The influence of the design methodology in the response of transmission towers to wind loading

Abstract

From a theoretical approach, the design procedure for the establishment of wind loading on transmission towers was reviewed and current procedures, such as Davenport's gust response factor (GRF), were compared with the statistical method using influence lines (SIL), which is considered more realistic. This latter approach can account for unbalanced loading effects, shear and axial loads and the effects of higher modes of vibration in the calculation of the response factors. Several responses due to certain assumed transverse wind characteristics were calculated for some typical transmission towers. The main findings were: (a) Peak loads calculated using SIL were larger than peak loads given by the GRF. (b) The dynamic response of transmission structures is strongly dependent on the turbulence intensity level and its spectrum. (c) For members in which there is reversal in the forces on the load position, the resonant response in the second mode of vibration was bigger, even by four to five times, than the corresponding one in the first mode. Although this effect is not as severe in terms of resulting stresses when all the components are computed in the peak responses, it can lead to fatigue problems. From the current results it can be concluded that the incorporation of the dynamic properties of transmission structures in the design methodologies is needed and that the statistical method using influence lines is a more correct approach since it allows for the inclusion of a larger number of factors in the design methodology.