Abstract
Deficiencies of the four spectral formats i.e., 2%/50-yr, 5%/50-yr, 10%/50-yr and AASHTO (American Association of State Highway Officials) 2009 demand modification of the spectral formats for bridge design application in Canada. Among them the 10%/50-yr spectrum is dropped from current investigation as its difference with Canadian Highway Bridge Design Code (CHBDC) 2006 is too large to modify. This study introduces an approach calibrating on the values of elastic seismic response coefficient to provide a new shape of the Canadian bridge design spectrum based on modified 2%/50-yr, modified 5%/50-yr and modified AASHTO spectral formats. A Digital Visual Fortran program was prepared to determine the optimum values of the modification factors incorporated into the three spectral formats calibrated on the data of 389 cities of Canada. Thus, here it is developed the strategies of modifying the three spectral formats based on the best probability level for CHBDC using site-specific Uniform Hazard Spectrum (UHS). Finally, select the most suitable spectral format to apply for the design base shear calculations for the bridges of Canada.
Highlights
The standardized spectrum, which is constructed using an idealized shape anchoring on a single control point and has long been used in codes demonstrates several shortfalls
Since the format of 2%/50-yr and 5%/50-yr spectra is developed for adoption in National Building Code of Canada (NBCC) (2005), the question of applicability of this format for bridge design can be raised
There is no ambiguity of building-bridge compatibility issue for using modified American Association of State Highway Officials (AASHTO) spectrum into Canadian Highway Bridge Design Code (CHBDC) since the spectrum is specialized for bridge application
Summary
The standardized spectrum, which is constructed using an idealized shape anchoring on a single control point and has long been used in codes demonstrates several shortfalls. Besides the effort of other researchers, an approach of determining the elastic seismic response coefficient, Csm using various design spectra of (i) NBCC (2005) format using 4th generation seismic hazard maps of 2% in 50-yr, 5% in 50-yr, 10% in 50-yr as defined in CHBDC (2006), (ii) AASHTO (2009) format, and (iii) CHBDC (2006) format has been evaluated in the most recent study It compared the Csm values with those of CHBDC (2006), tracked the magnification and reduction of Csm for a set of periods and investigated the best probability level for CHBDC using site-specific UHS. C. 10%/50-yr – a spectrum that is drawn using spectral coefficients Sa(0.2), Sa(0.5), Sa(1.0) and Sa(2.0) of 4th generation seismic hazard maps with 10% probability of exceedance in 50-year according to Section 4.1.8.4 of NBCC (2005). The most suitable spectral format from those modified spectra is recommended for CHBDC edition
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