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>Significance of SSI and non-uniform near-fault ground motions in bridge response Ⅱ: Effect on response with modular expansion joint
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Significance of SSI and non-uniform near-fault ground motions in bridge response Ⅱ: Effect on response with modular expansion joint
This is the second part of the study of soil-structure interaction (SSI) and ground motion spatial variation effects on bridge pounding responses. The first part [Chouw N, Hao H. Significance of SSI and nonuniform near-fault ground motions in bridge response I: Effect on response with conventional expansion joint. J Eng Struct 2008;30(1):141-53.] concentrated on studying the responses of bridges with a traditional expansion joint between adjacent girders. The main objective of this second paper is to investigate the influence of spatial variation of ground motions and SSI on the minimum total gap that a modular expansion joint system (MEJS) between two bridge frames must have to prevent any pounding between the adjoined girders. This minimum total gap is critical in a MEJS design because it ensures intact expansion joint and adjacent girders. Additional investigations of pounding response with a large total gap of a MEJS are performed to study the characteristics of pounding responses when collision does occur e.g. due to unintended underestimation of the ground excitation magnitude, which may be different from the pounding responses between bridge girders with a small gap of a conventional expansion joint. The spatially varying ground excitations are simulated stochastically based on an empirical near-source response spectrum and an empirical coherency loss function. The investigation reveals that neglecting spatial variation of ground motions and SSI can significantly underestimate the total gap of a MEJS required to avoid pounding between the adjacent bridge girders. The results also show that pounding between girders with a large gap of a MEJS in general causes stronger impact forces. Compared with the results reported in the first part of this study, using a MEJS with a large gap is likely to completely preclude bridge girder pounding, and consequently to prevent local damage at the girder ends. However, a large girder movement results in large bending moment in bridge piers, which compensates the advantages of using MEJS in bridges to resist earthquake loading.
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机译：这是研究土-结构相互作用（SSI）和地震动空间变化对桥梁碰撞响应的影响的第二部分。第一部分[Chouw N，Hao H. SSI和非均匀近断层地震动在桥梁响应中的意义I：常规伸缩缝对响应的影响。 J Eng Struct 2008; 30（1）：141-53。]专注于研究在相邻大梁之间具有传统伸缩缝的桥梁的响应。第二篇论文的主要目的是研究地震动和SSI的空间变化对两个桥梁框架之间的模块化伸缩缝系统（MEJS）必须产生的最小总间隙的影响，以防止相邻大梁之间发生任何碰撞。在MEJS设计中，此最小总间隙至关重要，因为它可以确保完整的伸缩缝和相邻大梁。对MEJS具有较大总缺口的冲击响应进行了其他研究，以研究碰撞确实发生时的冲击响应特性，例如：由于地面激励幅度的意外低估，这可能与传统伸缩缝间距较小的桥梁大梁之间的冲击响应有所不同。基于经验近源响应谱和经验相干损失函数，随机模拟空间变化的地面激励。研究表明，忽略地面运动和SSI的空间变化可能会大大低估了MEJS的总间隙，避免了相邻桥梁之间的碰撞。结果还表明，通常，具有大间隙的MEJS的大梁之间的撞击会引起更强的冲击力。与本研究第一部分中报道的结果相比，使用具有较大间隙的MEJS可能会完全避免桥梁的撞击，从而防止梁端的局部损坏。但是，大梁运动会导致桥墩弯矩较大，这弥补了在桥梁中使用MEJS抵抗地震荷载的优势。
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