NEESR-II: Towards Developing an Engineering Procedure for Evaluating Building Performance on Softened Ground

最近的地震提供了无数液化破坏作用的例子。建筑物性能的观测包括建筑物的冲压、承重故障和建筑物的侧移。虽然已经学到了很多，但这些案例的评价仍存在很大的不确定性，这阻碍了反向分析和改进分析方法的发展。不确定性的主要来源是地面运动的特征，缺乏液化顺序、地面破坏和建筑物性能的记录，以及地面条件的固有变异性。在离心机测试中，可以仔细跟踪输入运动、地面条件和地面/结构响应，然后对这些模型进行高级反向分析，以促进该专业对地面破坏及其对结构的影响的理解。通过拟议的研究，利用加州大学戴维斯分校的大型离心机，开发了一系列记录良好的、在发生严重和中度地面破坏的场地上的建筑性能的“案例”。土-基础-结构-相互作用是NEESR的一个关键研究重点，通过对不同地基条件下的不同建筑系统进行离心机测试来解决这一问题。这很重要，因为地面故障似乎部分是由于上面结构的动力反应造成的，而建筑物损坏显然与地面反应有关。此外，将在其中一些实验中探索对粉土的地震响应知之甚少，而不是在过去十年中继续努力在Centri-Fuge实验中只测试干净的均匀沙子。将探讨液化土层厚度及其密度的相对重要性，同时研究不同建筑物和基础条件对可液化土层响应和建筑性能的相互影响。作为该项目的一部分，创建了一个面向高中生的重点“学生地震工程研讨会”(SEE)，重点是少数民族学生。该推广计划采用了一种在过去43年里在北加州的科学领域运作良好的战略。许多高中生已经参加了学校的科学博览会。通过引导他们的兴趣和他们的老师的兴趣在地震减灾涉及的具有挑战性的问题上，我们可以激发下一代地震工程师和科学家的热情。正如在NRC(2003)中所强调的，“NEES应该被用来超越自由场液化的预测，这将是预测结构变形的能力……通过考虑建造特征附近土体强度损失的时间、顺序和位置。”迈向这一目标的第一步是生成记录良好的液化地基上建筑反应的“案例”，这些仔细执行的离心机模型试验将实现这一点。这些说明性的模型研究还将为应急经理和教师提供一种戏剧性的替代方案，以取代目前已有的倾斜建筑的静态图片。带有动画测量响应数据的视频剪辑将使液化的地震危险及其对建筑物的影响变得生动起来。

ABSTRACTRecent earthquakes have provided countless examples of the damaging effects of liquefaction. Ob-servations of building performance included building punching, bearing failure, and lateral shifting of buildings. Although much has been learned, significant uncertainty exists in the evaluation of these case histories, which has hampered back-analyses and the development of improved analytical methods. Key sources of uncertainty are the characteristics of the ground motions, lack of documentation of the se-quence of liquefaction, ground failure and building performance, and the inherent variability of ground conditions. Centrifuge testing, where the input motion, ground conditions, and ground/structural response can be carefully tracked, followed by advanced back-analyses of these models are warranted to advance the profession's understanding of ground failure and its resulting impact on structures. Through the proposed research, a series of well documented model "case histories" of building per-formance at sites undergoing severe and moderate ground failure are developed by using the UC Davis large centrifuge. Soil-foundation-structure-interaction is a key NEESR research priority that is addressed through this centrifuge testing of different building systems on various ground conditions. It is of para-mount importance, because ground failure appeared to be caused in part due to the dynamic response of the overlying structures, and building damage was clearly linked to ground response. Additionally, the poorly understood seismic response of silt will be explored in some of these ex-periments, as opposed to continuing efforts over the past decade to test just clean uniform sands in centri-fuge experiments. The relative importance of the thickness of the liquefiable soil layer and its density will be explored, while examining the interacting effects of different buildings and foundation conditions on the response of the liquefiable soil and building performance. As part of this project, a focused "Student Earthquake Engineering Symposium" (SEES) that reaches out to high school students, with an emphasis on minority students, is created. The outreach program utilizes a strategy that has worked well for the sciences for the last 43 years in Northern California. Many high school students already participate in their schools' science fairs. By channeling their interests and their teachers' interests on the challenging problems involved in earthquake hazard mitigation, we can excite the next generation of earthquake engineers and scientists. As emphasized in NRC(2003), "NEES should be used to move past the prediction of free field liquefaction to the next level, which would be the ability to predict deformations ... for structures ... by considering the timing, sequence, and location of soil strength loss in the vicinity of the constructed feature." The first step towards this goal is the generation of well documented "case histories" of building response on liquefied ground, which these carefully performed centrifuge model tests will achieve. These illustrative model studies will also offer emergency managers and teachers a dramatic alternative to currently existing static pictures of tilted buildings. Video clips augmented with animated measured response data will allow the seismic hazard of liquefaction and its effect on buildings to come alive.