Eliminating the Exposure Category from Wind Design Pressure

Current practice in determining wind loads on a structure is based on the recommendations in the American Society of Civil Engineers Standard 7 (American Society of Civil Engineers (ASCE) 2010), Minimum Design Loads for Buildings and Other Structures. An exposure category is typically selected to represent the surface roughness surrounding a site, this from four discrete exposure categories that approximate all surface roughness conditions. The quantification of these exposure categories are primarily based on research work that was completed in the early 1960s. This paper includes a review of surface roughness and why it is important to wind design, and a review of how findings from current research utilizing geographic information systems (GIS) mapping can address exposure from multiple directions. As an alternative approach to the traditional exposure categories, GIS mapping data that contains surface roughness information for the United States can be used to calculate surface roughness surrounding a site. The data is available from the United States Geological Survey (USGS) and from many local governments. The paper presents a GIS-based approach to determining surface roughness using data directly, without the intermediate step of estimating exposure from the traditional categories.