Development of a modified low-cycle fatigue model for semi-rigid connections in precast concrete frames

Earthquake-induced damage to connections in precast concrete (PC) structures can cause serious destruction and even the collapse of the entire structure. This indicates the importance of damage and failure estimates of connections in the seismic performance assessment and design of a PC structure. To characterize the damage development and failure state of semi-rigid PC connections appropriately, the low-cycle fatigue model is introduced. The fatigue characteristics of semi-rigid PC connections and applicability of the existing fatigue model are studied through cyclic tests of typical welded connections, in which the effects of both external excitations and internal connection parameters are considered. To capture the fatigue performance of the PC connections better, the fatigue model is modified according to the experimental results, from the perspective of enhancing the damage contribution of the maximum deformation. The accuracy of the low cycle fatigue life prediction is significantly improved compared with the test results, proving the reasonability and applicability of the proposed modification. The reasonability and general adaptability of the modified fatigue model are further verified by the test results from previous studies and more general values of the parameters in the fatigue model can be obtained for the orientation of the structural design. The development of the modified low-cycle fatigue model in this study provides a feasible method for damage and failure estimation of PC connections and can contribute to the seismic performance assessment and design of the structures.