"Cracking Repair, and Ductility Enhancement of Large-Size Steel Beam-to-Column Connections Subjected to Dynamic CyclicLoading"

“动态循环荷载下大尺寸钢梁柱连接的裂纹修复和延性增强”

• 批准号: 9416266
• 负责人: Le-Wu Lu
• 金额: $ 10.01万
• 依托单位: Lehigh University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1994
• 资助国家: 美国
• 起止时间: 1994-08-15 至 1996-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9416266&HistoricalAwards=false
• 关键词: Cracking; Repair; Ductility; Enhancement; Large

9416266 Lu One of the significant issues that were brought forth, quite unexpectedly, by the Northridge earthquake is the vulnerability of some welded moment connections in steel frames subjected to dynamic ground shaking. It has been reported that in more than 50 low- and high-rise buildings cracks were found in the beam-to column connections. Two distinct types of cleavage cracks were observed to form at the beam bottom flange groove welded connection to the column flange face. Both types of cracks had their origin at the natural crack-like condition that results with a left- in-place steel backing bar. Preliminary investigations indicates that the deposited weld metal has unusually low fracture toughness. However, the mechanical and chemical properties of the structural steel generally meet the AISC and ASTM standard requirements. Of concern is whether a connection should be retrofitted if it has not detectable change. The issue of how to "protect" critical connections has been raised as well as approaches to lessen strength and deformation demand on these connections, has been raised as well as approaches to lessen strength and deformation demand on these connections. It is vitally important that reliable connection design and fabrication methodologies be established as soon as possible so that structures constructed in the future would not experience similar failures. The research under this project has the following objectives: (1) to determine the probable causes of cracking, (2) to evaluate the adequacy of the recommended repair methods, (3) to find rational and cost-effective ways to improve connection performance and/or to reduce demand on connections, and (4) to develop reliable design and fabrication procedures for welded connections. The research plan includes six tasks: (1) studies of welding procedure and quality of weld metal (including performing procedure qualification tests on electrodes to be used for repairs to insure adequate fracture toughness), (2) dynamic experiments on large-size connections, (3) dynamic experiments on repaired connections, (4) dynamic experiments on modified connections with enhanced ductility, (5) analytical studies, and (6) development of recommendations. A total of 16 tests will be conducted on 8 large-size connection specimens with cyclically applied dynamic load. The experiments will be performed in the ATLSS Laboratory at Lehigh University. The experiments will be performed in the ATLSS Laboratory at Lehigh University. An interdisciplinary team including structural engineers and welding metallurgist will carry out the study. The results will permit the development of definitive recommendations related to: weld metal and welding procedure, repair of cracked connections, and performance enhancement of connections. The study will also establish probable causes of connection cracking. ***

北岭地震出人意料地提出的一个重要问题是，钢框架中一些焊接弯矩连接在动力地面震动下的脆弱性。据报道，在50多座低层和高层建筑中，梁柱连接处发现了裂缝。在梁底法兰槽与柱法兰面的焊接处，观察到两种不同类型的解理裂纹。这两种类型的裂纹都是在自然裂纹状的条件下产生的，这是由留下的钢衬条造成的。初步研究表明，沉积的焊缝金属具有异常低的断裂韧性。然而，结构钢的力学和化学性能一般满足AISC和ASTM标准的要求。值得关注的是，如果连接没有可检测到的变化，是否应该进行改造。提出了如何“保护”关键连接的问题，以及降低这些连接的强度和变形要求的方法，以及降低这些连接的强度和变形要求的方法。尽快建立可靠的连接设计和制造方法是至关重要的，这样以后建造的结构就不会出现类似的故障。该项目的研究有以下目标：(1)确定开裂的可能原因，(2)评估推荐的修复方法的充分性，(3)找到合理和具有成本效益的方法来提高连接性能和/或减少对连接的需求，以及(4)开发可靠的焊接连接设计和制造程序。研究计划包括六项任务：(1)焊接工艺和焊缝金属质量的研究（包括对用于修复的电极进行工艺资格测试，以确保足够的断裂韧性），(2)大尺寸连接的动态实验，(3)修复连接的动态实验，(4)增强延展性的改进连接的动态实验，(5)分析研究，(6)提出建议。8个大尺寸连接试件在循环加载动载荷下共进行16次试验。实验将在利哈伊大学的ATLSS实验室进行。实验将在利哈伊大学的ATLSS实验室进行。一个由结构工程师和焊接冶金学家组成的跨学科团队将进行这项研究。研究结果将有助于制定有关以下方面的明确建议：焊接金属和焊接工艺、裂纹连接的修复以及连接性能的增强。这项研究还将确定连接开裂的可能原因。＊＊＊