Full-scale testing of the bending behaviour of UHPC gravity–grouted sleeve–prestressed anchor joints in assembled frame tunnels

Abstract

Joints are weak parts of a prefabricated tunnel frame structure, and the joint bending resistance is a crucial factor controlling the deformation and bearing capacity of the tunnel structure. This study proposes a joint with dual anchoring of ultrahigh-performance concrete (UHPC) gravity-grouted sleeves and prestressed steel reinforcement. The material strain, opening amount, deflection, stiffness, rotation angle, and ductility of the grouted sleeve-prestressed anchor joint and grouted sleeve joint types were tested through full-scale bending tests, and with the help of noncontact measurement technology, the dynamic process of joint bending failure was captured. In addition, the finite element method was used to evaluate the influences of the prestressing magnitude and the position of the prestressing steel bars on the bending performance of the joints. The results indicate that the damage to the concrete joint is concentrated at the top of the joint and that the damage to the top surface of the joint concrete is distributed in an "m" shape, indicating that the damage to the concrete in the area between the sleeves is relatively extensive. Owing to the turning points of grouting material fracture and joint yielding, the joint bending process clearly shows a three-stage change. The grouted sleeve-prestressed anchor joint exhibits greater bending stiffness than the grouted sleeve joint does, and the slip of the grouting material in the sleeve is smaller. Prestressing plays a key role in enhancing the bearing capacity and deformation resistance of joints. Considering that excessive prestress may increase the brittleness of the structure, the prestress of the grouted sleeve-prestressed anchor joint is recommended to be 200 kN. This study provides theoretical support for the joint design and construction of prefabricated tunnel frame structures.