Deterioration of existing bridges has become a severe problem and seriously affect the serviceability and durability of railway system in many countries. A preventive maintenance strengthening method using rubber-latex mortar, Glass Fiber Reinforced Polymer (GFRP) plates, lightweight rapid hardening concrete, and reinforcement was introduced this study, which can be used to strengthen the both steel bridge superstructures and bridge piers. In order to confirm the real effects of the present strengthening method, field loading test on a short-span railway bridge and laboratory tests on a steel column were performed. The results on both original and strengthened specimens were summarized and compared. For the railway bridge superstructure, theoretical results were also provided to confirm the strengthening effects. For the steel piers, however, numerical models were built to provide the load carrying capacity of the original pier. The load-displacement curve and load-strain response at key sections were measured in the loading tests and reported in this paper. According to the results, the present renovation method could greatly enhance the rigidity of old steel railway bridge superstructures and the load carrying capacity of existing piers, resulting in the extension of the residual service life of short-span railway bridge superstructures and improvement of seismic behavior of steel piers.

Steel-concrete composite twin l-girder bridges have been built a lot in both Europe and Japan, but the lack of redundancy has always been a concern in U.S. and many other countries. In addition, few experimental studies have been performed on the mechanical performance of such bridges, particularly for the intact bridges. On this background, a steel-concrete composite twin l-Girder bridge model was designed according to the current highway bridge design specification in Japan and tested in the laboratory. The static loading tests were performed, and two loading conditions including both symmetrical loading and unsymmetrical loading were applied. Load versus deflection relationships were measured in the loading test, and the failure mode of the test specimen was discussed. The flexural strain development on bottom flanges of two main girders was also reported in this paper to confirm the load transfer between two main girders. In addition, the theoretical results on the basis of the classic theory were also provided to compare with the test results. The comparison indicates that the theoretical analyses can predict the behaviour of the twin l-girder bridges very well in the elastic stage by considering the effective width of the slab. The load transfer paths in such bridges were also discussed on the basis of the test results under un-symmetrical loading.

Deterioration of aging bridges is a serious problem that affects their serviceability and durability. Appropriate repair, strengthening, or replacement work should be performed on aged bridge structures to ensure they remain in good condition. A novel strengthening method using rubber-latex mortar, glass-fiber-reinforced polymer plates, lightweight rapid-hardening concrete, and reinforcement bars is proposed in this article. The strengthening method can be used to strengthen both steel railway bridge superstructures and piers. To confirm the effectiveness of the strengthening method, field tests on a short-span railway bridge and laboratory tests on longitudinal-lateral beam connections and steel piers were performed. Because the structural stiffness of aged steel structures is directly related to the fatigue performance and the seismic behavior of steel piers, the applied load versus displacement and strain responses of the test specimens were of primary interest in the tests. Strain results at key sections were experimentally measured and are reported in this paper. According to the experimental results, the present renovation method can significantly enhance the rigidity and reduce the stress levels in bridge girders, connections, and piers, resulting in the extension of the residual service life of such structures. (C) 2017 American Society of Civil Engineers.

Techniques for structural repair and maintenance are becoming increasingly important because of increasing problems associated with aging structures. This paper introduces a method for strengthening aged steel columns by using new construction materials such as glass-fiber-reinforced polymer (GFRP) plates, rapid-hardening concrete, rubber-latex mortar, and reinforcing bars. The purpose of the present study is to investigate the mechanical performance of steel columns before and after strengthening, thereby assessing the effectiveness of the proposed strengthening method. Depending on the possible directions of applied load (major axis or minor axis) and the corrosion conditions, three specimens were employed in the loading tests. Static loading tests were performed on steel columns with and without strengthening. Test results, including load-deflection relationships and the strain development process of the columns, were measured and compared between the original and strengthened columns. Moreover, three-dimensional finite-element models were built to compare the strengthened and original steel columns. Both the experimental and numerical results indicate that the proposed strengthening method can significantly enhance the stiffness in the elastic stage and the load-carrying capacities in the plastic stage, resulting in significant extension of residual service life under real service conditions and improvement of seismic performance during earthquakes. (C) 2017 Elsevier Ltd. All rights reserved.

An experimental program was performed to investigate the postfracture performance of composite twin I-girder bridges in the fatigue crack condition. An intact specimen and a damaged specimen were tested under one-point load to understand the effect of fracture on the bridge response and safety. In addition, nonlinear numerical analyses were performed to study the mechanical behavior of the models. The results showed that the fracture of the entire web and bottom flange at the midspan section can result in a considerable increase in the shear strain on the studs near the middle section. The fracture of the bridge in the midspan section governed by bending failure is found to be most critical in terms of the remaining load-carrying capacity, and the fracture near the support location governed by shear failure is found to be brittle, which can result in a sudden collapse of the bridge system. The effects of the fatigue crack on the safety of the composite twin I-girder bridge can be mitigated by using a continuous span instead of a simply supported span or by using a stronger and thicker concrete slab. (C) 2017 American Society of Civil Engineers.

This study is carried out to investigate the post-fracture behavior of the composite twin I-girder bridge systems. In the experimental program, one intact specimen and one damage specimen were tested under static load with displacement control method. Different cases of fractures are performed in numerical analyses based on finite element method and nonlinear analyses. Significant reduction of system stiffness and load carrying capacity is observed in post-fracture condition. The failure modes of both intact and damage specimen are governed by the crush of the concrete slab. Nevertheless, composite twin I-girder bridge system will not collapse under dead load and be able to carry a certain level of live load. Numerical analyses for different damage conditions proved that the fracture at mid-span section is the most fracture critical location for composite twin I-girder bridge system.

In the next 20years, more than half of the bridges in Japan would be in service for more than 50years. These include truss bridges those are generally consideredto benon-redundantand fracture critical. With ageing, these bridges are facing an increasing risk of bridge collapse under extreme conditions.Therefore, it is essential to evaluate alternate load paths on existing bridge structures to avoid bridge collapse or replacement. In this paper, after-fracture redundancy of truss bridges is investigated through a case study for a five-span continuous truss bridge. Field tests were performed, and the displacements on key sections were measured in the test. According to the experimental observations and test results, a numerical model capable of simulating the present truss bridge was built and was used to investigate the after-fracture redundancy of the target bridge. Fracture of truss members in typical locations was considered in the numerical analyses, and the R' values of both intact and damaged trusses were compared. On the basis of the numerical results, a critical member in this bridge was also determined.

The Kintai-kyo Bridge is a unique, five-span wooden bridge with three arches across the Nishiki River, the largest river of the Yamaguchi Prefecture, Japan. The central wooden rib arch is very rare in the world. The bridge has become a famous landmark because of its elegant structure and its aesthetic appearance that is in harmony with the surrounding picturesque landscape. It is a popular historical site and attracts many tourists. The wooden bridge has been rebuilt several times since its inauguration in 1673. The latest rebuilding was done in 2004 which was almost 50 years after the previous one. The original span length of the Kintai-kyo Bridge was close to the limit allowed for construction of wooden bridges during that time. In order to strengthen the bridge against floods, the best combination of wood and stone was used. Arch structure was adopted for the superstructure, and hollow stone piers of spindle-shaped cross-section were adopted in the substructure. This paper studies the origin of the arch structure of the Kintai-kyo Bridge because this arch is unique and different from the voussoir arch or the corbel arch, and its resulting elegant appearance. In addition, as a unique feature, periodical inspections of the Kintai-kyo Bridge have been conducted by the Waseda University every 5 years since 1953, where the weight of local high-school students is used as the load for testing.

The effects of the inclination angle on the buckling of continuous composite bridges (CCBs) with parabolic arch ribs remain to be elucidated. Static tests were conducted on an on-site prototype of a CCB with parallel arch ribs to verify the validity of proposed numerical finite element method models of CCBs with inward and outward arch ribs. We found that the expressions for the equivalent slenderness ratios and buckling coefficients should consider the interactions between the in-plane and out-of-plane buckling, given the inclination of the arch ribs. With respect to the buckling modes, the arch ribs of all the models buckled in the first lateral mode. In addition, two types of interactions were observed between the buckling modes, namely, that between in-plane and out-of-plane buckling and that between global and local buckling; these were affected by the inclination angle, especially in the case of the CCB with the outward arch ribs.

Gusset plates of a joint in a steel truss bridge are the key parts of the structure system, because they are connecting several main truss members. However, the detailed failure mode of gusset plates subjected to compression has not been well examined yet. Therefore, this paper discusses the failure mechanism of the gusset plates of a joint subjected to compressive force through the diagonal member. The failure mode is examined by both numerical and experimental method. And It is clearly shown that the failure mode demonstrated by these two methods are quite consistent with each other. Then, a strength equation for the gusset plates subjected to compression is finally created on the basis of the failure mode.

Bridge accessories, such as parapets, service ducts, and track slabs, are commonly used in railway bridges, but their real effects on the structural behavior of the bridges are still unknown because very few studies have been reported on this significant aspect. In engineering practice, lack of information on the contribution of bridge accessories may cause problems for bridge design, bridge health evaluation and monitoring, bridge management and operation, and bridge maintenance. Given this background, field tests were performed on a railway bridge with typical bridge accessories to confirm their contribution to bridge rigidity (or stiffness), as well as their effects on the sectional normal strain distribution. Both displacements in the midspan and strain results on key sections were measured in the field test and reported in this paper. Based on the field test observations, a numerical model capable of simulating the present railway bridge was built and was used to investigate the effects of the bridge accessories and their expansion joints. Longitudinal normal stress distributions on concrete slabs, steel main girders, and single-parapet panels were given, and parametric analysis considering different arrangement methods of expansion joints in the bridge accessories was also performed. Based on the numerical results, a stress concentration on the concrete slab near the expansion joints was confirmed. The results obtained in this study can be used for improving the design method used in new railway bridges and the maintenance of old railway bridge structures. (C) 2015 American Society of Civil Engineers.

Perfobond connectors are a certain type of shear connectors used in steel and concrete composite structures. In composite bridges with narrow connector distances or shallow rib heights, it is unfavorable to enhance shear connection by using large circular-hole perfobond connectors. To solve this problem, an alternative perfobond connector was developed by making long-holes on steel rib plates. In this paper, 21 push-out specimens were fabricated and loaded to failure. The main objective was to compare the failure mode, shear capacity and slip behavior of perfobond connectors using circular-holes and long-holes. Furthermore, 87 nonlinear finite element simulations were performed to further study the effects of hole geometry and concrete strength. The parametric results were generated to evaluate the shear capacity equations for perfobond connectors. Finally, an analytical model was proposed to predict the shear strength of both circular-hole and long-hole perfobond connectors. (C) 2015 Elsevier Ltd. All rights reserved.

As the national bridge inventory ages and traffic volumes increase, the government is spending more on maintaining their existing structures to extend the service life of the current bridge inventory. This includes two-girder bridges that are classified as fracture critical and non-redundant. Owing to the increased inspection costs associated with these fracture-critical bridges, there is a need to evaluate alternate load paths and to implement retrofit methods on existing bridge structures to avoid bridge replacement. In this paper, after-fracture redundancy of two-girder bridges is investigated through a case study for a four-span continuous steel-concrete composite twin boxgirder bridge. The finite element analysis was carried out to evaluate the load-carrying capacity after failure of one girder of the two-girder bridge. Two types of the main-girder damage, including fracture of the bottom flange only, and fracture of both bottom flange and the web were considered respectively in this study. Typical damage locations including mid-span section of the main girder and the sections near the intermediate support were also considered in the numerical analyses. On the basis of the numerical results, the present continuous steel-concrete composite box-girder bridge was classified as a redundant bridge, and the concrete deck was considered as the key member for ensuring the bridge redundancy after severe damages occurred on the main girders.

This research offers a new composite revamping method for railway bridges by assuming composite remodelling process of existing steel bridges having no specific fissure damages or serious corrosions and effectively making use of relatively new materials to it. Effects of noise reduction and improved stiffness were further confirmed through hammer impact tests (vibration measurement tests) and loading tests in order to prove the efficacy of the composite remodelling.

In steel and concrete composite girders, the load transfer between the steel beam and the concrete slab is commonly ensured by installing shear connectors. In this paper, to investigate the nonlinear behavior of perfobond connectors, a total of 60 push-out specimens were fabricated and tested with the variables for the hole diameter, the concrete strength, the thickness of concrete slab, the diameter, strength and existence of perforating rebar, the thickness, height and distance of perfobond ribs. The failure mode and the load-slip behavior of perfobond connectors were obtained. A theoretical model was put forward to express the load-slip relationship. Analytical formulas of shear capacity and peak slip were also proposed considering the interaction between the concrete dowel and the perforating rebar. The calculation results of the proposals agreed well with the experimental values.

Continuous composite beams represent an efficient structural form in many structural systems, such as buildings and bridges, due to additional advantages associated with the favorable redistribution of internal forces across the member and the easier satisfaction of serviceability checks. Moreover, in the regions of hogging moments, e.g. at the internal support regions of continuous members, a large part of the composite beam section is subjected to torsional moment under certain loading conditions and in curved composite structures or flyovers, thus the bottom flange and the web are susceptible to local instabilities and the concrete slab may crack during its service stage. In this study, two steel-concrete composite beams were tested to investigate their mechanical performance under combined hogging bending and torsional moments. Load and deflection relationships, strain distribution and development in the reinforcement, and the slip on the steel-concrete interface were recorded in the test and reported in this paper.

In current practice and design, composite twin I-girder bridges are predominantly used in highway bridges design due to their low cost comparing to other types of bridges. While classified as non-redundant structural system according to AASHTO specifications, previous practical experiences have shown that this type of bridges is capable of surviving some accident events such as losing of one support or sudden fracture of web and bottom flange. For this reason, an experiment was carried out to investigate the redundancy level of composite twin I-girder system. The fracture is limited to the whole web and bottom flange as the top flange is fully connected with the slab by shear connectors. Results show that after the fracture of full web and bottom flange, the composite twin I-girder bridge is still capable of carrying some load before losing its functionality and reaches the ultimate failure state. Base on the results of this study, the redundancy level of tested specimens is higher than 1.0. There for, the simply supported composite twin I-girder model in this study is concluded as a redundant bridge structure.

鉄道橋では合成桁が多く使用されている．これらの合成桁の設計では，鋼桁と床版以外の高欄やスラブ軌道などの付属構造物については，安全側の観点から剛性を考慮しないのが一般的である．しかし，従来の計測結果からこれらの付属構造物についても剛性への寄与が認められていることが報告されている．これらの剛性の寄与は，終局耐力時には失われる可能性があるため，設計の合理化にはつながらないと考えられてきた．したがって，これまでの研究ではこの剛性寄与の効果について詳細に検討することは行われてこなかった．しかし，近年，維持管理における健全度評価に，桁剛性の計測結果を用いることが多く，これらを厳密に評価する必要が出てきている．そこで本研究では，鉄道用連続合成桁の測定結果をもとに，橋梁の実剛性をより厳密に算定する方法を検討した．

Redundancy is one of the most important factors to evaluate the safety of a bridge as it shows the possibility of the bridge to survive after an incident that can cause partial or full damage on the critical member of the bridge. The purpose of the present study is to evaluate redundancy level of three span continuous twin I-girder composite bridges, which is widely used in current highway bridges. Bridge models were studied and analyzed by using the finite element method with the aid of DIANA Software. Firstly, experimental results were used to verify the validity the present numerical model. Thereafter, fracture of one mid-span girder was assumed in order to determine the redundancy level of damaged bridge models. This study also shows the importance of secondary members in transferring and redistributing the load after the fracture at the mid-span of one main girder of the bridge.

This paper describes the effects of SFRC on improving the mechanical performance of composite steel and concrete beams subjected to hogging moment. Four specimens with different concrete slabs and different shear connectors were examined experimentally in this study. Steel fiber reinforced concrete (SFRC) was used for two specimens, and normal concrete was applied for the other two specimens. Different types of shear connectors, including shear studs and Perfo-Bond Strips (PBLs), were used on steel-slab interface of the specimens. Shrinkage of the normal and steel fiber reinforced concrete, load versus mid-span deflection relationship, crack formation and its propagation process, and slip development on the steel-slab interface were measured and investigated. The test results show that the inclusion of steel fibers decreased both the crack sparing and crack width of the concrete slab. The specimens with steel fiber reinforced concrete have relatively large initial cracking load, and crack width of the concrete slab can be controlled appropriately in the service stage. The effects of the SFRC on the ultimate load carrying capacity of the beam depend on the shear connectors applied on the steel-slab interface. The application of SFRC could enhance the load carrying capacity of the specimen with stud shear connectors, however, the effects of SFRC on the load carrying capacity of PBL specimen were found to be declined in some extent. Besides, the current specifications, such as AASHTO, EUROCODE-4 and JSCE, are typically conservative in predicting the ultimate load carrying capacity for composite beams under hogging moment. (C) 2014 Elsevier Ltd. All rights reserved.

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The horizontally curved continuous composite steel-concrete beams, for instance, curved continuous composite bridges, have excellent qualities, such as quick construction, good seismic performance, saving construction formwork and convenience in spatial arrangement etc. At present, the application research of this kind of structures is becoming more of a concern, but very few studies have been conducted to study the mechanical performance of composite beams subjected to combined hogging (negative) bending and torsion. The purpose of the present study is to investigate the effects of curvatures on both elastic and inelastic behaviours of curved continuous steel-concrete composite beams in the interior support regions. Based on the experimental observations in a straight composite beam, a three-dimensional FE model capable of analysing the composite beams subjected to negative bending moment is built. Further numerical studies on curved composite beams with different curvatures are performed in this study. Strength and load carrying capacity, sectional strain distribution and movement of composite neutral axis before and after cracking, as well as the strain results of longitudinal reinforcing bars are investigated. Besides, the interaction equation for ultimate bending and torsional moments is proposed.

Preventive maintenance on aged steel railway structures is all important due to their long service time after completion. This paper introduced a strengthening method for old steel railway bridges by using rubber-latex mortar, glass fiber reinforced polymer (GFRP) plates, lightweight rapid hardening concrete, and reinforcing bars. Both laboratory tests and field tests were performed to confirm the effects of the present strengthening method. In total, two old railway bridges were employed in this study. One of them has been in service for around 100 years. The static loading test was performed in the laboratory. Experimental results, including load-deflection response, strain distribution on the structural steel, GFRP plates as well as concrete, were given and compared between the original steel railway bridge and the strengthened bridge. Theoretical results were also provided to make a comparison with the experimental results. Both the experimental and theoretical results indicated that the present renovation method could greatly enhance the rigidity and reduce the stress levels of old steel members, resulting in the extension of the residual service life of the old steel railway bridge. In addition, field tests were performed on the other old railway bridge, which has been used for 86 years, and stress variation on the railway bridge under the running train was measured and the effects of the present strengthening method in the real service condition were also confirmed.

Bridge Redundancy Evaluation is getting more attention in both designing new highway bridges and repairing or retrofitting old bridges after several bridge collapses or failure incidents happened around the world in recent years. This study is tempted to evaluate effects of secondary members on redundancy of three-span composite twin I-girder bridge. Two types of secondary members were studied including I-shape transverse beams and L-shape X-type bottom lateral bracing. Results show that three-span composite twin I-girder bridge can be considered as redundant. The redundancy level can be increased by adding bottom X-type lateral bracing. I-shape transverse beams alone is found not effective in increasing the redundancy of the bridge, but is found useful to increase the efficiency of the bottom X-type bracing to increase the load carrying capacity and redundancy of bridge.

As the bridge inventory ages and traffic volumes increase, the bridge owners are spending more on maintaining their current structures. AASHTO considers virtually all two-girder bridge systems as non-redundant, and each girder is considered as the fracture-critical member (FCM). Redundancy analysis of the two-girder bridges considering the uncertainty (damage scenarios) is investigated through a case study on a three-span, continuous twin I-girder bridge. The FE analysis is employed to evaluate the load-carrying capacity after fracture of one main girder of the twin girder bridge. The damage locations are chosen at the mid-span section of the middle span, the side span, and the section near the continuous pier support. Damage to shear connectors near the moment contra-flexure regions and missing one bearing at the middle and end support locations are also considered as potential damage scenarios in this study. On the basis of the direct redundancy analysis results, the present continuous two-girder composite bridge can be classified as redundant.

Structural repairing or maintenance technique has been a hot issue in recent years due to the increasing aging problems of old railway bridges. A strengthening method for welded joints in old steel railway bridges by integrating the rapid hardening concrete, rubber-latex mortar, and reinforcing bars is introduced in this paper. The purpose of the present study is to investigate the mechanical performance of the strengthened connection joints in old steel railway bridges. Depending on the locations of the concrete and possible loading conditions, the joint needs to sustain both negative and positive bending moment, therefore, two experimental plans were employed. The static loading tests on the steel joints before and after strengthening were performed to confirm the effects of the present strengthening method. Moreover, three-dimensional FE models were built to make a comparison study between the strengthened and original steel joints. Load versus deflection relationship and strain development process on the web of the joints were measured and compared between the original joints and the strengthened joints. Both experimental and numerical results indicate that the present strengthening method can greatly enhance the stiffness and reduce the stress levels of steel joints, resulting in the extension service life of aged steel railway bridges. (C) 2013 Elsevier Ltd. All rights reserved.

A partially encased composite l-girder with flat or corrugated web has been proposed to improve the structural performance of continuous composite girder under hogging moment. The flexural behavior of such structure under two points symmetric loading has been experimentally and analytically investigated. Static flexural loading tests showed that the partially encased girder improved bending strength in comparison to steel I-girder, as local bucking of steel flange was restricted by encased concrete. Especially for the corrugated web girder, the ultimate bending strength was improved about 20%, and the ductility also increased about 3 times. In addition, the limitation of width-to-thickness ratios for steel and concrete-encased composite I-girders with corrugated web were suggested to prevent premature failure due to local buckling of compressive flange. Moreover, the analytical methods of flexural strength under service and ultimate state for partially encased composite girder were proposed and verified with experimental results. It was found that the analytical bending strengths agreed well with the experimental ones at both service and ultimate state, which means the proposed analytical equations can be applied in predicting flexural strength accurately for such encased composite girder with flat or corrugated web. (C) 2013 Elsevier Ltd. All rights reserved.

Limited experimental results have been reported in the literature on the fatigue and ultimate static loading behavior of composite beams subjected to negative bending moment. This paper examines experimentally the behavior of composite steel-concrete beams. Eight composite specimens were tested to study the various aspects of composite beams under a negative bending moment, including the effects of repeated loading, shear connectors (studs and PBLs), rubber-latex mortar coating, and steel fiber-reinforced concrete (SFRC) on their structural performance. Load versus midspan deflection, crack formation and its developing process, slip distribution on the steel-slab interface, and the flexural strain results of shear connectors were measured and studied. The test results show that the initial cracking-level repeated load did not show obvious effects, while the stabilized cracking-level repeated load can reduce the rigidity and loading capacity of composite beams. The experimental results indicate that the plastic bending moment criteria in the current AASHTO load and resistance factor design specifications are typically conservative for composite beams under a negative bending moment. In addition, the effects of SFRC on crack width control and adhesion bonding effects of rubber latex on the steel-slab interface were confirmed in the testing. (C) 2013 American Society of Civil Engineers.

In continuous steel-concrete composite structures, cracking of the concrete slab in the hogging bending moment region decreases the global stiffness of composite structures and reduces the effect of continuity, resulting in making the structural behaviors highly nonlinear even for low stress levels. Because of this, special consideration is necessary. The purpose of the present study is to investigate the effects of rubber-latex mortar and different types of shear connectors on inelastic behavior of composite girders subjected to hogging moment. Two overturned simply supported steel-concrete composite girders with different shear connectors such as Studs and Perfo-Bond Strips (PBLs) were tested under concentrated load in the mid-span. Based on the experimental observations, a three-dimensional FE model capable of analyzing the composite beams subjected to negative bending moment was built. Strength and load bearing capacity, sectional strain distribution and movement of composite neutral axis before and after cracking were observed in the test and compared with the numerical results, and the results predicted by this modeling method are in good agreement with those obtained from the tests. Research results indicate that the PBL connectors could slightly improve the rigidity of the composite girder under both the serviceability limit state and the ultimate limit state, while Stud specimens have relatively better mechanical behavior in regard to the initial crack and the "crack closure" of the test specimens. Besides, research results indicate that the current specifications such as AASHTO, JSCE, and EUROCODE-4 can provide appropriate values for ultimate strength of a composite girder under negative bending moment. Moreover, noise reduction, shear stud stiffness increase and the adhesion bonding effect of rubber-latex mortar on interface slip were confirmed in the tests.

As the Japan bridge inventory ages and traffic volumes increase, the government is spending more on maintaining their existing structures to extend the service life of the current bridge inventory. This includes two-girder bridges that are classified as fracture critical and non-redundant. Owing to the increased inspection costs associated with these fracture-critical bridges, there is a need to evaluate alternate load paths and to implement retrofit methods on existing bridge structures to avoid bridge replacement. In this paper, fracture redundancy of the two-girder bridge is investigated through a case study for a three-span continuous twin I-girder bridge. The finite element analysis is carried out to evaluate the load-carrying capacity after fracture of a girder of the two-girder bridge. Damage of studs near the moment contra-flexure regions are also considered in this study. Spacing between the transverse beams is discussed as possible techniques to improve redundancy and reduce the fracture potential of two-girder bridge structures. The concrete slab is indicated to be a significant member for guarantying the redundancy of the two-girder steel-concrete composite bridges.

Structural repair or maintenance technique has been a hot issue in recent years due to the increasing aging problems of old railway bridges, which have been used beyond or approaching their design service life. A strengthening method for old steel railway bridges by integrating the new structural members was adopted in engineering practice in this context. Rubber-latex mortar, GFRP plates and rapid hardening concrete were integrated with the old steel railway bridge to increase its rigidity and reduce both stress levels and structure-borne sound levels of the old steel bridge. The purpose of the present study is to investigate the mechanical performance of the renovated hybrid railway bridge. The material test on aged structural steel, the static loading test on the strengthened bridge, and the impact hammer test on the old bridge before and after strengthening, were performed to confirm the effects of present strengthening method. Moreover, three-dimensional FE models were built to make a comparison study between the strengthened and the original steel bridge. Both experimental and numerical results indicate that the renovation method can greatly enhance the stiffness and reduce the stress levels of steel members, resulting in the extension of the service life of the old steel railway bridge. Furthermore, noise reduction effects by using concrete and rubber-latex mortar were confirmed in the impact test. (C) 2013 Elsevier Ltd. All rights reserved.

This paper describes the fatigue behavior of composite steel and concrete beams subjected to negative bending moment. Fatigue tests with repeated load limited to initial cracking and stabilized cracking, were performed on two steel-concrete composite beam substructures respectively. Test results indicated that when the repeated load was equivalent to the initial cracking load, the fatigue test had only limited influence on beam stiffness or crack patterns. However, when the repeated load was equivalent to the stabilized cracking load, a number of residual cracks occurred in the initial static test and the beam became less stiff as the load cycles increase. Failure of the bond between studs and surrounding concrete was confirmed in intermediate static tests; flexural stiffness of studs became smaller as the increase of load cycles. In addition, final static tests were performed on fatigue test specimens and another specimen without fatigue test. The comparison indicated that when the repeated load was larger than the initial cracking load, fatigue test could decrease beam stiffness and its ultimate load carrying capacity. (C) 2012 Elsevier Ltd. All rights reserved.

Shear behavior of partially encased composite l-girders with corrugated web has been investigated analytically and numerically in this paper. A 3-D finite element model with geometric and material nonlinearity is established and verified by the experiments. Subsequently, a parametric study is carried out to examine the effects of geometric and material properties on the shear behavior which includes corrugation, height, thickness, connection degree between steel web and concrete encasement. It is found that the ultimate shear strength of steel l-girders is improved with increases in the thickness, height and yield strength of corrugated web, while the ultimate shear strength of partially encased composite I-girders increases with the thickness, yield strength of corrugated web and the thickness, compressive strength of concrete encasement. However, the stud stiffness has little influence on the ultimate shear strength. Moreover, the concrete encasement improves the shear strength of steel l-girders, the degree of improvement increases with the thickness and compressive strength of the concrete, but decreases drastically with the thickness of corrugated web. Therefore, it is suggested that concrete should be poured on the corrugated web with thin thickness or low yield strength to prevent buckling occurrence before yielding of steel web. Finally, shear strength prediction equations are proposed and verified by numerical results. The calculated shear strength agree well with the numerical results for steel l-girders before and after composite with concrete, which indicates that the proposed analytical equations can be applied to predict the shear strength of such partially encased composite girders with corrugated web. (C) 2012 Elsevier Ltd. All rights reserved.

A new type of partially encased composite I-girder with corrugated steel web has been proposed to improve the structural performance of continuous girders under hogging moment. The shear behavior of such partially encased composite I-girders under anti-symmetric loading has been experimentally and analytically investigated. Experimental results show that the partially encased composite girders has superior shear strength compared to steel I-girders, since shear bucking of steel web is restricted by concrete encasement. The shear stiffness of the composite section is based on the total summation of corrugated web and concrete encasement with average thickness before cracking, and the ratio of shear resistance shared by the steel web and the concrete encasement depends on their shear stiffness. In addition, predicted shear strength of the partially encased composite girder with corrugated web is proposed according to the experimental failure mode and strain distribution. The analytical shear stiffness and shear resistance ratio at the elastic stage are verified by experimental results. And the calculated shear strength for steel and composite girders agree well with the experimental results. The comparison shows that the proposed analytical methods can be applied in predicting elastic shear stiffness and design shear strength for such partially encased composite girders with corrugated web. (C) 2012 Elsevier Ltd. All rights reserved.

The composite bridges with corrugated steel webs have excellent properties, such as lightness of girders, efficiency of introducing prestress forces, short construction period, optimum force distribution, good seismic performance, and aesthetics appearance etc., which have greatly promoted the application of such bridges. The objective of this paper is to provide and summarize important references related to the analysis, design and construction of composite bridges with corrugated steel webs. Subjects discussed in this review include (1) structural configuration and application; (2) shear behavior; (3) bending behavior; (4) torsional behavior; (5) patch loading resistance; (6) dynamic behavior; (7) long-term behaviors including fatigue and creep; (8) component connections; (9) analysis method and theory; (10) new concept application. The literature survey presented herein mainly focuses on papers written in English, Japanese, German and Chinese in relation to composite bridges with corrugated steel webs.

Maintenance of existing steel structures has been a hot issue in recent years. A hybrid bridge was created from an original steel structure by integrating with the concrete members. The purpose of the present study is to investigate the mechanical behavior of the renovated girder. Based on the experimental observations, a three-dimensional FE model capable of analyzing these kinds of composite structures was built. Strength and deformation response, sectional strain distribution and movement of composite neutral axis before and after concrete cracking were observed in the test and compared with the numerical results, and the results predicted by this modelling method are in good agreement with those obtained from the tests. Results indicate that the renovated structure can greatly enhance the stiffness and reduce the stress levels, resulting in the extension service life of the structure.

The important accidents that the diagonal members of the steel truss bridge have broken due to severe corrosion damages occurred recently. Therefore it is expected to establish the rational and efficient maintenance management technique depending on the bridge type and structure characteristic. Especially, the corrosion damages of the main members may have a serious influence on the safety of the bridge system, and the technique for the investigation and checking is appropriately demanded. In this study, for the corroded gusset plate connection which was cut out from the steel truss bridge, we measured the corrosion shape in detail using the surface roughness measurement equipment, and evaluated the actual state by the surface corrosion of the outside and the narrow inside of the gusset plate connection.

In continuous composite steel-concrete structures, cracking of the concrete slab in the hogging moment region decreases the global stiffness of composite steel-concrete structures and reduces the effect of continuity, thus making the structural behaviour highly nonlinear even for low stress levels, so special consideration is necessary. An experimental investigation on the behaviour of steel-concrete composite beams in hogging moment region is presented in this paper. A total of four specimens were tested under point load in the mid-span. Two of the composite beams with headed studs as the shear connectors, while the other two specimens are using Perfo-Bond Strips (PBLs) as the connection devices between the steel girder and the concrete slab. Ultimate load bearing capacity of composite sections in negative moment region was calculated and compared with experimental values. Crack formation, crack widths development process and strain distribution of the composite section before and after cracking were observed and presented in this study. Interface slip distribution was also given. Research results indicate that the current specifications such as AASHTO, JSCE, and EUROCODE-4 can provide appropriate values for ultimate strength of a composite girder under negative bending moment.

The horizontally curved composite girder bridges have excellent properties, such as quick construction, good seismic performance, saving construction formwork and convenience in spatial arrangementetc, which have greatly promoted the application of such bridges. The objective of this paper is to provide and summarize important references related to the analysis, design and construction of curved composite girder bridges. Subjects discussed in this review include (I) different curved girder bridge configurations and their applied range; (2) current specifications; (3) construction issues; (4) design methods; (5) analytical methods; (6) load distribution; (7) torsional behavior; (8) warping stresses; (9) stability; (10) ultimate load-carrying capacity; (11) dynamic and seismic response; (12) loading test; (13) long-term behavior; and (14) design details. The literature survey presented herein mainly focuses on papers written in English. Japanese and Chinese in relation to curved composite girders.

Ten specimens are tested to investigate the cyclic behavior of beam-to-column joints of steel frames with joint panels. The performances of the joints with respect to strength, rigidity, and hysteretic performance are examined. Three different loadcarrying mechanisms can be identified. Panel resistance ratio (Rp) is presented for predicting the buckling patterns. The validityof Rp is confirmed through the present experimental results. On the basis of the experimental results of steel beam-to-columnmoment joints, 3-D nonlinear finite element models are established to analyze the mechanical properties of these connections.The load-displacement curves of the finite element analysis are in good agreement with those of the tests in terms of strengthand unloading stiffness. A shear lag phenomenon was captured in the beam flanges by not only experimental results but alsonumerical analysis. Parametric studies are conducted on the connections under monotonic loading to investigate the influencesof connection dimension, resistance ratio on the connection behavior. It was found that the failure modes are influenced by theresistance ratio, while the thickness of joint panels resulting in large effects on the strength and stiffness under shear failure mode. © Springer, Part of Springer Science+Business Media.

Negative bending moments acting on the support regions of continuous composite girders generate tensile stresses in the concrete slab and compressive stresses in the lower steel profile. As a result, the mechanical behaviour of these girders becomes strongly nonlinear, which needs special study. In this paper, static experimental tests on four half-scale models of steel and concrete composite girders with different shear connectors such as studs and Perfo-Bond Strips (PBLs) under hogging moments are cautiously conducted in order to investigate the reduction of flexural stiffness and the inelastic behaviour after cracking. In the test results, crack development, crack widths and strains of the composite section before and after cracking were observed. The crack width evaluation methods based on design codes for steel and concrete composite girders under negative bending moment were compared. Crack widths should be controlled appropriately within an allowable value in the slab under service load. The strains in reinforcing bars obtained through the static tests agreed well with the values calculated through the application of the existing tension stiffening theory. The test specimens could be assumed to be a full composite section until the ultimate state on the basis of load and slip relationship results of shear connectors. It follows that analytical and experimental studies can be served as a basis for the design of continuous composite bridges. (C) 2009 Elsevier Ltd. All rights reserved.

本研究は，橋梁の構造形式で連続合成桁を採用する際に検討しなければならない中間支点部において，負曲げにより生じるRC床版のひび割れの挙動を把握することを目的としている．特に，現在ではまだ検討事例の少ない疲労試験を行い，疲労挙動の解明に着眼点をおいている．RC床版のひび割れ挙動の把握を行う際に，近年の連続合成桁における設計指針や研究事例に数多く取り入れられているコンクリートの応力分担効果すなわちテンションスティフニング効果の考え方を導入した．連続合成桁の中間支点部を模擬した載荷実験を行うことにより，疲労試験におけるひび割れ幅は繰り返し載荷回数の増加と共に安定することを確認した．

This paper is concerned with the identification of bifurcation points occurring on the mechanism paths of a linkage, in which the structural system consists of links and revolute joints. The way that the links are assembled is mathematically described by compatibility conditions. The present paper mainly deals with the kinematic paths of mechanism that goes through special configurations of kinematic bifurcations. In general, Such special Configurations are called uncertainty configurations or singular configurations. The Jacobian derived from the compatibility conditions has been used as a measure of the distance away from the singular configurations. The Jacobian does not always give Sufficient results for the detection of bifurcation points. This Suggests that it is necessary to consider higher-order infinitesimals for examining approximate Solutions of compatibility conditions. The Hessian matrix derived from the Jacobi matrix is considered to be one of the promising measure and may clarify the nature of the singular configuration as to whether the system is at a bifurcation point or not. In this paper, the theory behind the kinematic bifurcation of mechanisms of a linkage is explained and the numerical analysis of illustrative examples is discussed in detail.

Firstly, failure mode and shear strength of stud connectors were investigated based on push-out test results. Secondly, the practicability of a proposed analytical method was verified on the basis of a comparison with test results and the failure mechanism of the grouped arrangement was investigated. Lastly, parametric analyses on concrete strength and on the longitudinal spacing of stud connectors were conducted and shear strength reduction equations of the grouped arrangement of stud connectors were proposed.

自由度の高い複合構造を計画・設計・施工するためには, 汎用性の高い時間依存性解析が必要となる. 本研究では, 架設途上やコンクリートの経時挙動による断面図心の変動の影響を図心ずれとして考慮し, クリープ予測式の形態に影響を受けないstep-by-step法を基本とし, 逐次積分を組み合わせることでステップ分割の粗密による影響を改善, さらに, クリープ等の固定端断面力については部材内でひずみが放物線分布すると仮定し, 精度向上を図った解析法を提示した. 同解析法を用いた事例により, 拘束鋼材の効果や図心ずれの影響度を示した.

The authors have proposed an equation for estimating the ultimate strength of T-shaped socket joints. However, the effect of cyclic loading and external diagphragms, applicability to the cross-shaped joint and other issues must be verified. Therefore, the static loading tests by using the T-shaped joint specimens were carried out in order to investigate the effects of loading method and the diaphragm. Monotonic static loading tests by using the cross-shaped joint specimens were also carried out. The test results indicate that the loading method and the diaphragm affect the ultimate strength, and that the application of the proposed method to the cross-shaped joint is promising.

ソケット接合と呼ばれる柱梁接合構造について, 筆者らは, T形模型試験体を用いた静的単調載荷実験を行い, 本接合部の終局強度を推定する算定式を提案している. しかし, 実構造物への適用を想定した場合には, 繰返し荷重の影響, 外ダイアフラムの影響, 十字形接合部への適応性などについて検証する必要がある. そこで, 既に実施した一連のT形接合部の静的単調載荷実験に加え, 載荷方法や外ダイアフラムの寸法をパラメータとした追加実験および十字形模型試験体を用いた静的単調載荷実験を実施した. その結果, 終局強度に対する繰返し荷重と外ダイアフラムの影響を明らかにできた. さらに, 提案した終局強度算定式が十字形接合部へ適応が可能であることも示した.

既設の箱形断面鋼製橋脚は補剛材剛比が比較的小さいため, 強震時には局部座屈の発生による耐力低下が危惧される. そこで梁要素σ-εモデルの弾塑性有限変位解析により, 強震時の箱形断面鋼製橋脚の最大変位および残留変位を評価する手法について検討した. 局部座屈による劣化の影響を受ける範囲を塑性劣化ヒンジと定義し, シェル要素FEM解析により塑性劣化ヒンジの動的挙動を確認した. そこからフランジとウェブの座屈応力, 軟化型応力-ひずみ関係および除荷剛性の変化を定式化し, 梁要素の応力-ひずみ関係として使用した梁要素解析により, 局部座屈を伴う箱形断面鋼製橋脚の地震時動的応答がシェル要素FEM解析と同程度の精度で得られたことから, 提案する手法が既設鋼製橋脚の耐震性能の評価に利用できることを確認した.

This paper deals with load carrying capacity of corner joints between concrete filled steel columns and beams, with the help of loading tests and FEM analyses. For the loading tests, the model tests were carried out on four specimens by changing the position of stiffeners, the cross-section of beams. In the FEM analyses, six models were compared with each other to supplement the loading tests. As a result, it was found that each filling concrete in the corner hollow section has a constantly strong effect on the ultimate strength of cornerjoints regardless of whether the ring stiffeners are applied or not. The loading tests also confirmed that filling concrete circular steel pipes used for beam members were expected to two times post-yielding ductility to that of the filling concrete rectangular section member, the hollow circular section one.

The composite girders are mainly used for bridges, in which cracking of concrete slab plays an important role. Crack width is calculated by using strain of reinforcement and crack interval. In this study, a new calculation technique for the estimation of the strain is proposed with EC 4. Moreover, simplified analysis for steel fiber reinforced concrete (SFRC) is also proposed. The proposed technique is validated by comparison with experiments of girders with the shaft tension.

Synopsis: The study is aimed at obtaining basic data for evaluating the residual strength and deformability of damaged reinforced concrete members.
The behavior of members that suffered damage during cyclic loading such as cracking that penetrate into the cross section, plastic deformation or partial failure was compared with that of member tested under simple torsion. Reversed cyclic torsion was applied for loading because few studies have been reported in open literature although it has been estimated to cause the most brittle failure.
Tests and analyses identified the effect of reversed cyclic torsion with varying numbers of cycles and with varying amplitudes had on the reduction of residual strength and torsional rigidity. It was also confirmed that a closed joint that encircles longitudinal reinforcement at the ends of transverse reinforcement was stronger and more resistant to deformation than a lapped joint.

コンクリート床版と鋼桁よりなる合成構造を用いた連続桁は, 橋梁に多く用いられつつある. その中間支点部においては, 負曲げが生じるため, ひび割れに対する検討が必要である. ひび割れに対する検討は, 従来よりコンクリートを無視した鉄筋と鋼桁のみの断面で設計計算を行ってきたが, ひび割れ発生後の挙動に及ぼす, ひび割れが生じる以前の挙動の影響 (テンションスティフニングなど) については, あまり注目されて来なかった. EUROCODE 4では, ひび割れ発生以前の状態と発生後の状態を, 床版に作用する引張軸力で関連付けている. 本研究では, 日本で従来より用いられているひび割れ間隔を示す式と合わせて, 新しいひび割れ幅制御の計算手法を提案する. 提案した手法は, 合成桁の負曲げ実験と比較し, 妥当性を検討した.

本研究は, 兵庫県南部地震で実際に被災した橋梁をモデルに縮小した2径間の橋梁模型を製作し, 2次元振動台を用いて振動させたときの橋桁や橋脚の動的応答から桁間衝突による落橋のメカニズムを調べたものである. まず, 落橋防止連結板を取り付けていない場合について, 桁の衝突による落橋の有無を観察し, 桁間衝突が落橋におよぼす影響について検討した. その結果, 橋桁の落下には橋脚を中心とした設計振動単位の共振現象が強く影響することが確認できた. さらに, 落橋防止連結板に緩衝材を挿入し, それによって衝撃的な外力を吸収できるかどうか検討し, 緩衝材として望ましい材料特性について検討した.

「狭小箱桁」は従来の箱桁に比べ, ウェブ間隔を狭小化することにより縦リブ・リブを幅に削減し, 併せて床版を強化することで縦桁も省略した構造である. 本構造は上記の特徴から床版支間長がきくなるという点では, 2主桁などの少数主桁橋と同様に長支間床版の革新的な技術が要求されるが, 主桁のねじり剛性などの性能が異なるため, 設計上の多くの点で2主桁橋に比べて優れていると考えた. そこで全体挙動の把握と, 桁の省略・簡素化を一つの到達点としたさらなる構造の合理化を目指して, 立体FEM解析を用いた検討を行った. さらに, 床版の長支間化によって床版および床版と主桁の接合部に生じる作用力について, 2主桁との比較を交えながら構造上の安定性を検証した.

鋼とコンクリートの合成桁において, 鋼板孔を用いたずれ止めである埋込み接合を利用すると, 従来のスタッドを用いたずれ止めと比べ, 鋼フランジの溶接が不要になり, 施工が容易になるという利点を有する. 埋込み接合に関しては, 過去に押抜きせん断試験や桁としての載荷実験が行われており, その有用性が認められているが, いずれの実験も鋼ウェブに平行な面内の挙動の検討にとどまっており, 偏心荷重や水平横力に起因してウェブ上端に交互曲げが生じる現象 (首振り現象) に対する検討は少ない. 偏心外力載荷時の首振り現象に関する模型実験およびFEM解析を行い, 鋼板孔を用いたずれ止めの設計方法についても考察を行ったので報告する.

わが国における石積み構造は、その文化財的価値だけでなく、伝統的な工法の優秀さがこれまで数多く指摘されてきた。しかしながら、石積み橋脚に関する技術的あるいは力学的面からの検討は比較的少ない。本論文では、石積み橋脚の耐震安定性を力学的な面から検討し、歴史的に価値があるとされている空石積み橋脚の耐震安定性を考察することを主な目的としている。汎用有限要素法を用いた2次元動的応答解析により、周辺地盤を含む空石積み橋脚の耐震安定性について検討した結果、空石積み橋脚は、基礎地盤の影響を受け、せん断破壊しやすいことが分かった。

現在道路橋に用いられている合成桁橋のコンクリート床版は, 現場で場所打ちされたものが多く, ひび割れ等の床版の損傷が問題となることがある. このため, 床版の補修が容易であり, 高品質なコンクリート床版として評価の高いプレキャスト床版を用いた構造についての検討が諸機関でなされている.<br>本研究では, 連続合成桁橋中間支点上の負の曲げモーメントを受ける区間に着目し, 支点上の負曲げによるひび割れ対策を講じる目的から, 橋軸方向プレストレスを導入した構造について静的負曲げ載荷試験を行った結果について報告する. 実験では, 床版の打設方法, プレストレスの導入方法, スタッド間隔を変えることによる合成桁の力学的性状の違いについて比較検討した.

The purpose of the present paper is to demonstrate a nonlinear dynamic response analysis of steel bridge piers under seismic loading, in which a simplified model is employed as a constitutive equation and the effects of local buckling on the global cyclic plasticity of steel bridge piers are examined. On the basis of the fact that local buckling of steel component plates during earthquakes reduces the stiffness of steel bridge piers and cyclic loading degrades the strength of the steel piers, a simplified method for nonlinear dynamic response analysis of hysteretic steel bridge piers is investigated by using a pertinent one dimensional model.

本論文では弾性基礎上に横たわる無限厚板の過渡波動伝播現象を解析する一手法を Fourier 変換と固有関数を用いて提案している. 基礎かちの反力は基礎に接する厚板底面の変位に比例するという Winkler の仮定を用いた. 静止している厚板の表面に集中荷重が衝撃的に負荷され, 直ちに定速度で移動する問題を取り上げ, 載荷点かち少し離れた厚板内のある一空間点に注目し, 静止から最初の波面到達によって引き起こされる初期の擾乱, ならびに後続到達する波動の伝播速度, 伝播経路等の違いによって誘起される擾乱を境界での反射現象と関連づけて明らかにした.