Study on the circumferential tensile behavior of steel shell-concrete pylon wall

Steel shell-concrete (SSC) composite pylons, as a novel type of composite bridge pylon structure, have been increasingly applied in long-span bridges. However, the actual stress state and load-carrying mechanism of the pylon walls in the anchorage zone under horizontal cable forces remain insufficiently understood. First, segmental model tests were conducted to identify the circumferential tension-dominated stress state of the side pylon wall. Subsequently, a refined finite element (FE) model was developed to quantify the load contribution of individual structural components. The results indicate that circumferential tensile response of the pylon wall can be divided into five stages with four characteristic points, while the ultimate state is governed by the attainment of the ultimate tensile strain in the faceplate. Parametric analyses show that the faceplate thickness and transverse PBL thickness dominate both load-bearing capacity and stiffness, whereas the contribution of transverse rebar is limited. The concrete does not directly participate in tensile resistance after cracking; instead, it provides a lateral confining strengthening effect on the faceplate, thereby enhancing the equivalent elastic modulus and yield level of the steel and improving the global load-bearing capacity and stiffness. Based on the above mechanism, a modified constitutive model for the faceplate considering the confining strengthening effect of concrete was proposed, and a fiber-based analytical model for the full-range circumferential tensile behavior of SSC pylon walls was established, enabling a stage-based elastic-elastoplastic-plastic design approach. The proposed method can accurately predict full-range load-deformation response, stiffness degradation, and internal force distribution.