Prediction of seismic drifts in multi-storey frames with a new storey capacity factor

Standard procedures exist for the estimation of the total (or roof) displacement of a structure for seismic design, based on the response spectra of single-degree-of-freedom systems. However, for a more realistic prediction of the seismic demands, especially in the context of the performance based design, an appropriate estimation of the storey drift distribution is necessary. A few general approaches are available in the literature, and these often require certain structural modeling analysis. The present paper aims to provide a simple alternative method for the prediction of the storey drift distribution and the critical drift concentration in a RC frame. A new storey capacity factor is introduced, to represent the combined effect of the storey strength and stiffness on the distribution of storey drift along the frame height, while the storey strength and stiffness are evaluated, taking into account different possible plastic mechanisms. The structural regularity is subsequently evaluated based on the storey capacity factor. Nonlinear pushover and dynamic response history analyses are performed on several representative multi-storey frames, to verify the correlation between the storey capacity factor profile and the distribution of the actual storey drifts. Results indicate that the inverse of the storey capacity factor correlates well with the storey drift distributions. An empirical relationship between the critical drift concentration factor and the overall regularity index is derived based on the dynamic analysis results.