A critical assessment of the DRWPs used in CAN/CSA-A440-M90

A review of the derivation of the driving-rain wind pressures (DRWPs) currently used in Canadian Standard CAN/CSA-A440-M90 shows three main areas for improvement. First, order statistics on observed annual extremes was performed on non-continuous wind data giving rise to uncertainty in the representative averaging time of the extreme wind pressure estimates. Second, prior to about the mid 1960’s, anemometers at Canadian airports were often located on rooftops at heights greater than 10m. No attempt was made to standardize the wind data for use in the analysis. Third, one-hour rainfall totals were estimated as opposed to using measured one-hour rainfall totals when available and the estimates only as necessary. Weather data from fourteen Canadian airport sites are examined to address the above uncertainties and to quantify the associated errors. It is found that the ten-year DRWPs currently used in the standard are 55% higher on average those derived in this study.