Experimental Evaluation of the Behavior of Composite Prestressed Joist Floors

Composite prestressed joist floors are one of the economical roof systems, which are increasingly used in Iran. In this research, the composite behavior of prestressed joists in composite joist floors has been experimentally evaluated. What can prevent the composite behavior of the prestressed joist and the in-situ concrete slab is the lack of proper transfer of horizontal shear at the contact surface of the prestressed joist and the in-situ concrete. In prestressed joist floors, unlike truss joist floors, it is difficult to install horizontal shear reinforcement between precast and in-situ concrete. This research was carried out in two stages and in each stage the final load as well as the cracking load and moment were evaluated. In the first stage, two prestressed joist samples were tested and the quality of the joists was ensured by matching the laboratory results and the calculated values. In the next stage, samples of composite joist slabs without horizontal shear reinforcement and with the proposed shear reinforcements were made and tested in the laboratory. Based on the results, the slab samples without shear reinforcement were able to resist the fast laboratory loading up to the calculated load based on the bending strength, but they almost immediately suffered brittle failure due to horizontal shear slip, which makes their use under long-term loading in the structure problematic. The proposed reinforcements were able to improve the composite behavior of the joist and in-situ concrete by improving the horizontal shear strength and improve the bearing capacity of the slab up to 27 percent.