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. © 2022 Xi'an Highway University. All rights reserved.