承台结构形式对分幅连续刚构桥地震响应的影响研究

Study of Influence of Pile Cap Structures on Seismic Responses of Twin-Deck Continuous Rigid-Frame Bridge

为选择合理承台结构形式,以满足地震高烈度区分幅连续刚构桥的抗震性能,以G75兰临高速公路上的一座(64+115+64)m分幅双肢薄壁墩连续刚构桥为背景,根据分幅连续刚构桥地震响应作用机理,采用MIDAS Civil软件建立桥梁空间杆系动力分析模型,利用设计反应谱法从桥梁纵向和横向进行激励,对比研究整体式、分离式2种承台结构形式的分幅连续刚构桥桥墩内力、位移响应能力与需求。结果表明:2种承台形式的桥梁均有一定抗震能力储备,采用整体式承台将增大桥梁整体刚度,提高基频,内力需求增加、位移需求减少,其中横向地震作用影响尤为显著;采用分离式承台,虽然位移需求有所增加,但优势明显;在以地震响应为主控设计的地震高烈度区,分幅连续刚构桥建议采用分离式承台设计。

Rational pile cap structures are beneficial to the seismic responses of twin-deck continuous rigid-frame bridge in high seismic intensity areas.In this study,a twin-deck continuous rigid-frame bridge on Lanzhou-Lintao Expressway(part of G75 expressway),which has three spans of 64,115 and 64 m and is supported on double-thin-wall piers,is taken as a case.In accordance with the seismic response mechanism of the bridge of such type,a spatial link element model was established by MIDAS Civil,which was excited longitudinally and transversely using the design spectrum method.The twin-deck continuous rigid-frame bridges equipped with integral and separated pile caps respectively were compared from aspects of internal forces of piers,displacement response and load bearing demands.It is shown that either the integral pile cap or the separated pile cap can ensure the bridge to have a degree of seismic resistance.In the case of integral pile cap,the global stiffness and natural frequencies of the bridge are improved,the internal forces in the piers are increased and the displacement demand is lowered,and the effect of transverse seismic actions is more significant.While in the case of separated pile cap,the displacement demand is increased,but the seismic resistance of the bridge is improved.Separated pile caps are recommended for twin-deck continuous rigid-frame bridges in high seismic intensity areas where seismic responses of structures dictate the design.