NEESR-II: Sidesway Collapse of Deteriorating Structural Systems

了解、预测和预防坍塌一直是地震工程学的主要目标。坍塌是造成人员伤亡的主要原因。因此，它构成了需要预测的工程极限状态，以便以概率形式评估生命安全性能水平，这是社会主要关注的问题。在地震风险管理方面，需要一个能够对坍塌概率进行严格评估的过程，以便做出符合社会最佳利益的知情决定。在抗震设计的背景下，这一过程需要简化，以便工程专业人员可以使用基于诸如强度、刚度和延性(变形性)等参数的工程技术来推导出符合所需倒塌安全级别或可容忍倒塌概率的特定目标的结构特性。本项目将解决这两种情况。它将为预测一种临界倒塌模式提供一种方法和可靠的数据，即与侧移失稳有关的临界倒塌模式，即一层(或一系列)层发生足够的位移，使得二阶P-Delta效应完全抵消一阶楼层剪力，发生动力失稳，即结构体系失去其重力荷载抗力。这种倒塌模式的预测是一个具有挑战性的问题，因为结构部件在达到倒塌极限状态之前将在强度和刚度方面劣化，并且地震输入的描述和控制结构接近倒塌的响应的参数具有很大的不确定性。该方法将以分析模拟和实验模拟相结合为基础，前者在斯坦福大学进行，后者的主要工作是在布法罗大学的NEES设施进行钢结构模型的振动台坍塌试验。拟议研究的成果将是：(A)预测劣化结构系统侧向倒塌的方法；(B)关于结构钢和钢筋混凝土部件劣化性能的广泛数据库，包括考虑建模和材料不确定性的不确定性措施；(C)在OpenSees平台中纳入部件劣化模型；(D)利用涵盖5层钢框架结构从弹性行为到初始倒塌响应范围的数据记录全面倒塌试验；(E)计算考虑危险、地面运动和结构(材料，建模)不确定性，以及(F)坍塌安全设计的工程建议。智力上的优点。这项拟议的研究将在理解和预测结构在严重地震下的侧向倒塌方面取得开创性的进展。主要的挑战是考虑到结构性能的恶化与P-Delta效应的结合，以及在地面运动描述中固有的不确定性，以及在控制大非弹性变形(或对于脆性元件的小变形)时控制动力响应的组件的行为建模方面的固有不确定性。这些挑战意味着在部件和结构层面上进行广泛的建模工作，并在评估结构的倒塌安全性时纳入可靠性概念。另一个主要挑战将是计划和实施振动台坍塌实验，其主要目的是证明坍塌预测确实是可行的。在充分利用NEES网格的模拟、可视化和协作工具的同时，本研究采用了在NEES场地振动台上进行物理模拟和在OpenSees平台上进行计算模拟的综合方法。对地震工程研究和实践的更广泛影响。这项研究的目的是为了在新的设计中提供足够和一致的倒塌安全，并评估现有结构的倒塌危险。这些需要需要填补在数据和工具方面存在的知识空白，以及对崩溃现象的了解。拟议工作对研究和实践的影响将是开发数据库、先进的劣化模型和计算工具，使预测复杂结构的倒塌安全成为可能，并允许在基于性能的地震风险管理的背景下更合理地分配资源。这种影响将在教学和研究的学术环境、工程设计办公室以及与风险管理有关的组织中感受到。

Understanding, predicting, and preventing collapse have always been major objectives of earthquake engineering. Collapse is the main source of injuries and loss of lives. Thus, it constitutes an engineering limit state that needs to be predicted in order to evaluate, in a probabilistic format, the life safety performance level, which is of primary societal concern. In the context of earthquake risk management, a process is needed that permits a rigorous assessment of the probability of collapse to make informed decisions in the best interest of society. In the context of earthquake resistant design, this process needs to be simplified so that the engineering profession can use engineering techniques, which are based on parameters such as strength, stiffness, and ductility (deformability), to derive structural properties that comply with specified targets for a required level of collapse safety, or a tolerable probability of collapse. This project will address both contexts. It will provide a methodology and reliable data for predicting a critical mode of collapse, namely that associated with sidesway instability in which an individual story (or a series of stories) displaces sufficiently so that the second order P-delta effects fully offset the first order story shear resistance and dynamic instability occurs, i.e., the structural system loses its gravity load resistance. Prediction of this mode of collapse is a challenging problem because structural components will deteriorate in strength and stiffness before the collapse limit state is reached, and great uncertainties are associated with the description of the seismic input and of the parameters that control the response of structures close to collapse. The methodology will be based on a combination of analytical and experimental simulations, with the former being carried out at Stanford University and the main effort of the latter, a shaking table collapse test of a model of a steel structure, being carried out at the NEES facility at the University at Buffalo. The outcomes of the proposed research will be (a) a methodology for predicting sidesway collapse of deteriorating structural systems, (b) an extensive database on deterioration properties of structural steel and reinforced concrete components, including uncertainty measures accounting for modeling and material uncertainties, (c) incorporation of component deterioration models in the OpenSees platform, (d) documentation of a comprehensive collapse experiment with data that covers the range of response of a 5-story steel frame structure from elastic behavior to incipient collapse, (e) a methodology for computing the probability of sidesway collapse that accounts for hazard, ground motion, and structural (material, modeling) uncertainties, and (f) engineering recommendations for design for collapse safety. Intellectural Merit. The proposed research will lead to seminal advances in understanding and predicting sidesway collapse of structures subjected to severe earthquakes. The major challenges are to account for deterioration in structural behavior in combination with P-delta effect, and for the uncertainties inherent in ground motion description and in modeling the behavior of the components that control the dynamic response at large inelastic deformations (or at small deformations in the case of brittle elements). These challenges imply extensive modeling efforts at the component and structure level and the incorporation of reliability concepts in assessing collapse safety of structures. Another major challenge will be the planning and execution of a shaking table collapse experiment, whose main purpose is to demonstrate that collapse prediction indeed is feasible. The research involves an integrated approach of physical simulations at a NEES site shaking table and computational simulations on the OpenSees platform, while fully utilizing the simulation, visualization, and collaboration tools of the NEESgrid. Broader Impacts on Earthquake Engineering Research and Practice. The research is motivated by professional needs to provide adequate and consistent collapse safety in new designs and to assess the collapse hazard of existing structures. These needs require the filling of knowledge gaps that exist in regard to data and tools and the understanding of collapse phenomena. The impact of the proposed work on research and practice will be the development of databases, advanced deterioration models, and computational tools that will make it feasible to predict the collapse safety of complex structures and will permit more rational allocation of resources in the context of performance-based seismic risk management. The impact will be felt in the academic environment in teaching and research, in engineering design offices, and in organizations concerned with risk management.