Experimental research and numerical analysis on mechanical behavior of lightweight-design precast bent caps with large cantilevers

Two innovative lightweight-design schemes for large cantilevered precast bent caps (PBCs) commonly used in China are proposed in this study. In Scheme 1, a monolithic bent cap is divided into two symmetrical precast pieces that are parallel to the bent cap center line (hereafter referred to as PPBCs) and connected together by a cast-in-place wet joint. In Scheme 2, U-shaped and inverted U-shaped cross-section bent caps are designed to facilitate monolithic precast. Four scaled bent cap specimens are loaded monotonically to study the crack development, failure mode, deformation of the cantilevers, and ultimate load-carrying capacity. The test results show that all the specimens failed in the desired bending. However, the connectivity of the two precast pieces in the PPBCs was damaged after cracking occurred in the wet joint, leading to a slightly decreased ultimate load-carrying capacity, compared to the corresponding monolithic bent cap. The tensile stresses of the stirrups in the cavities of the U-shaped and inverted U-shaped cross-section bent caps were larger than those at other positions. Therefore, the arrangement of the stirrups should be strengthened in the cavities. The numerical modeling strategy validated by the test results was used to predict the mechanical behavior of full-scale lightweight-design bent caps from construction to final failure. The analysis results indicated that, all lightweight-design PBCs remained uncracked in both the construction and service stages. Finally, the PPBC and hollow cross-section PBCs failed under load combinations that were 1.9- and 1.7-time the Strength I load combination.