Numerical analysis of the effective stiffness of elastomeric bearing pads under precast beams for the limit load of lateral instability

Abstract Precast concrete girders on bearing pads are subjected to instability depending on several variables such as span length, initial imperfections and bearing pads behavior. On this paper, numerical models are developed in order to assess the instability limit loads and the rotational stiffnesses of the pads in many combinations of span length, cross section of the girder and lateral sweep. The lift off phenomenon is considered in each analysis by a bearing pad model composed by springs with compression only behavior, with good results in comparison with the experimental values of the technical literature. The increase in spans and initial imperfections causes a decrease in the rollover limit load. The lift off effect is aggravated as the lateral eccentricities increase. In the analyzed combinations, the reduction of the rotational stiffness is about 37% for the critical situation, which span length about 40 m and lateral sweep of L/300, with loss of contact between 50% and 60%.

摘要：支承垫板（bearing pads）上的预制混凝土梁，其失稳特性受跨度、初始缺陷及支承垫板性能等多种因素影响。本文构建数值模型，用于评估不同跨度、梁截面及横向侧弯（lateral sweep）组合下的失稳极限荷载与垫板转动刚度。本研究采用仅受压缩的弹簧单元构建支承垫板模型，在各分析工况中考虑了支座脱空（lift off）现象，所得结果与现有技术文献中的试验值吻合良好。跨度与初始缺陷的增大，会导致倾覆极限荷载降低。横向偏心率增大时，支座脱空效应愈发显著。在本次分析的组合工况中，临界工况（跨度约40m、横向侧弯为L/300，接触面积损失率达50%~60%）下，垫板转动刚度降幅约为37%。