Study of Structurally Irregular Building Frames Subjected to Seismic Excitations

Abstract

Past earthquakes in India have revealed that majority of the buildings are not designed to be earthquake resistant. Generally, buildings are designed taking into account only the gravity loads. Also, the current design seismic codes are not fully practiced while designing a building. Hence, a higher degree of damage may be expected during an earthquake if the seismic resistance of the building is inadequate. The present work describes the various reinforced concrete (RC) frames having different irregularities but with same dimensions which have been analysed to study their behaviour when subjected to seismic lateral loads. All the frames were analysed with the same method as stated in IS 1893-Part-1:2002. From the results, it has been interpreted that the base frame (regular) develops least story drifts while the building with floating columns shows maximum storey drifts on the soft story levels. Hence, this is most vulnerable to damages under this kind of loading. The other buildings with irregularities also showed unsatisfactory results to some extent. The frame with heavy loads develops maximum storey shears, which should be accounted for in design of columns suitably. The analysis proves that irregularities are harmful for the structures and it is important to have simpler and regular shapes of frames as well as uniform load distribution around the building. Therefore, as far as possible irregularities in a building must be avoided. But, if irregularities have to be introduced for any reason, they must be designed properly following the conditions of IS 13920:1993. The complex shaped buildings are now days getting popular, but they carry a risk of sustaining damages during earthquakes. Therefore, such buildings should be designed properly taking care of their dynamic behaviour