考虑上部结构影响的山区桥梁支座刚度设计方法研究

Investigation on design methods for the bearing stiffness of bridges in mountain areas considering influence of upper structures

为了合理计算山区桥梁支座刚度,针对桥墩高度不相同的特点,考虑上部结构对桥墩顶部的转动约束作用,提出在横桥向可将墩顶视为自由约束,而在纵桥向将墩顶视为定向约束。分别按照地震作用下各墩底剪力和弯矩相等的原则,推导桥梁支座纵、横桥向的刚度设计公式,并给出各桥墩支座的设计方法。为验证方法的正确性,以墩底剪力相等的原则为例,利用OpenSees建立一座墩高不等的5跨连续梁桥模型,并依支座刚度取值不同分三种工况:工况一各桥墩支座刚度相同;工况二按墩顶自由计算各支座的纵、横桥向刚度;工况三按墩顶定向约束计算各支座的纵、横桥向刚度。分别对三种工况下的桥梁结构输入三条地震动记录进行时程分析,考察各桥墩的底部剪力。分析结果表明:工况一各桥墩纵、横桥向的底部剪力均不相同;工况二各桥墩横桥向的底部剪力相同而纵桥向的底部剪力不同;工况三各桥墩纵桥向的底部剪力相同而横桥向的底部剪力不同。上述结果表明在桥梁支座设计时,横桥向桥墩的抗推刚度应按墩顶自由计算,而纵桥向桥墩的抗推刚度应按墩顶为定向约束计算。

To calculate the bearing stiffness of mountain bridges with different pier heights,it was proposed that the pier top can be regarded as free constraint in the transverse direction and orientation constraint in the longitudinal direction after considering the rotation restraint effect of upper structures.The formulas of bearing stiffness in the transverse and longitudinal directions were derived based on the principle of equal shear force and bending moment at the pier bottom.To verify the correctness of the proposed design method for pier bearings,a 5-span continuous bridge model with different pier heights was established using the OpenSees,and three cases were selected:In case 1,the bearing stiffness for each pier is the same;In case 2,the bearing stiffness in the transverse and longitudinal directions were calculated in terms of free constraint at the pier top;In case 3,the bearing stiffness were calculated in terms of orientation constraint at the pier top.Time-history analysis was conducted on the bridge structure under three ground motion records,and the shear forces at pier bottom were investigated under the three cases.The analysis results show that the base shear forces of each pier in the transverse and longitudinal directions are different in case 1.The base shear forces in the transverse direction are the same,while those in the longitudinal direction are different in case 2.The base shear forces in the longitudinal direction are the same,whereas those in the transverse direction are different in case 3.These results indicate that in the design of bridge bearings,the bearing stiffness in the transverse direction should be calculated as the pier top is free,and those in the longitudinal direction should be calculated as the pier top is orientation constraint.