Comparison of Directional and Envelope Wind Load Provisions of ASCE 7

Abstract

ASCE 7-10 allows the design of the main wind force resisting system (MWFRS) of buildings with a mean roof height of less than 18.3 m (60 ft) by using either the directional procedure of Chapter 27 or the envelope procedure of Chapter 28 (sometimes referred to as the all heights and low-rise procedures, respectively). These two procedures were developed based on research that used very different methodologies to develop enveloped wind loads. As a result, the two methods may predict very different wind loads and subsequent structural behavior. This paper presents motivation for the research and a comparison of the structural demands calculated by using the two procedures; identifies some situations for which the low-rise procedures may give unconservative MWFRS member loads, proposes changes to the provisions, and identifies avenues for future research.