钢桁梁整体焊接节点疲劳性能模型试验

整体焊接节点钢桁梁具有广阔的应用前景，其疲劳性能由整体焊接节点所决定。以长清黄河大桥为研究对象，通过理论分析和两尺度疲劳破坏试验对钢桁梁整体焊接节点的疲劳性能进行了研究。首先通过全桥杆件内力分析和多尺度疲劳损伤分析确定了控制主桁疲劳性能的整体焊接节点位置及其控制构造细节；在此基础上设计了2类共21个试验模型，其中包括20个构造细节试样模型和1个足尺节段模型，进行了疲劳破坏试验，确定了整体焊接节点控制构造细节的主导疲劳开裂模式、应力集中系数和疲劳强度。研究结果表明：节点顶板、横梁上翼缘与节点板熔透对接焊连接细节是整体焊接节点疲劳性能的控制构造细节，其主导疲劳开裂模式为从节点板焊趾起裂并沿板厚扩展；实际受力模式下，控制构造细节中节点板焊趾应力集中系数为1.163，横梁上翼缘焊趾应力集中系数为1.789；2类试验模型的宏观疲劳裂纹起裂寿命均占总疲劳寿命的75%以上，故将2类试验模型的疲劳失效判据统一定义为出现宏观疲劳裂纹；基于此，2类试验模型所得到的控制构造细节疲劳强度等级基本一致；控制构造细节2种开裂模式名义应力疲劳强度等级均建议采用公路钢结构桥梁设计规范中的FAT80，热点应力疲劳强度均建议采用欧规中的FAT90。

Experimental Study on Fatigue Performance of Integral Welded Joints in Steel Truss Bridges

The steel truss bridges with integral welded joints have wide application prospect, and its fatigue performance is determined by the integral welded joint. Based on the Changqing Yellow River Bridge, the fatigue performance of integral welded joints was systematically studied through theoretical analysis and two-scale fatigue failure tests. Firstly, the integral welded joint that control the fatigue performance of the truss bridge and the critical detail of the joint were determined by internal force analysis and multi-scale fatigue damage analysis. Then, 21 test models of two-scaled fatigue test were designed, including 20 detailed scale models and 1 full-scale model. Fatigue tests were carried out to study the dominant fatigue cracking mode, stress concentration factor and fatigue strength of the critical detail. The results indicate that the critical detail of integral welded joint is the full penetration butt welding detail which connecting the top plate of joint, the upper flange of crossbeam and the gusset plate. The dominant fatigue crack is initiating from the gusset weld toe and propagating along the gusset plate thickness direction. The stress concentration factor of the weld toe of the gusset plate in the critical details is 1.163, and that is 1.789 in the weld toe of the upper flange of the crossbeam. The life of macro crack initiation of the two types of test models account for more than 75% of the total fatigue life. Therefore, the fatigue failure criterion of the two types of test models was uniformly defined as the occurrence of macroscopic fatigue cracks. Based on this, the fatigue strength of the critical detail obtained from the two types of test models are in good agreement. The nominal stress fatigue strength of critical detail is recommended to adopt FAT80 of the Specifications for design of highway steel bridge, and the hotspot stress fatigue strength is recommended to adopt FAT90 of Eurocode 3.