Experimental push‐out tests have been playing an essential role for the evaluation of the structural behaviour of shear connectors in steel‐concrete composite beams along with the development of analytical design guidelines for predicting the respective longitudinal shear capacity. Although standard push‐out tests allow to quantify the global response of the specimen in terms of load‐slip behaviour, numerical simulations are usually needed to broaden the mechanical insight with a special focus to the areas involved in the mechanical failure. This holds in particular for composite steel truss and concrete beams, where a dedicated shear connection does not exist. The shear connection relies instead on a mechanical interlock between the steel parts and the concrete.
Modern measurement devices allow expanding the experimental insight to internal mechanisms of combined concrete‐steel failure. This paper reports on the instrumentation of push‐out tests on composite steel truss and concrete (CSTC) beams with the support of a distributed fibre optical sensing (DFOS) system and evaluates the experimental results. The content presents different concepts of fibre installation and discusses the respective rate of success and the measurement ranges along the global load‐slip curves of the push‐out specimens. The results from the DFOS system provide the strain field histories along essential structural elements embedded in concrete within a crucial range of the load‐slip curves. Hereby it was possible to gain more insight into the load‐bearing mechanisms and identify the material component most likely involved in the stiffness degradation of the push‐out specimens.
The assessment of the load‐bearing capacity and fatigue strength of existing railway bridges has been playing an increasingly important role in the infrastructure management of railway operators for several years now. Currently, many bridge structures have been in operation longer than it was foreseen during their planning and construction. In addition, the axle loads on many lines, as well as the demands on the reliability of the verification results, have steadily increased. As the material properties and construction techniques in existing structures differ to some extent from nowadays structures, e.g., riveting instead of welding, it is important to provide engineers and operators with recommendations for the assessment of existing steel bridges. This article summarises the studies conducted as part of a research project initiated by Deutsche Bahn Netz AG for possible updates to DB RiL 805, which is used for the verification of railway bridges in the Deutsche Bahn (DB) network. The studies concerned the transition of verification concepts against static and fatigue loads used in the past to limit state verifications with partial safety factors in accordance with the Eurocodes. While initially related to an upgrade of a specific operator's design recommendation, the findings in this article are of more general nature and could form the basis for similar developments of recommendations for the assessment of existing, riveted structures independently throughout Europe.
The Composite Steel Truss and Concrete (CSTC) beam represents an effective and structurally economical solution which can look back to a long tradition of successful use in Italy. This type of structural element consists of a truss made of structural steel which is partly or entirely encased in in-situ cast concrete. The shear transfer mechanisms activated in these elements do not rely on dedicated shear connectors but on a mechanical interlocking between the truss and the surrounding concrete. In order to investigate the shear transfer mechanism and to support the development of appropriate design rules, 39 push-out tests have been planned in accordance with EN 1994-1-1 B.2 testing procedure and they are presented in this work. Also, a finite element (FE) model was developed to study in detail the stress and strain field of the specimens. This paper will present the findings of the experimental campaign and numerical studies on the longitudinal shear transfer in CSTC beams.
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