Influence of Stud Shear Connectors Fatigue on the Entire Reliability of Composite Bridge Superstructure

Based on multiple bridge inspections results, it was noticed that some composite steel–concrete bridges showed signs of a decrease in stiffness of their superstructures (in particular, additional sagging) after 20–30 years of operation. As one hypothesis, a reduction in the stiffness of the beam-slab joint elements can be considered. Most design codes (EN, AASHTO, among others.) are considered mandatory for fatigue check for joint elements, but in some codes (SP, Russia) fatigue check is not regulated. The purpose of this research is to assess the influence of fatigue damage accumulation in stud shear connectors on the performance of the entire superstructure and, in particular, on its reliability index. Based on the results of previous studies, a generalized model of the dependence of stud shear connector stiffness on the amount of its damage value has been proposed. Using this relationship model, a nonlinear finite element model of a simple composite beam has been developed that allows the calculation of the value of the load-bearing capacity objective function (by ULS criteria) depending on the number of load cycles. Using SOFiSTiK modules, the dynamics of declining the value of the load-bearing objective function were analyzed in both a deterministic formulation and using the probabilistic FORM method. To optimize the process of reliability index calculation, a search for an optimal model for clustering load cycles was performed. As a result of the research, the method for calculating the reliability index by considering the damage accumulation in stud shear connectors was proposed. This method can be used to substantiate the need for fatigue checks on joint elements numerically and determine reliability indices of bridge superstructures when combined with other methods. A series of calculations that simulate the operation of the superstructure model over various loading cycles was performed. The simulations revealed a significant decrease in quantitative reliability indicators as the number of loading cycles increased. This confirms the importance of ensuring the fatigue resistance of the joint elements in steel-reinforced concrete superstructures through reliability analysis methods.