New Extended Finite Element Method for Pinching Effect in Reinforced Concrete Columns: Fid-Bau Portal

New Extended Finite Element Method for Pinching Effect in Reinforced Concrete Columns

Yu, Jiangtao

Under seismic loads, the stiffness and strength of reinforced concrete (RC) structure may deteriorate, and the dissipation of energy will be through a degrading hysteretic behavior. Pinching effect is widely observed in the hysteretic behavior of RC structures. According to experimental studies, the pinching effect is associated with crack closure, shear lock, slippage of longitudinal reinforcement, and so on. To reveal the mechanism of pinching effect in flexure-dominant RC columns under seismic loads, a novel modeling method is developed with the following considerations: 1) using extended finite element method (XFEM) to model crack initiating and propagating in concrete; 2) using traction-separation law to consider concrete's post-cracking behavior; 3) using contact algorithm to simulate the crack closing; and 4) interaction between concrete and steel reinforcing bar to model multi-cracking in concrete. By modeling crack initiating, propagating and closing, the hysteretic constitutive relationship of concrete is automatically formed in simulation, instead of being not artificially defined. The special multi-cracking pattern in flexuredominant RC structural members is exhibited by modeling the strain variation of steel and concrete in adjacent cracks. The proposed approach is validated by comparing the numerical results with the experimental results in macroscopic scale, such as the load-displacement (or moment-curvature) loops and the skeleton curves. Moreover, the numerical simulation reveals the causes of pinching effect in mesoscale by comprehensively analyzing the respective contribution of concrete, reinforcing bar, and their interaction. This study provides a new numerical approach to simulate the hysteretic flexural behavior of RC structures under earthquake.