考虑土、上部结构和桥台相互作用的桥台抗震性能研究

RESEARCH ON ABUTMENT ASEISMIC PERFORMANCE CONSIDERING INTERACTION OF SOIL,SUPERSTRUCTURE AND ABUTMENT

在以往的桥梁设计中并不考虑基础提离和地基土屈服等土与桥台相互作用对桥台地震反应的影响。因此,为了研究桥台在地震中的抗震性能,采用Newmark时程分析方法对考虑土、上部结构和桥台相互作用的由扩展基础支撑的桥台进行分析。采用离散的质点–弹簧模型对土、上部结构和桥台系统进行建模。利用非线性模型,模拟上部结构和桥台的碰撞反应、桥台背部填土及地基土的弹塑性反应,并采用Winkler地基梁模型模拟地基土与桥台基础的相互作用。分析结果表明,桥台基础的提离作用可以减弱桥梁上部结构及桥台在强烈地震中的反应,减小桥台墙身底部在强震作用下发生的塑性变形,起到一定的减震隔震效果。同时,桥台底部土的屈服减小了传递到桥台底部塑性铰处的弯矩,进一步增强了桥台基础提离的效果。然而,由地基土屈服引起的永久性沉降也造成桥台基础的倾斜。因此,在桥梁的抗震设计中,必须考虑桥台基础的提离和地基土的屈服等土与结构相互作用对桥台抗震性能的影响。

Exciting earthquakes always cause larger displacement and settlement in abutment, which induce relative displacement between the superstructures and the bearing capacity of abutment. When the relative displacement is large enough, the superstructure will fall down and the bridge will lose its normal performance. In the past, the effects of soil-structure interaction such as uplift of foundation and yielding of underlying soil are not considered in the aseismic design of bridges. In order to evaluate the aseismic performance, the response of an abutment supported by spread foundation is analyzed under earthquake with time-dependent Newmark analysis.By utilizing discrete element method, the soil, superstructure and abutment systems are simulated by mass-spring models. In the discrete model, the pounding between the superstructure and the abutment, the elastoplastic responses of the backfill soil and the underlying soil are modeled by nonlinear springs. Moreover, the Winkler soil spring is used to simulate the interaction between the foundation of abutment and the underlying soil. The results show that the seismic isolation effect of foundation uplift is significant by alleviating pounding between the superstructure and abutment, and the plastic deformation of the plastic hinge regions at the bottom of the abutment stem is reduced. At the same time, the yielding of underlying soil also reduces the plastic deformation of abutment stem, and increases the effect of foundation uplift. However, the settlement induced by the yielding of underlying soil will make the tilt of abutment. Therefore, the soil, superstructure and abutment interaction such as foundation uplift and yielding of underlying soil should be considered in the aseismic design of bridges.