Basis for recommending an update of wind velocity pressures in Canadian design codes

Reference wind velocity pressures corresponding to specified return period wind speeds are provided in several Canadian design codes. A review of the two most recent editions of the National Building Code of Canada (NBCC) indicates that significant changes in some 50-year return period wind speeds, v_AH-50, were introduced in the 2010 version of the NBCC-2010 compared to the previous NBCC-2005. The changes are due to analysis approaches, available wind records, and a re-examination of anemometer histories. To potentially improve the estimates of v_AH-50, wind records in the Environment Canada HLY01 digital archive were processed. Two hundred and thirty-five meteorological stations are considered in the analysis, and height and exposure corrected annual maximum hourly-mean wind speed, V_AH, are extracted. Statistical analysis and distribution fitting were carried out using the Gumbel distribution and generalized extreme value distribution and several fitting methods were employed. The results indicate that it is preferable to treat V_AH as a Gumbel variate, and to carry out the fit using the generalized least-squares method. Wind speed contour maps for Canada are developed based on the estimated v_AH-T for T equal to 50, 500, and 1000 years. A comparison of the maps of v_AH-50 to those inferred from NBCC-2005 and NBCC-2010 shows that the developed map retains some of the smoothness of the wind speeds exhibited in NBCC-2010, while maintains the localized wind speed features presented in NBCC-2005. Results also show that the wind speed corresponding to the factored design wind load in NBCC-2010 is associated with a return period ranging from 200 to 5000 years, but for 90% of stations considered, the range narrows to 300 to 900 years.