The Effect of Composite Floor Behavior on the Failure of Steel Moment-Resistant Connections

1994年1月17日加利福尼亚北岭地震后，观察到钢框架焊接抗弯矩连接的独特断裂。这些故障可以分为结构性故障，主要与钢构件和焊缝的延展性和局部应变大于设计预期有关，或冶金性故障，主要与焊接缺陷、焊接工艺差、宽法兰构件的厚部分缺乏韧性以及存在应力产生器（如背板）有关。故障的主要原因的解决将决定必须修改的抗震设计规范的规定。它还将规定钢框架所需的修理和修复的性质，因为改造战略将根据主要故障原因而有所不同。该项目通过检查问题的载荷和阻力方面来解决结构行为问题。在阻力方面，本研究将探讨复合楼板的存在和连接面板区域的屈服是否会显著增加关键焊缝附近的局部应变。一项结合分析和实验的研究将集中在焊接连接的局部行为上，特别是在靠近底部梁翼缘的区域，那里发生了大部分的断裂。实验计划将包括三个梁柱组合的测试，包括一个没有板，一个有部分复合作用的板，一个有完全复合作用的板。三维非线性连续有限元分析将用于量化焊缝附近的局部应变以及混凝土/钢界面局部复合作用对力传递的影响。在荷载方面，本研究将通过使用能够跟踪水平和垂直加速度的三维非线性瞬态动力框架分析程序来解决地震期间结构中可能的力分布。如果能够证明当前的钢架横向抗力系统的地震分析和设计方法是不足的，那么这项研究将对钢结构的设计产生深远的影响，因为它们通常排除了复合楼板对结构行为的影响。这是北岭地震项目。＊＊＊

9416363 Leon Unique failures by fracture to welded moment-resisting connections in steel frames were observed after the Northridge, California earthquake of January 17, 1994. These failures can be categorized either as Ostructural,O which is associated primarily with larger ductilities and local strains in the steel members and welds than is envisioned in design, or Ometallurgical,O which is associated primarily with weld defects, poor weld workmanship, lack of toughness in thick sections of wide- flange members, and the presence of stress risers such as backing plates. The resolution of the primary cause of the failures will determine the provisions of the seismic design specifications which must be modified. It will also dictate the nature of the repair and rehabilitation that will be required in steel frames, since the retrofit strategies will differ depending on the primary cause of failure. This project addresses the problem of structural behavior by examining both the load and resistance aspects of the problem. With respect to resistance, this research will investigate whether the presence of a composite floor slab and the occurrence of yielding in the panel zone region of the connection significantly increased the local strains near the critical welds. A combined analytical-experimental investigation will be conducted to focus on the local behavior of the welded connections, and in particular on the region near the bottom beam flange, where most of the fractures occurred. The experimental program will include tests of three beam-to-column subassemblages, including one with no slab, one with a slab having partially composite action, and one with a slab having fully composite action. Three-dimensional nonlinear continuum finite element analysis will be used to quantify the local strains near the welds and the effect on force transfer of partial composite action at the concrete/steel interface. With respect to loading, this research will address th e probable force distribution in the structure during the earthquake through the use of a three-dimensional, nonlinear, transient dynamic frame analysis program capable of tracking both horizontal and vertical accelerations. This research will have a profound effect on the design of steel structures if it can be demonstrated that current seismic analysis and design methodologies for steel frame lateral-resistance systems are inadequate, since they usually exclude the effect of the composite floor slabs on the structural behavior. This is a Northridge Earthquake project. ***