海底地震动特性及其对跨海隔震桥梁的影响研究

In recent years, the construction of sea-crossing bridges is developing rapidly in China. The damage inspection and repair of submarine piers after earthquakes are difficult, so the isolation bridge system has become an important selection. The onshore strong motion records are still used for the time history analysis of sea-crossing isolated bridges, the reason is the incomprehension for characteristics of offshore ground motions. So this has led to insufficient understanding of the regularities for the earthquake response of sea-crossing bridges on the offshore site. This project intends to analyze the response spectra of offshore strong motions around the world. Then, consider the nonlinearity of saturated soil on the seafloor, the numerical simulation of propagation process for offshore ground motions is realized by combining the free-field wave analysis program and the finite element software. The influences of water depth, offshore topography, offshore site condition and other factors on the offshore ground motion will be explored by combining the strong earthquake observation and the numerical simulation. The characteristics of offshore ground motions and simplified (design) response spectra will be obtained. In this study, the continuous bridge with isolated rubber bearings is used as a research object. A three-dimensional analysis model for the seismic response of sea-crossing isolated bridges is presented by considering the pile-soil-seawater-bridge coupling and the nonlinearity of soil. Meanwhile, an underwater shaking table test of pile-soil-seawater-isolated bridge is performed to verify the reasonability for the influence factors of numerical model and to improve the accuracy of the numerical simulation. The study can provide input ground motions for the design of marine structures such as sea-crossing bridges.

近年我国跨海桥梁建设发展迅速，水下墩柱震后损伤检查及修复困难，梁桥采用减隔震体系就成为重要选择。跨海隔震桥梁时程分析目前仍采用陆地强震记录，原因是对海底地震动特性把握不足，由此也导致海域场地跨海桥梁地震反应规律认识不够充分。本项目拟进行世界范围内海底强震记录的反应谱等的统计分析，再考虑海底饱和土非线性，采用自由场波动分析程序与有限元软件的结合，实现海底地震动传播过程数值模拟。利用强震观测与数值模拟相结合方式，剖析水深、海底地形和海底土层构成等的影响，有望获得海底地震动特性深入认识及获得简化（设计）反应谱。以跨海隔震橡胶支座连续桥梁为例，综合考虑桩-土-海水-桥梁耦合作用和土体非线性等，提出跨海隔震桥梁精细化地震反应三维分析模型及分析方法。进行桩-土-海水-跨海隔震桥梁水下振动台试验，以验证数值模型考虑因素取舍的合理性及提升模型计算效果。研究可为跨海桥梁等海洋结构物设计提供输入地震动基础。

海底地震动的特性与陆地相差较大，但限于其研究尚不完整，导致在跨海桥梁等海洋结构物的抗震设计中仍使用陆地强震记录。因此，课题首先利用海底实测记录与数值模拟分析，深入研究了水深、地形、场地条件（考虑软土非线性）、震源机制等因素对海底地震动的影响，为跨海桥梁抗震分析提供了地震动输入的理论依据。其次，结合跨海桥梁的环境特点，提出了一套考虑桩-海床-海水-跨海隔振桥梁相互作用的地震反应分析方法，进而研究了海水层、场地条件、地形、动水效应等对跨海隔振桥梁地震反应的影响；并与桥梁常规抗震设计方法比较，确定地震动种类、输入方法与数值建模方法等对桥梁地震反应的影响，为跨海桥梁抗震分析提供了地震动输入的实现方法。再其次，研究建立了考虑钢筋屈服、混凝土损伤，以及钢筋滑移的隔振桥墩精细化动力分析模型。利用振动台试验数据验证其准确性后，分析海底地震动作用下隔振桥墩的损伤机理。最后，课题提出了一种纵桥向设置防屈曲支撑（BRB）的跨海桥梁减震方案与优化设计方法；此外，延续本课题的研究目标，还提出了海洋环境下锈蚀桥墩失效模式的判别方法，并计算了考虑剪切作用的锈蚀桥墩易损性。综上，课题研究成果有助于实现海底强震记录在跨海桥梁抗震设计中的应用，进一步了解跨海隔振桥梁的地震作用机理，并提高该生命线工程的抗震安全性。