斜交简支梁桥地震位移响应特征与落座分析

Seismic displacement response features and unseating analysis of simply-supported skewed bridges

为了提高斜交简支梁桥在地震中防落座的能力,结合汶川震害特点,选取跨径为30m的典型斜交简支T梁桥,考虑材料和接触非线性因素,采用时程分析法研究了斜交角、挡块强度和伸缩缝大小对斜交简支梁桥地震位移响应特征的影响,基于板式橡胶支座的滑动状态探讨了斜交主梁的落座特征。研究表明:上部结构的位移响应在斜交角小于30°时以纵向为主,大于30°时以横向为主,主梁平面转角在斜交角为30°时最大;挡块强度的增大可降低支座纵、横向位移和主梁平面转角,但当挡块强度达到某一数值时(本文桥例为30%恒载支反力),其限位效果逐渐趋于平缓;伸缩缝处的不均匀碰撞导致斜交桥主梁两侧角点处的碰撞力明显更大,靠近桥面中心线处碰撞力最小甚至为零,且主梁容易沿着自身锐角端向桥面内发生转动。适当加强斜交主梁锐角端的挡块强度可有效降低桥梁的落座风险。

In order to improve the ability of simply supported skewed bridge to prevent unseating in earthquakes,a typical bridge with spans of 30m is selected as an illustration bridge based on the damage survey in the Wenchuan earthquake.Considering the material and contact nonlinearities,the effects of the skew angles,retainer capacities and expansion joint width were examined on the seismic displacement response characteristics of simply supported skewed bridges by using time history analysis method.The unseating characteristics of skewed girders were discussed based on the sliding states of the laminated rubber bearings.The results show that the displacement responses of superstructure is mainly along the longitudinal direction of the bridge when the skew angles are less than 30°,and along the transverse direction when the skew angles are greater than 30°.The largest rotation responses of superstructure is found when the skew angle is 30°.The increase of the retainer capacity can reduce the longitudinal and transverse displacement responses of bearings,as well as the rotation responses of superstructure.However,when the retainer capacity reaches a certain value(30%reaction force of the dead load in this case),the effects of displacement control by the retainers tend to be limited.The non-uniform pounding at the expansion joints results in significantly greater pounding forces at the corners on both sides of girder,and minimal or even zero pounding forces near the centerline of girder.The girder is more likely torotate towards the acute angles.By strengthening properly the retainers at the acute-angles of the skewed girder,the unseating risk of the bridges can be reduced effectively.