为探究钢桁腹-混凝土组合外接式节点的疲劳性能并验证该新型结构应用于高速铁路桥梁的可靠性，设计制作了两个缩尺比为1:3的节点模型并开展了疲劳试验，研究了组合外接式节点疲劳破坏模式、荷载-位移关系和荷载-应变曲线，考察了不同应力幅作用下外接式节点疲劳受力特征。试验结果表明：在设计应力幅作用下，组合外接式节点疲劳寿命超过251万次，节点未破坏且刚度未减小，抗疲劳性能满足要求；在1.4倍设计应力幅作用下，节点实测疲劳寿命为140万次；外接式节点的疲劳破坏模式为受拉侧外露节点板的开裂，组合外接式节点疲劳性能的控制构造细节是外露节点板与加劲板之间的焊缝连接细节；疲劳裂纹引起节点板的应力重分布，裂纹上下节点板的应变最多减小了81%，裂纹附近节点板应变最多增大了33%；根据一点法所得S-N曲线，组合外接式节点对应于设计应力幅53.2 MPa作用下的疲劳寿命为436万次，是设计寿命的2.18倍。

Two joint models with a scale of 1:3 were fabricated and fatigue tests were carried out to investigate the fatigue performance of steel truss web-concrete composite external joints and verify the reliability of the new structure applied to high-speed railway bridges. The fatigue damage mode, load-displacement relationship, and load-strain curve of the composite external joints were investigated, the fatigue force characteristics of the external joints under different stress amplitudes were investigated. The experimental results showed that the fatigue life of the composite external joint exceeds 2.51 million loading cycles under the design stress amplitude, the joint is not damaged, the stiffness is not reduced, and the fatigue resistance performance meets the requirements. Under the action of 1.4 times design stress amplitude, the measured fatigue life of the external joint is 1.4 million times. The fatigue damage mode of the external joint is the cracking of the exposed gusset plate on the tensile side, and the critical detail of composite external joint is the welding detail which connecting the exposed gusset plate and the stiffening plate. The fatigue crack causes the stress redistribution in the gusset plate, the strain in the gusset plate above and below the crack is reduced by 81% at most, and the strain in the gusset plate near the crack is increased by 33% at most. According to the S-N curve obtained by the one-point method, the fatigue life of the composite external joint corresponding to the design stress amplitude of 53.2MPa is 4.36 million times, which is 2.18 times of the design life.

U24

国家自然科学基金项目（面上项目，重点项目，重大项目）