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Simplified design of bridges for multiple-support earthquake excitation

机译：简化多支座地震激励桥梁设计

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This paper presents a novel, bridge-dependent approach for quantifying the increase of design quantities due to spatially variable earthquake ground motion (SVEGM). Contrary to the existing methods for multiple support bridge excitation analysis that are either too complicated to be applied by most practitioners or oversimplied (e. g. Eurocode 8, Annex D provisions), this method aims to strike a balance between simplicity, accuracy and computational efficiency. The method deliberately avoids generating support-dependent, acceleration or displacement, asynchronous inputs for the prediction of bridge response. The reasons behind this decision are twofold: (a) first, the uncertainty associated with the generation of asynchronous motion scenarios, as well as the exact soil properties, stratification and topography is high while, (b) the response of a bridge is particularly sensitive to the above due to the large number of natural modes involved. It is therefore prohibitive to address SVEGM effects deterministically in the framework of a design code. Instead, this new method is based on two important and well-documented observations: (a) that SVEGM is typically globally beneficial but locally detrimental 1, and (b) that the local seismic demand increase is very closely correlated with the excitation of higher modes, which are not normally activated in the case of uniform ground motion 2,3. Along these lines, a set of static analyses are specified herein to complement the standard, code-based response spectrum analysis. These static analyses apply spatially distributed lateral forces, whose patterns match the shape of potentially excited anti-symmetric modes. The amplitude of those forces is derived as a function of the expected amplification of these modes according to the process initially proposed by Price et al. 4. Two real bridges with different structural configurations are used as a test-bed to demonstrate the effectiveness of the new method. Comparison of the results with those obtained through rigorous response history analysis using partially correlated, spatially variable, spectrum-compatible input motions 5 shows that, the simplified method presented herein provides a reasonably accurate estimation of the SVEGM impact on the response of the bridges examined at a highly reduced computational cost. This is essentially an elastic method that is found to be simple, yet precise enough to consist an attractive alternative for the design and assessment of long and/or important bridge structures in earthquake-prone regions.
机译：本文提出了一种新的、依赖于桥梁的方法，用于量化由于空间可变地震地震动 （SVEGM） 引起的设计量增加。与现有的多支桥激励分析方法相反，这些方法要么过于复杂而无法被大多数从业者应用，要么过于隐含（例如欧洲规范 8 附录 D 规定），该方法旨在在简单性、准确性和计算效率之间取得平衡。该方法刻意避免生成与支座相关的、加速度或位移的异步输入来预测桥梁响应。这一决定背后的原因有两个：（a）首先，与异步运动情景的产生相关的不确定性，以及确切的土壤性质、分层和地形高度，以及（b）由于涉及大量的自然模式，桥梁的响应对上述情况特别敏感。因此，在设计规范的框架内确定性地解决SVEGM效应是令人望而却步的。相反，这种新方法基于两个重要且有据可查的观察结果：（a）SVEGM通常对全局有利，但对局部有害[1]，以及（b）局部地震需求的增加与更高模式的激发密切相关，而在均匀地震动的情况下，这些模式通常不会被激活[2,3]。按照这些思路，本文指定了一组静态分析，以补充标准的、基于代码的反应谱分析。这些静态分析应用了空间分布的侧向力，其模式与潜在激发的反对称模态的形状相匹配。根据Price等人[4]最初提出的过程，这些力的振幅是这些模式的预期放大的函数。以两座不同结构构型的实桥为试验台，验证了新方法的有效性。将结果与使用部分相关的、空间可变的、频谱兼容的输入运动[5]进行严格的响应历史分析获得的结果进行比较，表明本文提出的简化方法以大大降低的计算成本提供了对SVEGM对所检查桥梁响应的影响的合理准确的估计。这本质上是一种弹性方法，它被发现简单，但足够精确，为地震多发地区长和/或重要桥梁结构的设计和评估提供了一个有吸引力的替代方案。

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