Abstract

Two recent developments have come into the forefront with reference to updating the seismic design provisions for codes: (i) publication of new seismic hazard maps for Canada by the Geological Survey of Canada, and (ii) emergence of the concept of new spectral format outdating the conventional standardized spectral format. The 4th generation seismic hazard maps are based on enriched seismic data, enhanced knowledge of regional seismicity and improved seismic hazard modeling techniques. Therefore, the new maps are more accurate and need to incorporate into the Canadian Highway Bridge Design Code (CHBDC) for its next edition similar to its building counterpart (NBCC 2005). In fact the code writers expressed such intentions with comments in the commentary of CHBCD 2006 as “New methods for defining ground motion (e.g., uniform hazard spectra) are being investigated for possible inclusion in future codes.” During the process of updating codes, NBCC 2005 and AASHTO 2009 lowered the probability level from 10% to 2% and 10% to 5%, respectively. This study has brought three sets of hazard maps (corresponding to 2%, 5% and 10% probability of exceedance in 50 years) developed by the GSC under investigation. To have a sound statistical inference, 389 Canadian cities are selected. The statistical analyses reveal that the design spectra under consideration need modification. A scheme of modification is developed to make the modified spectra work. Finally, validity of modified AASHTO spectrum is established and its adoption in the future CHBDC is recommended.