Experimental study on flexural behavior of segmental precast large-cantilevered prestressed concrete cap beam

Abstract

This study investigates the influence of epoxy joint configuration and longitudinal reinforcement continuity at the joints on the mechanical properties of segmental precast assembled large-cantilevered prestressed concrete (PC) cap beams under the co-action of flexural and shear internal forces. Accordingly, a practical project is considered, and five segmental precast-assembled large-cantilevered PC cap beam models as well as a comparative model of a monolithic precast large-cantilevered PC cap beam are designed and produced. The five segmental precast cap beam models were designed with a 1/5 scale ratio, and the joint interfaces were all connected using an epoxy resin binder. Three of these models whose longitudinal reinforcements at the joints were discontinuous utilized a large key tooth, a small key tooth, and corbel joint structures. The other two models whose longitudinal reinforcements at the joints were connected by grouted sleeves adopted large key-tooth and corbel joint configurations. Throughout the static loading test process of these six cap beam models, key results, such as the initial stiffness, cracking load, yield load, ultimate load capacity, concrete strain, deflection, and crack width, were obtained. The experimental results are as follows. The failure process and crack distribution patterns of each precast segmental cap beam model are fundamentally the same as those of the monolithic precast cap beam model. The crack distribution is sparse, cracks are wide, and the failure modes are all due to bending. Additionally, the mechanical properties of the three precast segmental cap beam models with discontinuous longitudinal reinforcement compared with those of the monolithic precast cap beam model were considerably degraded. The initial stiffness, yield load, ultimate load capacity, and ultimate deflection were only 81.4%, 80.4%, 81.1%, and 66.4%, respectively, of those of the monolithic precast cap beam model. Moreover, penetrating cracks formed in the concrete of the tensile zone on both sides of the epoxy joint interfaces during failure. Compared with the segmental precast cap beam models with discontinuous longitudinal reinforcement, the initial stiffness, yield load, ultimate load capacity, and ultimate deflection of the segmental precast cap beam models with continuous longitudinal reinforcement significantly improved. The mechanical properties of the latter were similar to those of the monolithic precast concrete cap beam model. Based on the experimental results, effective technical measures (such as grouted sleeves) were proposed to connect the longitudinal reinforcement at the joints. This ensured that the static performance of the segmental precast-assembled large-cantilevered PC cap beam was similar to that of the monolithic precast cap beam.