低重心斜拉桥边跨墩柱横向抗震措施研究

Study of Transverse Seismic Protection Measures for Pier Columns in Side Spans of Cable-Stayed Bridge with Low Gravity Center

针对低重心斜拉桥边跨墩柱的横向抗震问题,以某在建低重心斜拉桥为背景,进行边跨墩柱横向抗震措施研究。该桥主桥为(45+80+285+80+45)m双塔双索面混凝土斜拉桥,边跨墩柱高度仅为11 m。采用SAP2000建立全桥有限元模型,输入地震动,通过抗弯能力需求比R M评估桥梁的抗震性能,提出改变墩柱截面形式与采用防屈曲支撑构件(BRB)等8种抗震措施,并对比分析各措施墩柱关键截面的R M。结果表明:在地震作用下,设置横向固定支座的边跨墩柱墩底截面弯矩较大、R M均小于1,是低重心斜拉桥横向抗震的薄弱环节;8种抗震措施墩柱关键截面的R M均大于1,各措施均可改善边跨墩柱的横向抗震性能,措施Ⅱ-6(将边跨墩柱改为双肢截面,并在双肢间设置BRB)为该桥最优措施。

To investigate the transverse seismic protection of pier columns in side spans of cable-stayed bridge with low gravity center,a cable-stayed bridge of such type that is under construction is taken as the background project,to study the transverse seismic protection measures for the pier columns in side spans.The main bridge is a two-pylon concrete cable-stayed bridge with spans of 45,80,285,80 and 45 m.The stay cables are arranged in double cable planes.The piers in the side spans are only 11 m high.SAP 2000 was used to build the finite element model of the overall bridge,to which the ground motions were input to evaluate the seismic performance of the bridge via anti-bending performance demand ratio(R M).Eight seismic protection measures by changing the patterns of cross sections of pier columns and using buckling restrained brace(BRB)were proposed.The R M of each key cross section of pier columns was compared with peers.The results demonstrate that under the action of earthquakes,the bending moment in the pier-base cross section of pier columns with fixed bearings in the side spans is big,and the R M is lower than 1,which is considered the vulnerable parts in the transverse seismic protection of cable-stayed bridge with low gravity center.The R M of each key cross section of the pier columns in the side spans with the eight seismic protection measures respectively is bigger than 1,proving that each measure can improve the transverse seismic performance of the pier columns in the side spans.Measure II-6,that is to transform the pier columns in the side spans to the two-column section and install BRB between the two columns,is regarded as the optimum measure.