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.

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.

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.

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.

As the lessons from severe damage of civil infrastructures due to Tsunami and ground motion in the 2011 Great East Japan Earthquake, "Anti-Catastrophe" concept can be a paradigm shift in structural / seismic design method. In a conventional design, seismic safety of a structural system is verified against "design" ground motion. But "Anti-Catastrophe" concept requests for structural designers to concern the possibility of catastrophic event caused by severe action unestimated in the design method. JRA Design Specifications for Highway Bridges was revised in 2012 and a principle similar to "Anti-Catastrophe" concept was adopted. In this paper, "Anti-Catastrophe" concept in the specifications is summirised and challenges are considered to produce effective measure in seismic design method based on the review of recent domestic and foreign trend of structural design.

This paper describes the damage to RC rigid frame viaducts caused by the 2011 Great East Japan earthquake. In this study, a three-dimensional dynamic nonlinear analysis is carried out to investigate the extent of seismic damage of Daiichi Nakasone Viaduct columns with the scenario earthquake. The mechanism of the damage to each column members (side part of columns and middle part of ones) and the dynamic behaviour of the structure are also studied. Inparticular, the reason of the different degrees of damage in side and middle columns is considered in detail. The analytical results show that the greater rotational mode of deformation caused by the acceleration and displacement response in the perpendicular direction in the side columns is the main reason of the greater degree of damage in them as compared with the middle columns.

It is requested to implement the concept of "anti-catastrophie" property in the seismic design codes. It is not, however, a straight forward task because "anti-catastrophe" concept has various significant differences from existing design codes. This paper identifies problems of the development of "anti-catastrophe"- oriented seismic design codes, and proposed a new concept of "category 2." A framework of design code with "category 2" is also presented. We also discussed conditions required for the society and government to make such new design codes effective, based on theoretical framework of risk governance and proposed several practical policies.

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.

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.

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.

This paper presents some of the results achieved by Technical Committee on Systematization to Evaluate Structure and Durability Performance in Corroded RC Structure, which works to establish the use of numerical structural analysis as an evaluation method that allows numerical representation in space and time of durability of concrete structures with chloride induced damage（hereinafter, structural performance over time）, and an index of structural performance over time allowing the evaluation of total structural systems. This paper covers in particular methods to evaluate the spatial variability of the amount of corrosion that affects structural performance using probabilistic and statistical techniques, and constitutive models related to reinforcement corrosion and the bond between concrete and corroded reinforcement, which are essential for the finite element analysis of corroded concrete structures. Further, an index of structural performance over time is proposed and formulated, and trial calculation results for total structural systems are introduced.

Serious damage occurred at RC rigid frame viaduct sites of Tohoku Shinkansen in Esashi Ward, Oshu City, during the 2003 Southern Sanriku Earthquake (MJ7.1). 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, temporary seismic observation with very high density was conducted along the viaduct sites. Moreover, seismic waveforms along the viaduct were estimated based on the asperity model considering empirical site amplification and phase effects. The estimated ground motions will be useful in the detailed study of the damage mechanism.

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.

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.

Enormous damage occurred to the disaster countermeasures office, the river bridges and the fishery port facilities in Shizugawa, Minamisanriku Town due to the 2011 off the Pacific coast of Tohoku Earthquake (Mw9. 0). To evaluate the performance of structures before the attack of tsunami, it is necessary to estimate strong motions in Shizugawa Area with sufficient accuracy, taking into account site effects. In this study, seismic waveform in Shizugawa Area was estimated based on a super asperity model considering empirical site amplification and phase effects. The estimated seismic waveform will be useful in the detailed study of seismic performance of structures before the attack of tsunami.

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.

It is important to estimate the amount of corrosion products in existing RC structures subjected to chloride attack. However, the corrosion process of rebar has not been investigated because of difficulties with observing it. Recently, X-ray technology has been applied to the visualization of concrete cracking to investigate the behavior of fracture process zone in concrete. In this study, digital picture processing method to estimate the amount of corrosion products in RC members is provided for X-ray photography. Then, based on the observation of deteriorated RC member using X-ray photography, corrosion process of rebar is visualized, and the effects of the amount of corrosion products on the corrosion cracking width and flexural strength of RC beam are examined.

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.

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.

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.

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.

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.

Due to 2011 Great East Japan Earthquake and 2016 Kumamoto Earthquake, many bridges suffered serious damages at structural boundaries and connections. In order to evaluate seismic response of bridges focused on discontinuity in structural system, shake table tests of seismic isolators in 2D were conducted to make rational numerical model, and improvement of design of collapse prevention device in bridge was proposed. And in order to evaluate seismic response of bridge focused on uncertainty, dynamic response of multi-degree-of-freedom systems was evaluated by changing the predominant frequency component of narrow band input for seismic action with high uncertainty by random vibration theory. Furthermore, new techniques were proposed to improve the post-peak behavior of reinforced concrete structure

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. Whereas the seismic demand depends on the results of seismic hazard assessment, the deterioration of seismic capacity depends on the hazard associated with airborne chlorides. In an illustrative example, a RC bridge pier was modeled as single degree of freedom. 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 affected by the effect of airborne chlorides

It is important to estimate the amount of corrosion products in existing RC structures subjected to chloride attack. However, the corrosion process of rebar has not been investigated because of difficulties with observing it. Recently, X-ray technology has been applied to the visualization of concrete cracking to investigate the behavior of fracture process zone in concrete. In this study, digital picture processing method to estimate the amount of corrosion products in RC members is provided for X-ray photography. Then, based on the observation of deteriorated RC member using X-ray photography, corrosion process of rebar is visualized, and the effects of the amount of corrosion products on the corrosion cracking width and flexural strength of RC beam are examined

In this study, the development and the seismic design approach of high performance structures using RC and SRC members have been done. The results of the study from 2002 to 2004 are shown below.1. Shear strength characteristic of RC beams using high-strength materialsThe shear loading tests of RC beams without stirrup using high-strength concrete of compressive strength ranging to 130MPa have been carried out.(1)A shear strength equation of RC beams without stirrup using high-strength concrete has been suggested.(2)A shear strength equation of RC beams with stirrup using high-strength concrete and reinforcing bars has been suggested by referring to the previous test results.2. Uniaxial compressive strength characteristic of RC columns using high-strength materialsThe uniaxial compressive loading tests of RC columns (rectangular and circular section) have been carried out.(1)By measuring the strain distribution of the core concrete, it is possible to quantitatively evaluate the changing of failure region caused by the concrete strength and the quantity of tie reinforcement.(2)By using the compressive failure energy, the stress-strain relationship of confined concrete of normal to hi

The following are the principal achievements of the study.1.The mix proportions for super high strength concrete with compressive strength of 1,000kgf/cm^2 or more were established and the compressive strength, tensile strength, Young's modulus and other mechanical properties of the materials were investigated in detail.2.Steel reinforcement with a yield strength of about 7,000kgf/cm^2 and strain at tension failure time of 15% was developed.3.Bending loading testing of a reinforced concrete beam made of super high strength concrete and super high strength steel reinforcement was performed to study the mechanical properties of the beam under bending.4.Using concrete with compressive strength of 1,200kgf/cm^2 and steel reinforcement with yield strength of 7,000kgf/cm^2 as its tension reinforcement, the shear properties, particularly the shear dynamic strength, load-displacement relationship, and the state of the occurrence of strain and cracks of an RC beam without double reinforcement were experimentally studied. An experimental study of the shear properties of this kind of RC beam with double reinforcement was also done.5.Results of similar tests performed in the past were summariz

本研究では,システムの破壊確率を精度良く算定できる構造系信頼性評価法とSQP法に基づく構造最適化手法を組み合わせた構造系の信頼性設計手法を援用することにより,場所打ち杭の設計水平震度の設定例を提示した.場所打ち杭の設計水平震度は,RC橋脚の保有水平耐力に相当する震度k_<hp>と部分係数γ_0の積と定義し,耐力階層化の考えに基づき,橋梁システムが持つ全ての限界状態から計算される安全性指標を橋脚に関わる限界状態のみから計算される安全性指標で代表させるための部分係数γ_0の設定を試みた.本研究により得られた主な研究実績を以下に示す.(1)Sorensenらが用いた確率論に基づく部分係数算定のための目的関数に,構造系信頼性評価法を適用することで,耐力階層化を図るための部分係数を算定することができた.(2)地盤モデル毎に算定される部分係数γ_0は,地震時に生じる地表面の最大応答変位と概ね相関関係を有している.また,各確率変数のばらつきを考慮し,かつ地盤変形の

1. New evaluation method of lifetime risk in RC member is proposed on the basis probability matrix. It is clarified that current seismic method does not necessarily provide sufficient safety during the lifetime of RC structure.2. A new evaluation method for the probability of failure of a structural system based on reliability theory is proposed. From the numerical examples, it is demonstrated that this method possesses high accuracy and simplicity.3. Design flow charts which can cope with an arbitrarily given safety level are formulated by reliability-based optimal theory considering structural system. Then the proposed method is applied to the seismic design of rigid-frame bridge piers and RC bridge pier. As a result, it is confirmed that (1) the RC bridge piers so as to attain the prescribed reliability can be designed by the proposal method and (2) the safety of bridge piers, which are deigned based on the current code, are not uniform.4. The effect of uncertainties in reinforced concrete (RC) bridge systems on the response of the RC bridge pier and cast in place pile were statistically and analytically studied, and quantitative evaluations of variations in that response were o

国内の全重油使用料の約0.6%を使用する蒸気養生を必要としない製品用コンクリートが開発されれば、地球環境問題への貢献は大きい。また、生コンクリートとして使用可能であれば建設期間の短縮等によりコストの大幅な縮減につながると期待される。当研究グループでは、このニーズに応えるべく、この種の超早強性コンクリートの開発を試み、ある種の混和材料を使用することで超早強性を有するコンクリートを開発した。さらに、開発されたコンクリートに対する性能試験の結果、耐久性等に関しては従来の蒸気養生されたコンクリートと同等の性能を有することを実験的に確認した。最後に、この混和材の使用によりもたらされる超早強性の強度発現および耐久性のメカニズムの解明および各種配合条件とこれらの関係を化学的あるいは微視構造的に把握した。得られた実験成果を以下に記す.(1)蒸気養生不要の超早強性コンクリートについて、配合条件と各種物性値(圧縮強度、引

(1)研究代表者が先に提案してきた構造系信頼性設計手法を援用することで,構造系の信頼性を考慮した信頼性解析を行うことなく,設計対象構造系の破壊確率が要求信頼性レベル(目標破壊確率)を満足できる設計を可能にする安全係数の算定手法を体系化した.(2)橋脚の固有周期と降伏耐力比Ru(弾性応答水平力P_Hと橋脚の降伏耐力Pyの比(Ru=P_H/Py))より,エネルギー一定則から弾塑性応答変位を推定する際に含まれる安全マージンやばらつきを定量化し,信頼性解析で必要となる確率変数のパラメータの設定を行った.(3)断面形状やせん断スパン比などが異なる46基のRC橋脚を検討対象橋脚群として,提案手法により,その耐震設計に用いる基本安全係数を試算した.その結果,地震時保有水平耐力法により耐震設計されたRC橋脚の安全性指標βsysは,βsys=0.9〜2.4の範囲でばらついているのに対し,試算した基本安全係数と定義した設計規準式を用いることにより,確率・統計の計算を一切必要とすることなく,目標

構造物の信頼性に関する一般原則(ISO2394)に基づく設計規準の整合化が国際的に検討されており,今後,コンクリート構造物を対象とする設計規準においても,これに準拠する確率論的な概念を導入した限界状態設計法への移行が検討されると考える。こうした背景のもと,RC構造物を対象とした耐震信頼性設計法に関する研究を進めており,ある地震動作用下の条件付破壊確率と目標破壊確率の差を最小化する最適化問題を解くことにより,構造系の信頼性を考慮した信頼性解析を行うことなく,目標破壊確率を概ね確保した設計を可能にする安全係数の算定手法を体系化している。ただし,この手法では,建設地毎の地震ハザードの相違を考慮できないため,提示する安全係数は,ある特定の地震動作用に対する構造物の破壊確率を目標値に漸近させているに過ぎない。超低頻度な領域で,地震動を確率的地震ハザード曲線に基づき評価することには,種々の問題が指摘されているが,設計規準の国際整合化

開発した超高強度RC柱部材の年損傷確率を以下の手順で算定し,普通強度RC柱部材のそれと比較した.1.建設地点の選定と設計条件の設定:建設地点は,日本全国から任意に10箇所を選定した.対象構造は,上部構造は連続鋼鈑桁橋を想定し,地盤はI種地盤上に位置すると仮定した.そして,普通強度構成材料を用いて単柱式RC橋脚を耐震設計する.耐震設計する際は,現行の道路橋示方書の基準を満足するようにした.その上で,同じ断面諸元,鉄筋量のもとで,コンクリート圧縮強度を120N/mm^2,軸方向鉄筋降伏度を785N/mm^2,横拘束筋降伏強度を1400N/mm^2としたRC橋脚を耐震設計した.2.確率的地震ハザード曲線の作成:地震ハザード評価コードSHEATを用いた.3.時刻歴波形の合成とフラジリティカーブの作成:着目する地震動強さに対応した地震波(加速度時刻歴波形)を作成した.ここでは,振幅と位相のばらつきを考慮した地震波を合成した.任意の地震動強さの作用に対するRC橋脚の条件付損傷確率(終局変位を超過する確率)

In this study, high-strength concrete pile is investigated not to be damaged by large earthquakes even if it is embedded in liquefied ground. As the experimental results of static loading tests of proposed pile specimens and centrifuge tests of the pile embedded in soil, high seismic performance of the proposed high-strength concrete pile is indicated. Moreover, seismic design of the proposed high-strength concrete pile considering soil effect is proposed

This study presents a framework for estimating the remaining lifetime of reinforced concrete structures in a marine environment based on the observation information such as visual inspection of corrosion cracks and chloride concentration distributions. Random variables used in the prediction of corrosion process of concrete component could be updated by Sequential Monte Carlo Simulation. In addition, growth process of steel corrosion was visualized by X-ray photography in order to understand the spatial distribution of corroded steel used in the proposed framework

Structural performance of reinforced and prestressed concrete structures which had been deteriorated by reinforcement corrosion, alkali-silica reaction and frost damage were investigated through laboratory test, loading test of actual structures and nonlinear finite analysis. Number of experimental facts and mechanisms about influences of material deterioration in structures on the structural performance were found in this study. Evaluation method of residual structural performance of deteriorated existing structures based on on-site investigation and numerical simulation was proposed

本研究では，これまでの既存研究の知見を基に二方向入力を受ける場合を想定して摩擦振子型免震機構付き柱を設計し，震動実験によりその地震時挙動を確認した．一方向入力の場合と異なり，滑り曲面上を斜め方向に摩擦振子が滑る場合の滑り性能の確保，あるいはそれに適した滑り曲面形状や橋脚の配置方法などが問題となった．また，骨組解析モデルを用いた非線形動的解析も行い，提案構造の地震時挙動を数値解析的に評価するための基礎検討も行った．なお，これまでに観測されている範囲の鉛直地震動の大きさでは，本構造の地震時挙動に鉛直地震動が及ぼす影響は極めて限定的であることから，本実験では，鉛直方向成分の入力は行わなかった．

　断層パラメータ，強震動の距離減衰や津波伝播，あるいは構造物の応答評価や耐力算定などに介在する種々の不確定性を統合し，強震動，あるいは津波により構造物が損傷する確率を算定する一連の手順を示した．各パラメータの継続的な見直しは，当然，必要であるが，この一連の手順により，各パラメータの変動が着目する構造物の安全性に及ぼす影響を定量的に把握することが可能となる．限られた予算の中では，全てのハザードに対して最悪のシナリオを想定し，対策を施していくことは困難である．起こり得るシナリオと，その評価に伴う不確定性を反映し，着目する構造物の安全性に最も影響する支配的なハザードを抽出，あるいは最も安全性の低い構造物を同定する上で，提示した信頼性のアプローチは有用である．

(1) 鋼繊維補強コンクリート（SFRC）が有する繊維の配向性と分散性の問題に対し，X線撮影により鋼繊維を可視化し，それから曲げ引張への抵抗の大小を表現するパラメータ（RNF）を定義した．(2) RNFと，SFRCの引張軟化曲線の骨格曲線を規定するパラメータを関係付けることにより，X線画像からSFRCの引張軟化曲線を求められるようにした．(3) SFRCはりのX線画像を用いたFEM解析を実施し，実験結果と比較した．X線画像により鋼繊維が可視化され，各要素の引張軟化曲線をその情報に基づき定めることで，X線画像がない場合に比べて，実験と解析結果の差を小さくできることを確認した．

鋼繊維補強コンクリート（SFRC）は，鋼繊維の配向性と分散性の問題のため，同条件で製作した供試体であっても，その力学特性は供試体毎に大きく異なる．X線技術とディジタル画像処理を応用することで，コンクリート内に広がる鋼繊維を一本一本可視化し，それを数値解析の入力情報として取り込むことで，SFRC部材の力学特性の評価精度を大幅に改善できると期待される．この着眼のもと，本研究では主に次の成果を得た．(1)　SFRC部材内の鋼繊維分布を可視化するX線撮影と画像処理技術の確立(2)　鋼繊維分布のX線撮影結果を反映した数値解析用インプット情報の作成(3)　SFRC部材の構造実験結果とX線撮影・数値解析による計算値の比較に基づく精度検証

　本研究は，X線によりコンクリート内の鉄筋腐食の状態を撮影し，鉄筋の非腐食域の境界を捉えるためのディジタル画像処理方法などを検討した．具体的には，腐食量と腐食の分布が既知の鉄筋をコンクリート中に埋め込み，その状態をX線撮影し，ディジタル画像処理方法の違いがX線撮影画像から予測される鉄筋腐食量の精度に及ぼす影響などを検証した．次いで，電食にて劣化させたRCはり部材のX線撮影を行い，鉄筋質量減少率の不均一さの程度や形成過程を観察した．また，鉄筋質量減少率とコンクリート表面に表れる腐食ひび割れ幅の関係，さらには，部材内部の鉄筋質量減少率の空間的な変動と曲げ耐力の関係などに関する基礎資料を得た．

Reinforcedconcrete (RC) structures in a marine environment deteriorate with timedue tochloride-induced corrosion of reinforcing bars. This paper presentsreliability-based durability assessment of existing RC structure in a marine environment.A simple assessment criterion with partial factors that satisfy the targetreliability level within the remaining life-time of existing RC structure ispresented. A procedure to obtain the partial factors updated by the SequentialMonte Carlo Simulation is indicated. In this procedure, the chlorideconcentration distribution by coring test is used as observational data.Partial factors could be determined by taking into consideration the reductionof uncertainties associated with the prediction of chloride-induced corrosion.Partial factors for durability assessment of existing RC structures could bereduced compared with thosefor durability design of new RC structures.

　兵庫県南部地震以降，耐震解析手法には長足の進歩が見られるのに対して，地震動評価には依然として圧倒的な不確定性が存在する。このような不確定性に対峙し，構造物の地震時安全性を確保するためには，地震動の不確定性の影響を受けないほど構造物の性能を高める必要がある。コンクリート系の耐震部材の開発では，この手段として部材靭性率を大きくしてきた。既に，降伏変位の約20倍までの応答変位が生じても，安定した曲げ挙動を呈するRC柱も開発されている。しかし，部材変形能により地震エネルギーの吸収を期待した構造は，基本的に地震後にある程度の修復作業を必要とする。橋梁は，地震後の救助・救急活動や，都市の復興に重要な役割を果たすことを考えると，地震中の安全性と地震後の供用性をともに確保できる技術開発が必要である。この背景のもと，摩擦振子型免震機構を有するコンクリート橋脚を提案し，その震動台実験により，基本的な地震時の応答特性を確認した。摩擦振子が滑り曲面上を運動することで，上部工に作用する慣性力の下部構造への伝達が遮断され，滑り曲面の形状および摩擦振子と滑り曲面間の摩擦で決定されるせん断力に起因する断面力が橋脚基部や基礎に作用する。これにより，地震動の大きさに関係なく，橋脚基部や基礎に作用する最大断面力を構造諸元のみで決定できるため，橋脚や基礎の弾性設計が可能となる。さらに，免震支承等の特別な装置を必要とせず，構造形態のみの工夫により長周期構造を実現するため，免震化に伴うコスト増を抑えることができる。過去に実施した震動台実験により，地震中の橋梁の安全性を確保する上で，摩擦振子型免震機構を有するコンクリート橋脚の有用性を確認できた。ただし，地震後の供用性を本構造が確保できていることを示すには，摩擦振子と滑り曲面間で生じる地震後の相対変位（残留変位）についての検証が必要である。　一般的な単柱式橋脚で生じる残留変位に関する既往の研究には，例えば，川島らの残留変位比応答スペクトルに関する検討がある。残留変位は，1自由度系に置換した橋脚の骨格曲線をバイリニアで表現したとき，その初期剛性と2次勾配の比に大きく依存し，さらに地震動毎に得られる残留変位のバラツキは非常に大きいことが示されている。一方で，橋脚に生じる残留変位の発生要因を橋脚の損傷のみに起因するものとして捉え，橋脚下端部と上部工の慣性力作用位置の相対変位で橋全体系の残留変位の大きさを表現すること，および震動台実験や被災橋脚から実測された残留傾斜角との比較から，RC橋脚の残留変位の計算には相当に大きなモデル誤差が含まれることが指摘されている。　上記の背景のもと，本研究では，摩擦振子型免震機構を有するコンクリート橋脚の震動台実験を実施し，滑り曲面の形状，あるいは地震動特性などが残留変位やそのバラツキの大きさに与える影響を確認した。また，今回の検討に用いた地震動は，現行の耐震設計で規定されるレベル2地震動よりもさらに大きく，それによる最大滑り変位が生じた後にも，本構造に生じる残留変位は小さい値に抑えられることを確認した。今後の継続した実験的検討が必要なものの，本構造は，地震中の安全性と地震後の供用性を兼ね備えたダメージフリー橋梁の一つになり得るものである。一方で，実験的に得られる残留変位の大きさを解析により定量評価することは困難であった。残留変位を解析的に得るための数値モデルの高精度化が必要である。

　2011年3月11日に発生した東北地方太平洋沖地震により，東日本沿岸部にある社会基盤構造物（道路や鉄道ネットワーク）は壊滅的な被害を受けた．道路や鉄道には，地震後の避難や救助救急等の緊急活動，あるいは，ライフラインの復旧活動を支える交通基盤として重要な役割が期待されていたが，その機能を十分に果たすことができなかった．その原因となったのは，過去に発生した社会基盤構造物の地震被害で観察されなかった2つの新しい破壊形態が見られたことによる．(1) 津波による構造物の流出・倒壊(2) 塩害劣化により耐震性能低下が生じた構造物の強震動による損傷　近い将来に必ず発生する東海・東南海・南海地震でも，この(1)と(2)により太平洋沿岸部にある社会基盤構造物は相当の被害を受ける可能性がある．本研究では，(1)と(2)の損傷メカニズムを実験的・解析的アプローチにより解明するとともに，東海・東南海・南海地震に対する被害シミュレーション（リスク評価）と，その被害を軽減する方策を提言した．具体的な成果を以下に示す．　⇒国内外の社会基盤構造物の耐震設計基準で津波作用を考慮したものは存在しない．本研究では，数値シミュレーションにより，津波・構造物の連成解析を行い，それらに基づき橋梁の対津波落橋防止構造の設計法を構築した．　⇒東海・東南海・南海地震の影響を受ける海岸線近くの橋梁は膨大な数にのぼる．これら橋梁群の津波リスクを評価した．対津波落橋防止構造を既存橋梁に導入する投資と，それにより低減される津波リスクの比較を行い，この投資の価値を定量的に議論できるフレームワークを提示した．　⇒海岸線近くにある橋梁は，津波以外にも脅威となる自然作用が存在する．強震動と海洋からの飛来塩分である．東海・東南海・南海地震の影響を受ける地域にある社会基盤構造物は，建設後，既に50年近くになる構造物が多数あり，材料劣化が顕在化している．このような材料劣化が生じた構造物が強震動を受けた場合には，脆性的な破壊が生じる可能性が指摘されるものの，材料劣化が生じた構造物の安全性を評価する過程には未解決な問題が多数残されている．本研究は，材料劣化が生じた構造物の実験および解析を行い，この種の構造の耐震安全性評価法を提示した．　これら一連の成果として，地震・津波・塩害のマルチハザードを受ける社会基盤構造物のリスク評価法を提示している．

　兵庫県南部地震以降，耐震解析手法には長足の進歩が見られるのに対して，地震動評価には依然として圧倒的な不確定性が存在する。このような不確定性に対峙し，構造物の地震時安全性を確保するためには，地震動の不確定性の影響を受けないほど構造物の性能を高める必要がある。これまでのコンクリート系の橋梁耐震部材の開発では，この手段として部材靭性率を大きくしてきた。例えば，インターロッキング式帯鉄筋を有する鉄筋コンクリート（RC）橋脚，軸方向鉄筋や帯鉄筋の配筋方法，あるいはコアコンクリート内にスパイラル鉄筋を配筋するなどの工夫をしたRC橋脚，そして，鉄骨鉄筋コンクリート橋脚などの研究がある。しかし，このような部材変形能により地震エネルギーの吸収を期待した構造では，地震後に相当の残留変位が生じる可能性がある。橋梁は，地震後の救助・救急活動や，都市の復興に非常に重要な役割を果たすことを考えると，単に橋梁の地震中の安全性を確保するだけではなく，地震後の供用性までを考慮した部材開発が求められる。　この背景のもと，摩擦振子型免震機構を有するコンクリート柱を提案し，その振動台実験により，基本的な性能を確認した。橋脚を2つの部位に分割し，分割した位置に滑り曲面を設けている。上側にある部位（摩擦振子）が滑り曲面上を滑り，下側にある部位（滑り曲面を有する橋脚や基礎など）に作用する地震時慣性力を低減する。従来の曲げ破壊型のRC橋脚は，橋脚天端部に水平力が作用するとその下端部に大きな曲げが作用するのに対して，本構造は，滑りにより力の伝達を遮断し，さらに曲面の存在により地震後の残留変位を抑えることを期待している。　しかし，既発表の内容では，摩擦振子が半径一定の曲面（定曲面）上を滑るため，大きな地震力を受けると，桁の水平移動に伴いその上方への変位（アップリフト）や，橋脚下端に作用する地震時慣性力が大きくなり，橋脚の下端部や基礎などが損傷する可能性がある。これを避けるためには，半径の大きな曲面を用いることが考えられるが，その場合には，摩擦振子の原点回帰が期待できず，地震後に大きな残留変位が生じることが懸念される。　そこで，本研究では，摩擦振子が滑る曲面の形状を工夫することで，上記の問題の解決を試みた。具体的には，水平変位が小さいときには下に凸の小さな半径の曲面上を摩擦振子は滑り，さらに大きな地震力の作用を受けて水平変位が大きくなったときには，上に凸の曲面，あるいは直線上を滑るように曲面形状を変更した。この工夫をしたコンクリート柱を持つ橋梁模型を作製し，その振動台実験により地震応答特性を確認した。結果として，半径一定の滑り曲面を用いた場合に比べ，変動曲面上を摩擦振子が滑る場合には，コンクリート橋脚の下端部に作用する地震時慣性力を低減でき，一方で地震後の残留変位も大きくならないなど，その耐震性能を改善できることを示した。

　2011年東北地方太平洋沖地震により，岩手県・宮城県・福島県内にある多くの道路橋と鉄道橋が被災した．被災の原因は，地震動自体の動的作用によるもの，津波の作用によるもの，あるいは地震動により損傷し，その後の津波の作用により倒壊したもの，の３つに分類できる．本研究では，東北地方太平洋沖地震で被災した橋梁の被害分析を進め，復興時のインフラ整備にあたっての提言，あるいは近い将来に発生が予想される東海・東南海・南海地震への対策を提言することを目的とした．　平成23年春，夏，そして秋と，研究代表者は，土木学会地震工学委員会被災調査団メンバーなどの一員として，橋梁の被災状況を確認した．調査により明らかとなった課題は，以下の3つであった．（1）宮城県や岩手県沿岸部にある国道45号線に架かる道路橋，仙石線や気仙沼線などの鉄道橋（架道橋や架線橋）が津波により壊滅的な被害を受けていた．重さ数百トンもある橋梁上部工が数百メートルも流出している例も見られた．特に道路橋の流出は，現地の復興の大きな妨げとなった．（2）我が国で初めて，免震橋梁に大きな損傷が生じた．免震系の積層ゴム支承が完全に破断している事例もあった．現地の調査，およびその後に行った材料試験から，環境因子により材料的な劣化が生じ，それが地震被害を大きくした可能性が指摘された．（3）兵庫県南部地震以降，鉄道各社では耐震補強を積極的に進めてきた．落橋につながる脆性破壊となる柱を抽出し，優先的に耐震補強を行っている．しかし，今回の東北地方太平洋沖地震では，非常に多くの柱が損傷している．何故に耐震補強が見送られた部材で損傷が生じたのかを詳細に分析し，それに基づきこの種の部材に対する耐震補強策を講じる必要がある．　上記の3項目に対して，主に数値解析的な検討を重ねることで，以下の成果を得た．（i）津波の作用による橋梁の流出への対応法の提案：津波の作用に対する設計は全く行われていないが，我が国の橋梁は，フェールセーフ機能として，非常に頑丈な落橋防止装置を有している．この落橋防止構造の改良により，対津波用の落橋防止構造の設計要件を整理した．（ii）非常に長い地震動の継続時間とそれに伴う免震装置への過大な正負交番作用への対応法の提案：FEMをベースに免震支承部の非線形時刻歴動的解析を実施することで，継続時間やねじり，あるいは繰り返しの引張力が免震支承部の耐震性能に与える影響を検証した．また，ゴム支承の材料劣化と地震動の作用の複合による橋梁の安全性評価も実施した．（iii）部材破壊モード判定法の見直し：地盤の拘束や材料強度のバラツキ，さらには，曲げやせん断の耐力評価に伴うバラツキの影響により，曲げやせん断の破壊モードの判定には大きな不確定性が伴う．この種のバラツキの存在下でも確実に破壊モードの判定を実施できる手法を提案した．

　兵庫県南部地震以降，耐震解析手法には長足の進歩が見られるのに対して，地震動評価には依然として圧倒的な不確定性が存在する．このような不確定性に対峙し，構造物の地震時安全性を確保するためには，地震動の不確定性の影響を受けないほど構造物の性能を高める必要がある．これまでのコンクリート系の耐震部材の開発では，この手段として部材靭性率を大きくしてきた．鉄道橋では，既に，降伏変位の約20 倍までの応答変位が生じても，安定した曲げ挙動を呈するRC 系の柱も開発されている．しかし，このような部材変形能により地震エネルギーの吸収を期待した構造では，地震後に相当の塑性変形が残留する．橋梁は，地震後の救助・救急活動や，都市の復興に重要な役割を果たすことを考えると，単に構造物の安全性を確保するだけではなく，地震後の即座の使用性までを考慮した部材開発が必要である．　以上の背景のもと，本研究では，橋脚に摩擦振子型免震機構を適用し，曲面形状を適切に定めることにより，本来求められる性能を満たす橋梁（ダメージフリー橋梁）の提案を行った．提案するすべり面形状を含む複数の橋梁モデルを作製して1 方向振動台実験を行い，その性能を確認した．　本研究により得られた知見を以下に示す．1. 現行の耐震設計に使用する規定地震動に対しては無損傷，想定外地震動の作用時にも1 つの損傷モードしか起こらない橋梁をダメージフリー橋梁と定義し，円弧と直線のすべり面を有する曲面形状を用いた摩擦振子型免震機構を橋脚に適用した橋梁を提案した．2. 振動台実験により，提案する曲面形状が半径一定の円弧状の形状などの他の形状と比較して，優れた性能を有することを確認した．半径一定の円弧状の曲面形状では，曲率半径により固有周期を大きくすることで加速度の低減が図れるが，一方で変位は大きく発生し，これらはトレードオフの関係にあることが確認された．提案する曲面形状では，地震動強さが小さい場合には変位，地震動強さが大きい場合には加速度を低減させるといったように，地震動の強さに応じて性能を変化させられることを確認した．3. 最大加速度および最大変位は，簡単なバイリニアモデルで再現が可能である．しかし，残留変位については，摩擦係数を詳細に評価するモデルを用いたとしても再現が困難であることが確認された．そのため，摩擦振子型免震機構における可能最大残留変位を定義することで残留変位の最大発生値を評価する必要があることを示した．4. 曲面すべり面を有することによる鉛直変位の発生に対して，桁の損傷抑制の観点から満たすべき曲面形状について検討した．5. 提案する曲面形状を有するダメージフリー橋梁の設計フローを示し，実際に設計を行った．その結果，満たすべき性能を満足することを解析的に確認した．