整体式斜交桥抗震性能分析

Seismic analysis on skewed integral abutment bridges

相比正交桥,斜交桥在地震作用下其上部结构更易发生平面内大位移甚至落梁,而将主梁与桥台浇筑形成一个整体,成为整体式斜交桥有望有效减轻斜交桥震害,但在桥梁抗震分析与设计时需考虑桥台-土及桥台桩-土的动力相互作用。为深入掌握整体式斜交桥的动力特性及地震响应特点,以美国东蒙彼利埃桥为原型,采用SAP2000分析软件建立了不同斜交角度及台后土密实度的全桥三维有限元模型,利用模态分析及非线性时程分析对整体式斜交桥展开研究。结果表明:整体式斜交桥在地震作用下纵横向耦连明显,且存在明显的扭转效应。随着斜交角度的增加,台后土对于桥梁的纵桥向位移抑制作用逐渐减小,纵桥向抗侧刚度降低,桥梁纵横向耦连程度加强;随着斜交角度的增加,桥台钝角与锐角处最大土压力的比值增大,当斜交角为45°时可达2倍左右;随着台后土密实度的增加,桥台-桩节点处的桩顶弯矩降低,但随着斜交角度的增加,台后土密实度的影响趋于不明显。

Compared to non-skew bridges,the superstructure of skewed bridges is more likely to have large inplane displacement or even girder dislocation during the earthquake. By casting the main girder and the abutment monolithically and form the skewed integral abutment bridge（ SIAB）,earthquake damage to the bridge could be expected to be effectively reduced,but abutment-soil interaction and abutment pile-soil interaction need to be considered during bridge seismic design and analysis. In order to obtain a deeper insight into the dynamic features and seismic responses of SIABs,the East Montpelier Bridge was taken as the prototype,and bridge models with different skew angle and soil compactness were constructed using the analysis software SAP2000. Modal analysis and nonlinear time history analysis were used in the study of SIABs. From the research,it can be concluded that there was obvious coupling of the longitudinal and the transverse response of SIAB under earthquake effects,along with an obvious torsional effect. With the increase of the skew angle,the restraining effects of abutment backfill soil on bridge longitudinal displacement was getting weakened,the longitudinal stiffness of the bridge decreased,and the coupling effects of the longitudinal and the transverse directionwas enhanced. With the increase of the skew angle,the ratio of the maximum soil pressure on the abutment obtuse angle and acute angle had increased,and the ratio could reach 2. 0 when the skew angle equal to 45°. As the soil behind the abutment became more compact,the moment on the pile top at the pile-abutment intersection decreased,butthe effect of soil compactness became less and less obvious as the skew angle increased.