ASSESSMENT OF THE SEISMIC PERFORMANCE OF REINFORCED MASONRY AND REINFORCED CONCRETE SHEAR WALL BUILDINGS

Abstract

The concepts of seismic design have been in continuous development in the course of the past century. This startedby the realization that forces induced by seismic actions should be directly proportional to the structure mass;until including the effects of structure period on the seismic induced forces. Throughout this spectrum of studies and findings the buildings were supposed to be totally elastic under seismic loading, later, they were found to have an inherent property, ductility, which allows a structure to deform past its elastic limit without significant loss of strength. Currently, the method by which this ductility is accounted for in design codes is a reduction factor for the seismic forces calculated based on an elastic analysis of the structure.

To date, the assigned factor is based on experimental results obtained from testing individual elements (component level) under cyclic loading. A building is usually composed of different elements each having different ductility capacity and consequently a different design force reduction factor. There is a scarcity of research regarding evaluating the behavior of full structure (system level) related to the component level.

This study was performed to have further insight on the behavior of midrise buildings having Reinforced Concrete Masonry (RCM) and Reinforced Concrete (RC) walls as their main gravity and lateral load resisting system. The main objective was to investigate the behavior of the system level under eccentric lateral loading and try to relate it to the component behavior. A total of 120 analytical models for structures subjected to quasi-static cyclic lateral loading to achieve this objective. The models were chosen to test the effect of different parameters on the behavior of the structure, namely, lateral load eccentricity, wall arrangement and presence of walls orthogonal to the loading direction. The software used in this study is OpenSees and Response-2000.

The research was carried out over three phases. The first was a review of previous literature related to the focus of the study. This was carried out in order to have a clear and broad understanding of the previous findings in this field.

During the second phase, a modeling technique for RCM/RC walls and buildings was developed and verified against the experimental results of 11 individual walls and full structure available in literature. Some factors and recommendations regarding the modeling of RCM/RC walls under lateral loading using OpenSees were extracted from this phase. It was found that the devised technique could be incorporated for a full structure loaded under eccentric lateral loading. Some limitations were faced when using flanged and coupled walls in the full building model.

The results of the verification phase served as a basis for the last phase of the research during which a parametric study was generated in order to investigate the behavior of the system level. The parameters tested were the lateral load eccentricity and torsional effects, the wall configuration and the presence of walls placed orthogonal to the loading direction. The system behavior was defined in terms of maximum lateral strength, drift capacity and displacement ductility. Throughout this phase it was found that the eccentricity of lateral load had a degrading effect on the strength of the structure, yet the ductility of the structure increased. The arrangement of walls within the structure had a significant effect on both strength and ductility; it was also found that the presence of orthogonal walls had a beneficial effect regarding both strength and ductility of the structure.