Determination of optimal behavior of self-centering multiple-rocking walls subjected to far-field and near-field ground motions

Abstract

In recent years, innovative seismic resistant systems have been introduced based on the Damage Avoidance Design (DAD) philosophy rather than the conventional plastic design-based methods to reduce damages to buildings and to decrease post-earthquake repair costs. Self-centering multiple-rocking walls are amongst these innovative systems. This study aims to determine the optimum number of rocking sections in self-centering concrete multiple rocking walls. To this aim, the seismic behavior of self-centering (SC) concrete rocking walls of 8, 12, 16, and 20 stories with different numbers of rocking sections were examined. Several non-linear time-history analyses were carried out via OpenSEES software in a two-¬dimensional framework. Three sets of ground motions were considered including 22 Far-Field (FF), 14 Near-Field-Pulse (NFP), and 14 Near-Field-no Pulse (NFnP). Five types of quad-rocking walls and one type of dual-rocking walls were specified and compared with base-rocking walls and fixed-base walls. To perform this comparison, a set of utility coefficients was defined to integrate different response aspects including shear and moment demands as well as the residual drifts. The results showed that the effects of higher modes (shear and moment demand) increase with the increase in the height of the rocking structures. Furthermore, NFnP and FF records produced higher mode effects in rocking systems as compared to NFP records. The results suggested that the quad-rocking walls with the reduced tendon area in the first block (R4-S1) are highly effective in reducing the effects of higher modes in NFP and NFnP records. They showed maximum utility coefficients of 67% and 65%, respectively. Also, quad-rocking walls with the reduced tendon area in the third block (R4-S3) were more effective under FF records and their maximum utility coefficient was 65%. The residual roof drift of rocking walls was so negligible that its maximum value in the 8-story structure under NFP records was 0.0008.