Fatigue Assessment of Shear Studs for Steel-Concrete Composite Bridges Using the Hot-Spot Stress Approach

Abstract

Welded headed studs are the most common type of shear connector employed in steel-concrete composite bridges, and the design is typically governed by fatigue due to cyclic loading and inherent welding-induced imperfections. The use of nominal stress (NS) methods for the fatigue evaluation of shear studs is the current norm. Additionally, the current fatigue design provisions are not based on full-beam tests, rather, they are based on a conservative ‘push-out’ direct shear test, and the testing is severely lacking in high-cycle fatigue life data, in the domain for which most bridges are designed. Another direct shear testing method was recently developed, called the ‘push-plate’ method, which can enable efficient testing in the high-cycle domain and thus offer a formal basis for establishing an endurance limit. However, this method is highly-conservative in contrast to a full composite beam test. In order to relate results from these different test types to each other and to expected behaviour in the field, local stress approaches can be used to capture the effects of various factors attributed to the boundary conditions. This paper presents a hot-spot stress (HSS) analysis of 18 push-plate fatigue tests in the intermediate-life domain and presents a parametric study performed using the developed FE model. Results indicate that the location of the point-of-action of an equivalent shear force (lever arm), the thickness of the base plate (flange), and boundary conditions for the push-plate test can influence the fatigue life. It is recommended that future studies extend the HSS approach to full composite beams, so the current design provisions can be aligned with reality, rather than non-representative test results, and so future high-cycle push-plate testing can be performed to establish an endurance limit for use in future editions of relevant design standards. Additionally, other local stress approaches (e.g., effective notch stress) should be used to study the effects of the weld geometry (notch), as well as the influence of variations in weld quality and geometry on fatigue life.