大跨度斜拉桥双向曲面混合桥塔钢-混结合段受力性能研究

为研究大跨度斜拉桥双向曲面混合桥塔钢-混结合段的力学行为与传力机理,设计相似比为1:4的全截面静载试验模型,测试最不利及超载工况下结构的应力、变形、开裂等;结合有限元仿真分析,研究桥塔钢-混结合段的传力机理,并进一步探讨结构构造参数对其影响规律。结果表明:最不利荷载工况下,钢结构最不利压应力为-165.44 MPa,位于钢过渡段主跨受压侧壁板;混凝土最不利拉应力为8.65 MPa,叠加预应力效应后约为1.73 MPa,位于混凝土段边跨受拉侧;沿塔轴向,钢结构应力平缓降低并在承压板附近存在突变,混凝土应力较为平稳;剪力钉及PBL剪力键弯曲应力均呈"两头大、中间小"的马鞍形分布。模型各构件实测应力随荷载增加呈线性增长,模型整体处于弹性受力状态;结合段钢-混最大滑移值仅65 μm,钢-混之间协同受力良好;模型上下缘实测应力差异约为10%,表明双向曲面构造引起一定的空间受力特性,但挠度量值差异小。超载工况下,1.4倍加载时混凝土段边跨受拉侧出现裂纹;1.7倍加载时钢过渡段主跨受压侧局部应力屈服,模型受力整体表现为以钢过渡段受压侧及混凝土段受拉侧最为不利。2.0倍加载下,模型水平挠度随荷载变化均近似线性增加,转角近似满足线性变化,受混凝土开裂影响较小;最大水平挠度仅1.43 mm,挠跨比约为1/3 000,结构具有良好的刚度性能;结合段内混凝土局部开裂对受拉区的钢-混相对滑移影响较为显著。通过承压板、钢壁板及PBL板分别传递荷载66.3%、15.2%及18.5%,承压板为主要传力构件。参数讨论表明,原桥合理承压板、钢壁板厚度分别介于40~80、24~40 mm之间,剪力连接件刚度对结构传力影响较小。

Study on the Mechanical Behavior of Bi-directionally Curved Composite Pylon Steel-concrete Joints for a Long-span Cable-stayed Bridge

To study the mechanical behavior and force transfer mechanism of a steel-concrete composite joint for a bi-directionally-curved-surface pylon of a long-span cable-stayed bridge, a 1:4 scaled model with a full cross-section was designed. Various model parameters such as the stress, deformation, and cracks were then measured under unfavorable internal force compositions and overload conditions and the finite element analysis results used to investigate the force transmission of the joint. Furthermore, a parametric analysis was conducted to reveal the influence of the structural parameters. The results indicated that under the most unfavorable loading condition, the highest steel compressive stress (-165.44 MPa) was found in the compressive side of the steel transition section and the highest concrete tensile stress (8.65 MPa) was found in the tensile side of the concrete section, which was approximately 1.73 MPa after removing the prestressing effect. Generally, the stress on the steel structure decreased gradually along the axial direction of the pylon except for the abrupt increase near the bearing plate, and the stress on the concrete was relatively stable. The bending stresses on the shear studs and PBLs had as addle-shaped distribution along the pylon axis. The measured stress on each component increased linearly with the increasing load and the entire model operated in an elastic state when loaded. The maximum slip between steel and concrete was only 65 μm, indicating that the steel and concrete collaborated well. The stress difference between the upper and lower sides of the model was approximately 10%, indicating that the bi-directionally curved structure induced certain spatial stress characteristics even though the deflection difference was small. Under overloading conditions, the concrete section cracked in the tensile side under 1.4 times loading and the steel yielded in the compression side of the steel transition section under 1.7 times loading, which indicated that the compression side of the steel transition section and tension side of the concrete section were most unfavorable. Under 2.0 times loading, the horizontal deflection and rotation angle increased linearly and were hardly affected by concrete cracking. The maximum horizontal deflection and deflection-span ratio were approximately 1.43 mm and 1/3 000, respectively, which indicates that the structure has good stiffness performance. However, concrete cracking had a significant influence on the slip in the tension zone of the composite segment. Approximately 66.3%, 15.2%, and 18.5% of the load were transferred through the bearing plate, wallboard, and PBL plate, respectively, and the bearing plate was the main force transfer component. The parametric study showed that the reasonable thickness of the bearing and wallboard plates in the original bridge were 40~80 and 24~40 mm, respectively, and the stiffness of the shear connectors had little influence on the force transmission.