Mechanical performance and stiffness calculation of integral abutment joints in Ⅰ-shaped composite girders

To investigate the influence law of different pile types on the mechanical performance of integral abutment joints in Ⅰ-shaped composite girders, reinforced concrete (RC) piles, H-shaped steel piles, and ultra-high-performance-concrete (UHPC) piles were used as variables to conduct full-scale model tests, develop finite element models, and analyze the mechanical characteristics, load-transfer mechanisms, and failure modes of the joints. A joint stiffness calculation method was proposed based on the principle of the force method. Analyse results show that all joint specimens with different pile types exhibit excellent longitudinal deformation performance under overall temperature rise loads. Failure forms of joints are caused by pile failure. The studs are not bent or damaged, and the overall performance of the joints is great. Under equivalent vertical bearing capacity conditions, steel piles demonstrate the highest shear and bending stiffness, followed by RC piles, while UHPC piles show the minimum values. H-shaped steel piles exhibit optimal longitudinal deformation adaptability and bearing capacity, followed by UHPC piles, with RC piles performing least favorably. Two stiffness mutation positions, including pile tops and beam-abutment interfaces, are identified as key points of the joint design of Ⅰ-shaped composite girders. By comparing the theoretical formula with the finite element results, the longitudinal deformation error of the bridge under temperature effects is less than 2.7%. verifying their reliability. The theoretical formula can be used to calculate the integral longitudinal deformation of the bridge. The proposed stiffness calculation method of different pile types achieves less than 5% deviation compared to experimental results. The research results provide theoretical support for the refined design of integral abutment joints in steel-concrete composite girders.