الفهرس 
CHAPTER 1Only 14 pages are availabe for public view
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Abstract
Reinforced concrete frames with unreinforced masonry infill walls are a common form of construction all around the world. Often, engineers do not take into consideration the masonry infill walls during the design process for the reason that the final distribution of these elements may be unknown to them, or because masonry walls are considered as non-structural elements. In fact walls and frames act reciprocally during earthquakes or any lateral loads and this leads to a structural response that is completely different than the response expected from the usual design process. The presence of masonry infills can result in higher stiffness and strength and it is cheap and built with low cost labor.
Under lateral loads, Masonry walls act as diagonal struts subjected to compression, while reinforced concrete confining members (Frames) act in tension and/or compression, depending on the direction of lateral earthquake forces.
In this study, the contribution of the masonry infill walls to the lateral behavior of reinforced concrete buildings was investigated with the aim to develop a realistic matrix for the response modification factors for medium-rise skeletal buildings with masonry infills. For this purpose, five, seven and ten stories buildings are modelled as bare and infilled frames. The numerical study was built using the non-linear 3D FE program “SeismoStruct” used to analyze different types of buildings. The masonry infill wall was modeled as a four-node masonry panel element. The panel element is composed of diagonal vertical struts that are each allocated to carry either axial or shear forces.
The parameters investigated were infill ratio, panel aspect ratio, unidirectional and bidirectional eccentricities. These models were analyzed under static pushover analysis with an incremental load. The study presented an investigation on the strength capacity increase in the structure due to the contribution of masonry infills, also a comparison between the behavior of infilled frames buildings, with different number of stories, to their corresponding bare frame buildings; furthermore, a comparison between the behavior of infilled frames buildings with different walls configurations in a symmetric and asymmetric plan.
Analyses showed that the lateral strength and stiffness of the buildings with masonry infill walls increased significantly due to the contribution of the infill walls, these results were illustrated by relational charts.
Furthermore, response modification factors were studied and an inverse proportionality relationship between the percentage of infills and the ductility factor as well as the building global drift was concluded and it was also found that the symmetry in walls distribution throughout the story increase the ductility and the global drift of the buildings.
By presenting different values of the ductility factor corresponding to the performance of buildings with different infill ratio, this thesis has proved that using fixed values for this factor across all the similar types of structures was shown to be unreasonable, and may yield overly conservative designs for the ductile building structures.
The study also includes a set of equations and relational charts presenting the ductility factor and the percentage of max. global drift as a function of infill ratio and eccentricity.
The study concludes that the response modification factors presented in national and international codes needs revisiting because the margin of overestimation of the seismic forces is considered large given the inherent strength and ductility of the system. This shall lead to more efficient and economic designs if the response modification factors are related to infill percentages and distributions.