Moment Frame Connections Revisited: A Fundamental Fracture Mechanics Approach

1994年1月17日发生在加州圣费尔南多谷的6.8级地震，并没有造成任何钢结构的倒塌，但是过去用传统的简化规范和常见的现场焊接技术自信地设计和建造的连接，被发现没有达到我们的期望。本项目将研究结构的性能取决于连接的性能。这将通过分析弯矩连接的断裂强度和韧性来完成。载荷效应是由结构的整体响应决定的，其性能是由局部材料特性和几何构型控制的。将评估水平和垂直地震力的相互作用和相对重要性。组合作用（混凝土楼板对钢梁）和板区变形的影响将被考虑在内。在局部，详细的非线性有限元模型将提供进行断裂分析所需的应力状态信息。弯矩连接的断裂强度将考虑热处理区韧性降低的影响；采用直线裂纹和半椭圆裂纹模拟焊缝缺陷；这些位置的应力强度因子将量化这些弱点对接头最终强度的影响。人们已经认识到，描述结构构件强度性能的最佳方法，现在必须遵循类似的“回归基础”方法来进行连接设计。断裂力学的提出提供了基础：基于理论分析的经验关系将被提出，以估计弯矩连接的极限强度，抵抗地震荷载和脆性断裂***

9703864 Chen The 6.8 magnitude earthquake that shook California's San Fernando Valley on January 17th in 1994, did not cause the collapse of any steel structures but connections, confidently designed and constructed in the past with traditional code simplifications and common site-welding techniques, were discovered no to meet our expectations. This project will study the performance of structures depends on the performance of connections. This will be accomplished by analyzing the fracture strength and toughness of the moment connection. The load effect as determined by a structure's global response, and its performance as controlled by local material properties and geometric configuration will be considered. The interaction and relative importance of horizontal and vertical seismic forces will be evaluated. The effect of composite action (concrete floor-slab on steel girder) and panel zone deformation will be included. Locally, a detailed nonlinear finite element model will provide the stress state information needed to perform a fracture analysis. The fracture strength of the moment connection will consider the effect of reduced toughness in the heat treated region; line and semi-elliptic cracks will be used to simulate weld flaws; stress intensity factors at these locations will quantify the effect these weaknesses have on the ultimate strength of the joint. It has been recognized that the best means to describe the strength performance of structural members, must now be followed by a similar "back to the basics" approach to connection design. Fracture mechanics is proposed to provide that foundation: empirical relationships based upon theoretical analyses will be presented to estimate the ultimate strength resistance of moment connections to seismic loads and brittle fracture ***