FINE FINITE ELEMENT ANALYSIS OF SLAB-COLUMN JOINTS AFTER PUNCHING SHEAR

The fine finite element models of slab-column joints were established according to the reinforcement detailing in real structures, in which the concrete and reinforcement were simulated by solid and beam elements, respectively. The element deactivation technique was adopted to simulate concrete cracking during the process of punching and the rupture of reinforcing bars after punching shear. The simulation method was validated via the comparison between the numerical and experimental results of three typical punching shear tests. The validation showed that the displacement and capacity of the punching and post-punching stages were accurately simulated by the developed method. Based on the numerical model, the analyses were further conducted to explore the mechanical behavior of the joints with in-plane constraints during a whole punching shear process. The results indicated that the contributions of integrity reinforcement and flexural reinforcement were 42% and 58%, respectively, to the post-punching resistances of the tested joints with in-plane constraints. The increase of reinforcement ratio leaded to the improvement of the stiffness of the joints at both punching and post-punching stages. On the other hand, increasing the slab thickness only significantly enhanced the capacity and stiffness of the joints before punching shear. That the redundant strength was at least 36% of the designed punching shear strength was found for the joints with in-plane constraints when using the calculation methods in European, American, Australian and Chinese codes. The predicted post-punching capacity calculated by the existing methods, in which the contribution of the flexural reinforcement was underestimated, was also lower than the tested capacity.