EVALUATION OF THE STABILITY AND DYNAMIC CHARACTERISTICS OF FREE-STANDING COMMUNICATION MASTS SUBJECTED TO SELF AND ENVIRONMENTAL LOADINGS
In a quest to improve the resilience of free-standing steel towers to wind-induced failures, static and dynamic characteristics of the widely used 30 m, 3-leg-telecommucation lattice mast of varying bracing types under turbulent wind action were evaluated. The mast structures were modelled using the Staad. Pro stiffness-matric based software employing the 3-D beam elements for both the mast legs and bracings. Wind actions as the primary live load on the structure alongside self-weight of the structure and a surcharge load to simulate the commutation gadgets on them were considered for the analyses. Basic wind speed of 35 m/s and turbulence effects for critical ground condition were employed to generate the vertical gradient of the wind action. The patch loading approach for open mast structure was employed. Thereafter the static as well as modal dynamic analyses were carried out. Findings from the study show that the mast base width of 1/13th of the 30 m height is stable for all bracing types considered in the study. The Z bracings masts are identified as the most cost effective in construction/erection compared to the other bracing types with cost savings of about 14%. 42.9% and 7.97% when compared to the K, diagonal and the X bracings respectively. Further findings show that the K bracing masts is more resilient to the loadings employed with maximum displacement up to 23% lower than all other bracing types considered. Maximum combined stresses are also lower in the K bracings compared with the other bracing types considered in a similar proportion. Results from the modal dynamic analyses however show that the K bracings masts are more susceptible dynamic response with the least natural frequency of 0.755Hz and the Z bracing more stable dynamically with a fundamental frequency of 0.89 Hz. It is recommended that the K bracings may be employed for 3-leg telecommunication mast up to 30 m high but with additional features to enhance its dynamic response. The findings in this paper are useful for planning and design of telecommunication masts and other similar structural systems.
Authors : Aboshio, A and Uche, O.A.
Category : Open Access Volume (Issue) : 10(2) Date Uploaded : 21st July 2024