Publication Date : 01/08/2009

Author(s) :

Gambo, A.H, Ogork, E.N, Aboshio, A.

Volume/Issue :
Volume 4
Issue 2
(08 - 2009)

Abstract :

The Stability of masts used for telecommunication purposes in Nigeria are often threatened by loads imposed on them by the weather; primarily Wind loads. This periodic load interacts with these slender structures thereby exciting a dynamic response from these structures.Failures of a number of these masts in Nigeria were recorded in the recent past. Field inspection of some of these failed masts has identified observable deformations due to vibrations and deflection of mast members leading to a progressive mode of failure as the main problem. Thus, this study assesses the dynamic stability of existing mast in Nigeria, considering the four (4) leg and three (3) leg free standing mast of heights 20m, 30m, and 40m and tip dimensions varied at 1/30th, 1/40th and 1/50th of the effective height of mast for Diagonal bracing, Zee bracing, Kee bracing and Diagonal bracing with no horizontal beam.Parametric study of the dynamic analysis results identifies the K-bracing as the most effective bracing arrangement for the tubular secton – 20mm diameter with the highest natural frequency of 0.748 Hz, 0.532Hz and 0.347Hz for 20m, 30m, and 40m effective height of mast respectively and having the least tip deflections of 106.37mm, 245mm and 471.69mm for 20m, 30m and 40m effective height of mast respectively. For the geometric stability of these masts, it was also established that given the base dimension of masts kept at 1/13th of the effectively height of masts (Chandra 1977) the tip dimensions should range between 1/35th to 1/45th of the height of mast.

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