Behavior of Steel-Concrete Composite Beams Under Fatigue Loads

Besides the static load, the cyclic load caused by the vehicles always exists in the bridge structures. This kind of loading may cause failure even when the nominal maximum loads have not exceeded the ultimate resistance of the structure. So, the main objective of this paper is to evaluate the fatigue behavior of composite beams at the sagging moment regions. A numerical model is described to predict the fatigue response of each part of the composite section. The accuracy of the developed numerical model is validated using existing test data. Also, the transformed section method is used to evaluate the fatigue response of the composite beams in terms of deflection, strains in the concrete flange and the steel beam, plastic deformation, reduction in the static strength of the shear connectors, and residual capacity of the composite beam. The cumulative damage rule is analyzed through the S-N curve to assess the procedures presented in the design code. A rapid growth in the residual deformations of the composite beams is obtained at the starting and the end of the fatigue life with the number of cycles while a linear increase in the remaining part of the fatigue life occurs. In addition, a reduction in the static strength of the shear connectors is developed with the number of cycles and subsequently causes a drop in the monotonic beam capacity which can be calculated based on the new shear connection strength.