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Performance improvement of long period building structures subjected to severe pulse-type ground motions

Anderson, James C.; Bertero, Vitelmo V.; Bertero, Raul D.

PEER-1999/09, Pacific Earthquake Engineering Research Center, University of California, Berkeley, 1999-10, 229 pages (400/P33/1999-09)

Following the 1994 Northridge, California, earthquake, concerns were expressed for the safety of highrise buildings that may be subjected to pulse-type motions. Thus, it was decided to conduct the current study of medium-to-tall buildings having long periods. In addition to considering the performance of existing buildings, both traditional strategies and innovative procedures for improving the performance of these structural systems were investigated. The results obtained for two steel buildings and two reinforced concrete buildings are reported. Three of the buildings are existing structures dating from as early as 1965. The buildings range in height from 15 to 41 stories with lateral resistance provided by moment-resistant frames. Fundamental periods of vibration range from 1.78 seconds for the 30-story reinforced concrete frame to 3.2 seconds for the 15-story reinforced concrete frame to 5.4 seconds for the 41-story steel frame. The results of inelastic dynamic analyses using four recorded pulse-type ground motions indicated that the maximum interstory drift requirement for these structures was excessive, ranging between 3.5% and 5.4%. For these reasons, it was decided to investigate strategies for improving the performance of these buildings. The conventional strategy for improving the performance is to stiffen and strengthen the system. For steel frames, this usually implies the addition of lateral bracing in the form of diagonal bracing or chevron bracing. For the reinforced concrete frames, the use of various shear wall configurations was considered for one and the application of steel joint jackets and confinement plates was considered for the other. These techniques did not prove to be very efficient for this group of longer period structures. Based on the results, it was decided that some form of energy dissipation was required. An attractive means of accomplishing this appeared to be the use of supplemental (passive) damping. For purposes of this study, a damping of 30% of critical was used. Results of using supplemental damping proved very encouraging in these initial studies. The maximum interstory drift of 5.4% was reduced to 2.1% and the corresponding plastic rotation demands were reduced to 2.1%. Similar types of reductions in force and displacement demands, although not as dramatic, were attained for all of the structures.

Available online: http://peer.berkeley.edu/publications/peer_reports/reports_1999/9909.pdf