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In the framework of sustainable development policies, it is essential that infrastructure owners can rely on effective repair or strengthening solutions, designed and tested in relevance to actual service conditions. In the case of steel structures, fatigue damage is a major concern that can significantly affect the lifespan of the structure, and so far, there are very few operational methods capable of preventing fatigue cracks in the field. Adhesively bonded carbon fiber reinforced polymer (CFRP) composites are being successfully applied to the rehabilitation of concrete structures for more than two decades, and they are currently receiving much interest for the strengthening of steel elements, but mainly for curative purpose after severe damage has occurred. In the present study, which is part of a European project called FASSTbridge, a specific CFRP system has been developed as a preventive method against fatigue damage of steel structures. The proposed system consists of a commercially available ultra-high modulus (UHM) CFRP composite plate compatible with the stiffness of the host steel structures, which is bonded to the steel support using a novel hybrid epoxy/polyurethane adhesive. A first part of the paper presents the main specifications that should be adopted in the design of CFRP strengthening systems applied to steel structures, and that were identified from an extensive literature survey. These specifications have guided the development of the polymer adhesive and the choice of a peculiar commercial CFRP plate in the preliminary phase of the project. Experimental characterizations were then conducted (i) on the formulated hybrid polymer adhesive to optimize its curing schedule and check the previous specifications are fulfilled, and (ii) on CFRP reinforced steel specimens in order to verify the effectiveness of the proposed strengthening system. This experimental program involved both short term and durability tests that were performed by different laboratories. Such an inter-laboratory study made it possible to verify the performances of the developed strengthening system and to assess the influence of installation parameters and environmental conditions. The authors wish to acknowledge Epsilon Composite Company for supporting the study. This work is part of the FASSTBRIDGE project. This project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 31109806.0008. FASSTbridge is co-funded by Funding Partners of The ERA-NET Plus Infravation and the European Commission. The Funding Partners of the Infravation 2014 Call are: MINISTERIE VAN INFRASTRUCTUUR EN MILIEU, RIJKSWATERSTAAT, BUNDESMINISTERIUM FÜR VERKEHR, BAU UND STADTENTWICKLUNG, DANISH ROAD DIRECTORATE, STATENS VEGVESEN VEGDIREKTORATET, TRAFIKVERKET – TRV, VEGAGERÐIN, MINISTERE DE L'ECOLOGIE, DU DEVELOPPEMENT DURABLE ET DE L'ENERGIE, CENTRO PARA EL DESARROLLO TECNOLOGICO INDUSTRIAL, ANAS S.p.A., NETIVEI, ISRAEL - NATIONAL TRANSPORT INFRASTRUCTURE COMPANY LTD, FEDERAL HIGHWAY ADMINISTRATION USDOT

Shear has been observed to be often the governing failure mode of RC cantilever deck slabs of bridges without shear reinforcement subjected to concentrated loads when tested under a quasi-static application of the load. However, concentrated loads of heavy vehicles have a repetitive nature, causing loss of stiffness and potential strength reductions due to fatigue phenomena. In this paper, the fatigue behavior of cantilever bridge deck slabs is investigated. A specific experimental programme consisting on eleven tests under concentrated fatigue loads and four static tests (reference specimens) is presented. The results show that cantilever bridge deck slabs are significantly less sensitive to shear-fatigue failures than beams without shear reinforcement. Some slabs failed due to rebar fractures. They presented significant remaining life after first rebar failure occurred and eventually failed due to shear. The test results are finally compared to the shear-fatigue provisions of the fib-Model Code 2010 and the Critical Shear Crack Theory to discuss their suitability.

Assessing the strength of existing structures has become a major issue for structural engineers. Such analyses are often performed after changes of use of the structure or due to new design codes requirements. This is particularly relevant with respect to the shear strength of post-tensioned concrete bridges. Such structures were often designed in the past with fairly low amounts of shear reinforcement and do not comply with current code requirements in terms of amount of transverse reinforcement or shear strength. However, it should be noted that codes of practice cover the design of a wide range of cases and sometimes neglect some load-carrying actions or may be too conservative for assessing others. Therefore, the use of more refined models may potentially increase the predicted shear resistance and avoid unnecessary strengthening of existing structures. In this paper, an investigation on the behaviour of post-tensioned beams with low amounts of shear reinforcement and flanges is presented. First, the results of an experimental programme on twelve reinforced concrete beams (10.0 m long, 0.78 m high) failing in shear are described. The test series is used to analyse the most significant parameters influencing the shear strength and the failure modes. Its results are compared to a number of design codes showing different levels of accuracy. The test results are finally compared to the results of analyses based on elastic–plastic stress fields. This technique shows excellent results when compared to the test results and allows investigating on the role of the various shear-carrying actions, of the prestressing level and on the transverse reinforcement amount with respect to the various potential failure modes.