General tendencies and classification of vertical structures under gust buffeting

The 3-D gust effect factor (GEF) technique is an efficient method to determine the maximum displacements and internal forces of vertical structures subjected to alongwind, crosswind and torsional gust-excited vibrations. All these effects and the related equivalent static forces may be evaluated through one non-dimensional quantity referred to as the 3-D GEF, whose expression was found in closed form. This property makes very attractive the use of functional analysis to establish general tendencies and classification strategies. Confirming some previous results limited to alongwind vibrations, this paper shows that such tendencies are mainly related to the shape of the fundamental modes of vibration. Structures are thus classified into homogeneous categories and general rules are provided to assess a priori the distribution of internal forces. Errors inherent the determination of internal forces by the classical gust response factor technique are also discussed. Among several aspects of engineering interest, those concerning wind actions on the foundation and the stress state for wind-induced fatigue deserve particular attention.