Steel-concrete hybrid structures were first applied to Japanese railway fields a century ago. The research and development have been carried out for more than half a century for composite girders and steel-framed reinforced concrete (SRC) structures followed by various hybrid structures such as concrete-filled steel tube (CFT) structures, which have been contributing to the development and practical application of new structures and evaluation methods. This paper summarized research and developments for steel-concrete hybrid structures, mainly focusing on composite girders, SRC structures, CFT structures and renewal method of existing bridges based on the existing document surveys with the future prospects.

 In Standard Specifications for Hybrid Structures specified by JSCE, it is required to check at the service-ability condition, that the remarkable residual displacement in shear connectors is not generated. Therefore, in the specification, the corresponding displacement or shear force on the shear force-displacement relation before unloading is specified as the critical value for verification. However, when the headed studs with the arbitrary property of stud and concrete are employed as the shear connectors, the critical value of the shear force does not always agree with the one of the displacement on the shear force-displacement relation specified in the specification. In this paper, focusing on the serviceability condition, the critical values of the shear force and the displacement on the shear force-displacement relation specified in the JSCE specification are examined concretely, when the headed studs with the arbitrary property of stud and concrete are employed as the shear connectors.

 In the development of reinforcement method for plain concrete lining of waterway tunnels reinforcement extent and area was examined with full scale specimens. A cavity on the outer surface of the tunnel crown and cracks in lining concrete were considered on experiments, and reinforcement effect was confirmed for various situations of cracks and thickness of concrete lining. Load bearing capacity and deformation suppressing performance were evaluated, changing the extent and area of CFRP strand sheet and embedding reinforcement bar into the tunnel invert where the application of CFRP strand sheet is difficult. Obtained results showed that the reinforcement with CFRP strand sheet and ceramic mixed epoxy resin mortar could significantly improve load-resistant capacity and deformation suppressing performance of plain concrete lining of waterway tunnels in case of appropriate extent and area of reinforcement. Moreover, from the view point of the reinforcement design of this method, the verification method of the CFSS reinforcement amount based on the results of the full scale specimens test was suggested.

 FRP is a composite material made by mixing fiber such as glass with resin plastic to increase its strength. In this study, focusing on the temperature application time when performing the thermal cycle application test and the dry treatment before tensile and bending tests, the temperature cycle application test was conducted in which the time of one cycle was changed for GFRP using unsaturated polyester resin. After that, a tensile test and a flexural test are performed, and the purpose is to clarify the change in mechanical properties of the target material depending on the temperature application time and water content. As a result, it was found that tensile and bending properties were not affected much by the temperature application time in the case of non-drying treatment before the cyclic test, and that strength were affected by the thermal cycle in the case of drying treatment.

 Conducted herein is a tensile fatigue test of the Hand lay-up GFRP and the fatigue strength and the stiffness degradation due to repeated loadings was investigated. The fatigue strength were assessed based on the S-N diagram, and it was clarified that the fatigue limit was 35% of the static strength. It was also found that the stiffness decreased significantly at the initial stage of repeated loading, and then gradually decreased. Furthermore, attempt was made to evaluate the stiffness degradation of the Hand lay-up GFRP using the existing prediction formula. It is found that the stiffness degradation in the case of fatigue fracture can be predicted and the constants used in the evaluation formula were proposed.

 The current practice of performance evaluation on existing structures is mainly based on material degradation aspects. Although this evaluation is generally on the safe side, rational improvement is necessitated through the quantitative assessment of degradation impacts. On the other hand, enormous inspection data recently being available ranges widely as a nature from representing “structure symptom” to utilized as “model input”, and most data is solely an indirect index for the satisfaction level of required performance. Under such circumstances, the reliability of performance evaluation depends inevitably on an engineer’s competence. This paper reports about state of the art on the systemic practice among inspection, analysis, and performance evaluation, and we propose future directions through the experiences of blind structural performance evaluation, towards the further improvement and implementation of evidence-based quantitative structural performance evaluation.

 A research subcommittee on design and construction of concrete slab renovation technology of existing bridge was established from August 2018 in committee on hybrid structures of JSCE. This committee published a book entitled “Current Situation and Development of Concrete Slab Renovation Technology for Continuous Composite Bridges” to prepare for the increasing large-scale renewal works in the future. The books published by this committee include overview of composite girders, survey of past construction methods of concrete slab replacement work, joint structure between girders and slabs, problems and solutions for slab replacement, reinforcement methods for steel girders, and surveys on elastic composite girder bridges.