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A Parametric Study of the New Diaphragm Design Force Methods

October 6, 2022 from 1:30pm to 2:30pm Mountain Standard Time

John W Lawson

Since its introduction into U.S. building codes and standards, a single generally-accepted method has existed for determining seismic design forces on roof diaphragms. Recently, an alternate procedure was introduced in ASCE 7-16, and then an additional alternate procedure was introduced in ASCE 7-22 for single-story tilt-up and masonry buildings. Suddenly the determination of these diaphragm forces has become much more complex. The two newer methods are based on better research; however, it is of general interest to the engineer and their client to evaluate which method might be most cost efficient to select. This presentation provides a brief background of these three diaphragm design force methods and evaluates them side-by-side for a typical large single story tilt-up building. It is revealed that the choice of the most cost-efficient method is not necessarily straight-forward, and is instead dependent upon the building size, shape, response modification factor R, and the building site's seismicity. Armed with this knowledge, the design engineer can evaluate the balance of cost efficiency and modeling appropriateness when selecting a diaphragm seismic design force method on a particular project.

LEARNING OBJECTIVES

  • Awareness of the new diaphragm design force methods
  • Recognizing the limitations of the three diaphragm methods
  • Evaluating which diaphragm method is most cost effective
  • Evaluating which diaphragm method is most appropriate

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