ANALYSIS ON RESIDUAL DISPLACEMENT OF REINFORCED CONCRETE BRIDGE PIERS STANDING IN LIQUEFIABLE FIELD

To study the influence mechanism of site liquefaction on Reinforced Concrete (RC) pier residual displacement, the numerical simulation method of liquefied site-structure upon OpenSees finite element platform was described at first, and the reliability was verified by comparing with centrifuge test results. Then based on a practical extended pile-shaft, a liquefied site-RC pier simulation method was developed, the nonliquefied site-pile-RC pier numerical model (model 1) and liquefied site-pile-RC pier numerical model (model 2) were established, near-fault ground motions were inputted two models for dynamic time history analysis. Model 2 site liquefaction was discussed firstly, then site displacements, pile displacements, pile maximum curvature ductility coefficients, pier residual displacement and variation of pier residual displacement with peak ground acceleration (PGA) were compared between Model 1 and Model 2. The results show that liquefaction is different along depths in model 2 site during the earthquake. The upper-middle soil reaches a complete liquefaction state, soil loses most horizontal ultimate resistance, and pile lateral constraint is seriously reduced. Liquefaction results in a significant increment in liquefied site residual displacement post-earthquake, and pile top residual displacement may increase due to the enhanced post-earthquake constraints of pile body. The pile plastic deformation increases significantly, maximum plastic deformation position of pile downward obviously, and pile plastic deformation zone expands, which leads to more serious plastic damage to pile and further increases pile top residual displacement. The increase of residual displacement post-earthquake in liquefaction site and the reduction of pile constraint during the earthquake lead to an increment of pile top residual displacement, which is amplified by pier and transferred to pier top, causing increase of pier top residual displacement. The pier residual displacement in liquefied site is significantly faster than that in non-liquefied site with the increase of PGA, which may be due to the deepening of site liquefaction with the increase of PGA.