A Critical Assessment of the Driving-Rain Wind Pressures Used in CSA Standard CAN\CSA-A440-M90 by Peter Felix Skerli Faculty of Engineering Science Subrnitted in partial fulfillment of the requirements for the degree of Master in Engineering Science Faculty of Graduate Studies The University of Western Ontario London, Ontario January 1999 O Peter Felix Skerlj 1999 National Library Bibliothèque nationale I+I of,", du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395. nie Wellington Ottawa ON KIA ON4 Ottawa ON K1A ON4 canada canada The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribue or sell reproduire, prêter, distriiuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/film. de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la thèse ni des extraits substantiek may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. Abstract Strong winds coinciding with heavy rainfall provide a formidable challenge in the design of safe and serviceable building envelope systems. Rain penetration through the outer layer of a wall cm not oniy Iead to great econornic Iosses associated with structurai repair or replacement but may aiso compromise the hedth and comfoa of the building's occupants. In Canada, use has been made of the airport weather records archived by the Atmospheric Environment Service of Environment Canada to develop ciimatologicai inputs to the design of waterproof wails. The climatoIogicaI input parameters are five- and ten-year extreme wind pressures derived from wind data reported during hours with rainfail totals equal to or greater than 1.8 mm. The Canadian Standard CANKSA-A440- Mg0 lists the drïving-rain wind pressures for 637 Canadian sites and outiines their usage in the window selection criteria. Documentation on the derivation of the driving-rain wind pressures is provided in a report written by Welsh, Skinner and Morris (1989) entitled A Clirnnrology of Driving Rain Wind Pressures for Canada- A detailed review of the anaiysis methodology and of the weather data used in the denvation of the driving-rain wind pressures was conducted and three main areas for improvement were identified. First, conventional order statistics on observed annual extreme wind pressures was performed using hourly observed one- or two-minute mean speeds, Le. non-continuous observations, giving rise to uncertainty in the representative averaging time of the extreme wind pressure estimates. Second, prior to about the rnid 19603, anemometers at Canadian airports were often Iocated on rooftops of airport buildings at heights greater than 10 m, which is the reference height implied in the building standard. No attempt was made to standardize the wind data for use in the analysis. Third, one-hour rainfail totals were estimated from six-hour precipitation (rain. freezing rain, snow, etc.) measurements and hourly present weather observations as opposed to using the actuai measured one-hour rainfalls from automatic rain gauges when ..- 111 availabIe and the estimates ody as necessary. Weather data fkom fourteen Canadian airport sites were examined to address the above uncertainties and to quanti@ the associated errors. For this, a technique was developed to predict extrerne one-hour mean wind pressures From hourly observed short- duration mean wind speeds using a database comprising continuous one-minute average wind speeds. The method was applied to re-evaiuate the driving-rain wind pressures at the fourteen airport sites considering at the sarne time the non-stationary aspects of the wind records and the available one-hour rainfall measurements. Using the ten-year driving-rain wind pressure as the reference, the resuits of the analysis show that, for the fourteen stations examined, the design pressures currentiy used in the standard are on average 55 3 higher than the one-hour mean pressures denved in this study and range from 20 to 97 % higher. It is recommended that the Canadian driving-rain wind pressures be re-evaluated on a national scale, taking advantage of techniques descnbed in this work and of more than ten years of additionai weather data now available. Keywords: wind-driven rain, cirivingrain wind pressures, driving-rain index, extreme wind speeds, extreme wind pressures, CAMCSA-A440-Mg0 Acknowledgements I would like to thank several people for helping me during my joumey to cornpleting this research paper. To Dr. Dave Surry, for your support, insight. advice and ~bovedl your patience and unders tanding- To Atmospheric Environment Service, for supplying the data which was key to my research, and especially to Mr. Stapf for your help with the high frequency database and to Mr. Morris and Mr. Welsh for your help with the interpretation of Canada's national weather archives. To Anna, for your constant s~pportand for being a sounding board without even really understanding what my thesis was about. To my colleagues, in particular Rob, Darryl and Jim Bob Ray for providing me with the necessary distractions to reenergize myself and keep my sanity. To my parents, for your financial support. for keeping my freezer stocked hl1 of home cooked rneals, for your unending encouragement. and for keeping the empty picture frame dusted in the hopes that one day it would be filled with my Masters degree. Table of Contents Certificate of Examination Abstract Table of Contents List of Figures List of Tables Nomenclature Chapter 1.0 Introduction 1.1 Bac kground 1.2 Scope of Research Chapter 2.0 Published Research 2.1 Introduction 2.2 Driving-Rain 2.3 Extreme Wind Speeds During Rainfali Chapter 3.0 Description of the Meteorological Data 3.1 Introduction 3 -2 One-Minute Database 3.2.1 Brevoort Island Station 3-22 St. John's Station 3.2.3 Downsview Station 3 -3 One-Hour Database 3.3.1 Wind Data 3.3.2 Rainfall Data Chapter 1.0 On the Uses of Hourly Observed Short-Duration Mean Wind 95 SP~ 4.1 Introduction 95 4.2 Time Series of Mean Wind Speed 97 4.3 Dependence of Spot Wind Speeds on One-Hour Means 100 4.4 Parent Distribution 107 4.5 Extreme Value Distribution 115 4.5.1 Epochd Extremes 116 4-52 Extrernes fiorn the Parent Population 128 4.6 Concluding Rernarks 134 Chapter 5.0 Evaluation of Canadian Driving-Rain Wind Pressures 5.1 Introduction 5.2 Andyses of Canadian DRWPs 5.2.1 Base Analysis - Welsh, Skinner and Moms ( 1989) 5-32 Analysis 1 - Use of Fitered Wind Records 5.2.3 Analysis 2 - Use of Modified Spot Wind Data 5-24 Analysis 3 - Use of Rainfall Measurements 5.2.5 Analysis 4 - Use of Lieblein's BLUE 5.3 Cornparisons of Canadian DRWPs 5.4 Concluding Remarks Chapter 6.0 Conclusions and Recommendations 185 References 188 Appendix A Relationship Between Wind Speed, Rainfall Intensity 193 and Driving-Rainfall Intensity Appendix B Parent Wind Speeds During Rainfail 197 Appendix C Extreme Wind Speeds During Rainfdi 213 Vita List of Figures Orientation of reference area for rainfd intensity and driving-raiddl intensity Annual mean driving-rain index (m2!s) for the British Isles, from Lacy (1971) Annual mean driving-rain index (m2/s) for Canada, from Boyd (1963) Twelve-point compass roses showing annual mean simultaneous drivuig- rain index (m2/s) for 22 locations in the Bntish Mes, from Lacy (197 1) Sixteen-point compass roses for Toronto International Airport showing a) relative frequency (%) of wind during rainfdl b) sixteen-year simultaneous driving-rain index (% of total) c) relative frequency (%) of wind during all hours, from Robinson and Baker (1975) Annual mean simultaneous driving-rain index and three-year return period simultaneous drïving-rain spell index (logarithrnic units, scale indicated on figure) for 12 wind directions, from Pnor (1985) Illustration of the correspondence between precipitation and wind speed data used by Murakami et al. ( 1987) in the case of a) wind speeds recorded every one hour and b) wind speeds recorded every three hours Annual extrerne wind speeds (ds)during rainfall for Tokyo based on a) the Type4 extreme value distribution and b) Equation 2.5, after Murakami et ai. ( 1987) Reference 10 m ten-year return period Driving Rain Wind Pressures (Pa), from Welsh et al. (1989) AnnuaI extreme wind speeds (ds)during rainfall for Mascot based on the Type-LU extreme value distribution, afier Choi (1992) Annual extreme wind speeds (m/s) during rainfail for Singapore based on the Tme-1 extreme value distribution with V '.after Choi ( 1994) 3.1 Station locations of the One-minute Canadian Data Base 3.2 Photograph of the POSS Doppler radar, after Sheppard (1990) 3.3 Photograph of Brevoort Island Station 3.4 One-hour mean wind speeds at Brevoon Island Station for the month of September, 1994 3.5 One-hour mean wind speeds at Brevoort Island Station for the seven-hour period beginning on Aupst 27, 1994 3.6 One-hour mean wind speeds at Brevoort Island Station for the seven-hour period beginning on October 15, 1994 3.7 Distribution of absent wind data by month at Brevoort Island Station 3.8 Photograph of St. John's Station 3.9 One-hour mean wind speeds at St. John's Station for the month of November, 1994 3.10 One-hour mean data at St.