TY - JOUR ID - 2987 TI - Evaluation of the Vertical Distribution of Base Shear Force in Base-Isolated Structures JO - Scientia Iranica JA - SCI LA - en SN - 1026-3098 AU - Rofooei, F.R. AD - Department of Civil Engineering,Sharif University of Technology Y1 - 2007 PY - 2007 VL - 14 IS - 1 SP - EP - DO - N2 - Application of the base-isolation systems, as a means to limit the seismic-induced response of structures, has attracted the attention of many engineers and researchers. Due to their importance, the Uniform Building Code (UBC) has incorporated a special section for the seismic analysis and design of base-isolated structures since its 1991 edition. The present work investigates the vertical distribution of the lateral seismic force for base-isolated structures provided by the 1997 edition of UBC (UBC97). Di erent 6 and 8-story, 3-D base-isolated structural models with LRB isolators are considered, having a variety of e ective periods and e ective damping ratios. The UBC97 analysis procedure for the base-isolated structures is used to determine the minimum lateral seismic force and its vertical distribution for di erent oors. Since the number of stories above the isolation interface is more than four for the considered isolated structural models, the response spectrum analysis is used, considering the equivalent linear properties for isolation systems. Also, the UBC97 recommended that the 5%-damped design spectra be properly modi ed to account for the actual modal damping ratios of an isolated structure. Extensive nonlinear dynamic analyses were performed for 8 types of LRB isolators, using appropriately normalized earthquake accelerograms recorded on SA and SB soil pro les. Both the superstructure and the isolators are allowed to behave nonlinearly, in order to evaluate the seismic induced demand shear force on di erent oors. The peak base center and corner displacements, maximum base and story shear forces and the maximum inter-story drifts are determined for di erent base-isolation systems and earthquake records. The results, together with their mean and mean plus one standard deviation values, are used for the evaluation of UBC97 response spectrum analysis procedures for these buildings. The results indicate that the UBC97 suitably predicts the seismic lateral forces for base-isolated buildings. However, it does not provide a good estimate of the shear force distribution over the height, especially for the highly damped base-isolation systems. Furthermore, the number of columns per story that behaved nonlinearly during the time history analyses is included for comparison. UR - https://scientiairanica.sharif.edu/article_2987.html L1 - https://scientiairanica.sharif.edu/article_2987_9f5d1a14ee78cc8181a72cd9e68edd59.pdf ER -