Nonlinear long-term behavior of high-strength concrete wall panels

Abstract

This thesis investigates the time-dependent behaviour of slender reinforced high-strength concrete (HSC) panels, with particular emphasis on the combined effects of creep and shrinkage on the buckling capacity and its degradation with time.

The short-term response of one-way HSC panels is studied first, in order to set the basis for the long-term analysis. A theoretical model is developed, which accounts for the geometric and material nonlinearities including the strain softening and cracking of concrete, tension-stiffening and reinforcement yielding. An experimental study is carried out, including testing to failure of eight one-way full-scale panels under in-plane loads with different load eccentricities, slenderness, and reinforcement ratios. The failure of all panels was a sudden buckling failure. A close correlation between the theoretical model and the experimental results is obtained.

The time-dependent response of one-way HSC panels is then investigated. A nonlinear theoretical model is developed based on a time-stepping analysis to account for the variation of the internal stresses and deformations with time. A rheological generalized Maxwell chain model is used to account for creep of the concrete as well as its shrinkage, cracking, tension-stiffening and aging through strain- and time-dependent springs and dashpots. The incremental governing equations are solved numerically at each time step. An experimental program is conducted, which consists of testing five one-way HSC panels under sustained in-plane loads with various eccentricities and load levels. Two panels failed by creep buckling and the rest exhibited long-term stable behaviour, which were then loaded to failure. Good agreement is achieved between the test and theoretical results.

Finally, the long-term behaviour of two-way HSC panels is examined by developing an incremental nonlinear model that uses the Von Karman plate theory with large displacement kinematics. The rheological generalized Maxwell chain model is used to model the creep of concrete, including the shrinkage and cracking. The numerical and parametric study reveals that the time-dependent behaviour can be significantly weakened by cracking of concrete.

Based on the results presented here, it can be concluded that creep and shrinkage can significantly influence the load-carrying capacity of HSC panels. The theoretical models developed here provide effective tools to predict their time-dependent response.