This study discusses about the seismic performance evaluation procedures of reinforced concrete buildings. Currently, the Capacity Spectrum Method (CSM), which is regulated by ATC-40 recommendations, has become one of major procedures for such evaluation worldwide. The concept of the CSM has also introduced in Japanese building seismic code since it was revised in 2000. The CSM is based on the theory of the equivalent linearization method and is fundamentally applicable to buildings which have the predominant first mode in their seismic response. Thus, using the CSM, we can generally predict seismic responses of low or middle-rise symmetric buildings with sufficient accuracy. In contrast, if a building has plan irregularity, we need furthermore consider the torsional effects when applying the CSM. As the torsional effects, we must obviously consider the following two items at least.
i) Two-directional effect of seismic ground motions
ii) Dynamic amplification effect of torsion
However any seismic design code based on the concept of the CSM does not regulate the specific procedure to consider the above items. In fact mostly the buildings have some plan irregularities or eccentricities and torsional effects due to them may cause more serious damage. Therefore this study investigates procedures to evaluate torsional effects in the CSM and examines applicability of the CSM to the reinforced concrete structures with plan irregularity.
In this study, three types of reinforced concrete walled frame models with seven stories, which are symmetric model, one-directional eccentricity model and two-directional eccentricity model, are analyzed. For input ground motions, 1995 JMA Kobe, 1940 El-Centro and 1968 Hachinohe are used. Seismic response displacements of each analytical model are predicted by the CSM considering torsional effects.
The predicted values are compared with response results calculated by nonlinear time history analyses and applicability of the CSM to the building structures with plan irregularity is discussed.