Abstract

In current practice of the selection of earthquake records for the time-history analysis of structures, the parameters considered are earthquake magnitude, distance from the earthquake source to the site where the record is obtained, soil condition at the site, and type of earthquake. The strong-motion duration of the record is not considered in this process. A number of studies have been conducted on the investigation of the effects of strong-motion duration on the structural response; however the conclusions from these studies are contradictory. Some studies report significant effects while others report minimal or no effects. The objective of this study was to investigate the effects of strong-motion duration of earthquake records on the seismic response of reinforced concrete frame buildings.
For the purpose of the study, three reinforced concrete frame buildings (4-, 10-, and 16-storey) designed according to the 2005 edition of the National Building Code of Canada were considered in the analyses. The buildings were located in Vancouver, which is in a high seismic zone in Canada. Nonlinear time-history analyses were conducted on three building models using two sets of accelerograms as seismic excitations. One set consists of simulated accelerograms representative of the ground motions in Vancouver, and the other set consists of real accelerograms recorded from earthquakes in California. The ground motions were scaled to three excitation levels, i.e., 0.5Sa(T1), 1.0Sa(T1), and 2.0Sa(T1) in which Sa(T1) was the spectral acceleration at the dominant period of the building. The four definitions of strong-motion duration considered in the study were uniform duration, bracketed duration, significant duration, and effective duration. The structural responses were represented by interstorey drift, beam curvature ductility, column curvature ductility, roof displacement and base shear.
Based on the results from the study, it was found that the effects of the strong-motion duration on the structural response depended on the dynamic characteristics of the building and the seismic excitation level. They did not depend on the response parameter considered and the type of the record used in the analysis. Moreover, regression functions between the structural response and the strong-motion duration could not be developed with respect to the response parameters and the definitions of the strong-motion duration considered in this study.