During the September 2014 SE University session, Designing for ASCE 7-10 Wind Loads – Main Wind Force Resisting System, Don Scott, SE, from PCS Structural Solutions, asked and answered the question, “Why is Building Period Important?” Don talked about how the period affects the Gust Effect Factor, which in turn affects the building pressure.
As part of this discussion, Don also discussed the idea that a higher period is conservative for wind design, while for seismic design, a lower period is conservative. In the article Building Periods: Moving Forward (and Backward) from the June 2008 issue of STRUCTURE Magazine, Will Jacobs, PE, of Stanley D. Lindsey & Associates, Ltd. in Atlanta, GA (an SE University company), explored the difference between the period calculated for seismic and wind loads, and further explained why the period should be calculated differently for the different types of analysis.
Just as Don mentioned during the SE University session, Will specifically notes in the article that using the approximate equations from the seismic section of the code to calculate the building period and convert that to the natural frequency for the wind load can result in unconservative wind loads. Instead, engineers should be sure to use the equations from the wind load section of the code to determine natural frequency. The article includes a chart of approximate parameters for calculating the wind load period, which refers to equations in the commentary. In the updated ASCE 7-10 code, these equations are 26.9-2 through 26.9-5.
SE Solutions would like to extend a thank you to Will Jacobs, PE, SE, Principal at Stanley D. Lindsey & Associates, Ltd., and Don Scott, PE, SE, Vice President/Director of Engineering at PCS Solutions for their contributions on this topic.