Performance-Based Seismic Design of Concentrically Braced Frames

基于性能的同心支撑框架抗震设计

• 批准号: 0301792
• 负责人: Charles Roeder
• 金额: $ 29.63万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-06-01 至 2006-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0301792&HistoricalAwards=false
• 关键词: Performance; Based; Seismic; Design; Concentrically

Performance-Based Seismic Design of Concentrically Braced Frames 0301792PI: Charles Roeder, University of WashingtonPerformance-based seismic design requires structures that can be designed to meet multiple performanceobjectives and engineering models that are accurate enough to assess the system performance. Steel concentrically braced frames (CBFs) can be designed to meet the required objectives of PBSD. CBF are stiff and strong, which are attributes need for serviceability limit states. In addition, special concentrically braced frames (SCBFs) have been developed to assure stable cyclic inelastic seismic performance, which enables SCBF to satisfy life safety and collapse prevention performance levels as well. More recent research has resulted in the development of unbonded brace CBFs (UBCBFs). In these framing systems, the unbonded braces yield in both tension and compression without brace buckling to provide a superior level of seismic resistance and are ideal candidates for PBSD. Currently, the seismic performance of both SCBFs and UBCBFs is limited by the connection performance or the connection design requirements. Current design provisions for SCBFs attempt to ensure adequate connection resistance to avoid premature connection failure, while permitting significant inelastic connection rotation due to brace buckling. Connections of UBCBFs must be designed to prevent buckling or excessive deformation prior to development of the full bonded brace ductility. Although these design requirements are conceptually simple, the objectives are difficult to achieve using current design provisions since engineers must use approximate and empirical rules to accomplish these design objectives. For example, for SCBFs, design provisions required that the factored resistance is larger than the expected tensile yield strength of the brace. Although the provisions attempt to achieve a rational yielding hierarchy, the present application is flawed. The use of the resistance factor severely penalizes the connection design and may result in uneconomically large connections that adversely affect the seismic performance of the system. Even for proportional connections, the seismic performance of the system is unknown, and therefore, brace fracture may precede connection yielding, significantly decreasing the system capacity.To overcome the shortcomings of current design, a rational, PBSD procedure will be developed to improvethe connection design and seismic performance of both UBCBF and SCBF systems. The research will build upon the existing CBF design requirements and use innovative techniques developed for moment-resisting steel frames during the SAC Steel Project. In that project, design procedures were developed to balance desirable yield mechanisms and to restrict undesirable failure modes to achieve the desired seismic performance. Here, similar design procedures will be developed to balance the brace and connection behavior to achieve multiple performance objectives. The research program will evaluate and improve existing engineering models, develop a rational PBSD procedure for both SCBF and UBCBF systems, evaluate, modify and validate the design procedure using experimental research results. Finally, the procedure will be used to design several frames. A conceptual test frame will be developed for proposedfuture testing to demonstrate the performance of the complete system using the future University of Minnesota NEES facility.The structural engineering profession recognizes that the connection design provisions for CBFs represent asignificant gap present in current design provisions. The proposed research program will result in robust design procedures and accurate engineering models. These tools will permit engineers to design efficient and effective SCBF systems to fulfill current and future seismic engineering needs. To facilitate the transfer of the research result to practice, the research team will partner with prominent structural engineers and structural engineering societies (letters provided in Supplementary Documents). In addition to educating today's engineers, the researcher team will use the research process and results to educate future engineers, including graduate and undergraduate students. Students will observe the testing to familiarize them with the experimental research process. In the classroom, the student will compare the test results to estimates of the connection strength using code standards (undergraduate) and engineering models (graduate) found in the literature. The students will use the proposed design equations and compare the results with the code standards. This exercise will provide the students with a basis for discussion of and insight into alternative design methods.

基于性能的抗震设计的同心支撑框架0301792 PI：查尔斯Roeder，华盛顿大学基于性能的抗震设计需要结构，可以设计，以满足多个性能目标和工程模型，是准确的，足以评估系统的性能。钢中心支撑框架（CBF）的设计可以满足PBSD的目标要求。CBF的刚度和强度是正常使用极限状态所需的属性。此外，特殊的中心支撑框架（SCBF）已被开发，以确保稳定的循环非弹性抗震性能，这使得SCBF，以满足生命安全和倒塌预防性能水平以及。最近的研究导致了无粘结支具CBF（UBCBF）的发展。在这些框架系统中，无粘结支撑在拉伸和压缩下屈服而没有支撑屈曲，从而提供了上级抗震水平，并且是PBSD的理想候选者。目前，SCBF和UBCBF的抗震性能受到连接性能或连接设计要求的限制。SCBF的当前设计规定试图确保足够的连接阻力，以避免过早的连接失效，同时允许由于支撑屈曲引起的显著的非弹性连接旋转。UBCBF的连接件必须设计成在完全粘结支撑韧性发展之前防止屈曲或过度变形。虽然这些设计要求在概念上是简单的，但使用当前的设计规定很难实现这些目标，因为工程师必须使用近似和经验规则来实现这些设计目标。例如，对于SCBF，设计规定要求系数抗力大于支撑的预期拉伸屈服强度。尽管这些规定试图实现合理的收益等级，但目前的适用存在缺陷。阻力系数的使用严重损害了连接设计，并可能导致不经济的大型连接，从而对系统的抗震性能产生不利影响。即使对于比例连接，系统的抗震性能是未知的，因此，支撑断裂可能先于连接屈服，显着降低系统的能力。为了克服现有设计的缺点，一个合理的，PBSD程序将被开发，以改善连接设计和抗震性能的UBCBF和SCBF系统。该研究将建立在现有的CBF设计要求的基础上，并使用SAC钢铁项目期间为抗弯矩钢框架开发的创新技术。在该项目中，开发了设计程序，以平衡理想的屈服机制，并限制不希望的破坏模式，以实现理想的抗震性能。这里，将开发类似的设计程序来平衡支撑和连接行为，以实现多个性能目标。该研究计划将评估和改进现有的工程模型，开发一个合理的PBSD程序SCBF和UBCBF系统，评估，修改和验证的设计过程中使用的实验研究结果。最后，将使用该程序设计几个框架。一个概念性的测试框架将被开发，用于未来的测试，以证明使用未来明尼苏达大学NEES设施的完整系统的性能。结构工程专业认识到，CBF的连接设计规定代表了当前设计规定中存在的一个重大差距。拟议的研究计划将导致强大的设计程序和准确的工程模型。这些工具将允许工程师设计高效和有效的SCBF系统，以满足当前和未来的地震工程需求。为了促进研究成果转化为实践，研究团队将与著名的结构工程师和结构工程学会合作（在补充文件中提供的信件）。除了教育当今的工程师外，研究团队还将利用研究过程和结果来教育未来的工程师，包括研究生和本科生。学生将观察测试，以熟悉他们的实验研究过程。在课堂上，学生将使用规范标准（本科生）和工程模型（研究生）在文献中找到的连接强度的估计比较测试结果。学生将使用建议的设计方程，并将结果与规范标准进行比较。这个练习将为学生提供一个讨论和洞察替代设计方法的基础。