Error analysis and improvement of the large mass method used in elastic-plastic response analysis of bridges subjected to non-uniform seismic

Aiming at the error of the large mass method (LMM) used in elastic-plastic responses analysis of long-span bridges subjected to non-uniform seismic, a continuous rigid frame bridge with spans of (56+100+56) m was used as an engineering background. Based on the elastic-plastic theory, the non-uniform elastic-plastic analysis model set up by Midas Civil 2015 was utilized, in which the boundary conditions were modeled by the LMM. Then, the elastic-plastic seismic responses of the bridge were calculated by inputing three field measured seismic waves, the error of LMM was discussed, and the improved method for the LMM was proposed. The results show that there are errors resulted from the LMM used in elastic-plastic seismic responses analysis of long-span bridges and the bending moment at the key section of the bridge pier tends to be smaller. The fundamental reason is that the LMM changes the boundary conditions of the structure, it changes the fixed constraints into the sliding constraints, and results in less bending moment under constant load. By adding an elastic constraint with stiffness of K along the input direction of ground motion in the original LMM and modifying the input seismic wave according to the formula üg+αug+ug, a high-precision correction of the LMM was realized, where K took the same value as the large-mass coefficient M. With the calculation condition in the paper, the relative error of the elastic-plastic bending moment at the key section of bridge pier is reduced to 0.135% by the modified LMM. The results can be used to calculate the non-uniform elastic-plastic seismic response of large span structures. © 2020, Editorial Office of Journal of Vibration and Shock. All right reserved.