MPA方法在不同高度桥墩地震响应分析中的适用性研究

桥梁通常是线路中的控制工程,其抗震性能显得尤为重要。作为梁桥重要组成部分的桥墩,往往是地震作用下容易受到损伤的构件。结合西部山区梁桥的典型桥墩结构形式,基于纤维模型的有限元方法建立桥墩的非线性数值分析模型。采用MPA方法对不同高度桥墩的地震响应进行分析,以非线性时程分析方法的计算结果为基准研究MPA方法的适用性。计算表明MPA方法在分析高阶模态参与程度较高的高墩构件时适用性较差。

Application of Modal Pushover Analysis Method to Seismic Response of Piers with Different Heights

Bridges are usually lifeline engineering-in-traffic projects, and their seismic performance is very important. As an important bridge construction component, piers are vulnerable to damage under strong ground motion. In this paper, in accord with the typical pier structure form of bridge piers in mountainous areas, a nonlinear numerical analysis model is constructed based on a fiber model. The seismic response of different piers under El-Centro is performed using modal pushover analysis (MPA). By comparison with the nonlinear time history analysis method, the applicability of the MPA method for the seismic analysis of different piers is investigated. The results show that the MPA method is not suitable for higher piers where the contribution of higher modes in seismic response is significant. With the implementation of the Western Development Program in recent years, a lot of highways and railways have been planned and built in western China. For bridges with high piers in mountainous areas, a nonlinear numerical analysis model is constructed based on a fiber model. The finite-element analysis is simulated with the code OpenSees, which was developed by Pacific Earthquake Engineering Research (PEER). The Mander model is used to imitate the constitutive model of concrete, and the Giuffré-Menegotto-Pinto model is used to imitate the constitutive model of reinforcement. The incremental dynamic analysis is used to research distribution features of pier section curvature under strong earthquake motions. As a result of the effects of higher modal contributions, the seismic response and seismic performance of bridges with high piers are complicated. The forming and development of a plastic range in the upper position of a pier, the damage process, and the failure mechanism of high piers under different earthquake motions are studied. The base section curvature of high piers and its top displacement are not simultaneous; it is inappropriate for pier top displacement to be used as the performance index. By taking pier section curvature as the performance index, seismic performance characteristics of bridges with high piers in the plastic stage are discussed; the complexity of the seismic performance of bridges with high piers because of the contribution from higher modes is revealed further. The spectral characteristics of ground motion have a great influence on the seismic performance of bridges with high piers. This paper studies six earthquake waves from the PEER database that are class II sites. Because of space constraints, this study involves only the seismic performance of bridges with high piers under transversal earthquake action. After a careful analysis, it is discovered that one pier base section curvature is greater than any other piers when all the piers are plastic; the location of the most dangerous pier depends on the magnitude of the contributions from higher modes. Unlike bridges with low piers, sometimes the damage of higher piers could be more serious than that of lower piers for bridges with high piers. The envelopes of section curvature above the pier base plastic region do not have a linear trend; the occurrence of plastic hinges at the middle and upper parts of piers is attributed to the contribution of higher modal shape. Additionally, the extent and the size of this plastic region are affected by the spectral characteristics of the ground motion. Because of the contribution from higher modes, the bridge with high piers is not safe when designed according to the existing specifications.