Fatigue design method of encased composite beams with welded shear studs

Abstract

Currently, both Chinese and international standards have not addressed the fatigue design for encased composite beams with welded shear studs (ECB-S), which undoubtedly limits the application of encased composite structures under fatigue loading conditions. This paper, combining a series of existing fatigue test results for ECB-Ss, proposes a fatigue design method for ECB-S that can serve as a reference for practical engineering design. Regarding the flexural fatigue failure characteristics of ECB-S, the overall safety of ECB-S is ensured through individual fatigue designs for key components such as the embedded steel sections, tensile rebars, and encasing concrete. Specifically, the fatigue design or verification of tensile rebars is based on the design S-N curve obtained from forty-two S-N data points in ECB and ECB-S fatigue tests, taking into account the effect of stress ratio. The fatigue design or verification of embedded steel sections is based on the S-N curve derived from eight S-N data points in ECB-S fatigue tests, considering the coupling effects of fractures between embedded steel sections and tensile rebars. For the compressive concrete, the fatigue design methods in the current reinforced concrete structural codes are directly applied for verification. Finally, the feasibility and rationality of the ECB-S fatigue design method proposed in this paper are validated by fatigue test results, and corresponding fatigue design recommendations are provided. The mean values of ratios of fatigue lives between the calculated values by the design method and experimental values are 0.403 for embedded steel sections and 0.280 for tensile rebars. Additionally, the maximum compressive stress in concrete remains below its compressive fatigue strength. The findings of this paper can offer reference and guidance for the practical engineering design of ECB-S.