A Gust Factor Model for Storm Winds

Abstract

This paper describes the development of a gust factor model for use in the design of offshore, onshore and coastal structures. The gust factor is an important parameter for design with the gust speed being routinely used to evaluate the maximum wind pressure acting on structures. This is of special interest when dealing with extreme wind risk assessment at locations where only scarce measurements are available. In the oil and gas industry, the ISO 19901-1 (2005) code is the standard approach to estimate the gust factor for offshore structural design. The methodology is based on the analysis of extensive marine data from the Island of Fro̸ya on the Norwegian coast by Andersen and Lo̸vseth (1993). However, this approach exhibit significant limitations at coastal and onshore locations. Therefore, in this study, another methodology is proposed. This is based on the latest developments of the Engineering Sciences Data Unit gust factor model (ESDU, 2003; Vickery and Skerlj, 2005). This model has been further validated by making use of additional storm wind records at various offshore, onshore and coastal locations. The relationship is function of latitude, height and surface roughness. The latter is prescribed for onshore locations and calculated offshore as a function of the mean wind speed. The model compares well with the observed gust factors and outperforms, especially over land, the ISO code currently used in the oil and gas industry.