墩身惯性力对墩底地震剪力的影响及计算方法

Effects of the inertia forces of pier shaft on the seismic shear at pier bottom and its calculation method

为探究考虑墩身地震惯性力贡献的墩底剪力简化计算方法,以某铁路简支梁桥为研究对象建立三维有限元模型,在分析了墩身质量对结构动力特性影响基础上,通过非线性时程分析方法研究了不同墩高、场地类型以及地震动峰值加速度(PGA)下墩身惯性力在桥墩地震剪力中的贡献比例,给出墩身惯性力在计算墩底地震剪力时不可忽略的判别条件;并采用模态Pushover分析法对墩底剪力进行简化计算,对结果的准确性加以验证。结果表明:桥墩进入塑性后,墩身惯性力对墩底剪力的贡献比例受场地类别影响小,主要影响因素为墩高,当墩高小于20 m时,可不考虑墩身惯性力作用,而采用能力保护设计理念计算墩底剪力;但当墩高大于20 m后,不应忽略桥墩自身的惯性力贡献,可按所提出的一阶模态Pushover方法简化计算墩底剪力。

In order to explore the simplified calculation method of pier bottom shear considering the contribution of seismic inertia force of pier,a three-dimensional finite element model of a railway simply supported beam bridge was established.Based on the analysis of the influence of pier mass on structural dynamic characteristics,the contribution proportions of pier inertia force to seis⁃mic shear force at pier bottom under different height of bridge pier,site type and peak ground acceleration(PGA)were studied with nonlinear time history analysis method.The criterion of inertia force of pier which can't be ignored in calculating seismic shear of pier bottom was also suggested.The modal pushover analysis method is used to simplify the calculation procedure of pier bottom shear,and its accuracy is also verified.The results show that when the pier was in plastic stage,the contribution of inertia force to the shear force at the bottom of the pier was seldom affected by the site type,and the key influence factor was the pier height.When the pier height was less than 20 m,the inertia force of the pier could be ignored,and the shear force demand at the bottom of the pier could be calculated by the concept of capacity protection.However,when the pier height was larger than 20 m,the contri⁃bution of inertia force of the pier itself should not be ignored.The shear force demand at the bottom of the pier could be obtained by the proposed first-order modal Pushover simplified method.