A simplified method for seismic analysis of lattice telecommunication towers

Abstract

A simplified static method for estimating the member forces in self-supporting lattice telecommunication towers due to both horizontal and vertical earthquake excitations is presented in this paper. The method is based on the modal superposition technique and the response spectrum approach, which are widely used for seismic analysis of linear structures. It is assumed that the lowest three flexural modes of vibration are sufficient to correctly estimate the tower's response to horizontal excitation, while only the lowest axial mode is sufficient to capture the response to vertical excitation. An acceleration profile along the height of the tower is defined using estimates of the lowest three flexural modes or the lowest axial mode, as appropriate, together with the spectral acceleration values corresponding to the associated natural periods. After the mass of the tower is calculated and lumped at the leg joints, a set of equivalent static lateral or vertical loads can be determined by simply multiplying the mass profile by the acceleration profile. The tower is then analyzed statically under the effect of these loads to evaluate the member forces. This procedure was developed on the basis of detailed dynamic analysis of ten existing three-legged self-supporting telecommunication towers with height range of 30-120 m. The maximum differences in member forces obtained with the proposed method and the detailed seismic analysis are of the order of ±25% in the extreme cases, with an average difference of ±7%. The results obtained for two towers with heights of 66 and 83 m are presented in this paper to demonstrate the accuracy and practicality of the proposed method.Key words: self-supporting tower, earthquake, vertical excitation, dynamic analysis.

Determining the Optimal Scalar Intensity Measure of Floor Communication Towers

“…e results revealed that the ground motion parameters (intensity measures, IM i ) suitable for the study of structural seismic performance differed with the type of structures and ground motion characteristics. For lattice towers, including transmission towers and communication towers, currently, the seismic intensity measures identified by dynamic time history analysis or amplitude modulated ground motion predominantly involve peak acceleration (PGA) [6,7], peak velocity (PGV) [8], spectral acceleration Sa(T 1 ) corresponding to the natural period of the structure [9,10] and the ratio of peak velocity to peak acceleration (V/A) [11]. In theoretical research and engineering practice, ground motion intensity is typically quantitatively characterised by ground motion parameters, in which scalar parameters predominantly include amplitude parameters, spectrum parameters, duration parameters, and energy parameters [12][13][14].…”

Quantification of the Seismic Behavior of a Steel Transmission Tower Subjected to Single and Repeated Seismic Excitations Using Vulnerability Function and Collapse Margin Ratio

“…However, earthquake effects on towers may be more severe than wind effects and seismic lateral load cannot be ignored, particularly in high-seismic zones, because seismic lateral loads can also cause significant damage to the transmission and telecommunication steel towers. Thus, design checks, even if simple ones, must be incorporated to account for seismic-event induced lateral load [8]. It is also imperative to perform a vulnerability assessment on transmission steel towers that have been subjected to earthquakes.…”

Lattice and Tubular Steel Wind Turbine Towers. Comparative Structural Investigation

“…Harikrishna et al [21] and Holmes [22][23][24], seismic loading by Khedr [25] and Khedr and McClure [26] and dynamic loading by Madugula [27]. The implementation of lattice towers as support structures for wind energy generators has only been introduced recently and the investigation of their structural response against multiple types of loading has been the work of Gencturk et al [28], Long and Moe [29], Long et al [30] and Zwick et al [31].Very limited work has been devoted in the optimization of lattice tower design, opening the field for the high-quality and original work conducted in the present paper.…”