Wind Speeds in ASCE 7 Standard Peak-Gust Map: Assessment

Abstract

The ASCE 7 peak-gust map divides the United States into two main adjacent wind speed zones that do not reflect correctly the country’s differentiated extreme wind climate. Following a request by the National Institute of Standards and Technology (NIST), CPP Inc. through Texas Tech Univ. provided information used for the development of the map and for its a posteriori justification. Using this information we show that the methodology used in the map’s development averages out real climatological differences and causes severe bias errors for the following reasons: (1) the estimation of the speeds was based on superstations, of which 80% included stations that were also contained in one or more other superstations; (2) stations with significantly different physical geography and meteorology were in many cases included in the same superstation; (3) legitimate wind speed data were omitted from data records in cases in which analyses resulted in speeds different from those postulated in the map; (4) and off-the-shelf smoothing software was used that does not account for physical geography and meteorological differences. Case studies show that the map entails severe bias errors, causing unnecessary waste due to overestimated wind loads or potential losses due to underestimated wind loads.