Simulation Platform for the Earthquake Response of Reinforced Concrete Structures

动机：钢筋混凝土结构（RCS）是一种强非均质复合材料，其性能取决于脆性混凝土和延性钢筋之间的微妙相互作用。在极端地震事件下，这两个组件之间的相互作用对RCS的安全和生存至关重要，最近发生在土耳其、台湾、日本和美国的地震就证明了这一点。目的：建立三维地震反应模拟平台SPER，模拟RCS在地震事件作用下的渐进式破坏。由Farhat博士团队为解决大型流固耦合问题而开发的fem - feti并行有限元架构为提出的地震模拟环境提供了基础平台。SPER将采用一种新颖的非线性求解器，使用不完全消除，以及一种创新的界面模型来捕获混凝土中的局部开裂和剪切破坏。为了证明概念，将检查RC柱，其中准静态破坏以级联事件的形式发生，例如混凝土覆盖层剥落，钢筋的逐步剥离，横向箍筋的屈服和破裂，以及随后轴向钢筋的屈曲。作为系统分析的示例，将选择一个两跨钢筋混凝土桥梁结构，以突出桥梁上部与桥墩之间的3-dim相互作用，并展示SPER的可扩展性。长期目标设想以阪神高速公路为例的高架交通系统的多层地下结构模型，该高速公路在1995年神户地震中表现出严重的多段破坏。方法：提出的SPER软件将基于多层/多网格、区域分解和不完全非线性消除方法的组合。粗略地说，在这些算法中，(i)域分解提供了并行性，（ii）多层提供了与问题大小和并行计算机上的处理器数量相关的可扩展计算环境，而（iii）不完全消除消除了非线性求解器对局部奇点的敏感性。相关性：RCS的逐步退化在地震工程中是一个非常重要的问题。目前的设计理念已经转向了基于性能的方法，这需要对超出弹性范围的结构行为进行可靠的评估。SPER的设计目的是模拟现有RCS的抗震性能，这些RCS是根据旧的、通常是非保守的地震规定建造的，并协助开发快速、经济有效的修复程序。外联：SPER将通过一个网站传播，该网站将记录RCS基于模型的地震模拟软件的进展和结果。从长远来看，其目的是最终将SPER的3-dim功能整合到即将到来的NSF地震工程模拟网络（NEES）中，并在其中开发基于互联网的地震模拟功能，供学术界和地震工程界的同事使用。人力资源与教育：探索性研究将由三位分别来自土木工程、计算机科学和航空航天工程的研究生研究助理参与，他们将由三个系的四位Co-Pi指导和监督。他们将在一个跨学科的环境中工作，包括民用基础设施系统、并行计算技术和数值解决方案。模拟平台SPER将被用作科罗拉多大学土木工程专业提供的一些本科和研究生课程的教育工具，如钢筋混凝土结构设计、地震工程和计算力学。SPER还将作为公共宣传的示范工具，特别是向高中教师和K-12学生宣传地震灾害意识。这项工作将利用科罗拉多大学新的综合教学实验室（ITLL），该实验室因其通过发现学习的新方法而受到全国关注。

Motivation:Reinforced Concrete Structures, RCS, are strongly heterogeneous composites, the performance of which depends on the subtle interaction of the brittle concrete and the ductile reinforcement. Under extreme seismic events, the interplay between the two components is critical for the safety and survival of RCS as demonstrated by dramatic failures recent earthquake in Turkey, Taiwan, Japan, and the USA.Objectives:It is proposed to develop a 3-dim simulation platform for the earthquake response, SPER, to model progressive failure of RCS subjected to seismic events. The parallel finite element architecture of FEMS-FETI, which was developed by the team of Dr. Farhat for the solution of large fluid-structure interaction problems, provides the basic platform for the proposed earthquake simulation environment. SPER will feature a novel nonlinear solver using incomplete elimination, and an innovative interface model to capture localized cracking and shear failure in concrete. For proof of concepts, a RC column will be examined in which quasi-static failure takes place in the form of a cascade of events, such as spalling of the concrete cover, progressive debonding of the reinforcement, yielding and rupturing of the transverse stirrups, and subsequent buckling of the axial reinforcement. As an illustrative example on system analysis, a two-span RC bridge structure will be selected to highlight the 3-dim interaction between the bridge super-and the pier and to showcase the scalability of SPER. The long-term objective envisions multilevel substructure models of elevated transportation systems exemplified by the Hanshin Express Way, which exhibited dramatic multiple segment failure during the 1995 Kobe earthquake. Methodology:The proposed SPER software will be based on a combination of multilevel/multigrid, domain decomposition and incomplete nonlinear elimination methods. Roughly speaking, in these algorithms, (i) domain decomposition provides the parallelism, (ii) multilevel provides a scalable computing environment with respect to problem size and the number of processors on parallel computers, while (iii) incomplete elimination removes the sensitivity of the nonlinear solver to localized singularities. Relevance:Progressive degradation of RCS is a matter of great importance in earthquake engineering. The current design philosophy has moved to a performance-based approach which requires reliable assessment of the structural behavior beyond the elastic range. SPER is designed to simulate the seismic performance of existing RCS which have been built according to older and often non-conservative earthquake provisions, and to assist the development of rapid and cost-effective rehabilitation procedures. Outreach:SPER will be disseminated through a web site which will document the progress and outcome of the model-based earthquake simulation software of RCS. In the long haul, the intention is to eventually incorporate the 3-dim capabilities of SPER into the forthcoming NSF Network for Earthquake Engineering Simulation (NEES), and to develop therein an internet-based capability for earthquake simulations which may be used by colleagues in academia and the earthquake engineering community.Human Resources and Education:The exploratory research will involve three graduate research assistants from the Civil Engineering, Computer Science and Aerospace Engineering, respectively, which will be guided and supervised by the four Co-Pi's in three departments. They will work in an interdisciplinary environments that encompasses civil infrastructure systems, parallel computing technologies, and numerical solution schemes. The simulation platform SPER will be used as an education tool in a number of undergraduate and graduate courses that are being offered in the Civil Engineering Program at the University of Colorado, such as the Design of Reinforced Concrete Structures, Earthquake Engineering, and Computational Mechanics. SPER will also serve as a demonstration tool for public outreach, especially to high school teachers and K-12 students, on earthquake disaster awareness. This effort will take advantage of the new Integrated Teaching and Learning laboratory (ITLL) at the University of Colorado which has received national attention because of its novel approach to learning through discovery.