Seismic sensitivity of tall guyed telecommunication towers

In the wireless, microwave, and satellite communications industry, guyed towers are one of the important structural subsystems. They support a variety of antenna broadcasting systems at great heights, or are themselves radiators in order to transmit radio, television, and telephone signals over long distances. Very tall towers are a fundamental component of post-disaster communication systems. Therefore, their protection during a severe earthquake is of high priority, and accordingly the seismic performance of such structures should be properly evaluated.;To the best of the author's knowledge, there have been no simple rules to account for seismic sensitivity of guyed towers, and very limited attention has been paid to the seismic behaviour of such structures to date. Since guyed towers may exhibit significant geometric nonlinearities, their detailed nonlinear seismic analysis is complex and time-consuming. In addition, climatic loads such as wind and ice are likely to govern the design in most cases. As a result, earthquake effects are often ignored or improperly evaluated (based on current procedures) by an equivalent static lateral load proportional to the tower weight, as it is done in most building codes. These effects, however, may yield to a loss of serviceability due to excessive antenna displacements resulting in an unacceptable signal attenuation, and in extreme cases, to permanent deformations. Therefore it is necessary to develop more complete guidelines for seismic design of tall guyed towers.;The main objective of this research is to propose some seismic sensitivity indicators which may be used by tower designers to assess whether a particular tower is sensitive to earthquake effects, and if so, whether a detailed nonlinear modelling study is necessary. A detailed nonlinear numerical modelling study of eight existing tall guyed telecommunication towers (heights varying from 150 to 607 m) has been carried out. Each tower was subjected to three different classical seismic excitations (El Centro, Parkfield and Taft earthquakes) for the seismicity level of the Victoria region, which has one of the highest seismicity levels in Canada. The conclusions drawn from this study are employed to propose some simplified models and develop some guidelines to relate the overall seismic sensitivity of tall guyed towers to their essential structural properties. The simplified models proposed are used to predict the maximum tower base shear, the distribution of horizontal earthquake forces along the tower height, and the distribution of the maximum dynamic component of most axial forces along the tower height due to combined vertical and horizontal earthquake motions. The guidelines developed are used to estimate the maximum dynamic component of the mast axial force at the base due to combined vertical and horizontal earthquake motions, the seismic amplification factor of cable tension, and the maximum shear and bending moment in the mast.