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

摘要最近的地震提供了无数关于液化破坏性影响的例子。对建筑物性能的观察包括建筑物冲孔、承重破坏和建筑物的侧向移动。虽然我们已经了解了很多，但在对这些病例历史的评估中存在着重大的不确定性，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、地面失效和建筑性能的文件记录，以及地面条件的内在可变性。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先进的反向分析，以提高专业人员对地面故障及其对结构的影响的理解。通过提出的研究，通过使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建筑性能模型“案例历史”，这些模型是在经历严重和中度地面破坏的地点建立的。土壤-基础-结构-相互作用是NEESR研究的一个关键重点，通过在不同地面条件下对不同建筑系统进行离心试验来解决这个问题。这是非常重要的，因为地面破坏似乎部分是由上覆结构的动力反应引起的，而建筑物的损坏显然与地面反应有关。此外，我们还将在一些实验中探索淤泥的地震反应，而不是在过去十年中继续努力在离心实验中测试干净均匀的沙子。探讨了可液化土层厚度及其密度的相对重要性，同时考察了不同建筑物和基础条件对可液化土响应和建筑物性能的相互作用影响。作为该项目的一部分，一个重点关注高中生的“学生地震工程研讨会”（SEES）被创建，重点是少数民族学生。外展项目采用了一种策略，这种策略在北加州过去43年的科学研究中一直行之有效。许多高中生已经参加了学校的科学展览。通过引导他们和他们的老师对减少地震危害的挑战性问题的兴趣，我们可以激发下一代地震工程师和科学家的兴趣。正如NRC（2003）所强调的那样，“NEES应该用于超越自由场液化的预测到下一个水平，这将是预测变形的能力……对于结构…通过考虑土体强度损失在构筑物附近的时间、顺序和位置。实现这一目标的第一步是生成在液化地面上建立响应的有据可查的“案例历史”，这些精心进行的离心机模型试验将实现这一目标。这些说明性模型研究还将为应急管理人员和教师提供一个引人注目的替代方案，以取代目前现有的倾斜建筑物的静态图片。视频片段与动画测量响应数据的增强将使液化的地震危险及其对建筑物的影响栩栩如生。

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.