Analysis and Design Of Microwave Antenna Lattice Towers

Abstract

Due to the expansion of telecommunications and broadcasting systems, a large number of lattice towers are used to support the microwave antennas. The tower supports the radio, television and telephone antenna to transmit telecommunication signals over the long distances. Therefore damage to them can significantly increases losses due to natural disasters. The main feature in designing the tower is its height; it is usually several times larger than the corresponding horizontal dimension. The primary objective of work is to understand the effect of wind on microwave towers and to carry out wind analysis of these structures. Lattice tower due to its height is mainly predominant towards the wind, therefore static analysis and dynamic analysis due to the randomly varying wind action is essential as the natural frequency of tower becomes very low due to the wind action. The comparison of wind analysis and seismic analysis is done to evaluate the critical effect out of the two for designing of the tower. The analysis for the lattice tower is based on IS 875 (part-III), 1987. Static analysis is carried out manually, with help of staad-pro software and forces on tower as a whole is calculated. Parametric study is carried out to find the economical aspect of the tower. The main parameters considered for the study are the base width and vertical profile of the tower. The main objective of parametric study is to see the effects of parameters considered on the weight and deflection of the tower because microwave towers in particular are required to obey very stringent serviceability criteria, usually specified in the terms of tilt and twist limits. The tower behaves essentially as a cantilever structure fixed at the base. The deflection goes on reducing as the height of the tapering portion increases. At the same time there is reduction in deflection as the base width increases because the stiffness of structure is increased due to its slanting legs which slant more with increase in base width making tower more sensitive for vertical deflections compared to horizontal deflections.