Experimental study on the in-plane shear performance of precast concrete slabs with wide and narrow joints

The precast concrete slab (PCS) is an important element for transmitting shear forces in precast concrete frames. In this paper, in-plane shear tests of a widely jointed slab (WJS), narrowly jointed slab (NJS), and cast-in-place slab (CIPS) were carried out, and the failure modes and internal force transfer mechanisms of the specimens were analysed. The results indicate that the bearing capacities of WJSs and NJSs can be calculated based on CIPSs of equal thickness and post-cast layer thickness, respectively, and the initial stiffness is 0.9 times that of the corresponding CIPSs. The failure mode of all three specimens was diagonal concrete crushing failure, and bending cracks preceded diagonal cracks in each specimen. The bending cracks in the PCSs were mainly concentrated at the joint gaps of the new and old concrete. When the specimens failed, the precast layer of the WJS was well bonded to the post-cast layer, while the precast base slab of the NJS was detached from the post-cast layer. A comparison of the calculated results of the code methods and strut-and-tie methods with the test results suggested that the design of the shear capacity of slabs can adopt the strut-and-tie method in the ACI 318-19 code.