The validity of conventional seismic analysis by the ‘Equivalent Static Force Method’ (ESFM) has been studied by comparing the results with dynamic analyses of two dimensional reinforced concrete buildings for the recorded data of two major earthquakes of the past; i.e., the El Centro earthquake in USA (1940) and the Kobe earthquake in Japan (1995).

The studies done for 1, 2, 5 and 10-storied Reinforced Concrete buildings indicate significant underestimation of seismic forces (i.e., shear forces and bending moments) by the conventional method in all the cases studied. For example, the maximum shear forces in the first floor beams obtained by the Equivalent Static Force Method and the structural dynamic analyses (for El Centro and Kobe data) are as follows

The results obtained by the time domain linear dynamic analysis are explained by corresponding frequency domain analyses, which are based on the concepts of dynamic magnification factor and resonance.

In the studies performed here, the model 2-storied building proves most vulnerable in El Centro earthquake while the model 5-storied building is at maximum risk in Kobe, both due to resonance of the structure with the recorded data. Thus the effect of resonance is highlighted and the common belief that taller structures always provide more critical seismic design criteria is refuted. The results from these studies demonstrate the importance of dynamic seismic analysis.