Earthquake Amplification Factors for Self-supporting 4-legged Telecommunication Towers

Telecommunication towers are among the few steel structures that little attention has been paid to their seismic behavior in existing design codes. Due to lack of design provisions, the designers apply the existing building design codes to telecommunication towers. However, the seismic behavior and response of telecommunication towers is very different from that of building structures. For example, the base shear values obtained for telecommunication towers using the building codes is much higher than what it actually is. In this research, for obtaining the seismic amplification factors, ten of the existing self-supporting four-legged telecommunication towers in Iran with heights ranging from 18 to 67 meters are selected. Then, strong motion earthquakes are applied to these towers in both vertical and horizontal directions. By performing linear dynamic analysis, the base shear and vertical response of the towers are calculated. Dividing the obtained base shear or the vertical response by the product of the tower mass and maximum horizontal and/or vertical acceleration components will result in seismic amplification factors of both horizontal and vertical earthquake components. At the end, by drawing the amplification factors versus the fundamental flexural mode and the first axial mode of the towers, relations for estimating the base shear and the vertical response of the telecommunication towers are obtained.