Effects of Structural Irregularities on Low and Mid-Rise RC Building Response

Abstract

Albanian building stock is composed of reinforced concrete and masonry buildings. Most of these buildings are designed according to earlier versions of Albanian Seismic Codes (KTP Codes) and some of them were constructed without a definite construction project. Considering these facts and the observations done in Albanian construction industry, presence of structural irregularities is very common in these buildings. Irregularities are weak points in the building which may cause failure of one element or total collapse of the building during an earthquake. Irregularities encountered in Albanian construction practice consist of short column, large and heavy overhangs and soft story. Since Albania is country with moderate seismicity which has been hit many times from earthquakes of different magnitudes establishes the need to study the effect of irregularities. All these irregularities are taken in consideration in this study under lateral loads on low and mid-rise buildings of Albanian construction practice. In order to get the effect of structural irregularities on RC buildings response several numbers of Nonlinear Static (Pushover) analyses are done. The considered frames consist of regular frames, frames with soft story because v of higher height and lack of masonry infill walls in ground story or because of the presence of both cases, presence of short column because of semi-infilled bays, overhangs because of presence of balconies, presence of soft story and heavy-overhangs. These irregularities are considered for two types of structures, 3 and 6- story frames representing low and mid-rise buildings respectively. The analyses has been performed by using ETABS and Seismosoft software. Effect of structural irregularities and performance of the considered frames are achieved by using capacity curves of the frames and performance point by considering two different response spectrums, from EC 8 and KTP codes. The results of the analyses indicate that low and mid-rise structures with soft story- two sided overhangs and short column are more vulnerable during earthquakes. Frames with soft story and two sided overhangs showed 266% and 300% lower strength, 120% and 92% lower stiffness than 3 and 6 story reference frames respectively; frames with short column showed 100% and 92% lower stiffness and 140% and 122% lower strength than 3 and 6 story reference frames respectively.