Out-of-plane instability of rectangular reinforced concrete walls under in-plane loading.
Thesis DisciplineCivil Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Structural wall system has been one of the most common lateral load resisting elements in reinforced concrete structures. A relatively high stiffness is provided by a structural wall along its in-plane direction making it the main lateral force resisting system of the structure. Observations of wall damage in some modern buildings in several earthquakes that took place in the 2010s proved the fact that some of the wall failure modes, interacting with each other and occurring successively in some occasions, are not yet well understood. The research presented here seeks to address the out-of-plane instability of rectangular walls which was observed in some well-confined modern walls and raised concerns about the reliability of current design code provisions.
A numerical modeling approach is developed in this research which is the first numerical model successful in capturing the trigger and evolution of out-of-plane deformation and ultimate failure due to out-of-plane instability under perfectly concentric and cyclic in-plane loading and without introducing any artificial imperfections. Experimental results of cantilever wall specimens which failed in different failure modes including out-of-plane instability are used for verification of the adopted modeling and analysis approach. The mechanism of out-of-plane instability failure in rectangular structural walls under in-plane loading has been studied by scrutinizing the sequence of events resulting in this mode of failure and using the validated numerical model. The parameters controlling this mode of failure are identified to be the wall thickness as well as the parameters that influence the maximum tensile strain developed in the longitudinal reinforcement.
Although out-of-plane instability failure was observed in several wall experiments, its evolution and the controlling parameters have not been fully investigated. An experimental campaign has undertaken as a part of this research to investigate the effects of different parameters on out-of-plane deformation of rectangular walls. The experimental program was designed based on a parametric study using the verified numerical model. Data analysis, presented here, has been done to provide an improved understanding of the mechanism of out-of-plane instability and the parameters influencing this mode of failure. The experimental findings regarding the evolution of this mode of failure and the influential parameters are in good agreement with the numerical predictions. The inherent and mostly unmeasurable eccentricities, which could be comprised of the material, geometry, and loading imperfections and were not included in the model, are found to affect the initiation and rate of increase in out-of-plane displacement. Also, the experimental findings have been used to evaluate the assumptions made in the available analytical models used for prediction of wall instability failure.