Reliability of steel frames designed in accordance with the National Building Code of Canada seismic provisions and its implication in codified design

Abstract

The 2005 edition of the National Building Code of Canada (NBCC) that replaces the 1995 edition of the NBCC has been released recently. The new edition incorporated many changes to the seismic provisions. The rationale behind these changes is documented in the literature. However, a quantitative assessment of the implied reliability level of the designed structures according to the seismic provisions in the new and previous editions of the NBCC is lacking, and the target reliability levels used to calibrate the new seismic design loads, if any, is not spelled out. In this study, a reliability assessment of six steel moment resisting frames designed according to these codes is carried out. The assessment uses a ductility-based procedure and the obtained results are compared with those obtained using the procedure developed for use in the SAC project. The estimated reliabilities for the designed frames using both procedures are in good agreement. In addition, the reliability levels for frames designed in accordance with the new and previous editions of the NBCC are consistent. Use of the ductility-based procedure for calibrating seismic design loads to meet specified target reliability levels considering both incipient damage and incipient collapse are illustrated. The results suggest that, depending on the displacement ductility capacity factor, the seismic design level could be governed by the considered target reliability levels for the incipient damage or incipient collapse.