INFLUENCE OF LONGITUDINAL REINFORCEMENT ON THE PUNCHING SHEAR RESISTANCE OF REINFORCED CONCRETE SLABS

Abstract

This work presents the results of experimental tests on reinforced concrete slabs with different longitudinal reinforcement ratio ρ under concentrated load. Five series of specimen were made and tested, a total of ten slabs. The measurements of the specimens were 2135×2135×140 mm (Fig. 3). Longitudinal reinforcement ratio ρ = 0,449–1,90 %, the diameter of reinforcing bars was 8–16 mm, reinforcement bore yield stresses, spacing between bars was 100 mm. The protective concrete layer of the longitudinal reinforcement in all slabs was 20 mm. The cubic compressive strength of concrete fc,cube = 33,4–46,6 MPa. In the course of the experiment the measurements of the collapsing punching force, the radial and tangential deformations of the compression zone were made, the curves of their expansion were given, displacements of the column head were measured. The surface of the punching cone, irrespective of the longitudinal reinforcement ratio ρ, makes a ˜35° angle with the bottom (compression zone) surface of the slab. Deformations of radial and tangential directions in the compression zone during the course of cracking of the slab do not reach the ultimate compressive strains of concrete (3,50 ‰), the mean value of deformations in the radial direction is 1,6 ‰, the mean value of deformations in the tangential direction is 1,8 ‰, which allows to make a conclusion that the slab is punched-through under transverse collapsing force. The strength criterion of biaxial stress state proposed by Zalesov et al. (1973) and the expression of the resultant transverse force of the dowel action of the longitudinal reinforcement ratio ρ as proposed by Theodorakopoulos et al. (2002), were used to get the expression of the collapsing transverse force Vu which is given in equation (2). The factor of the influence of longitudinal reinforcement ratio ρ expressed through the resultant transverse force Vd of the dowel action makes 40–50 % of the collapsing force, Vd increases with increasing of the longitudinal reinforcement ratio ρ. The resultant transverse force Vc of the compression zone of concrete in the critical section makes 50–60 % of the collapsing force, Vc increases with increasing of the longitudinal reinforcement ratio ρ.