Seismic response of the built environment in densely populated urban areas

地震是世界范围内工程结构的长期危害。在人口密集的城市地区尤其如此，在这些地区，最近发生的大震级地震表明，建筑物的密度对地震破坏的代价具有显著的乘数效应。目前通常的做法是确定与周围城市环境隔离的结构的地震反应。实际上，在人口密集的城市地区，建筑物经常被其他结构所包围，这些结构要么在设计上相似，要么非常不同（例如，一座40层的建筑紧挨着一座5层的建筑）。具有相邻建筑块的城市区域可以被认为是一个复杂的结构系统，这些结构可以通过连接它们的地面相互作用。在密集的城市环境中，结构的实际地震反应可能与使用基于孤立结构行为的当前方法预测的结果显著不同（甚至更大）。如果相邻的结构间距足够近，并且振动彼此不同步，则由于相邻结构之间的“冲击”-瞬时碰撞，随后可能发生损伤。与孤立结构相比，如果结构与结构的相互作用增加了建筑物的反应，这种情况将会恶化。此外，结构的紧密排列/间距也使得灾难性破坏的后果更加严重，因为相邻结构可能会发生重大的附带损害。尽管先前对该领域的研究已经通过数值模拟为结构-土壤-结构相互作用提供了良好的初步见解，但在将这些知识和理解实际应用于人口密集的城市地区的工程设计之前，仍有许多问题需要解决。值得注意的是，这包括当应变可能在非弹性范围内时，当前土壤行为的弹性理想化是否适用于大地震，以及是否选择了适当的控制参数。本提案所述的工作将主要包括一个物理模型试验方案，在土工离心机内对建立在真实土壤上的邻近结构的小比例模型进行试验，以满足这些需要。这项工作将代表在实际土壤上建立的结构所涉及的基本现象的第一个系统的实验研究。研究结果随后将用于评估使用当前隔离结构模型来评估密集城市地区建筑物的有效性，并评估基于线性弹性土壤行为的当前结构-土-结构相互作用模型适用的地震条件范围。物理测试数据数据库还将提供观测到的物理行为的有用数据库，可用于校准未来更先进的数值模拟工作。

Earthquakes are a perennial hazard to engineered structures worldwide. This is particularly true of densely populated urban areas (cities) where recent large magnitude earthquakes have demonstrated that the density of structures has a significant multiplicative effect on the cost of seismic damage. It is common practice at present to determine seismic response of structures in isolation from the urban environment which surrounds them. In reality, buildings in densely packed urban areas are often surrounded by other structures which may either be similar in design or very different (e.g. a 40-storey building next to a 5 storey building). An urban area with a block of adjacent buildings may be considered as a complex system of structures which may interact with each other through the ground which connects them. The actual seismic response of a structure within a dense urban environment may be significantly different (and larger) to that predicted using current methods based on isolated structural behaviour. If the adjacent structures are closely enough spaced and vibrate out-of-phase with each other, damage can subsequently occur due to 'pounding' - transient collision between adjacent structures. This will be worsened if structure-to-structure interaction increases the building response compared to an isolated structure. Furthermore, the close packing/spacing of structures also makes the consequences of a catastrophic failure more critical, as significant collateral damage to the adjacent structures may occur. Although previous research into this area has provided good initial insights into structure-soil-structure interaction using numerical simulation, there remain a number of issues to be addressed before this knowledge and understanding can be practically applied to engineering design in densely-packed urban areas. Notably, this includes whether current elastic idealisations of soil behaviour are appropriate during large earthquakes when strains may be in the inelastic range, and whether the appropriate controlling parameters have been selected. The work described in this proposal will consist primarily of a programme of physical model tests to be conducted on small scale models of adjacent structures founded on real soil within a geotechnical centrifuge to address these needs. This work will represent the first systematic experimental study of the fundamental phenomena involved for structures founded on real soil. The results will subsequently be used to assess the validity of using current models for isolated structures to assess buildings in densely packed urban areas and assess the range of earthquake conditions for which current structure-soil-structure interaction models based on linear elastic soil behaviour are applicable. The database of physical test data will additionally provide a useful database of observed physical behaviour which may be used to calibrate future more advanced numerical modelling work.