Evaluation of the behavior factor of vertically irregular moment resisting reinforced concrete frames considering the influence of masonry infill walls

Although infill panels are considered as non-structural elements in analysis and design process of building frames, these members may significantly affect the seismic performance of the frames. Nowadays, tendency to design and construct the irregular buildings has increased. Behavior factor plays an important role in the seismic design of buildings. Seismic codes usually present the same Behavior factor for the regular and irregular lateral load-carrying systems. In this investigation, the influence of masonry infill walls on the behavior factor of the vertically irregular moment resisting reinforced concrete frames was evaluated. To do so, 3-, 6-, 9- and 12-story moment resisting reinforced concrete frames with various types of vertical irregularities were considered. These frames were assessed with/without considering the influence of infill walls. The capacity curves of the frames were derived using incremental dynamic analysis using 14 acceleration ground motions and then the behaviour factors were achieved. Outcomes demonstrated that infilled frames present higher response modification factors and more efficiently performance in lateral load-carrying rather than bare frames. Furthermore, it was shown that vertical irregularity affects the seismic responses and the behavior factor of moment resisting reinforced concrete frames. Eventually, two approximate relations were developed to acquire the response modification factors of bare- and infilled- vertically irregular moment resisting reinforced concrete frames.