Under strong earthquake vibrations, Reinforced Concrete (R. C. C.) structures have often behaved unsatisfactorily in recent earthquakes in USA, Japan, Taiwan, Turkey, India and many other countries. Results of two-dimensional linear dynamic analyses of R. C. C. structures have shown that the ‘equivalent’ static forces predicted by the existing building codes are often much smaller than the dynamic forces. Two-dimensional nonlinear dynamic analyses have shown that the static forces may not be adequate for a safe design against severe earthquakes. Therefore, this work is conducted with a view towards extending the studies to nonlinear three-dimensional analysis. The linear three-dimensional analysis of R. C. C. frames performed in this study is a step in that direction.

Recorded ground motion data from the Kobe earthquake (Japan, 1995) and the Northridge earthquake (USA, 1994) are used to conduct structural dynamic analyses.

Three-dimensional linear dynamic analyses are conducted on 2, 5 and 10 storied buildings with ‘adequate’ structural dimensions from static point of view. The results indicate that the maximum shear forces in the ‘critical’ beams and columns of these buildings predicted by the 2-dimensional and 3-dimensional analyses are often quite different and may be significant from design point of view. Also the shear forces predicted by the static analyses are found to be much smaller than the earthquake-induced forces in all the cases studied here.