Wind Load Statistics for Probability-Based Structural Design

ASCE Standard 7, “Minimum Design Loads for Buildings and Other Structures,” has contained provisions for load combinations and load factors suitable for load and resistance factor design since its 1982 edition. Research in wind engineering in the intervening years has raised questions regarding the wind load factor 1.3 and load combinations in which the wind load appears in ASCE 7-95. This paper presents revised statistical models of wind load parameters based on more recent research and a Delphi, and reassesses the wind load combinations in ASCE Standard 7 probabilistically. The current approach to specifying wind loads in ASCE 7 does not lead to uniform reliability in inland and hurricane-prone regions of the country. It is recommended that the factor accounting for wind directionality effects should be separated from the load factor and presented in a separate table in the wind load section, that the wind load factor should be increased from 1.3 to approximately 1.5 or 1.6 to achieve reliability consistent with designs governed by gravity load combinations, and that the exposure classification procedure in ASCE Standard 7 should be revised to reduce the current high error rate in assigning exposures.