Gust loading factor—past, present and future

Abstract

Wind loads on structures under the buffeting action of wind gusts have traditionally been treated by the “gust loading factor” (GLF) method in most major codes and standards around the world. In this scheme, the equivalent-static wind loading used for design is equal to the mean wind force multiplied by the GLF. Although the traditional GLF method ensures an accurate estimation of the displacement response, it may fall short in providing a reliable estimate of other response components. To overcome this shortcoming, a more consistent procedure for determining design loads on tall structures is proposed. This paper highlights an alternative model, in which the GLF is based on the base bending moment rather than the displacement. The expected extreme base moment is computed by multiplying the mean base moment by the proposed GLF. The base moment is then distributed to each floor in terms of the floor load in a format that is very similar to the one used to distribute the base shear in earthquake engineering practice. In addition, a simple relationship between the proposed base moment GLF and the traditional GLF is derived, which makes it convenient to employ the proposed approach while utilizing the existing background information. Numerical examples are presented to demonstrate the efficacy of the proposed procedure in light of the traditional approach. This paper also extends the new framework for the formulation of wind load effects in the acrosswind and torsional directions along the “GLF” format that has generally been used for the alongwind response. A 3D GLF concept is advanced, which draws upon a database of aerodynamic wind loads on typical tall buildings, a mode shape correction procedure and a more realistic formulation of the equivalent-static wind loads and their effects. A numerical example is presented to demonstrate the efficacy of the proposed procedure in light of the traditional approach. It is envisaged that the proposed formulation will be most appropriate for inclusion in codes and standards.