الفهرس 
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Abstract
Reinforced concrete (RC) frames with unreinforced masonry (URM) infill walls are commonly used as the structural system for buildings in many seismically active regions around the world. Structural engineers recognize that many buildings of this type have performed poorly during earthquakes. On the other hand, URM infill walls are generally treated as non-structural elements because they are used mainly for architectural purposes, and structural engineers often ignore their effect during structural design. But the continuity of these walls is not always assured, due to the need to have an open floor for parking, which may cause a soft story effect at the building.
Seismic design codes are majorly based on strength philosophy, where structures are designed as per force-based design approach (FBD), while taking the nonlinearity by using a response modification factor (R). It is clear that the main concept of this philosophy is strength rather than displacement capacity.
The research aims to change this philosophy by applying Performance-based seismic design (PBSD) which went virally throughout the past years and by introducing recently defined performance factor (P) as an alternative to response modification factor (R) overcoming any limitations restricted by the usage of (R) factor, and by studying the performance objective under seismic events.
In this research, the effect of infill walls’ presence and distribution on the performance of the soft-story R.C frames will be studied by generating finite element models for 2D frames with different number of floors, infill percentage and different preliminary design levels. Diagonal strut approach was chosen for modeling the infills in the analytical models as an example of macro-modeling method.
The analytical analysis by finite element programs was verified by available results from previous experimental study. First, the results of the pushover curves were compared with those of the thesis. After that, 2D fully infilled frames generated by a previous study were used to perform the parametric study by removing the infills from the base stories. The parametric study was carried out to investigate the effect of soft storey on different parameters which reflects the seismic behavior of the frames including the change in P-Factor, inter storey drift and performance levels of the frames.
The results obtained from the parametric study showed that the soft storey models shows poorer behavior considering the P-factor and performance levels, and higher drift values, and that the percentage of P-factor reduction due to removal of infill from stories relies on the initial level of performance the bare frame was designed upon where the highest reduction was in the code complaint design (CCD) models, then the life safety (LS) models and collapse prevention (CP) models respectively, which is coping with previous studies conclusion that the frames designed based on the guidelines set by codes drift limits can absorb much higher percentage of seismic energy than the infills as compared to other less performing frames, thus leaving infills less susceptible to early damage during an earthquake.