Two Key Factors in Determining Wind Load

Are our buildings being designed for enough wind load?

Colorado’s climate is undoubtedly an average of extremes with high winds, epic blizzards, sweltering summer heat, pounding rain, and hailstorms alike.

High winds in particular, however, account for a substantial portion of property damage claims that we at Pie investigate.

Wind loads are calculated using two factors: basic wind speed and the category of a structure’s particular exposure to the elements (exposure category).  This criterian is based upon the recommendations in The American Society of Civil Engineers Standard 7 (ASCE 7).  Basic wind speed data is calculated by evaluating the statistical analysis of the region’s climate, and is associated with an annual probability of the occurrence of “0.02”; a wind event that occurs once every 50 years.  The Front Range of Colorado sits in a “special wind region” and the predetermined wind loads for building design can vary from 90 miles per hour (mph) to 180 mph based upon the reading of a 3-second gust.

Pie recently investigated and made repair recommendations for a four-story structure located on the southeast side of Denver (see photos below). The roof of the building had been ripped off during a wind storm in the summer of 2011. Note the location of the structure in relation to the adjacent open space, which is an important component in design protocols for wind load.

wind damage imagewind damage image

Although the original construction documents were not available, it would be interesting to see what wind load and Exposure category this building was designed for.

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About Nicole Ellison:

Nicole Ellison, P.E., LEED®AP, Pie Structural Engineer, serves as one of only two female engineers in the Forensic Department.  Ellison specializes in structural engineering design, evaluation, and repair. Her technical expertise includes: building investigation, building renovation, construction renovation, construction administration, historical structural assessment, auto impact evaluation, and fire damage evaluation and repair. Nicole is a HAAG Certified Roof Inspector and a LEED Accredited Professional.

Did you know? Longs Peak holds the record high wind speed at 201 mph set in the winter of 1981.

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