A Critical Assessment of the Fatigue Verification Concept of Stud Shear Connectors in Steel-Concrete-Composite Structures

Stud shear connectors in steel-concrete-composite structures transfer the stresses from one composite layer to the adjacent one and thus represent vital elements for the load-bearing capacity of the structural member under consideration. In bridge structures, the fatigue strength of the stud shear connectors, which are welded onto a steel member, is especially important. Verification concepts for the fatigue strength have been developed and implemented in design codes, such as EN 1994 [1]. These design concepts generally focus on the verification of the steel while the interaction of steel and concrete, resulting in flexure of the stud shear connector and in extreme, locally confined concrete pressure, is considered only by indirect means, if at all. Studies (see [2] and [3]) showed this influence to be substantial. The verification concepts provided by design codes focus on the shear-stress-range and the corresponding number of load cycles until fatigue failure occurs. These procedures neglect the amplitude and mean stress level of the concrete, which have been proven to have significant influence on the fatigue strength [4]. This paper will analyse and explain available verification concepts. Shortcomings will be discussed and an improved approach to the S-N curve for the verification of the stud shear connectors will be presented.