate change could significantly exacerbate tsunami disasters since the sea level is a critical parameter affecting the intensity of tsunamis. Considering the impacts of future climate change on the ocean, a method to consider the effects of sea-level rise on the tsunami hazard intensity is needed to precisely predict future tsunami disasters. This paper presents a novel framework for probabilistic tsunami hazard assessment, considering the sea-level rise and associated uncertainties. A probabilistic assessment of the sea-level rise hazard is performed using the available data and climate models considering several climate change emission scenarios. Conditional tsunami hazard curves are estimated by conducting tsunami propagation simulations given a sea-level rise while considering the uncertainties associated with fault movement (i.e., rake angles and average stress drops). Radial-basis-function-based surrogate models and quasi-Monte-Carlo simulations are employed to obtain tsunami hazard curves. Finally, the tsunami hazard curves considering the effects of sea-level rise are estimated by convolving the corresponding regional sea-level rise hazard with the conditional tsunami hazard curves based on the total probability theorem. An illustrative example is provided, in which the proposed framework is applied to several municipalities in the Mie Prefecture of Japan that would be affected by tsunamis during the anticipated Nankai-Tonankai earthquake. The effects of sea-level rise on the tsunami hazard intensities associated with the municipalities are discussed.

In recent years, interest in the effect of the spatial variability associated with steel corrosion on the safety and reliability of reinforced concrete (RC) structures in harsh environments has increased. However, updating the reliability based on observations of existing RC structures remains a challenge. In this paper, an advanced framework for updating the time-dependent reliability incorporating the effect of the spatial steel corrosion distribution in existing RC members is presented. Probabilistic concepts are adopted to model random variables associated with material corrosion as random fields. With the application of a particle filter, spatially observed information obtained at discrete locations on RC members can be utilized to update the associated random variables. This reduces the epistemic uncertainty associated with structural performance assessments. In an illustrative example, time-dependent reliability updating is conducted on a RC bridge girder with the inspection results of the steel corrosion crack width. The effects of the number and space interval of observed locations on the updated structural reliability are investigated. The results demonstrate that the accuracy of the estimation of the time-dependent reliability of RC structures can be improved by using spatial observation information with a greater number of observed locations.

The deterioration of reinforced concrete (RC) structures due to chloride-induced corrosion is not spatially uniform because of the spatial variability related to material properties and environmental stressors. This variation has a substantial effect on the reliability of RC structures. However, few experimental studies have focused on the effect of the interaction of corrosion pits among tensile rebars on the reliability of RC structures. Therefore, in this paper, an experimental procedure that incorporates X-ray and digital image processing techniques was conducted on RC slab specimens subjected to accelerated corrosion. Using the experimental results, the parameter of the transverse correlation function of steel weight loss distributions was estimated to investigate how the corrosion pits in corroded rebars are correlated. Based on the experimentally obtained model parameters, the spatial steel weight loss distributions were simulated by spectral representation method. A three-dimensional (3D) nonlinear finite element (FE) analysis of RC structures with simulated steel weight loss distributions was conducted to obtain the ultimate bending capacity of RC structures. In an illustrative example, the effect of the transverse correlation among steel weight loss distributions of multiple tensile rebars on the failure probability of RC girders was quantified.

The accurate and efficient simulation of steel fibre reinforced concrete (SFRC) is of great significance for its further application in civil engineering. Problems of existing modelling methods can be recognized as two points; (1) the integral model only simplified fibre contribution into the unified post-peak ductility in concrete element but cannot reflect the material variation caused by real fibre distribution, and (2) the separate model built the concrete matrix and fibre inclusions respectively, but the directly random fibre distributions still need to be refined based on the actual material. In this paper, based on the X-ray image recognition results from real SFRC material, a mathematical model of fibre distribution and orientation is proposed for SFRC simulation, and the detailed value distributions of geometrical parameters are optimized for convenience and accuracy of material modelling. In the geometrical extraction of near 4000 fibres from X-ray images, the whole comprehensive procedure of image processing, enhancement and recognition is presented with technologies like pixel semantic classification and Hough transform. With the proposed geometrical mathematical model, the modelling method that consists of multiple refined sampling is illustrated with mechanical applications. After the model verification by experimental comparison, the detailed contribution of steel fibre and the effect of fibre distribution refinement are discussed as well.

The structural performance of steel fiber-reinforced concrete (SFRC) members primarily depends on the distribution and orientation of the fibers. Previous experimental studies revealed that the distribution and orientation of fibers are random and hardly controlled during the fabrication process. The centrifugal forming technique may improve the orientation and distribution of steel fibers in hollow circular SFRC piles and increase the shear strength of the piles. Accomplishing this task can lead to the possible replacement of shear reinforcements with steel fibers in piles, thereby improving the demanding productivity that is desired in the pile construction industry by saving considerable time and labor. This paper presents a novel experimental program to (a) develop the casting procedure for SFRC piles and (b) investigate the shear strength of SFRC piles without shear reinforcement compared to that of conventional reinforced concrete (RC) piles with shear reinforcement. With the aid of X-ray technology, different mix proportions and casting methods were investigated to determine the optimum procedure, which produced fiber distributions and orientations in SFRC piles superior to those of RC piles. The centrifugal forming method influenced the orientation of the fibers so that they were oriented in the shear stress direction (i.e., circumferential direction). The loading test demonstrated that the steel fibers effectively worked as shear reinforcement and that the shear capacity increased with the steel fiber content. Moreover, the SFRC piles exhibited stable crack propagation and improved post-cracking stiffness without severe concrete damage compared to that of the RC piles.

The amount of disaster waste is one of the most important performance indicators in quantifying the resilience of a community. In fact, disaster waste can have significant negative impacts on the environment in affected regions and hinder the postdisaster recovery process. Appropriate disaster waste management should be developed in Japan before the occurrence of the Nankai Trough earthquake. It is expected that the seismic and tsunami intensities caused by the anticipated Nankai Trough earthquake will be substantially larger than those caused by the 2011 Great East Japan earthquake. In this paper, a risk-based methodology is presented for estimating the amount of disaster waste generated by both the ground motions and the tsunami due to the anticipated Nankai Trough earthquake. First, Monte Carlo simulation-based probabilistic hazard analyses are performed to obtain seismic and tsunami hazard curves considering the uncertainty associated with fault movement along the Nankai Trough. Structural damage data associated with past earthquakes are used to develop seismic and tsunami fragility curves. The amount of disaster waste generated from a single structure is defined as the generation unit and is determined based on past disasters. Finally, with the aid of a geographic information system, the risk of disaster waste can be estimated using the hazard and fragility curves and the generation units. As an illustrative example, the risk curves and expected values associated with disaster waste in Mie Prefecture, Japan, are estimated based on the proposed framework.

Corrosion-induced crack width can provide effective information on the deterioration level of in situ corroded reinforced concrete (RC) structures. However, the uncertainty associated with the relationship between corrosion-induced crack width and steel corrosion in RC structures is quite large. In this study, a probabilistic framework for estimating the structural capacity of corroded RC structures using the observational corrosion-induced crack width distribution and machine learning is proposed. Based on the experimental results of corroded RC beams, random field theory, and finite element (FE) analysis, artificial samples composed of corrosion-induced crack width and steel weight loss distributions over the RC beams are generated. Two machine learning-based models are then developed using these samples to estimate the steel weight loss distribution from the observational corrosion-induced crack distribution. Finally, a Monte Carlo-based FE analysis with the estimated steel weight loss distribution as the input data is conducted to obtain the probability density function (PDF) of the structural capacity of corroded RC beams. For illustrative purposes, the effect of observational corrosion-induced crack width distribution on the PDF of flexural capacity of an existing RC beam is investigated using the proposed framework. The results show that the proposed framework using a machine learning-based model is a reliable and computationally efficient approach for estimating the structural capacity of corroded RC members and demonstrates the potential for assessing the deterioration condition of existing RC structures based on the corrosion-induced crack width distribution.

Corrosion of reinforcement steel is one of the primary factors leading to performance degradation of bridge structures located in coastal marine environment. To preserve adequate performance levels of RC bridges under traffic loads and a severe airborne chloride environment, frequent maintenance activities are required. These activities increase the total life-cycle cost (LCC). As an alternative to conventional reinforcement, stainless steel (SS) reinforcement can be a promising option to avoid corrosion problems and reduce the maintenance cost. It is necessary to identify appropriate geographical locations where the use of SS rebars proves economical since airborne chloride intensity depends on the meteorological condition and distance from coastline. In this paper, a novel probabilistic method for LCC estimation of RC girders under traffic and airborne chloride hazards is established. The critical distances from the coastline for SS rebar application in RC bridges under different coastal environments in 30 cities in Japan are determined based on the proposed method.

To develop disaster mitigation measures in regions affected by both ground motions and tsunamis, it is important to consider the effects of both seismic and tsunami hazards and assess the social impacts associated with economic losses and reduced network functionality. In this paper, a procedure is presented for estimating the risk and resilience of bridge networks under both seismic and tsunami hazards. Using the proposed framework, it is possible to estimate risk as the economic loss and resilience as the functionality and recovery time of a network after an earthquake. In an illustrative example, the road networks in two Japanese cities expected to be affected by the anticipated Nankai Trough earthquake, which would cause strong ground motions and a subsequent tsunami, are analyzed. Using risk and resilience as performance indicators for social impacts, the effectiveness of retrofitting a road structure can be quantified. Finally, the retrofitting prioritization for various structures can be determined.

In this paper, a procedure to update the structural reliability considering the effect of spatial steel corrosion distribution is proposed. The covariance matrix decomposition method is applied to simulate the spatial random fields of the associated random variables in the deterioration prediction model. When the observational data at discrete locations on the aging reinforced concrete (RC) bridge structures can be obtained, the spatial random fields are updated by particle filter for stochastic interpolation. Subsequently, the structural reliability of RC bridge structures can be updated simultaneously. As an illustrative example, the reliability analysis of the RC bridge girder considering spatial steel corrosion using the observational data is presented. The observational data from visual inspection results of crack width is used to update the structural reliability.

Chloride-induced steel corrosion is a dominant cause of deteriorated RC structures in marine environments. The distribution of corrosion is found to be highly varied over RC structures. Previous studies reported that the assumption of uniform steel corrosion is an oversimplification, which leads to an error in estimating the structural performance of corroded RC structures. Therefore, it is important to consider the effects of spatial variability associated with steel corrosion for evaluating the structural performance of corroded RC members. Moreover, as RC members are commonly reinforced with multiple rebars, the correlation of corrosion among the rebars can have a great influence on their structural behaviors. The main objective of this paper is to conduct the experimental and computational studies for investigating the effect of spatial localized corrosion of multiple rebars on the structural performance of corroded RC beams.

Corrosion is spatially distributed over RC structures due to several factors, such as different environmental exposure, concrete covers, and concrete qualities. Ignoring the effect of spatial variability is a drastic simplification for the reliability assessment of corrosion-affected RC structures. In this paper, a novel approach is established to assess the reliability of RC girders using finite element (FE) and probabilistic analyses considering the spatial variability of steel corrosion. An experiment was conducted to study the effect of current density on the spatial steel corrosion of RC beams. In the FE model, the spatial variability of steel corrosion was modeled by Gumbel statistics deduced from the experimental data. The results of FE analysis show that using the Gumbel distribution parameters derived from the steel weight loss data associated with higher current density cannot reproduce the non-uniformity of corrosion distribution, leading to an underestimation of flexural failure probability of RC girders.

Bridge structures play a crucial role in the recovery process after an earthquake; however, the need to produce a resilient structure requires the implementation of expensive materials that are essentially limited to critical structures. To achieve a low-cost resilient system, a novel friction pendulum sliding system fabricated from only steel and concrete was experimentally evaluated. Simple concave shapes mounted transverse to one other; and spherical shapes with variable curvatures fabricated by a three-dimensional printer were evaluated. Bidirectional shaking table tests were conducted with different acceleration intensities, and the input acceleration was reduced by 50% during sliding. The spherical shapes exhibited stable hysteresis responses even when subjected to strong ground motions. The proposed friction pendulum sliding system for bridge structures provides a low-cost design solution that can ensure post-event operability.

Corrosion of steel reinforcement is spatially distributed over RC structures due to several factors such as different environmental exposure, concrete quality and cover. Ignoring the effect of spatial variability is a drastic simplification for the prediction of the remaining service life of RC structures. Therefore, it is essential to identify the parameters influencing the spatial steel corrosion and structural performance of corroded RC structures. In this paper, an experimental research was conducted to study the effects of current density, concrete cover, rebar diameter, and fly ash on the spatial variability of steel weight loss, corrosion crack, and structural behavior of corroded RC beams using X-ray and digital image processing technique. The test results showed that low current density induced highly non-uniform corrosion associated with few large pits and cracks at certain locations while higher current density produced more uniform corrosion and cracks occurred over the whole beam. Gumbel distribution parameters were derived from the experimental data of steel weight loss to model spatial steel corrosion. A novel approach was established to assess the reliability of RC structures using finite element analysis and probabilistic simulation considering the spatial variability in steel weight loss. Using the Gumbel distribution parameters derived from the steel weight loss data associated with higher current density may underestimate the non-uniformity of corrosion distribution which can lead to an overestimation of the load capacity of corroded RC structures.

A novel procedure for updating the reliability of existing reinforced concrete (RC) structures in a marine environment by incorporating spatial variations of steel weight loss is proposed. Since the properties of concrete and steel bars are uncertain, it is necessary to deal with the long-term structural performance based on probabilistic concepts and reliability-based methods. In this paper, epistemic uncertainties of material properties are updated using inspection results associated with steel weight loss prediction using Sequential Monte Carlo Simulation (SMCS). Possible distributions of steel weight loss over RC members are generated by a stochastic field method based on simple Kriging and inspection results at several observational points. Effect of the distance from the observational points on the reliability is discussed in an illustrative example.

A procedure for estimating risk of road structures subjected to seismic ground motion and subsequent tsunami is proposed. In the 2011 Great East Japan earthquake, many bridges and embankments were severely damaged due to the strong ground motion and/or subsequent tsunami. The damage to these structures caused significant economic losses associated with the reconstruction and disruption of the road network. Given a limited budget, it is important to estimate the economic loss due to the damage to structures in road networks and determine the retrofitting prioritization for effective risk mitigation. In an illustrative example, the risk of road networks under both seismic and tsunami hazards caused by the anticipated Nankai Trough earthquake is estimated. The numerical results show that the retrofitting prioritization can be determined by comparing the risk of road networks.

It is widely recognized that reliability-based optimization methodologies are rational and promising tools to perform the life-cycle management (LCM) of civil engineering structures. In order to realize the optimal design and maintenance of asphalt pavement, a comprehensive reliability-based optimization methodology considering the life-cycle cost (LCC) is proposed in this paper. Considering the powerful ability of Artificial Neural Networks (ANNs) to solve complex and nonlinear problems, ANNs are implemented to predict the performance of asphalt pavement based on the training data (i.e. structural, traffic, climatic, and performance parameters) selected from the Long-Term Pavement Performance (LTPP) program. Monte Carlo simulation (MCS) with Importance Sampling (IS) is conducted based on the obtained ANNs model to calculate the life-cycle reliability of asphalt pavement. Finally, the expected LCC including the initial construction cost, the preventive maintenance cost, inspection cost, users cost, and salvage value is minimized while maintaining a prescribed life-cycle reliability level for asphalt pavement. Several applications are presented to investigate the effects of traffic and climatic parameters on reliability-based optimum cost solution.

The repair of corroded reinforced concrete (RC) structures is a critical issue for structural designers and managers because the repair cost significantly dominates the life-cycle cost. Moreover, in chloride-containing environments (e.g. coastal environments), RC structures repaired with conventional methods may corrode again since the ingress of chloride ions, water, and oxygen into the concrete will not be completely restrained. In this paper, a novel repair method for corroded RC beams using stainless steel (SS) rebars and externally bonded carbon-fibre-reinforced polymer (CFRP) sheets is proposed. The flexural behaviour of a group of RC beams repaired using the proposed method is experimentally investigated. The test variables include the longitudinal reinforcement types (i.e. carbon and SS), shear reinforcement configurations, and CFRP sheet wrapping schemes. Experimental results demonstrate that a carbon steel (CS) reinforcement can be replaced with an SS reinforcement to reduce future repair costs since there is no significant difference in the flexural behaviour of beams reinforced with CS and SS rebars. The effectiveness of CFRP sheet wrapping schemes on the flexural performances of SS-RC beams is approximately identical to that of CS-RC beams. In addition, the present paper discusses the serviceability and ultimate limit states of RC beams retrofitted with SS rebars and CFRP sheets based on the current design codes for ordinary RC beams strengthened using CFRP sheets. The predictions are in good agreement with the experimental results.

Reinforcement corrosion is highly nonuniform and spatially distributed in reinforced concrete (RC) structures. Since RC members are reinforced with multiple rebars, corrosion of one rebar might affect another rebar in the transverse direction, thereby influencing the behavior of the structure. Hence, greater attention should be paid to studying the effects of the correlation of localized corrosion between adjacent rebars on the structural performance of RC members. In this paper, the effects of localized corrosion and the correlation of steel corrosion between tensile rebars on the structural performance of corroded RC beams were investigated through experiments and finite element (FE) analyses. The experimental results indicated that compared to the RC beams corroded over their entire length, the partially corroded RC beams with highly localized steel corrosion in the mid-span experienced large reductions in both loading capacity and ultimate deflection. Moreover, for beams with multiple rebars, the results showed that the beams with higher correlation coefficients of cross-sectional area loss between rebars had lower load and deflection capacities than the beams with lower correlation coefficients. The load–deflection responses of the beams with multiple rebars simulated by the 3D FE model were found to be in better agreement with the experimental results than those of the 2D FE model. Furthermore, a Monte Carlo simulation (MCS) was performed using a 3D FE model for two different cases: correlated and uncorrelated steel corrosion in the transverse direction of the RC beam. The results showed that a stronger correlation of steel cross-sectional area loss on different tensile rebars led to a larger variation in the load capacities of the corroded RC beams.

Several parameters during the fabrication process cause segregation and poor orientation of the fibers in steel fiber-reinforced concrete (SFRC) members. With its high flowability and compactability, self-compacting fiber-reinforced concrete (SCFRC) can be used as an alternative to conventional SFRC, as it exhibits improved orientation and lesser fiber segregation. This study aims to investigate (1) the effects of concrete type (i.e., SCFRC versus SFRC), fiber content, and specimen depth on the fiber distribution and orientation and (2) the structural performance of SCFRC and SFRC beams considering their fiber distribution and orientation using X-ray images. The X-ray images showed that owing to the high-flow properties, the SCFRC beams exhibited a lower fiber segregation and better fiber alignment than the SFRC beams. The bending test results demonstrated that the SCFRC beams exhibited better flexural performance than the SFRC beams owing to the improved distribution and orientation of the fibers. Moreover, a finite element (FE) analysis was performed to evaluate the structural performance of the beams considering the varying fiber distribution properties observed in the X-ray images. The FE method could differentiate the superior structural performance of the SCFRC beam from that of the SFRC beam.

Reinforced concrete (RC) bridges under traffic loads and a severe airborne chloride environment require more frequent and intensive maintenance activities to preserve an adequate performance level. The use of stainless steel (SS) reinforcement in lieu of carbon steel (CS) reinforcement can be a promising alternative to avoid corrosion problems and reduce the maintenance cost. As the airborne chloride intensity depends on the meteorological condition and the distance from coastline, it is essential to determine the appropriate geographical locations where the use of SS rebar provides economic benefits. The main purpose of this paper is to present a novel approach for identifying the location of RC bridge suitable for SS rebar use considering the hazard intensity associated with the airborne chloride based on the probabilistic life-cycle cost (LCC) analysis. A novel probabilistic method for LCC estimation of RC bridge girders under traffic and airborne chloride hazards is established. In an illustrative example, the suitable location and critical distance for SS rebar application in RC bridges under different coastal environments in Japan are identified based on the proposed method. Sensitivity of LCC to four key parameters including discount rate of money, corrosion rate of SS rebar, concrete cover, and water-cement ratio is performed.

A novel low-cost friction sliding system for bidirectional excitation is developed to improve the seismic performance of reinforced concrete (RC) bridge piers. The sliding system is a spherical prototype developed by combining a central flat surface with an inclined spherical segment, characterized by stable oscillation and a large reduction in response accelerations on the flat surface. The inclined part provides a restoring force that limits the residual displacements of the system. Conventional steel and concrete are employed to construct a flat-inclined spherical surface atop an RC pier. The seismic forces are dissipated through the frictions generated during the sliding movements; hence, the seismic resilience of bridges can be ensured with a low-cost design solution. The proposed system is fabricated utilizing a mold created by a three-dimensional printer, which facilitates the use of conventional concrete to construct spherical shapes. The concrete surface is lubricated with a resin material to prevent abrasion from multiple input ground motions. To demonstrate the effectiveness of the system, bidirectional shaking table tests are conducted in the longitudinal and transverse directions of a scaled bridge model. The effect of the inclination angle and the flat surface size is investigated. The results demonstrate a large decrease in response acceleration when the system exhibits circular sliding displacement. Furthermore, the inclination angle that generates the smallest residual displacement is identified experimentally.

After recent large earthquakes, field investigations confirmed that several bridges were severely damaged and collapsed not only due to the earthquake, as an independent hazard, but also to the subsequent tsunami, landslide or fault displacement. In addition, long-term material deterioration might have an important impact on seismic damage to bridges. Therefore, it is important to study both independent and interacting hazards and their effects on the reliability and risk of bridges and bridge networks. Although earthquake is still a dominant hazard to bridges in many earthquake-prone countries, a life-cycle reliability and risk approach has to consider both independent and interrelated hazards causing bridge failure. Such an approach is presented in this paper. In addition, issues related to life-cycle analysis, design, risk, resilience and management of bridges under earthquake and other hazards are discussed. Finally, the concepts and methods presented are illustrated on both single bridges and bridge networks.

RC bridges near Japan coastal regions deteriorate due to chloride-induced steel corrosion. In such severe airborne chloride environments, RC bridges demand frequent maintenance activities to preserve the desired structural performance. However, maintenance cost causes a surge in their lifetime cost. Resource scarcity is amplifying the need to search for better corrosion-resistance material than carbon steel (CS) rebar. With superior corrosion resistance, stainless steel (SS) rebar can be a better alternative. Nevertheless, its high initial cost raises the initial cost of RC structures. As airborne chloride attenuates with the distance from the coastline, it is essential to develop an approach to integrate the chloride hazard assessment into the life-cycle cost (LCC) analysis for considering cost-effective application of SS rebar. This paper aims to establish a probabilistic LCC method for identifying the suitable distance from the coastline for SS rebar application in RC bridges under an airborne chloride environment.

Asphalt pavement is a complex engineering system which deteriorates due to several mechanical and environmental stressors (e.g. moisture damage, freeze-thaw cycles and traffic load). To predict the time-dependent performance of asphalt pavement, it is necessary to develop a deterioration model incorporating the associated variables under uncertainty. Artificial Neural Networks (ANNs) are effective intelligence technologies to develop an accurate prediction model with a large amount of data. In this paper, a time-dependent reliability assessment method based on the ANNs model is presented. ANNs are used to develop the performance prediction model of asphalt pavement according to the training data selected from the Long-term Pavement Performance database. The life-cycle reliability of asphalt pavement is calculated using the ANNs model based on Monte Carlo simulation with Importance Sampling. Two case studies are presented to investigate the effects of sublayers thickness and traffic levels on the life-cycle reliability.

The uncertainties associated with the prediction of long-term structural performance of existing reinforced concrete (RC) structures can be reduced by updating the model parameters using observational information. However, those parameters have been updated ignoring the spatial steel corrosion, and this assumption could lead to an overestimation of the structural reliability. In this paper, an approach is proposed to update the reliability of deteriorating RC structures considering the effect of the variables that cause non-uniform steel corrosion. The stochastic interpolation process of the particle filter method is utilized to update the model parameters based on the observational data obtained at discrete locations on the structures. In an illustrative example, the life-cycle reliability of a RC girder is presented. Visual inspection results of corrosion crack width are applied to update the reliability, and the effect of the observational information on the reliability updating of the RC girder is discussed.

To develop disaster mitigation measures in coastal regions affected by earthquakes, it is important to consider the effects of both seismic and tsunami hazards on road structures and assess the social impacts associated with the economic loss and reduction in network functionality. In this paper, a risk- and resilience-based assessment framework is established for road networks under both seismic and tsunami hazards. In the proposed methodology, the risk and resilience are quantified by the economic loss and postdisaster functionality of road networks, respectively. Uncertainties associated with estimations of fault movement, hazard intensity and structural vulnerability are considered when estimating the failure probability using Monte Carlo simulation. Moreover, structural vulnerability against tsunamis is estimated considering the effects of ground motion-induced damage on the reduction in tsunami capacity. As an illustrative example, the road networks in two Japanese cities expected to be affected by the anticipated Nankai Trough earthquake, which would cause strong ground motions and a subsequent tsunami, are analyzed. Finally, the retrofitting prioritization for various structures is discussed based on the risk and resilience quantified as performance indicators for social impacts.

Corrosion of steel reinforcement is spatially distributed over RC structures due to several factors such as different environmental exposure, concrete cover, and concrete quality, among others. Ignoring the effect of spatial variability is a drastic simplification for the prediction of the remaining service life of RC structures. Therefore, it is essential to identify the factors influencing the spatial steel corrosion and structural performance of corroded RC structures. In this paper, an experimental research is conducted to study the effects of main parameters (i.e. current density, concrete cover, rebar diameter, and fly ash)on the spatial variability associated with steel weight loss, corrosion crack, and structural behavior of accelerated-corrosion RC beams using X-ray radiography and digital image processing. The test results showed that low current density (Icorr ≤ 50 µA/cm2)induced highly non-uniform corrosion associated with few large pits and cracks at certain locations while higher current density produced more uniform corrosion and cracks over the beam length. Gumbel distribution parameters were derived from the steel weight loss data for modeling spatial steel corrosion. A novel approach was established to assess the reliability of RC structures using finite element (FE)analysis and probabilistic analysis considering the effects of modeled spatial variability of steel weight loss based on X-ray photographs. Using the Gumbel distribution parameters derived from the steel weight loss data associated with higher current density may underestimate the non-uniformity of corrosion distribution which can lead to an overestimation of the load capacity of corroded RC structures.

In contrast to reinforced concrete (RC) structures on land, RC shield tunnels in coastal regions deteriorate rapidly after their construction because of the combined effects of multiple mechanical and environmental stressors. In this paper, by considering the coastal hazards associated with chloride and the impacts of hydrostatic pressure, a novel approach is presented to estimate the life-cycle structural performance of a shield tunnel that has undergone deterioration due to chloride-induced steel corrosion. Deterioration processes in segmental linings are investigated via corrosion-accelerated experiments on individual segments, and the combined effects of corrosive agents and loads are emphasized. Monte Carlo simulation is used to estimate the time-variant failure probability of shield tunnels in a marine environment. In an illustrative example, the effects of structural location, hydrostatic pressure and material properties on the life-cycle reliability of shield tunnels are investigated.

Generally, various kinds of cracks are the main type of distresses during the service period of asphalt pavements. To save maintenance costs and improve the crack resistance of asphalt pavements effectively, this paper presents a unique design method for the material composition of small particle-size (SPS) asphalt mixture for controlling cracks in asphalt pavement. First, Stone Mastic Asphalt (SMA)-II was designed as a basic gradation according to the A.N. Talbot curve and SMA-II-1, SMA-II-2 and SMA-II-3 were designed according to the Superpave mix design method, the Bailey method and the Particle interference theory, respectively. Second, based on Marshall test results, the optimal fiber content and optimal asphalt content of three gradations were determined. Then, the influence of the passing rate of 1.18-mm sieve and 0.075-mm sieve on the air voids of SMA-II and the influence of the filler-asphalt ratio on the performance of SMA-II were investigated, and an appropriate range of filler-asphalt ratio was obtained. Finally, a high-temperature performance test, a water stability test, and a skid resistance test demonstrate that the overall performance of SMA-II can satisfy the specifications. A low-temperature bend test and analysis of bending strain energy density show that SMA-II with a crumb rubber modifier and a polymer fiber has better crack resistance performance than SMA-I (SBS-modified mixture). Life-cycle cost analysis shows the economic advantage of SPS asphalt thin overlays over traditional AC-13 thin overlays.

After the occurrence of various destructive earthquakes in Japan, extensive efforts have been made to improve the seismic performance of bridges. Although improvements to the ductile capacities of reinforced concrete (RC) bridge piers have been developed over the past few decades, seismic resilience has not been adequately ensured. Simple ductile structures are not robust and exhibit a certain level of damage under extremely strong earthquakes, leading to large residual displacements and higher repair costs, which incur in societies with less-effective disaster response and recovery measures. To ensure the seismic resilience of bridges, it is necessary to continue developing the seismic design methodology of RC bridges by exploring new concepts while avoiding the use of expensive materials. Therefore, to maximize the postevent operability, a novel RC bridge pier with a low-cost sliding pendulum system is proposed. The seismic force is reduced as the upper component moves along a concave sliding surface atop the lower component of the RC bridge pier. No replaceable seismic devices are included to lengthen the natural period; only conventional concrete and steel are used to achieve low-cost design solutions. The seismic performance was evaluated through unidirectional shaking table tests. The experimental results demonstrated a reduction in the shear force transmitted to the substructure, and the residual displacement decreased by establishing an adequate radius of the sliding surface. Finally, a nonlinear dynamic analysis was performed to estimate the seismic response of the proposed RC bridge pier.

This chapter aims to provide a state-of-the-art summary of research topics related to the physical, chemical, and mechanical processes involved in degradation mechanisms of concrete and steel structures located in severe environments. Although several factors affect the deterioration mechanisms of concrete and steel structures, this review mainly focuses on the effects of structural deterioration at the component and system levels. For concrete structures, the chapter investigates the effects of carbonation, chloride, frost, and chemical attacks, as well as alkali-aggregate reaction on material deterioration. In addition, it discusses the steel deterioration owing to corrosion and/or fatigue. The chapter further describes the effect of reinforcement corrosion on structural resistance deterioration. The analytical methods used to evaluate structural resistance deterioration must consider the reduction of the steel bar volume, cracking of the concrete cover because of corrosion product expansion, bond degradation between the concrete and steel, and nonuniformity of corrosion along the steel bars in RC members.

Uniform distribution of fibres which are orientated parallel to the direction of tensile stress is essential to improve the structural performance of steel fibre reinforced concrete (SFRC) members. However, the fibre distribution in concrete structures is hardly uniform due to the effects of many parameters during the fabrication process (vibration, placing methods, concrete moulds, etc.) which can negatively affects their structural performance. The use of self-compacting concrete (SCC) instead of normal concrete can be a good alternative where the fibres can be aligned in the direction of flow without the use of vibration. This paper presents an effort for improving the structural performance of fibre-reinforced concrete members by utilizing the high-flowability and self-placability properties of SCC to achieve better distribution and orientation of fibres. In the experiment, the self-compacting fibre reinforced concrete (SCFRC) was flown into beams and the X-ray image was taken over the whole length of each specimen to investigate the effects of flow distance from the casting point on the distribution and orientation of fibres. In addition, other specimens were also fabricated using SFRC (with normal concrete). The bending tests were performed to observe the flexural performance of SCFRC and SFRC specimens. By the comparison of their structural performance, it was found that SCFRC ones provided better performance due to the more uniform distribution of fibres which were aligned in the flow direction of SCFRC.

Deterioration of RC structures due to chloride-induced reinforcement corrosion is a common problem in an aggressive environment. Especially for shield tunnels in coastal regions, structures undergo a complex and rapid deteriorating process under the coupling effects of multiple mechanical and environmental stressors during their life-cycle, such as high hydrostatic pressure and aggressive agents. The very few existing studies on the deterioration processes of shield tunnels, especially considering the coupling effects, were not generally oriented to accurately assess the lifetime structural performance of these tunnels. In this paper, the chloride transport process in segmental linings with the impact of hydrostatic pressure is illustrated, two transport approaches of chloride are suggested, and the time to corrosion initiation is predicted. Finally, a Monte Carlo Simulation is used in conjunction with a time-dependent failure probability estimation associated with the deteriorated structural performance due to the steel corrosion.

It is well recognized that the material properties of a reinforced concrete (RC) structure and its dimensions are random due to the spatial variability associated with workmanship, environment and other factors. This randomness causes spatially corrosion damages such as corrosion crack, cover spalling and steel corrosion. Therefore, it is of great importance to simulate deterioration processes of RC structures in a stochastic field context. In this paper, based on a probabilistic model for steel corrosion in RC structures, steel corrosion distributions over RC slab is estimated using 2D Gaussian stochastic fields. In an illustrative example, a time-dependent structural performance of RC slab represented by the stochastic field was estimated using 2D nonlinear finite element method.

Recent large earthquakes in Japan including the 2011 Great East Japan earthquake and the 2016 Kumamoto earthquake caused not only damage and collapse of structures due to strong ground motions, but also washout of structures due to the subsequent giant tsunami and huge landslide. It is expected that the damage and the economic loss resulting from the anticipated Nankai Trough earthquake would be larger than those resulting from these two recent large earthquakes. Although the quantifications of risk and resilience associated with damage to structures and civil infrastructure systems under extreme events is still an important research topic in the structural engineering community, research studies on risk reduction and resilience enhancement in terms of structural control, restoration of structures and post-disaster debris management must be also developed. These research topics and studies are the main topic of this paper.

In this paper, a reliability-based durability design method for shield tunnels in a marine environment is introduced. In this context, a method for integration of the coupling effects of chlorides and hydrostatic pressure into reliability-based durability design of shield tunnels in a marine environment is proposed. By using the proposed method, material parameters of RC segmental linings can be determined. The target reliability-based durability design level shall be satisfied during structural lifetime.

Performance of corrosion-affected RC structures depends on the spatial variability of steel corrosion of reinforcing bars. The effect of spatial variability of steel corrosion on the remaining service life of concrete structures is significant. In this paper, an experimental study was conducted to investigate the effect of current density on the spatial variability of steel corrosion. This variability is modeled using Gumbel distribution derived from experiments and incorporated with FE method to estimate the yield loading capacity of RC beams. The results show that using Gumbel distribution parameters derived from the specimens with high current density may lead to an overestimation of load capacity of corroded RC beams.

A procedure for estimating risk and resilience of road networks associated with bridges and embankments subjected to seismic ground motion and subsequent tsunami caused by the anticipated Nankai Trough earthquake is proposed. Since road networks play a crucial role for the transportation system after a natural disaster, it is important to identify the degradation of functionality and economic loss due to damage to structures in networks. In an illustrative example, risk and resilience of road networks in Mie-Prefecture, where the effects of Nankai Trough earthquake would be very intense, are estimated. The numerical results show that the retrofitting prioritization can be determined by comparing the risk and resilience of road networks.

Ignoring the effects of spatial variability of steel corrosion can lead to an error in the long-term performance assessment of RC structures. Recent research has been focusing on modelling spatial steel corrosion using experimental data from the corroded RC members by means of the impressed current method. However, researchers have applied a wide range of current density neglecting its effects on the spatial steel corrosion and the reliability of corrosion-affected RC beams. This paper aims to study effects of current density on the spatial steel corrosion and reliability of RC structural beam using finite element analysis. Three RC beams were corroded using current density of 50, 100, and 500 μA/cm . The spatial growth in steel weight loss in RC specimens was quantified at different corrosion levels using X-ray and image processing techniques. It was found that low current density of 50 μA/cm induced more non-uniform steel corrosion than higher levels of current density. Gumbel distribution parameters were derived from the experimental results and used to approximately model the spatial steel corrosion. An illustrative example was provided to study the effect of the modelled steel corrosion associated with low and high current densities on the reliability analysis of a structural RC beam. It was found that the failure probability of the RC beam estimated using the modelled spatial steel corrosion associated with small current density was higher than that associated with high current density. 2 2

During the aggregate crushing process, natural aggregate and clinging mortar from existing concrete will inevitably produce small cracks and weak bonds between the aggregate and the existing cement mortar. The weaknesses of the existing cement mortar, adhered to a natural aggregate, negatively affect the properties of a recycled aggregate concrete, which prevents its application in reinforced concrete (RC) structures. Recycled aggregate can be classified into several categories, according to its physical and mechanical properties. The properties of concrete incorporated with the recycled aggregate of various qualities can be controlled, and the variability in its strength can also be reduced. This study aims to promote the application of recycled aggregate by investigating the effects of recycled aggregate quality (i.e., water absorption and the number of fine particles) classified by the Japanese Industrial Standards (JIS) on material properties, mechanical properties, and shear behavior of RC beams with recycled aggregate.

This paper proposes a novel probabilistic methodology for estimating the life-cycle reliability of existing reinforced concrete (RC) bridges under multiple hazards. The life-cycle reliability of an RC bridge pier under seismic and airborne chloride hazards is compared to that of a bridge girder under traffic and airborne chloride hazards. When conducting a life-cycle reliability assessment of existing RC bridges, observational data from inspections can provide the corrosion level in reinforcement steel. Random variables related with the prediction of time-variant steel weight loss can be updated based on the inspection results using Sequential Monte Carlo Simulation (SMCS). This paper presents a novel procedure for identifying the hazards that most threaten the structural safety of existing RC bridges, as well as the structural components with the lowest reliability when these bridges are exposed to multiple hazards. The proposed approach, using inspection results associated with steel weight loss, provides a rational reliability assessment framework that allows comparison between the life-cycle reliabilities of bridge components under multiple hazards, helping the prioritisation of maintenance actions. The effect of the number of inspection locations on the updated reliability is considered by incorporating the spatial steel corrosion distribution. An illustrative example is provided of applying the proposed life-cyle reliability assessment to a hypothetical RC bridge under multiple hazards.

Several studies have revealed that the fiber distribution is usually not uniform since many parameters during the fabrication process cause different fiber distributions and orientations within individual steel fiber-reinforced concrete (SFRC) members. This phenomenon results in large scattering in the post-cracking flexural responses among the material characterization specimens. Consequently, when estimating the flexural behavior of SFRC beams, conflicting results are often obtained using only a single constitutive stress-crack opening laws to characterize the material behavior in tension without considering the different fiber distributions and orientations. In this paper, a novel integrated approach is established to estimate the flexural behavior of SFRC beams using both a finite element (FE) method and X-ray imaging. In the prediction approach, a parameter that can be determined using the measured fiber distribution properties from an X-ray image is proposed to consider the variability of the fiber dispersion in each SFRC member. A method is presented for deducing the constitutive stress-crack opening laws using an FE analysis and the proposed parameter from X-ray images. In the numerical FE method, the variability of the fiber dispersion of the individual SFRC beams is determined by identifying the stress-strain relation in each mesh based on the proposed parameter from the X-ray images. The FE method provides better prediction results of the loading capacity for the SFRC beams.

After the Great Hanshin Kobe Earthquake (1995), extensive effort for improving the seismic performance of bridges in the Japanese engineering community have been carried out. Although, isolation system has become effective to ensure the seismic resilience of bridge structures, high axial load and large displacements under strong ground motions are not well understood; moreover, during Tohoku Earthquake (2011) and Kumamoto Earthquake (2016), some damages of laminated rubber bearing were observed. Undoubtedly, it is necessary to continue developing the isolation systems by exploring new concepts. In this study, seismic performance evaluation of a novel system to isolate the superstructure by forming a concave sliding surface on the top of the concrete bridge pier; is experimentally conducted. Any seismic devices are not included for lengthening the system to a longer natural period, and based on the principle of pendulum the seismic energy can be dissipated through the frictional force. Proposed Friction Pendulum Isolation System (FPIS) possess re-centering capability while sliding toward the initial position, and large displacement can be enhanced. The results exhibited shear force-displacement relationship with a smooth behavior in the longitudinal direction; furthermore, the longitudinal and transverse direction depicted an appealing circular displacement orbit.

After recent large earthquakes, field investigations confirmed that several bridges were severely damaged and collapsed not only due to the earthquake, as an independent hazard, but also to the subsequent tsunami, landslide or fault displacement. In addition, material deterioration might cause further seismic damage to bridges. Therefore, it is important to study both independent and interacting hazards and their effects on the reliability of bridge and bridge networks. Although earthquake is still a dominant hazard to bridges in many earthquake-prone countries, a life-cycle reliability approach has to consider both independent and interrelated hazards causing bridge failure. Such an approach is presented in this keynote paper. In addition, issues related to life-cycle analysis, design, risk, resilience and management of bridges under earthquake and other hazards are discussed. Finally, the concepts and methods presented are illustrated on both single bridges and bridge networks.

Tools, guidelines and standards for assessment of Life Cycle Cost (LCC) of built environment e.g. buildings, infrastructure assets etc. have gained impact over the past years. Owner and operator application of tools, guidelines and standards enhances optimization of operation and maintenance with due respect to their budgets. In order to aid owners, operators and their designers, a task group under fib has been established to prepare a state-of-the-art report regarding LCC analyses of concrete assets. The state-of-the-art report contains a description of existing LCC standards and guidelines, their applicability, the definition of different cost elements, and the treatment of uncertain information in a reliability or risk based framework, etc. providing the reader with background information and methodology for preparation of such analysis. Moreover, the report contains case studies, presenting the applicability of the LCC analysis methodology.

Since structural performance of corroded RC members primarily depends on localized corrosion damages on their reinforcements, modelling the spatial steel corrosion is important for the long-term performance assessment of RC structures. To achieve this purpose, there is a need to study the time-variant spatial distribution of steel corrosion. The impressed current technique by means of applying current density has been widely used to investigate the effect of steel corrosion on the structural capacity deterioration. It was reported that current density has great influence on the propagation of average crack width, steel corrosion, and structural behavior of RC members. However, the study of the effect of current density on the spatial variability of corrosion and cracking is scarce. Therefore, the main objective of this paper is to study, using X-ray and digital image processing techniques, the effects of current density on the spatial steel corrosion and corrosion cracking of corroded RC beams.

In this paper, the time-dependent reliability of PC girders in a marine environment is estimated considering the spatial variability of steel weight loss. Non-linear finite element (FE) analysis of aging PC girders is performed. Spatial variation of steel weight loss represented by uniform, Gaussian and non-Gaussian stochastic fields is included in the FE modelling. To obtain the relationship between input parameters and computational results from FE analysis, the response surface method is used for reducing the time required to repeat the structural analysis. The life-cycle reliability outcomes associated with three different models for the steel weight loss distribution are compared and discussed in an illustrative example. The authors would like to acknowledge Mr. Vasileios Christou for his help during the development of the random simulation algorithm.

Reinforced concrete (RC) structures in a marine environment deteriorate with time due to chloride-induced corrosion of reinforcing bars. Since the RC deck slabs of jetty structures are exposed to a very aggressive environment, higher deterioration rates can develop. In this paper, a reliability-based durability design and service life assessment of RC jetty structures are presented. For new RC jetty structures, the concrete quality and concrete cover necessary to prevent the chloride-induced reinforcement corrosion causing the deterioration of structural performance during the whole lifetime could be determined. Based on the airborne chloride hazard depending on the vertical distance from the sea level surface to the RC deck slab, the probability associated with the steel corrosion initiation is estimated. The water to cement ratio and concrete cover to satisfy the target reliability level are provided. For evaluating the service life of existing structures, the condition state based on the visual inspection of RC structure can be provided. The deterioration process of the RC jetty structure can be modelled as a Markov process. Therefore, the transition probability matrix at time t after construction can be updated by visual inspection results. A procedure to update the transition probability matrix by the Sequential Monte Carlo Simulation method is indicated. In an illustrative example, the effect of the updating on the life-cycle reliability estimate of existing RC deck slab in a jetty structure subjected to the chloride attack is presented.

The material properties of concrete structures and their structural dimensions are known to be random due to the spatial variability associated with workmanship and various other factors. This randomness produces spatially variable corrosion damages, such as steel weight loss and corrosion cracks. The structural capacity of reinforced concrete (RC) members strongly depends on the local conditions of their reinforcements. Modelling the spatial variability of steel corrosion is important, but steel corrosion in RC members can only be observed after severely damaging the concrete members. To understand the steel corrosion growth process and the change in the spatial variability of steel corrosion with time, continuous monitoring is necessary. In this study, X-ray photography is applied to observe steel corrosion in RC beams. The steel weight loss is estimated by the digital image processing of the X-ray photograms. The non-uniform distribution of steel weight loss along rebars inside RC beams determined using X-ray radiography and its correlation with longitudinal crack widths are experimentally investigated.

The 2011 Great East Japan earthquake and 2016 Kumamoto earthquake triggered discussion about more practical concept for seismic design assuming very intense seismic action. One of such concepts is referred to as a redundancy. In this study, reliability-based seismic design methodology for bridge pile foundation is developed taking into consideration the difference of redundancy. Redundancy depends on the longitudinal or transverse number of pile foundation. In an illustrative example, partial factors to consider the difference of redundancy and to ensure the target seismic reliability for bridge under uncertainty are determined based on Monte Carlo simulation. Proposed partial factors can provide motivation to design the bridge with high redundancy.

This paper presents a probabilistic framework for the life-cycle reliability assessment of existing bridges under multiple hazards. The life-cycle reliability of a bridge girder under traffic and airborne chloride hazards is compared with that of a bridge pier under seismic and airborne chloride hazards. When predicting the life-cycle reliability of existing bridges, observational data from inspection could be used to estimate the current material corrosion level. Random variables associated with the prediction of time-variant steel weight loss are updated by using Sequential Monte Carlo Simulation (SMCS). The life-cycle reliability of two bridge components under various hazards and inspection results are discussed in an illustrative example.

The use of Life Cycle Cost (LCC) tools in civil engineering is increasing, due to the need of infrastructure owners and operators to guarantee their assets maximum performance with an optimized budget. By considering these tools it will be possible to manage assets along their lifetime in a more sustainable and efficient way. Due to this reason, it was recently constituted a Task Group on fib to deal with existing LCC tools for concrete infrastructures. This paper gives an introduction to these tools, with a special emphasis to the added-value of LCC, and to the main contents of the fib TG 8.4 state-of-art technical report. This covers a description of existing LCC standards and guidelines, their applicability, the definition of different cost elements, the incorporation of risk in the analysis, etc.

Structural performance of deteriorated reinforced concrete (RC) members depends on the magnitude and location of steel corrosion. Finite element (FE) method has been applied to the structural performance assessment of corroded RC members; however, the difficulty in quantifying cross-sectional area of rebar embedded into the concrete has been reported as a main challenge for conducting the FE analysis precisely. The two main objectives of this paper are to: (1) experimentally investigate the effects of spatial variability associated with steel corrosion on the structural behavior of a corroded RC beam and (2) establish a FE numerical modeling to assess the structural performance of corroded RC beams. In the experimental study, the spatial variability associated with the steel weight loss over the RC beam is quantified using X-ray and digital image processing techniques. This experimental result is used as input data for the FE analysis. The proposed model provides good agreement with the test results.

 This paper presents a design concept of “anti-catastrophe” and proposes a framework of seismic design code for that concept. It proposes that the domain to be considered in the design should be extended in terms of three dimensions: phase, time, and space. We discuss the conditions required for the implementation of “anti-catastrophe”-oriented design. Since concepts of “anti-catastrophe”-oriented design is significantly different from that of conventional design, it is proposed to introduce “Category of Design” (CoD). We then present a design framework which consists of five stages. We also discuss institutional conditions required for this new design codes from the viewpoint of risk governance.

© 2017 Taylor & Francis Group, London.This paper presents a probabilistic framework for the life-cycle reliability assessment of existing bridges under multiple hazards. The life-cycle reliability of a bridge girder under traffic and airborne chloride hazards is compared with that of a bridge pier under seismic and airborne chloride hazards. When predicting the life-cycle reliability of existing bridges, observational data from inspection could be used to estimate the current material corrosion level. Random variables associated with the prediction of time-variant steel weight loss are updated by using Sequential Monte Carlo Simulation (SMCS). The life-cycle reliability of two bridge components under various hazards and inspection results are discussed in an illustrative example.

© 2017 Taylor & Francis Group, London.Structural performance of deteriorated reinforced concrete (RC) members depends on the magnitude and location of steel corrosion. Finite element (FE) method has been applied to the structural performance assessment of corroded RC members; however, the difficulty in quantifying cross-sectional area of rebar embedded into the concrete has been reported as a main challenge for conducting the FE analysis precisely. The two main objectives of this paper are to: (1) experimentally investigate the effects of spatial variability associated with steel corrosion on the structural behavior of a corroded RC beam and (2) establish a FE numerical modeling to assess the structural performance of corroded RC beams. In the experimental study, the spatial variability associated with the steel weight loss over the RC beam is quantified using X-ray and digital image processing techniques. This experimental result is used as input data for the FE analysis. The proposed model provides good agreement with the test results.

An earthquake of JMA magnitude 6.5 (first event) hit Kumamoto Prefecture, Japan, at 21:26 JST, April 14, 2016. Subsequently, an earthquake of JMA magnitude 7.3 (second event) hit Kumamoto and Oita Prefectures at 01:46 JST, April 16, 2016. An out-of-service Kyushu Shinkansen train carrying no passengers traveling on elevated bridges was derailed by the first event. This was the third derailment caused by an earthquake in the history of the Japanese Shinkansen, after one caused by the 2004 Mid-Niigata Prefecture Earthquake and another triggered by the 2011 Tohoku Earthquake. To analyze the mechanism of this third derailment, it is crucial to evaluate the strong ground motion at the derailment site with high accuracy. For this study, temporary earthquake observations were first carried out at a location near the bridge site; these observations were conducted because although the JMA Kumamoto Station site and the derailment site are closely located, the ground response characteristics at these sites differ. Next, empirical site amplification and phase effects were evaluated based on the obtained observation records. Finally, seismic waveforms during the first event at the bridge site of interest were estimated based on the site-effect substitution method. The resulting estimated acceleration and velocity waveforms for the derailment site include much larger amplitudes than the waveforms recorded at the JMA Kumamoto and MLIT Kumamoto station sites. The reliability of these estimates is confirmed by the finding that the same methods reproduce strong ground motions at the MLIT Kumamoto Station site accurately. These estimated ground motions will be useful for reasonable safety assessment of anti-derailment devices on elevated railway bridges.[Figure not available: see fulltext.]

© 2016 The Author(s).An earthquake of JMA magnitude 6.5 (first event) hit Kumamoto Prefecture, Japan, at 21:26 JST, April 14, 2016. Subsequently, an earthquake of JMA magnitude 7.3 (second event) hit Kumamoto and Oita Prefectures at 01:46 JST, April 16, 2016. An out-of-service Kyushu Shinkansen train carrying no passengers traveling on elevated bridges was derailed by the first event. This was the third derailment caused by an earthquake in the history of the Japanese Shinkansen, after one caused by the 2004 Mid-Niigata Prefecture Earthquake and another triggered by the 2011 Tohoku Earthquake. To analyze the mechanism of this third derailment, it is crucial to evaluate the strong ground motion at the derailment site with high accuracy. For this study, temporary earthquake observations were first carried out at a location near the bridge site; these observations were conducted because although the JMA Kumamoto Station site and the derailment site are closely located, the ground response characteristics at these sites differ. Next, empirical site amplification and phase effects were evaluated based on the obtained observation records. Finally, seismic waveforms during the first even

The severity of damage due to corrosion on reinforced concrete (RC) structures primarily depends on the magnitude and location of the steel corrosion. A finite element (FE) method has been used to evaluate the structural performance of RC members subjected to reinforcement corrosion. However, the difficulty in quantifying the residual rebar cross-sections in the concrete has been reported as the primary challenge in providing important parameters for modeling the corrosion damages on the steel reinforcement and concrete. The three primary objectives of this paper are to (a) experimentally investigate the effects of the spatial variability in the steel corrosion on the structural behaviors of five corroded RC beams, (b) establish a FE method to assess their deteriorated structural performances, and (c) develop Gumbel distribution parameters to estimate the spatial variability of corrosion for the rebars. In the experimental study, the spatial variability in the steel weight loss along the corroded rebars in the concrete medium was quantified using X-ray and digital image processing techniques. For the FE analysis, the experimental steel weight loss data was used for modeling the residual steel cross-sections, reduced concrete strength, and deteriorated bond interface. The flexural capacity obtained from the simulated beams is in agreement with experimental results.

Establishing consistent criteria for assessing the performance of structural systems and infrastructure networks is a critical component of communities' efforts to optimize investment decisions for the upkeep and renewal of the built environment. Although member-level performance and reliability assessment procedures are currently well-established, it is widely recognized that a member-oriented approach does not necessarily lead to an efficient utilization of limited resources when making decisions related to the management of existing deteriorating structures or lifeline systems, especially those that may be exposed to extreme events. For this reason, researchers have renewed their interests in developing system-level assessment methods as a basis to modern structural and infrastructure performance evaluation and design processes. Specifically, system-level performance metrics and characteristics such as reliability, redundancy, robustness, resilience, and risk continue to be refined. The objective of this paper is to extend the content of the accompanying paper on reliability-based performance indicators for structural members by reviewing proposals for the development and implementation of performance-based criteria for structural systems and infrastructure networks. The paper reviews established concepts of reliability design along with emerging ideas of performance-based and resilience-based design that are especially relevant for assessing and managing system-level risk. The paper also studies structural redundancy and robustness concepts as well as network-level performance metrics along with ranking approaches. Insights from these analyses reveal the need for transitioning structural and infrastructure design processes from a traditional component-level reliability-based approach, to one that seeks uniform levels of risk across scales (from structural systems to interconnected infrastructure networks across communities). Implementation examples are drawn from experiences with buildings, bridges, offshore oil and gas platforms, and a variety of infrastructure systems. The paper also reflects on promising avenues for pursuing practical and calibrated system-level performance indicators that support life cycle performance, safety, reliability, and risk of structural and infrastructure systems as integral parts of resilient communities.

Although several models are available for evaluating the structural performance of corroded reinforced concrete (RC) structures, seismic reliability assessments considering the effect of steel corrosion are currently scarce. Determining how long existing RC structures in an aggressive environment will be able to have a seismic safety level greater than the threshold remains difficult. Life-cycle reliability assessments of these structures under seismic hazards and hazards associated with airborne chloride are discussed in this paper. When predicting the seismic reliability of existing RC structures, observational data from inspection and/or nondestructive testing methods could be used to estimate the current material corrosion level. Considering the effect of steel corrosion in the plastic hinges of deteriorating structures on their seismic capacity is important. The displacement ductility capacity at the occurrence of longitudinal buckling of rebar in RC structures depends on the steel corrosion level in the plastic hinges. In this paper, the methodology to estimate the mean and variance of steel weight loss in the plastic hinge of corroded RC structures based on inspection results is presented. The number and space interval of inspection locations are considered when conducting the statistical estimation error process. The parameters to estimate the steel weight loss in the plastic hinges incorporating the spatial variability in steel corrosion are derived from experimental results to visualize the steel corrosion in RC members by X-ray technology. In addition, random variables associated with the prediction of time-variant steel weight loss are updated by sequential Monte Carlo simulations (SMCS) for consistency with the inspection results. The epistemic uncertainties can be reduced by SMCS. This process helps to conduct the reliability analysis more precisely. In this paper, a novel procedure for estimating the reliability-based life-cycle seismic reliability of existing RC structures in a marine environment by incorporating the spatial steel corrosion distribution is presented. In an illustrative example, the effects of the inspection results and frequency and the hazards associated with airborne chloride on the updated cumulative-time failure probability of a RC bridge pier in an earthquake-prone region are discussed.

Reinforced concrete (RC) bridges in a marine environment deteriorate with time due to chloride-induced corrosion of reinforcing bars. This paper presents a methodology for reliability-based durability assessment of RC bridges in a marine environment. A simple assessment criterion using partial factors that satisfy the target reliability level within the remaining lifetime of existing RC bridges is presented. A procedure to obtain the partial factors updated by the Sequential Monte Carlo Simulation is presented. In this procedure, the chloride concentration distribution by coring test is used as observational data. Partial factors are determined by taking into consideration the reduction in the uncertainty associated with the prediction of chloride-induced corrosion. Therefore, taking into account the reduction in the epistemic uncertainty, the values of the partial factors for durability assessment are different from those used for durability design.

The performance of corrosion-affected RC members depends strongly on localized damages of reinforcement. Therefore, modeling the spatial variability of steel corrosion is very important for the assessment of the remaining service life of corroded structures or time for maintenance. To study the changes of spatial variability of steel weight loss over time, a continuous monitoring is necessary. In this paper, a novel procedure of X-ray technique application in monitoring the spatial growth of a corroded bar in a RC specimen is demonstrated along with the digital image processing of X-ray images to estimate the steel weight loss. The relationship of steel weight loss and corrosion cracking is studied at different stages of corrosion. The validity of the estimation method of steel weight loss is also presented.

東日本大震災以降，設計で考慮する事象を超えた事象への対応についての関心が高まり，「危機耐性」という概念が共有されるようになってきた．しかしながら，その理念は理解されつつあるものの，それを如何に耐震設計体系に実装すればよいのか，まだ試行段階にある．一方で，危機耐性のような考え方は，技術者にとって全く新しい概念ではなく，例えば道路橋示方書では，地震時にも支承部が安定して挙動することを求めながらも，支承部の破壊を前提として機能する落橋防止システムの採用が記載されている．本論は，平成24年道路橋示方書を対象に，危機耐性に資することができる概念，事例を抽出し整理するとともに，国内外の動向を踏まえ，危機耐性に配慮した設計に対する課題を整理する．

東北地方太平洋沖地震において損傷を受けたRCラーメン高架橋に関して，これまで複数の文献においてその被害分析がなされており，プッシュオーバー解析等を行って柱部材の損傷進展について推察がなされている．本論文では，当該地震により柱部材に損傷を受けた第一中曽根高架橋について推定地震動を用いて3次元非線形動的解析を実施し，各柱部材および高架橋全体の地震時挙動を把握して，どのような過程で柱部材が損傷を受け，また各柱部材において損傷度になぜ差異が生じたのかについて考察した．RCラーメン高架橋の中間に位置する柱に比べて端部に位置する柱により大きな損傷が生じたのは，地震時に高架橋の回転変形モードが卓越したことが原因であるということを，数値解析的検討から明らかにした．

設計で考慮された外力を越える外力に対しても耐性を持つことを要求する「危機耐性」という概念を耐震設計体系に組み込むことが求められている．「危機耐性」は従来の耐震設計で用いられてきた概念とは異なる点も多く，適切な設計指針（コード）化には課題も多い．本稿では，「危機耐性」に基づく耐震設計体系の構築にあたっての課題や問題点を分析し，既存の耐震設計との整合性を確保するための枠組みとして，新たに「カテゴリー２」という概念を導入することを提案し，また，それにもとづく耐震設計体系の枠組みも提案した．さらに，そのような新しい耐震設計体系の実効性を維持するために，行政が考慮すべき社会的条件について，リスクガバナンスの理論枠組みとして考え方を用いて整理し，いくつかの基本的な方針を提案した．

The performance of corrosion-affected RC members depends strongly on localized damages of reinforcement. Therefore, modeling the spatial variability of steel corrosion is very important for the assessment of the remaining service life of corroded structures or time for maintenance. To study the changes of spatial variability of steel weight loss over time, a continuous monitoring is necessary. In this paper, a novel procedure of X-ray technique application in monitoring the spatial growth of a corroded bar in a RC specimen is demonstrated along with the digital image processing of X-ray images to estimate the steel weight loss. The relationship of steel weight loss and corrosion cracking is studied at different stages of corrosion. The validity of the estimation method of steel weight loss is also presented.

Serious damage occurred at Inohana Viaduct site along the Tohoku Shinkansen, Hanamaki City, during the 2003 Southern Sanriku Earthquake (M_J7.1). On the other hand, during the same eathquake, the nearby Nakasone Viaduct in Kitakami City did not suffer significant damage. In order to reveal the cause of of different performance of these structures, it is important to evaluate strong ground motions at the both viaduct sites. In this study, seismic waveforms at the viaduct sites were estimated based on the aftershock records at the viaduct sites and the main shock records at the nearby strong motion stations. In addition, the accuracy of the estimation methods with and without the aftershock records was discussed.

Reinforced concrete (RC) structures in a marine environment deteriorate with time due to chloride-induced corrosion of reinforcing bars. This paper presents reliability-based durability assessment of existing RC structure in a marine environment. A simple assessment criterion with partial factors that satisfy the target reliability level within the remaining life-time of existing RC structure is presented. A procedure to obtain the partial factors updated by the Sequential Monte Carlo Simulation is indicated. In this procedure, the chloride concentration distribution by coring test is used as observational data. Partial factors could be determined by taking into consideration the reduction of uncertainties associated with the prediction of chloride-induced corrosion. Partial factors for durability assessment of existing RC structures could be reduced compared with those for durability design of new RC structures.

Many bridges in Tohoku region of Japan were damaged and collapsed due to strong ground motions and/or liquefaction during the 2011 Great East Japan earthquake. Bridge superstructures were washed away due to the subsequent tsunami. In addition, bridges in the coastal area deteriorated further due to chloride induced corrosion. It is important to note that the seismic events can cause multiple disasters. The bridges located near the coastline in Japan need to be designed taking into consideration the risk associated with seismic and tsunami hazards, and continuous deterioration. This paper provides a key aspect of lifecycle design of bridges under multiple hazards, with an emphasis on earthquake, tsunami and continuous deterioration based on lessons learned from the 2011 Great Japan earthquake. A simple durability design criterion of reinforced concrete (RC) bridge in a marine environment is proposed to determine the concrete quality and concrete cover to prevent the chlorideinduced reinforcement corrosion causing the deterioration of structural performance during the whole lifetime. In addition, reliability-based capacity design of bridges with a hierarchy of resistance of the various structural components necessary to avoid catastrophic damage and to ensure prompt restoration after an extreme event is discussed.

Deterioration of RC members due to chloride-induced corrosion of reinforcing bars is a common problem in marine environment. After surface crack initiates, RC structures are prone to the occurrence of longitudinal surface cracks and concrete spalling. These deterioration mechanisms adversely cause significant reduction of the service life and performance of RC members. Therefore, it is important to create models to reliably predict the long-term performance of deteriorated RC structures. However, the very limited amount of experimental data on spatial variation of steel weight loss in relation to propagation of surface cracking widths has been reported to create difficulty in improving the degree of accuracy associated with the prediction models. This paper is aimed to experimentally investigate the non-uniform distribution of steel weight loss along reinforcing bars inside RC means by means of X-ray radiography and its correlation with longitudinal crack widths.

Even though accurate structural models have been developed for the performance of corroded structures subjected to monotonic flexure and/or shear, studies on seismic performance that include corrosion damage are scarce. For the lifetime assessment of structures in aggressive environments and earthquake-prone regions, the effects of corrosion on seismic performance need to be taken into consideration. Whereas the seismic demand depends on the results of seismic hazard assessment, the deterioration of seismic capacity depends on the environmental hazard assessment. The analysis of the life-cycle reliability of corroded reinforced concrete (RC) structures under earthquake excitations is the topic of this paper. It includes (a) estimation of the seismic capacity of corroded RC components; (b) seismic and airborne chloride hazard assessment and (c) life-cycle seismic reliability of bridges with corrosion damage. In particular, this paper introduces the visualisation of corrosion process in RC members using X-ray for modelling the spatial variability of rebar corrosion. A novel computational procedure to integrate the probabilistic hazard associated with airborne chlorides into life-cycle seismic reliability of bridge piers is presented. © 2013 © 2013 Taylor & Francis.

During the 2011 off the Pacific coast of Tohoku Earthquake, Nagamachi Viaducts on the Tohoku Shinkansen Line, Sendai City, Miyagi Prefecture, Japan, suffered significant damage. In order to analyze the damage mechanism, it is important to evaluate strong ground motions at the viaduct sites with high accuracy, taking into account site effects. In this study, seismic waveforms along the viaduct were estimated based on the SPGA model considering empirical site amplification and phase effects. Using the actual damage data and detailed distribution of the estimated ground motion, this study conducts the statistical analysis on the relationship between the damage ratio and several indices of the ground motion to construct fragility curves. The estimated ground motions and fragility curves will be useful in the detailed study of the damage mechanism.

In the Tohoku region, the effects of the seismic shocks and the tsunami waves due to the 2011 Great East Japan earthquake were felt with very high intensity. Many structures and infrastructures were severely damaged or washed away. Because tsunami effects have not been taken into consideration in the seismic design and retrofit specifications in Japan, code provisions regarding tsunamis need to be established based on the failure mechanisms observed in the tsunami-induced damage to bridges. In this paper, using both analytical fragility curves and tsunami hazard curves, the basic procedure to estimate the failure probability associated with tsunami hazard is presented. The tsunami fragility of a concrete girder bridge is estimated based on Monte Carlo Simulation (MCS). Seismic reliability of a bridge is compared with tsunami reliability of the same bridge. The need to consider the tsunami effect in the design of concrete girder bridge is discussed in an illustrative example.

When carbonation reaches the depth of the rebar embedded into the concrete, the high alkalinity of the concrete pore solution is neutralised and hydration products are dissolved. As carbonation progresses, the corrosion could extend enough to deteriorate the structural performance. In this paper, a time-dependent structural reliability analysis method, taking the carbonation into consideration, is proposed. To predict the corrosion process of reinforced concrete (RC) structures, spatial variability of corrosion has to be considered. A computational procedure to integrate the spatial variability of corrosion due to carbonation into life-cycle reliability assessment of existing RC structures is established. An illustrative example of a RC structure subjected to carbonation is presented. The emphasis is placed on investigating the effects of the spatial variation of inspected carbonation depths on the reliability estimates of RC structures. © 2014 American Society of Civil Engineers.

Reinforced concrete (RC) structures in a marine environment deteriorate with time due to chloride- induced corrosion of reinforcing bars. In this paper, a methodology for quantifying life-cycle reliability of RC jetties subjected to chloride attack is presented. The deterioration process of a RC jetty regarding the transition between the condition states is modeled as a Markov process. In addition, a procedure to obtain the transition probability matrix at time t after construction updated by the Sequential Monte Carlo Simulation (SMCS) method is indicated. Transition probability matrix could be updated in order to be consistent with the observational information. The methodology is illustrated on the superstructures of RC jetties located in a splash zone. The effect of the updating on the life-cycle reliability estimate of RC jetties is also discussed. © 2014 Taylor & Francis Group.

Tohoku-Shinkansen viaducts in eastern Japan were designed in accordance with specifications published in the 1970s. They have less shear reinforcement than required by current design specifications. Consequently, the No. 5 Inohana viaducts of Tohoku-Shinkansen failed in shear during the 2003 Sanriku-Minami earthquake. The viaducts were retrofitted by means of steel jacketing so that they had sufficient shear capacity. The retrofitted columns of the viaducts performed well during the 2011 Great East Japan earthquake. However, there is a lack of understanding of the impact of these retrofitting interventions on the vulnerability of the viaduct. It is important to recognise the relationship between the damage to the Shinkansen viaduct with retrofitted reinforced concrete columns and the ground motion intensity. After a brief review of the history of the performance of Shinkansen viaducts to several earthquakes prior to the 2011 Great East Japan earthquake, this paper presents fragility curves of the retrofitted and non-retrofitted Tohoku-Shinkansen viaducts based on nonlinear dynamic analyses and Monte Carlo simulation. It was found that the median of the fragility curve associated with the ultimate limit state for retrofitted viaduct is at least five times larger than that for as-built viaduct.

本稿では，鉄筋腐食を生じたコンクリート構造物の構造性能に関する耐久性能（以下，構造・耐久性能）を時空間で数値的に表現可能な評価手法としての数値構造解析の利用および構造全体系を評価できる構造・耐久性能指数の確立を目的として活動した「鉄筋腐食したコンクリート構造物の構造・耐久性能評価の体系化研究委員会」の成果1）の一部を報告する。特に本稿では，構造性能に影響する腐食量の空間的なばらつきを確率・統計的に推定する手法，腐食したコンクリート構造物の有限要素解析に不可欠な腐食鉄筋および腐食鉄筋とコンクリートの付着に関する構成則モデルを示した。また，構造・耐久性能指数の提案と定式化を行い，構造全体系の試算結果を紹介する。

2003年三陸南地震(MJ7.1)では，東北新幹線のRCラーメン高架橋(愛宕高架橋など)が損傷するなど，深刻な被害が発生した．一方で，愛宕高架橋に隣接する稗田高架橋での被災は確認されていない．愛宕高架橋ならびに稗田高架橋における本震時の地震動を推定することは，被災機構の分析等を行う上で非常に重要である．そこで本稿では，当該高架橋沿いにおいて高密度の地震観測を実施し，得られた記録に基づいて，サイト特性を評価した．そして，経験的サイト増幅・位相特性を考慮した強震動評価手法に基づき，2003年三陸南地震における愛宕高架橋・稗田高架橋沿いでの強震波形を推定した結果について報告する．

Even though accurate structural models have been developed for the performance of corroded structures subjected to monotonic flexure and/or shear, studies on seismic performance that include corrosion damage are scarce. For the lifetime assessment of structures in aggressive environments and earthquake-prone regions, the effects of corrosion on seismic performance need to be taken into consideration. Whereas the seismic demand depends on the results of seismic hazard assessment, the deterioration of seismic capacity depends on the environmental hazard assessment. The analysis of the life-cycle reliability of corroded reinforced concrete (RC) structures under earthquake excitations is the topic of this paper. It includes (a) estimation of the seismic capacity of corroded RC components; (b) seismic and airborne chloride hazard assessment and (c) life-cycle seismic reliability of bridges with corrosion damage. In particular, this paper introduces the visualisation of corrosion process in RC members using X-ray for modelling the spatial variability of rebar corrosion. A novel computational procedure to integrate the probabilistic hazard associated with airborne chlorides into life-cycle seismic reliability of bridge piers is presented.

Tohoku-Shinkansen viaducts in eastern Japan were designed in accordance with specifications published in the 1970s. They have less shear reinforcement than required by current design specifications. Consequently, the No. 5 Inohana viaducts of Tohoku-Shinkansen failed in shear during the 2003 Sanriku-Minami earthquake. The viaducts were retrofitted by means of steel jacketing so that they had sufficient shear capacity. The retrofitted columns of the viaducts performed well during the 2011 Great East Japan earthquake. However, there is a lack of understanding of the impact of these retrofitting interventions on the vulnerability of the viaduct. It is important to recognise the relationship between the damage to the Shinkansen viaduct with retrofitted reinforced concrete columns and the ground motion intensity. After a brief review of the history of the performance of Shinkansen viaducts to several earthquakes prior to the 2011 Great East Japan earthquake, this paper presents fragility curves of the retrofitted and non-retrofitted Tohoku-Shinkansen viaducts based on nonlinear dynamic analyses and Monte Carlo simulation. It was found that the median of the fragility curve associated with the ultimate limit state for retrofitted viaduct is at least five times larger than that for as-built viaduct. © 2013 © 2013 Taylor & Francis.

The probabilistic estimation of tsunami impact on bridges and the evaluation of potential tsunami risk are important topics, but they are still in very early stages of development. First, this paper presents the damage of bridges during the great Tohoku-oki earthquake and giant tsunami of 11 March 2011 based on the field damage investigation. The damage conditions and the possible failure mechanisms of bridges due to tsunami are particularly discussed. Second, tsunami fragility curves are presented. Empirical tsunami fragility curves based on the utilization of damage data associated with past tsunami disasters have been developed. In this paper, the tsunami fragility curves are established based on simulations. Bridge failure probability can be estimated using the tsunami hazard and fragility curves. Finally, an illustrative example of the reliability estimation of a bridge exposed to tsunami hazard is presented. © 2013, Earthquake Engineering Research Institute.

基礎構造物は，損傷の発見・修復の困難さから，レベル2地震動作用時にも弾性応答することが望ましい．この背景のもと，杭基礎の地震時保有水平耐力の向上を目的に，構成材料を高強度化し，断面中心部へプレストレスを導入したRC杭（高強度RC杭）を開発した．高強度RC杭は，かぶりコンクリートの曲げモーメント負担を期待するため，炭素繊維シートで被覆されている．本研究では，最初に，高強度RC杭の気中での単調曲げ載荷と正負交番載荷実験からその基本的な構造性能を把握した．次いで，実地盤中での正負交番載荷実験を実施し，既製杭に比べ，相当に大きな水平荷重の作用下でも弾性応答することを確認した．また，解析的な検討から，開発した高強度RC杭は既製杭と同様の手法で構造性能照査が可能であることを示した．

When designing bridges located in seismic hazard zones, the final design has to be determined by taking into consideration the functionality of the post-disaster road network. The effect of inelastic bridge behavior on the deterioration of the functionality of a road network after an earthquake needs to be incorporated in the seismic analysis. This paper deals with risk-based seismic design of RC bridges to ensure a specified postdisaster functionality of the road network. Computational results show that compared with bridges designed to minimize the seismic life-cycle cost, bridges designed taking into consideration the requirement of post-disaster traffic capacity of a road network need to have a higher seismic performance. © 2013 Taylor & Francis Group, London.

Due to the existence of uncertainties associated with mechanical properties, geometric configuration, loadings, and imperfect knowledge associated with the evaluations and predictions of material deterioration, probabilistic methods have been applied in the design and performance assessment of concrete structures to quantify these unavoidable uncertainties. This paper presents an approach for improving the accuracy in the life-cycle reliability assessment of reinforced concrete (RC) structures subjected to the carbonation by the Sequential Monte Carlo Simulation (SMCS). Using SMCS, multiple random variables related to observation information can be updated simultaneously, even if non-Gaussian random variables are involved and relationships between the observation information and random variables are nonlinear. The effect of the magnitude of inspected carbonation depth on the updated estimates of reliability associated with the occurrence of steel corrosion is discussed in this paper.

When designing bridges located in seismic hazard zones, the final design has to be determined by taking into consideration the functionality of the post-disaster road network. The effect of inelastic bridge behavior on the deterioration of the functionality of a road network after an earthquake needs to be incorporated in the seismic analysis. This paper deals with risk-based seismic design of RC bridges to ensure a specified post-disaster functionality of the road network. Computational results show that compared with bridges designed to minimize the seismic life-cycle cost, bridges designed taking into consideration the requirement of post-disaster traffic capacity of a road network need to have a higher seismic performance.

Many existing bridges designed before the 1995 Hyogo-Ken Nanbu earthquake have been retrofitted to prevent failure from strong excitations. However, in seismic bridge design and retrofit, the tsunami effects have not been taken into consideration. In this paper, using both the analytical fragility curve and tsunami hazard curve, the basic procedure to estimate the failure probability associated with tsunami hazard is presented. The tsunami fragility of a single-story RC rigid frame before and after seismic retrofit is estimated based on Monte Carlo Simulation. Seismic reliability of as-built and retrofitted frames is compared with tsunami reliability of the same frames. The need to consider the tsunami effect in the design of RC frame is discussed in an illustrative example. © 2013 Taylor & Francis Group, London.

The life-cycle assessment of reinforced concrete structures through economic, environmental, and social impact across the whole service life is now gaining more and more interest in civil engineering. The mechanical properties and long-term performance of structures using recycled aggregate concrete (RAC) were reported to be weaker than those of structures using natural aggregate concrete (NAC) given the same mix proportion. However, the studies on the durability of RAC subjected to carbonation are scare and limited in the literature. The main purpose of this study is to present the computational procedure for the life-cycle reliability estimations of NAC and RAC structures exposed to carbonation. The experimental results of NAC and RAC under the diffusion of carbon dioxide (CO2) are obtained from the literature reviews. A durability design factors and criterion for designing concrete structure using RAC that satisfy the target failure probability is presented. The effects of concrete properties (i.e. water to cement ratio) and concrete cover on the estimation of reliability of structures using natural and recycled aggregate are investigated in an illustrative example.

Reinforced concrete (RC) structures in a marine environment deteriorate with time due to chloride-induced corrosion of reinforcing bars. In this paper, a methodology for quantifying life-cycle reliability of RC structures subjected to chloride attack is presented. The deterioration process of bridge components regarding the transition between the condition states is modeled as a Markov process. In addition, a procedure to obtain the transition probability matrix at time t after construction updated by the Sequential Monte Carlo Simulation (SMCS) is indicated. Transition probability matrix could be updated to be consistent with the observational information. The methodology is illustrated on an existing RC superstructures of wharves located in a splash zone. The effect of the updating on the life-cycle reliability estimate of RC wharves is discussed in this paper.

Over the last two decades, the probabilistic assessment of reinforced concrete (RC) structures under seismic hazard has been developed rapidly. However, little attention has been devoted to the assessment of the seismic reliability of corroded structures. This paper presents a framework for computing the time-dependent seismic reliability of concrete bridges in an earthquake prone region and a marine environment. It includes: (a) estimate of seismic capacity of corroded RC components; (b) seismic and airborne chloride hazard assessment; and (c) seismic reliability of bridges with corrosion damage. The effects of seismic hazard, hazard associated with airborne chloride, and spatial distribution of steel corrosion on the time-dependent seismic reliability are investigated in this paper. The findings show that the time-dependent reliability of concrete bridge depends on both the seismic and airborne chloride hazards, and that the spatial distribution of steel corrosion has to be taken into consideration in the seismic reliability analysis.

The 2011 Great East Japan Earthquake caused multiple disasters, including (a) damage and collapse of bridges due to strong ground motions and/or liquefaction and (b) washout of bridge superstructures due to the subsequent tsunami. In addition, bridges in the coastal area deteriorated further due to chlorideinduced corrosion. Procedures for identifying and screening significant threat scenarios and for assessing and mitigating the risk of bridge damage and collapse under multiple hazards can be developed using probabilistic risk assessment.This paper provides a framework for estimating the life-cycle reliability of bridges under multiple hazards, with an emphasis on earthquake, tsunami and continuous deterioration. Reliability-based capacity design of bridges with a hierarchy of resistance of the various structural components necessary to avoid catastrophic damage and to ensure prompt restoration from an extreme event is discussed. © 2013 Taylor & Francis Group, London.

It is essential to update the model with reflecting observation or inspection data for reliability estimation of existing structures. Authors proposed updated reliability analysis by using Particle Filter. We discuss how to apply the proposed method through numerical examples on reinforced concrete structures after verification of the method with hypothetical linear Gaussian problem. Reinforced concrete structures in a marine environment deteriorate with time due to chloride-induced corrosion of reinforcing bars. In the case of existing structures, it is essential to monitor the current condition such as chloride-induced corrosion and to reflect it to rational maintenance with consideration of the uncertainty. In this context, updated reliability estimation of a structure provides useful information for the rational decision. Accuracy estimation is also one of the important issues when Monte Carlo approach such as Particle Filter is adopted. Especially Particle Filter approach has a problem known as degeneracy. Effective sample size is introduced to predict the covariance of variance of limit state exceeding probabilities calculated by Particle Filter. Its validity is shown by the numerical experiments.

宮城県本吉郡南三陸町志津川では，2011年東北地方太平洋沖地震による巨大津波の来襲により，土木施設に甚大な被害が及び，多数の死者・行方不明者が出た．志津川は比較的震源域に近いことから，津波来襲前の強震動により施設が損傷を受けていた可能性もあり，志津川における強震動の評価は非常に重要であるが，被害の生じた志津川平地部では本震記録として気象庁計測震度の値しか残されていない．そこで本研究では，志津川平地部において余震観測を実施し，得られた記録に基づいてサイト特性の評価を行い，スーパーアスペリティモデルに基づく強震波形計算を行うことにより本震時の強震波形を推定した．

In the seismic design of reinforced concrete (RC) bridge structures, there should be no brittle failures, such as shear failures, in the components, and a plastic hinge should be formed at the bottom of the bridge pier. These are important concepts in capacity design to guarantee the safety of bridges subjected to severe earthquakes. These concepts can maximise post-event operability and minimise the cost of repairing bridges after a severe earthquake. In this article, a reliability-based methodology to carry out capacity design with partial factors is proposed and applied to the seismic design of RC bridge structures. This ensures that (i) all of the components undergo the desired ductile failure mode, (ii) the damage due to an earthquake is induced only at the bottom of the bridge pier and (iii) the probability of failure is at most equal to a specified value. © 2012 Copyright Taylor and Francis Group, LLC.

In this paper, the hazard curve associated with airborne chlorides in a marine environment and the computational procedure to obtain the probability of occurrence of corrosion cracking in reinforced concrete (RC) structures are presented. A method for integration of the effects of airborne chloride into reliability-based durability design of RC structures in a marine environment is proposed. By using this method, it is possible to determine the probability of corrosion cracking due to airborne chlorides, regardless of region, distance from coastline, and the properties of the concrete controlled by the water to cement ratio. © 2012 Taylor and Francis Group, LLC.

An earthquake can cause multiple disasters. For the reliability estimation of coastal structures and infrastructures in Japan, seismic hazard, tsunami hazard and hazard associated with airborne chlorides need to be taken into consideration. Firstly, this paper presents the damage of bridges during the Great East Japan Earthquake and Tsunami on March 11, 2011 based on the Japan Society of Civil Engineers (JSCE) damage investigation. Especially, the damages condition and the possible failure mechanisms of bridges due to tsunami are discussed based on the field survey. Secondly, the tsunami fragility curves are presented. These are used to estimate the structural fragility under the tsunami hazards. Bridge failure probability can be estimated using the tsunami hazard curve and the fragility curve. Finally, an illustrative example quantifying the effect of bridge pier height on the reliability of a bridge under tsunami hazard is presented. © ASCE 2012.

This paper presents a framework for estimating the time-dependent reliability of prestressed concrete (PC) bridge girders in a marine environment. The analysis considers the spatial variability associated with concrete cover, surface chloride concentration, and coefficient of diffusion of chloride over the entire area. PC bridge girder is modeled as one-dimension spatial model. In addition, random variables for estimating the corrosion process of PC bridge girders are updated based on observational information such as chloride concentration distribution by coring test. Sequential Monte Carlo Simulation (SMCS) is used to update simultaneously multiple random variables relating to observational information. In an illustrative example, the effect of the spatial interval of observational information given by coring test on the updated estimate of a PC bridge girder reliability is investigated. © 2012 Taylor & Francis Group.

Since structural capacity of RC members depends strongly on localized condition of reinforcements, it is important to model the spatial variability of steel corrosion. However, steel corrosion in RC members can only be observed after severely damaging the concrete member. In order to understand the growth process of steel corrosion and how the spatial variability of steel corrosion increases with time a continuous monitoring is necessary. In this study, X-ray photography is applied to observation of steel corrosion in RC members. The steel weight loss is estimated by using a digital image processing of X-ray photogram. Comparing the steel weight loss estimated by weight measurement with that estimated by the digital image processing, applicability of X-ray photogram for the observation of corrosion process in RC members is demonstrated.

This keynote paper presents the damage of structures and infrastructures in the Tohoku Region during the Great East Japan earthquake and tsunami of March 11, 2011. Field investigations after this earthquake proved the effectiveness of upgrades of seismic specifications and seismic retrofit. Meanwhile, some of existing bridges without seismic retrofit were severely damaged due to strong ground motions. In addition, many superstructures were completely washed away by the tsunami, and several substructures were overturned due to scour. Some of reinforced concrete components and steel bearings were severely deteriorated due to chloride-induced corrosion. Life-cycle reliability of bridges in Japan has to be estimated taking into consideration the seismic hazard, tsunami hazard, and hazard associated with airborne chlorides. Lessons from the 2011 Great East Japan earthquake with emphasis on life-cycle structural performance is the topic of this keynote paper.

In the seismic design of reinforced concrete (RC) bridge structures, there should be no brittle failures, such as shear failures, in the components, and a plastic hinge should be formed at the bottom of the bridge pier. These are important concepts in capacity design to guarantee the safety of bridges subjected to severe earthquakes. These concepts can maximise post-event operability and minimise the cost of repairing bridges after a severe earthquake. In this article, a reliability-based methodology to carry out capacity design with partial factors is proposed and applied to the seismic design of RC bridge structures. This ensures that (i) all of the components undergo the desired ductile failure mode, (ii) the damage due to an earthquake is induced only at the bottom of the bridge pier and (iii) the probability of failure is at most equal to a specified value.

In this study, a prestressed reinforced concrete pile that uses high-strength material to increase the pile's flexural capacity was developed. The main structural characteristics of the developed pile include (1) the neutral axis is constantly near the centroidal axis of the pile, even if the longitudinal reinforcement yields due to a flexural moment, because the pile has a high axial compressive force that is induced by prestressed steel bars, and hence, the concrete in the compression region can contribute to increasing the flexural strength of the pile; and (2) the flexural strength of the pile increases because the high-strength concrete is confined by high-strength spirals and carbon-fiber sheets in combination with concrete infilling, and, together, these modifications provide a sufficiently high lateral-confinement pressure. The results of bending tests demonstrate that the proposed prestressed reinforced concrete pile with carbon-fiber sheets and concrete infilling had a much higher flexural capacity than a conventional precast concrete pile. In addition, an analytical approach is presented that can be used to obtain the relationship between the bending moment and the curvature of the proposed pile. Even if concrete bridge systems are constructed on strata that can experience soil liquefaction, such as very soft soil, bridge foundations that use the proposed piles could remain undamaged under the design seismic action. © 2011 Elsevier Ltd.

Over the last two decades, the probabilistic assessment of reinforced concrete (RC) structures under seismic hazard has been developed rapidly. However, little attention has been devoted to the assessment of the seismic reliability of corroded structures. For the life-cycle assessment of RC structures in a marine environment and earthquake-prone regions, the effect of corrosion due to airborne chlorides on the seismic capacity needs to be taken into consideration. Also, the effect of the type of corrosive environment on the seismic capacity of RC structures has to be quantified.

Over the last two decades, the probabilistic assessment of reinforced concrete (RC) structures under seismic hazard has been developed rapidly. However, little attention has been devoted to the assessment of the seismic reliability of corroded structures. For the life-cycle assessment of RC structures in a marine environment and earthquake-prone regions, the effect of corrosion due to airborne chlorides on the seismic capacity needs to be taken into consideration. Also, the effect of the type of corrosive environment on the seismic capacity of RC structures has to be quantified. In this paper, the evaluation of the displacement ductility capacity based on the buckling model of longitudinal rebars in corroded RC bridge piers is established, and a novel computational procedure to integrate the probabilistic hazard associated with airborne chlorides into life-cycle seismic reliability assessment of these piers is proposed. The seismic demand depends on the results of seismic hazard assessment, whereas the deterioration of seismic capacity depends on the hazard associated with airborne chlorides. In an illustrative example, an RC bridge pier was modeled as single degree of freedom (SDOF). The longitudinal rebars buckling of this pier was considered as the sole limit state when estimating its failure probability. The findings show that the life-cycle reliability of RC bridge piers depends on both the seismic and airborne chloride hazards, and that the cumulative-time failure probabilities of RC bridge piers located in seismic zones can be dramatically affected by the effect of airborne chlorides. © 2011 John Wiley & Sons, Ltd.

The need to replace conventional methods with performance-based design is well recognized. As performance-based design has come into use around the world, reliability theory will be used for the seismic safety or durability evaluation of concrete structures. The JSCE task committee 336 on “Reliability-Based Design of Concrete Structures” was established in 2006. The objectives of the activities of the committee are to investigate the techniques for introducing reliability-based design into design codes for concrete structures in Japan and, to present the practical examples of seismic safety or durability evaluation for concrete structures based on the reliability theory.

鉄筋コンクリート（RC）部材内で生じる鉄筋腐食の進展を観察できれば，鉄筋腐食の不均一さ（腐食の空間分布）の程度と形成過程の理解，あるいは，それと部材表面に表れる腐食ひび割れ幅・密度の関係の把握など，RC構造物の維持管理の高度化につながる情報が得られると期待される。本研究では，RC部材内の鉄筋腐食成長過程のX線撮影による観察の可能性を検討した。まず，腐食量が既知の鉄筋を埋め込んだRC供試体のX線撮影を行い，腐食量を精度良く再現するための撮影方法やディジタル画像処理方法，あるいは精度に及ぼすかぶりや水セメント比の影響などを検討した。次いで，電食にて劣化させたRC部材を連続的にX線撮影することで，鉄筋腐食成長過程，鉄筋腐食量と腐食ひび割れ幅の関係，あるいはそれらが部材曲げ耐力に及ぼす影響に関する基礎資料を得た。

For structures located in a moderately or highly aggressive environment, multiple environmental and mechanical stressors lead to deterioration of structural performance and, therefore, create maintenance issues. Such deterioration will reduce the service life of structures. The main purpose of this paper is to discuss a methodology previously proposed by the writers for the evaluation of long-term seismic reliability of reinforced concrete (RC) bridge piers in a marine environment and present new results. This methodology consists of three steps: (1) investigate the relationship between material deterioration and structural performance on an experimental basis; (2) consider both the seismic hazard and the hazard associated with marine environment; and (3) perform an analysis of the long-term seismic performance of RC bridge piers in an aggressive marine environment. © ASCE 2011.

An experimental and analytical study was conducted to investigate the ductility of concrete-encased steel piers, referred to as "steel-reinforced concrete (SRC) construction." Based on the cyclic lateral loading tests of SRC column specimens, the restorable and ultimate limit states are defined as the point when concrete cover spalling occurs (equivalent to longitudinal bar buckling) and the point when flange buckling of the H-shaped steel occurs, respectively. To estimate the lateral displacement capacity at both the restorable and ultimate limit states, the curvature distribution of the column was calculated based on the buckling analysis of the longitudinal bar, which was restrained by a concrete cover and transverse reinforcement, and of the steel flange encased in concrete. The lateral displacement was obtained by integrating the curvature distribution. Comparison of the computed results with experimental results, including other writers' reports, confirmed that the proposed method can appropriately estimate the lateral displacement at the restorable and ultimate limit states, and it can accurately evaluate the buckling characteristics of the longitudinal bar and steel flange components of SRC column specimens. © 2011 ASCE.

In the design of reinforced concrete (RC) structures in a marine environment, it is important to consider the effects of this environment on structural long-term performance. In this paper, a time-dependent structural reliability analysis method taking the hazard associated with airborne chlorides into consideration is proposed. Also, a procedure to obtain the failure probabilities of RC structures in a marine environment updated by Sequential Monte Carlo Simulation (SMCS) is indicated. In this procedure, the corrosion crack width is used as observational data. For illustrative purposes, time-dependent reliability analyses are presented for one-way RC slabs in a marine environment. Using SMCS, multiple random variables related to observation information can be updated simultaneously. This is realized by taking into consideration the joint probability density functions of the random variables. The effects of the hazard associated with airborne chlorides and an inspection result of corrosion cracking on the updated estimate of one-way RC slab reliability are discussed in this study. © RILEM 2011.

For structures located in aggressive environments and earthquake regions, it is important to consider the effect of material corrosion on seismic performance. This chapter presents a seismic analysis methodology for corroded reinforced concrete (RC) bridges. It is shown that the analytical results are in good agreement with the experimental results regardless of the amount of steel corrosion. The proposed method is applied to lifetime seismic reliability analysis of corroded RC bridge piers, and the relationship between steel corrosion and seismic reliability is presented. After the occurrence of crack corrosion, seismic reliability of the pier is significantly reduced. If corrosion cracks in the bridge pier are detected by visual inspection, additional detailed inspections need to be performed.

There are many kinds of uncertainties involved in the evaluation of corrosion process and deterioration of structural performance. Because of the presence of uncertainties, it is necessary that long-term structural performance be treated based on reliability concepts and methods. This paper presents a probabilistic framework for estimating the time-dependent reliability for existing prestressed concrete structures in a marine environment based on a non-linear filtering technique denoted Sequential Monte Carlo Simulation (SMCS). The results of manual measurement or automatic monitoring are used as observational information. The emphasis is placed on investigating the effects of the differences between manual measurement and automatic monitoring, and possible interruption periods of health monitoring on updated estimates of reliability of prestressed concrete bridges located in a marine environment. © 2011 Taylor & Francis Group, London.

A reliability estimation method is proposed to estimate the limit state exceeding probability of existing structures considering observation data by Sequential Monte Carlo Simulation (SMCS). Accuracy estimation is one of the important issues when MC approach is adopted. Specifically SMCS approach has a problem known as degeneracy. Effective sample size is introduced to estimate the accuracy of estimated limit state exceeding probabilities. Coefficient of variance of estimated probability is predicted based on the effective sample size ratio of the updated model. The proposed method is demonstrated through a numerical example of reliability analysis on deteriorating RC structures. © 2011 Taylor & Francis Group, London.

The importance of economical construction of infrastructures has recently increased. The application of spiral steel pipes to bridge piers is considered as one of the effective methods. Spiral steel pipes have been seldom used for bridge piers. Currently, spiral steel pipes have been mainly used as the foundations of buildings or bridges and are relatively economical because they are produced in large quantities in factories. However, roll forming processes of spiral steel pipes are different from those of bending roll pipes which have been generally used as bridge piers, so that seismic performance of spiral steel pipes may be different from that of bending roll pipes. Therefore, it is very important to grasp the ultimate strength and the ductility of spiral steel pipes. In this study, the finite element analysis was conducted for grasping the elasto-plastic behavior of hollow spiral steel pipes. Based on the analysis results, the seismic performance of hollow spiral steel pipes under compressive axial force and bending moment was examined and the influences of the structural parameters on the seismic performances of the spiral steel pipes are discussed.

鉄筋コンクリート（RC）部材内で生じる鉄筋腐食の進展を観察できれば，鉄筋腐食の不均一さ（腐食の空間分布）の程度と形成過程の理解，あるいは，それと部材表面に表れる腐食ひび割れ幅・密度の関係の把握など，RC構造物の維持管理の高度化につながる情報が得られると期待される。本研究では，RC部材内の鉄筋腐食成長過程のX線撮影による観察の可能性を検討した。まず，腐食量が既知の鉄筋を埋め込んだRC供試体のX線撮影を行い，腐食量を精度良く再現するための撮影方法やディジタル画像処理方法，あるいは精度に及ぼすかぶりや水セメント比の影響などを検討した。次いで，電食にて劣化させたRC部材を連続的にX線撮影することで，鉄筋腐食成長過程，鉄筋腐食量と腐食ひび割れ幅の関係，あるいはそれらが部材曲げ耐力に及ぼす影響に関する基礎資料を得た。

An experimental and analytical study was conducted to investigate the ductility of concrete-encased steel piers, referred to as "steel-reinforced concrete (SRC) construction." Based on the cyclic lateral loading tests of SRC column specimens, the restorable and ultimate limit states are defined as the point when concrete cover spalling occurs (equivalent to longitudinal bar buckling) and the point when flange buckling of the H-shaped steel occurs, respectively. To estimate the lateral displacement capacity at both the restorable and ultimate limit states, the curvature distribution of the column was calculated based on the buckling analysis of the longitudinal bar, which was restrained by a concrete cover and transverse reinforcement, and of the steel flange encased in concrete. The lateral displacement was obtained by integrating the curvature distribution. Comparison of the computed results with experimental results, including other writers' reports, confirmed that the proposed method can appropriately estimate the lateral displacement at the restorable and ultimate limit states, and it can accurately evaluate the buckling characteristics of the longitudinal bar and steel flange components of SRC column specimens.

In the design of reinforced concrete (RC) structures in a marine environment, it is important to consider the effects of this environment on structural long-term performance. In this paper, a time-dependent structural reliability analysis method taking the hazard associated with airborne chlorides into consideration is proposed. Also, a procedure to obtain the failure probabilities of RC structures in a marine environment updated by the Sequential Monte Carlo Simulation (SMCS) is indicated. In this procedure, the corrosion crack width and chloride concentration distribution by coring test are used as observational data. For illustrative purposes, time-dependent reliability analyses are presented for one-way RC slabs in a marine environment. Using SMCS, multiple random variables related to observation information can be updated simultaneously. This is realized by taking into consideration the joint probability density functions of the random variables. The effects of various marine environments, inspection results, and number of inspections on the updated estimates of an RC slab reliability are discussed in this paper. © 2010 Elsevier Ltd.

In the design of reinforced concrete (RC) structures in a marine environment, it is important to consider the effects of this environment on structural long-term performance. In this paper, a time-dependent structural reliability analysis method taking the hazard associated with airborne chlorides into consideration is proposed. Also, a procedure to obtain the failure probabilities of RC structures in a marine environment updated by the Sequential Monte Carlo Simulation (SMCS) is indicated. In this procedure, the corrosion crack width and chloride concentration distribution by coring test are used as observational data. For illustrative purposes, time-dependent reliability analyses are presented for one-way RC slabs in a marine environment. Using SMCS. multiple random variables related to observation information can be updated simultaneously. This is realized by taking into consideration the joint probability density functions of the random variables. The effects of various marine environments, inspection results, and number of inspections on the updated estimates of an RC slab reliability are discussed in this paper. (C) 2010 Elsevier Ltd. All rights reserved.

When a concrete structure fails, the damage is usually concentrated in a narrow region. The fracture zone and localization behavior have to be captured to accurately assess the structural behavior. In this research, large-scale high-strength reinforced concrete columns were tested under concentric loading. The experimental results show that in columns with sections ranging from 200 to 500 mm (7.88 to 19.7 in.), the length of the compressive fracture zone increases with the cross section dimension; however, the post-peak compressive fracture energies are independent of cross section dimension and column height, provided that the columns have the same concrete compressive strength and lateral confining pressure. A formalized stress-averaged strain model for confined concrete has been developed by using the compressive fracture energy. Regardless of gauge length, cross section dimension, and concrete strength, the proposed model provides good agreement with the test results. © 2010, American Concrete Institute. All rights reserved.

For reinforced concrete (RC) structures located in a marine environment it is important to consider the effects of this environment on their long-term performance. In this paper, a time-dependent structural reliability analysis method of RC bridge slabs taking the hazard associated with airborne chlorides into consideration is proposed. Also, a procedure to obtain the failure probabilities of RC bridge slabs in a marine environment updated by Sequential Monte Carlo Simulation (SMCS) is indicated. Using SMCS, multiple random variables related to observation information can be updated simultaneously. The effects of marine environment, inspection results, and the number of inspections on the updated estimates of bridge slab reliability are discussed. © 2010 Taylor & Francis Group, London.

スパイラル鋼管は，その製造工程の関係で複雑な塑性加工を受け，溶接シームも螺旋状になるため，ベンディングロールで製作されることの多い鋼製橋脚と耐震性能は異なる可能性がある．そこで，本研究ではコンクリートを充填しないスパイラル鋼管の正負交番載荷実験を行い，その耐力および変形性能といった耐震性能に関するデータの収集を行った．さらに，実験結果との比較により妥当性を検証した弾塑性有限変位解析により，より幅広くその耐震性能に関する情報を収集するとともに，溶接シームが耐震性能に与える影響等について考察を行った．そして，実験結果および解析結果から，既往の鋼製橋脚の手法をもとにしたスパイラル鋼管の耐震性能評価手法の提案を行った．

If concrete bridge systems are constructed in conditions such as very soft soil that can experience soil liquefaction due to a severe earthquake, it is difficult to prevent yielding of the pile foundation. In this study prestressed reinforced concrete pile using high-strength material to increase the pile's flexural capacity is developed. The main structural characteristics of the developed pile are that (1) the neutral axis is constantly near the centroidal axis of the pile, even if longitudinal reinforcements are yielding due to flexural moment, because the pile has a high axial compression force induced by the prestressing steel bars. This means that the concrete in the compression region can contribute to increasing the flexural strength of the pile; and (2) using carbon fiber sheets to prevent the spalling of the cover concrete can contribute to increasing the flexural strength of the pile. The results of the bending test show that the proposed prestressed reinforced concrete pile with carbon fiber sheets and infilling concrete has a higher flexural capacity than that of a pile without these sheets and infilling concrete, and the pile did not exhibit brittle behavior.

Inspection or test data of specific site as well as latest knowledge of degrading mechanism should be considered in order to perform accurate reliability estimation of existing structures. This study discusses the methodology to estimate limit state probability updated by inspection or test data. The formulation with sequential Monte Carlo simulation (SMCS) is introduced for updating of model parameters and limit state probability. After demonstrating the solutions by SMCS agrees well with theoretical solutions in a linear Gaussian problem, numerical examples on updating of chloride deterioration parameter of a RC structure and three kind of limit state probability are shown.

Concrete-filled circular spiral steel tubes (CFST) were tested under cyclic lateral force and a constant axial load. The welded part of this steel tube form a spiral and the seam-welded part is thicker than the steel tube wall. The test results showed that filling in steel tube with concrete enhanced the loading capacity and ductility of the CFST, and the spiral-welded part had no influence on the tube's flexural behavior. It was confirmed that the evaluation of the seismic performance of CFSTs does not need to take the existence of a spiral-welded part into consideration, and the relationship between load and horizontal displacement of CFSTs can be evaluated based on current design specifications.

It has been required to decrease the construction cost of infrastructures. The application of spiral steel pipes to bridge piers is considered as one of the effective methods. Spiral steel pipes are relatively economical because they are produced in large quantities in factories. However roll forming processes of spiral steel pipes are different from those of bending roll pipes which are generally used as bridge piers so that seismic performance of spiral steel pipes may be different from that of bending roll pipes. Therefore it is very important to investigate the ultimate strength and the ductility of spiral steel pipes. In this study in order to grasp the elasto-plastic behavior of spiral steel pipes piers cyclic loading experiments with two specimens were conducted and the effect of radius thickness ratio parameter on the ultimate strength and the ductility was observed. Furthermore the experimental results were compared with the analysis results by the previous seismic evaluation methods.

本研究は,コンクリート構造物の塩害に対する耐久性照査を信頼性理論に基づく限界状態設計法の枠組みの中で実現することを目的とした基礎的研究である。海洋からの塩分の飛来から銅材腐食の発生,さらには,その後の腐食ひび割れの発生までの予測に伴う種々の不確定性を考慮して設計耐用期間内の腐食ひび割れ発生確率を信頼性理論に基づき算定した。その上で,その腐食ひび割れ発生確率を目標値へと漸近させることのできる部分係数と設計規準式を提案した。提案した部分係数と設計規準式を用いることで,設計者は確率計算を行うことなく,意図した耐久信頼性を有するコンクリート構造物を設計できることを示した。

基礎は,損傷の発見や修復の困難さから,地盤条件などによらず,レベル2地震動作用時にも弾性応答することが望ましい。本研究では,杭基礎の地震時保有水平耐力の向上を目的として,高強度構成材料を使用し,断面中心部ヘプレストレスを導入したRC杭体(高強度RC杭体)を考案した。そして,導入プレストレスや鉄筋量を変化させた10体の高強度RC杭の曲げ実験を実施し,損傷進展や曲げ耐力の発現状況などを考察することで,この種の構造の力学特性に関する基礎データを収集した。また,高強度RC杭体の曲げ耐力を評価可能な断面解析法を提案し,本構造における各構成材料の曲げ耐力の負担割合等を明らかにした。

本研究は，塩害を受けるRC橋脚の耐震安全性を設計耐用期間内で確保するための耐震設計と耐久設計のあり方を信頼性理論に基づき検討したものである．具体的には，鉄筋腐食が生じたRC橋脚の耐震解析モデルを構築し，耐震解析に伴う不確定性を整理することで，健全RC橋脚と同等の耐震安全性（損傷確率）を有するとみなせる鉄筋腐食量の範囲などを検討した．次に，材料劣化の進展モデルに基づき，着目した各鉄筋腐食量に設計耐用期間内に到達する可能性を確率的に評価し，その確率値を許容値に抑えることができるかぶりを耐久信頼性設計により算定した．結果として，腐食ひび割れ発生点を限界状態とした耐久設計を行うことにより，設計耐用期間内の鉄筋腐食による耐震安全性の低下は無視でき，かつ合理的なかぶりの大きさを与えられる結果を得た．

コンクリート充填鋼管の一軸圧縮実験を行い,その力学特性に関する基礎データを収集した。主な実験因子は,銅管種別(電縫鋼管とスパイラル鋼管),および充填されるコンクリートの圧縮強度である。コンクリート圧縮強度が大きく,かつ鋼管の周方向応力の発現が遅れる場合には,RC柱と同じく,充填コンクリートに圧縮破壊の局所化が生じ,局所ひずみが後退または停滞する領域が現われることを確認した。また,鋼管の応力経路や充填コンクリートの平均化応力-ひずみ関係の比較から,充填コンクリートのコンファインド効果の評価ではスパイラル鋼管が持つらせん形のシーム(溶接)の影響は考慮する必要がないと判断された。

本研究は,コンクリート構造物の環境作用に対する性能照査を信頼性理論に基づく限界状態設計法の枠組みの中で実現することを目的とした基礎的研究である。沿岸部などの塩害環境に着目し,海洋からの塩分の飛来から鉄筋腐食発生,さらにはその後の腐食ひび割れの発生までの予測に伴う種々の不確定性について,観測・実験データをもとに評価し,耐用期間内に鉄筋腐食や腐食ひび割れが発生する確率を信頼性理論に基づき定量化した。耐久設計をする際の限界状態を鉄筋腐食発生点から腐食ひび割れ発生点に変更することで,ある目標限界状態到達確率を確保するための必要かぶりを大きく低減できる可能性が示された。

円形鋼管内のコンクリートで生じるコンファインド効果の発現メカニズムの解明を目的として,コンクリート圧縮強度が約20MPaと60MPaのコンクリートを充填した鋼管柱の一軸圧縮実験を行った。鋼管の軸圧縮力の負担程度によりコンファインド効果は大きく異なり,鋼管の円周方向応力の発現が遅れると,充填コンクリートの圧縮破壊領域で荷重が低下すること,鋼管に軸圧縮力をほとんど負担させないように載荷した場合には,その充填コンクリートの挙動は既往のRC柱の実験に基づき提案されているコンファインドコンクリートの平均化応力-ひずみ関係により概ね評価可能であること,などが明らかとなった。

SRC橋脚の耐震設計において,かぶりコンクリートの剥落を修復限界,H形鋼の局部座屈を終局限界とする部材損傷レベルを設定した。ファイバー解析によるSRC橋脚の動的解析を行った結果,単柱式橋脚では,橋脚基部の塑性変形が直接的に橋脚全体系の応答変位に影響するが,2層式ラーメン橋脚では,中層はりに修復限界以上の大きな塑性変形を許容した場合にも,橋脚に過大な応答変位は生じなかった。また,バイリニアモデルを用いた1質点系の動的解析とファイバー解析とを比較した結果,静的非線形解析と1質点系モデルを用いた簡易手法でも,地震時のSRC橋脚の最大応答変位や損傷状況を妥当に評価できた

場所打ち杭基礎・地盤間バネの評価に介在するばらつきを考慮した場合に,RC橋脚基部へ塑性ヒンジを誘導するためには,どの程度の耐力格差をRC橋脚・杭基礎間に設ければよいのかについて確率論的立場から検討を行った。その結果,杭基礎の降伏を防ぐためには現行の道路橋示方書の規定よりも大きな耐力格差を確保する必要があること,そして押込み支持力の上限値の推定精度を向上させることにより,橋脚・杭基礎間に必要とされる耐力格差が低減し,杭基礎の耐震設計の合理化が可能となることなどが明らかとなった。

Available test results and stress-strain models for poorly confined high-strength columns, more specifically for columns with a tie volumetric ratio smaller than 2.0%, are scarce. This paper presents test results loaded in the axial direction for square reinforced concrete (RC) columns confined by various volumetric ratio lateral ties including low volumetric ratio. Test variables include concrete compressive strength, tie yield strength, tie arrangement type and tie volumetric ratio. Local strains are measured using strain gauges bonded to an acryl rod. For square RC columns confined by lateral ties, the confinement effect was improved by changing tie arrangement type from type A to type B. A method to compute the stress in lateral ties at the concrete peak strength is proposed, as well as a new stress-strain model for the confined concrete. The model shows good agreement with stress-strain relationships established experimentally over a wide range of confinement parameters.

Available test results and stress - strain models for poorly confined high-strength columns, more specifically for columns with a tie volumetric ratio smaller than 2·0%, are scarce. This paper presents test results loaded in the axial direction for square reinforced concrete (RC) columns confined by various volumetric ratio lateral ties including low volumetric ratio. Test variables include concrete compressive strength, tie yield strength, tie arrangement type and tie volumetric ratio. Local strains are measured using strain gauges bonded to an acryl rod. For square RC columns confined by lateral ties, the confinement effect was improved by changing tie arrangement type from type A to type B. A method to compute the stress in lateral ties at the concrete peak strength is proposed, as well as a new stress - strain model for the confined concrete. The model shows good agreement with stress - strain relationships established experimentally over a wide range of confinement parameters. © 2006 Thomas Telford Ltd.

Investigation on high-strength concrete (HSC) beams with concrete compressive strength up to 130MPa is conducted. The results indicate that the increase of shear strength is insignificant with the increase of concrete compressive strength in higher strength ranges than 70MPa;on the contrary,the size effect of HSC beams becomes larger than that of normal strength concrete beams. The shear strength values calculated by current design codes are also compared with the test results to evaluate the precision for HSC beams. It is verified that the shear strength evaluated by many design codes should be unsafe for HSC beams failed by diagonal tension,and the effect of concrete compressive strength and effective depth should be re-estimated.

コンクリート圧糊鍍約40～80N/mm^2,横拘束筋降伏強度1400N/mm^2綴を用いた正方形断面を有するRC柱の一軸圧縮実験を行い,断面寸法が柱の圧縮破壊性状に与える影響などを考察した。実験には,一辺200mm,柱長さ600mmの小型RC柱から,一辺450mm,柱長さ1500mmの大型RC柱を用いた。実験により,横拘束筋からコアコンクリートに与えられる横拘束圧が一定の場合,断面寸法に関わらず,応力-塑性変位関係は一定となることが確認され,圧縮破壊エネルギーを介したコンファインドコンクリートの平均化応力-ひずみ関係を用いることにより,小型RC柱から大型RC柱までの実験結果を再現できることを示した。

正負交番載荷を受けるCFT柱では,鋼管の局部座屈後に鋼管のはらみ出しが進展することで座屈部周辺に亀裂が生じる。そこで,本研究では,角形断面のCFT柱を対象として,3次元FEMモデルによる鋼管の局部座屈解析を行った。そして,1)CFT柱では鋼管のはらみ出しが進展することで座屈部のひずみ履歴にある変化点が見出せること,2)この点を終局とすれば鋼管の亀裂発生に対して安全側の靭性能評価が可能になること,を示した。

普通強度から高強度までの構成材料を用いたRC柱の一軸圧縮実験を行い, 各実験因子とコンファインド効果の関係を考察した. 一軸圧縮実験を行う際には, 供試体中央位置にひずみゲージを貼付した異形角型アクリル棒を埋め込み, ポストピークで現れるひずみの局所化領域を実測している. そして, 一軸圧縮実験で得られたデータをもとに横拘束効果指標を定義し, これを用いたコンファインドコンクリートの平均化応力―ひずみ関係を提案した. 提案モデルは, コンクリート圧縮強度130 N/mm², 横拘束筋降伏強度1450 N/mm²程度までを用いたRC柱に適用可能なものであり, さらに, 圧縮破壊エネルギーを介していることから, ひずみの平均化長さの設定に関わらず使用できるなど, 既往のモデルに比べ高い汎用性を有している.

コンクリート構造物の環境劣化作用に対する性能照査が導入されてきている。本研究は,この性能照査を信頼性理論に基づく限界状態設計法の枠組みの中で実現するための基礎的研究として,塩害劣化作用を受けるRC構造物の損傷確率の定量化を試みる。まず,時間的,空間的ばらつきを考慮した確率モデルに基づき,塩害劣化作用のハザード曲線を作成した。また,塩化物イオンの浸透予測に伴うばらつきを考慮したフラジリティカーブを作成し,ハザード曲線と組み合わせることで,RC構造物で生じる鋼材腐食の発生確率を定量化した。

コンクリート圧縮強度34.1,65.3N/mm^2,横拘束筋降伏強度404～1413N/mm^2を用いた,円形断面を有するRC柱の一軸圧縮実験を行った。実験より,圧縮強度発現後にひずみが増加する破壊領域長さは,コンクリート圧縮強度や横拘束筋体積比の大きさにより変化することが確認され,それは,構成材料の強度と横拘束筋量から求められる有効横拘束圧を用いて定量化された。さらに,エネルギー基準に基づく平均化応力-ひずみ関係を提案し,ひずみの平均化長さ(圧縮変位の計測長)に関わらず本実験結果を再現可能であることを確認した。

確率的地震ハザード曲線とフラジリティカーブを用いた耐震信頼性解析を実施し,目標年破壊確率に近い安全性レベルを有するコンクリート構造物を耐震設計することが可能な安全係数および設計地震力の設定手法を体系化する。また,本手法を単柱式RC橋脚へ適用することで,確率的地震ハザード曲線や目標年破壊確率の相違に対応した設計水平震度と安全係数を試算した。そして,従来の地震時保有水平耐力法による耐震性能照査において,試算した設計水平震度と安全係数を用いることにより,耐震信頼性解析を一切行うことなく目標年破壊確率を概ね確保したRC橋脚が耐震設計されることを示した。

コンクリート圧縮強度39,80N/mm^2,横拘束筋降伏強度379,1420N/mm^2を使用し,横拘束筋体積比が0.55～2.16%と小さい正方形断面を有するRC柱の一軸圧縮実験を行った。その結果,横拘束筋の高強度化によりコンファインド効果を改善するためには,横拘束筋拘束形状に配慮する必要があること,最大荷重後にひずみが増加する局所化領域長さは,コンクリート圧縮強度と横拘束圧の大きさにより変化すること,などを確認した。また,最大荷重時の横拘束筋作用応力を用いることにより,構成材料の強度や横拘束筋拘束形状などに関わらず適用可能なコンファインドコンクリートの応力-ひずみ関係を提案した。

一定軸力と繰返し曲げを受けるRCおよびSRC断面のモーメント-曲率関係をモデル化した。提案モデルは,軸方向鉄筋と鉄骨の組み合せを考慮して履歴ループを連続的に変化させることで,RCからSRC断面までを一元的に取り扱うことができる。また,提案した履歴則に,軸方向鉄筋の座屈点算定法を組み込むことで,軸方向鉄筋の座屈発生時曲率を算定する。そして,はり要素を用いてモデル化された柱基部でのモーメント-曲率関係に提案モデルを用い,既往のRCおよびSRC柱の正負交番載荷実験の再現解析を行った結果,これらの軸方向鉄筋の座屈発生点や復元力特性が概ね再現できた。

レベル2地震動を受ける水道用PCタンク杭基礎の耐震設計に用いる解析モデルとして,地盤抵抗の非線形性や杭体(PHC杭)の曲げ剛性の変化を考慮した2次元骨組モデルとそのプッシュオーバー解析に用いる地震荷重モデルを提案した。本モデルでは,タンク杭基礎の形状を反映し,タンク底版に作用する慣性力や動水圧などの地震荷重を2次元骨組モデルに載荷するための簡単化がなされている。そして,3次元解析との比較から,提案した2次元骨組モデルを用いたプッシュオーバー解析は,レベル2地震動を受けるタンク杭基礎の耐震性能照査法として有用な解析モデルであることを確認した。

圧縮強度130MPaまでの高強度コンクリートを用いた腹鉄筋のないRCはりのせん断実験を行った. 斜め引張破壊する高強度RCはりでは, コンクリート圧縮強度の増加に対し, そのせん断強度が一定値に収束すること, および寸法効果の影響が普通強度RCはりよりも大きくなること, などが確認され, 既往のせん断強度式は高強度RCはりのせん断強度を過大評価した. 一方, せん断圧縮破壊する高強度RCはりでは, 既往のせん断強度式により, 各変動因子のせん断強度に与える影響を偏りなく評価できることを示した. 本研究では, 既往の高強度RCはりのせん断実験結果も収集し, 斜め引張破壊およびせん断圧縮破壊する高強度RCはりのせん断強度式の提示, さらには, 両算定式の精度を考慮し, 高強度RCはりの設計せん断強度の評価に用いる部材係数も提案する.

ISO対応などの理由により,信頼性理論を用いた性能照査型設計法の整備に関し議論が進められている。この設計法では,構造安全性に影響する不確定要因が抽出され,その設計への対処法が検討される。本研究では,破壊確率や損失期待値などの評価指標により耐震安全性を定量化し,これに与える影響が高い不確定要因を抽出できるフローをシステム信頼性理論や実験計画法などを基に提示した。本手法を既往の設計基準により耐震設計されたRC橋脚に適用することで,設計基準の変遷に伴う橋脚の耐震安全性の向上度を確率的に評価し,橋脚毎に抽出される主要な不確定要因の相違を考察するなどして,本手法の有用性を確認した。

構造物の弾塑性地震応答の統計的性質を評価するためには,実地震動の平均的な特性を反映した模擬地震動によるシミュレーションが有力な手段となる。本研究では,地震動の特性として,位相特性のばらつきに着目し,1質点系への置換が可能なRC橋脚および免震支承を有するRC橋脚の弾塑性応答に与える影響を考察した。その結果,1質点系にモデル化されるRC橋脚では,非線形化の程度により,応答塑性率の変動係数が異なること,また,免震橋梁では,非免震時の約2倍にまで長周期化することで,そのRC橋脚の応答値は大きく低減され,位相特性のばらつきによる応答の変動が小さくなること,などが分かった。

早強性混和材を使用したコンクリートの,強度発現メカニズムを検討した。細孔径分布に関する検討では,初期の同一材齢で比較すると,混和材の添加量とともに全細孔量は増大するものの,強度発現に関わる毛細管空隙量は,逆に減少していることが明らかになった。また,同一材齢で比較した場合,結合水量が混和材の量とともに増加していることが判明した。これらの現象は,ともに水和の促進と,エトリンガイトの生成を示すと考えられることから,混和材中の,生石灰の反応熱によるセメント水和の促進と,硫酸イオンの働きによる,エトリンガイトの生成が初期強度発現の要因であると推定される。

RC矩形断面を対象に,軸方向鉄筋の座屈発生時に対応する断面曲率をかぶりコンクリートと帯鉄筋の拘束を考慮した上で簡易的に導出できる手法を提示した。また,これに対応した塑性ヒンジ長を基にする曲率分布を組み合わせることで,道路橋示方書の終局変位算定法と同様の計算により,RC橋脚の座屈発生点に対応した終局変位が算定される。そして,既往の正負交番載荷実験との比較により,提案手法は,広範な断面諸元を有するRC柱のかぶりコンクリート剥落時や軸方向鉄筋の座屈発生時変位を精度良く評価できることを確認した。

レベル2地震動を受ける水道用プレストレストコンクリート製タンク(PCタンク)の時刻歴地震応答解析を行い,その耐震安全性を評価した。また,PCタンクの主たる地震荷重である動水圧による影響と等価な慣性力を与える付加質量を用いてモデル化した動的解析結果,およびエネルギー一定則に基づき簡易的に算定した円周方向応答ひずみと流体要素を用いて内容液との連成を考慮した弾塑性地震応答解析結果を比較することで,PCタンクの耐震性能照査法に関する一考察を行った。

性能規定に基づく設計体系への移行が求められている。本研究では,信頼性理論と構造最適化手法を統合させて,設定する任意の目標破壊確率を満足できる設計フローを構築し,連続ラーメン橋の橋脚躯体の耐震設計に適用した。そして,目標破壊確率の変化が,最適設計より得られる断面諸元に与える影響を評価するなどして,現行示方書に基づき耐震設計された連続ラーメン橋の橋脚躯体の耐震性能を検討した。

In order to reduce the labor needed in the arrangement of shear reinforcement, a new method of simple mechanical splice for shear reinforcement was developed. And also in order to examine the effect of this splice on mechanichal performance of RC member, (a) tensile test for reinforcements using developed splice, (b) uniaxial compression test for RC columns, (c) flexural-shear test for RC beams, and (d) reversed cyclic loading test for RC columns, were carried out. In these tests for RC columns and beams, the comparisons between specimens with shear reinforcement using conventional anchorage and using developed splice were made. Test results indicate that shear reinforcement using developed splice as well as using conventional anchorage have the effectiveness of preventing the buckling of the longitudinal bars, confinement associated with shear reinforcement, and shearing performance.

RC橋脚一杭基礎系の耐震設計では,損傷を各部位に適切に配分させる必要がある。本研究では,望ましい崩壊モードとして,橋脚基部の曲げ靭性で地震エネルギーを吸収し,杭基礎には地震後に補強を必要とする程度の損傷が発生しない場合を想定した。そして,信頼性理論に基づきRC橋脚一杭基礎系に介在する不確定要因を考慮した上で,設計上想定する崩壊モードが確実に生じるような,橋脚一杭基礎間の耐力の階層化を試みた。

本研究では, 著者等が先に提案した構造系安全性評価法に基づき, 構造変数間の相関関係を考慮した構造系安全性評価法を構築し, 構造変数間の相関が構造物の安全性に及ぼす影響を検討した. 検討にあたりまず, RC橋脚を対象に, その構造変数間に存在する相関を算定した. そして, この相関の影響を取り入れた場合のRC橋脚の地震時安全性評価を行った. その結果, 構造変数間の相関を考慮することで, 構造物の安全性評価が変化する場合があり, それは, その構造変数間の相関の強さと構造系の安全性を支配している限界状態に左右されることを明らかにした. さらに, 構造変数間の相関を考慮した安全性評価を基に, 耐震設計上考慮すべき点について考察を加えた.

本研究ではまず,柱や中層はりの剛性をパラメータにとり,RC2層ラーメン構造物の耐震性に影響を及ぼす部材の降伏過程を時刻歴地震応答解析により検討した.また,エネルギー一定則に基づき弾塑性応答変位を推定し,動的解析との整合性を検討した.そして,高架橋の降伏過程を考慮した静的非線形解析に基づくRC2層ラーメン高架橋の面内方向を対象とした耐震設計法の提案を行った.

信頼性理論に基づき,地震荷重を受ける構造物の複数の限界状態と不確定要因である耐力や外力の構造変数間の相関を考慮して破壊確率を算定する方法を提案した。これを基に,複数の限界状態式間の相関ばかりでなく,相関分析により算出した限界状態式内の構造変数間の相関がRC橋脚の安全性に及ぼす影響を検討し,耐震設計上考慮すべき点について考察を加えた。

本研究では,信頼性理論に基づき地震時の橋梁システムの安全性照査を目的とした。すなわち,著者が先に提案した構造系信頼性評価法をもとに,支承-RC橋脚一杭基礎から構成される橋梁システムを対象として地震時の各部位・部材の限界状態到達確率(破壊確率)の推移を把握することのできる評価法を構築した。そして,この信頼性評価法を用いて,地震応答解析を実施し,橋梁システムとしての破壊確率と各部位・部材の破壊確率の相互関係について検討した。その結果,本提案法を用いることにより橋梁系の安全性照査だけでなく各部材の破壊確率および対象橋梁系の支配的な限界状態を把握することができた。

起こることが予想される複数の限界状態に対し、これらを同時に考慮した構造系の限界状態到達確率の算定法を構築した。そして、地震時のRC橋脚の限界状態として耐力と変形能に関する照査を取り上げ、RC橋脚の安全性評価を行った。その結果、耐力比に着目した時のRC橋脚の安全性の相違を定量的に把握することができた。