09-10-2014, 03:27 PM
Seismic over strength of multi-storey reinforced concrete frames has been assessed by means of non7-linear pseudo-static analysis on 4-bay, 3-, 6-, and 9- storey frames designed for seismic zones I to V as per Indian codes. In pseudostatic analysis, the lateral forces have been applied in such a way that the first mode of vibration is excited. It is seen that the over strength varies with seismic zone, number of storeys, and with design gravity load. The dependence on seismic zone is the strongest. The average over strength of frames in zones V and I is 2.84 and 12.7, respectively. The over strength increases as the number of storeys decreases; over strength of the three-storey frame is higher than the nine- storey frame by 36 % in zone V and 49 % in zone I. Further, interior frames have 17 (zone V) to 47 (zone I) percent higher over strength as compared to the exterior frames of the same building. These observations have significance for formulation of seismic design codes which, at present, do not take into account the variation in over strength.