Gust-Front Factor: New Framework for Wind Load Effects on Structures

Abstract

In comparison with atmospheric boundary layer winds, which are customarily treated as stationary, winds associated with gust fronts originating from a thunderstorm/downburst exhibit rapid changes during a short time period, which may be accompanied by changes in direction. This introduces nonstationarity both in the mean and the standard deviation of wind fluctuations. In order to realistically capture characteristics of gust-front winds and their attendant load effects, a new analysis framework is presented, which is named here as the gust-front factor approach. This is akin to the gust loading factor format used in codes and standards worldwide for the treatment of conventional boundary layer winds. The gust-front factor expresses a generalized description of the genesis of the overall wind load effects on structures under both gust-front and boundary layer winds and it reduces simply to the gust loading factor for the case of conventional boundary layer winds. This approach encapsulates both the kinematic and dynamic features of gust-front induced wind effects on structures that distinguish themselves from those experienced in conventional boundary layer flows, i.e., variation in the kinematics of the velocity profile and its effects on the associated aerodynamics, dynamic effects induced by the sudden rise in wind speed, nonstationarity of turbulence in gust-front winds, and transient aerodynamics. To facilitate expeditious utilization of this framework in design practice and inclusion in codes and standards, the analysis framework and its workflow is introduced within a web-based portal. This eliminates the need for an in-depth understanding of the background within the framework and the need for associated computational effort. The portal has a user-friendly interface, which is available at http://gff.ce.nd.edu, permitting convenient analysis of several design scenarios with a host of potential loading conditions including the current ASCE 7-05 procedure in boundary layer winds for immediate comparison.