中文摘要：

为研究钢-混凝土组合桁架在疲劳荷载下的受力性能，提高组合桁架的疲劳寿命，为疲劳设计提供一定依据，以某大跨桥梁为基础设计6组组合桁架构件，采用有限元计算软件ANSYS和名义应力理论相结合的方法对其进行数值模拟和研究。由精细有限元分析模拟疲劳荷载引起单元的损伤，进而获得更加准确的修正S-N曲线。通过对模型施加常幅疲劳荷载，计算其在不同配筋率和混凝土抗压强度下的疲劳寿命，考察不同影响因素对组合桁架疲劳寿命的影响。结果表明，混凝土强度增加1个等级（约8％），疲劳寿命提高约20％；而配筋率也以约8％的速率增加时，疲劳寿命只提高约0．3％。混凝土抗压强度和配筋率均为影响组合桁架疲劳性能的因素，构件的疲劳寿命随混凝土抗压强度和配筋率的提高而增长，其中混凝土抗压强度的影响相比配筋率更为显著。研究结果可为组合桁架桥梁的设计提供了依据。

英文摘要：

In order to study the performance of steel-concrete composite trusses under fatigue loads and to improve the fatigue life of the composite trusses, 6 composite truss models of a large span bridge were built and analyzed by ANSYS software combined with the nominal stress method. The damage of elements caused by fatigue loads were simulated by a refined finite element analysis, and more accurate modified S-N curves were obtained. The fatigue life of the models with different rein- forcement ratios and concrete compression strengths under constant amplitude fatigue loading was simulated to study the influence of different factors on the fatigue life of composite trusses. The re- suits showed that when the concrete strength was increased by one grade with a rate of about 8% , the fatigue life was increased by about 20% , while the reinforcement ratio was also increased with the same rate of about 8% , the fatigue life was increased by only about 0. 3%. The concrete com- pression strength and the reinforcement ratio were both main influencing factors of the fatigue life.Fatigue life was increased while the concrete compression strength and the reinforcement ratio were increased, and the influence of concrete compression strength was more significant than that of the reinforce ratio. These results provide a basis for the design of composite truss bridges.