Author(s) :

Yusuf Yau, Tasiu Ashiru Sulaiman.

Volume/Issue :

Abstract :

ABSTRACT This paper is aimed at determining the effect of wind and earthquake on the self-supporting tower and also to find the most appropriate arrangement and cost-effective bracing system of the tower on four-legged self-supporting tower models of varying heights with different types of bracing system. Tower models of height 30m, 40m, 50m with angle section (for both vertical members and bracings) with different types of bracing system (K, XB, and XX) are subjected to both wind (using basic wind speed of 35m/s and 50m/s) and seismic loads (using seismic zone IV and V). And another tower model of height 80m with K-bracing system with different cross-sections (i.e. angle sections, circular hollow sections, square hollow sections, mixed angle with circular hollow sections and mixed angle with square hollow sections) is also subjected to the same loads, in order to find the most economical and optimum section for both the leg members and the bracings. The simulation is carried out using finite element modelling software SAP2000. Joint displacements at the top of the tower, stress at bottom leg members, base reactions, natural frequency and the total weight of each tower model are assessed. From the result of wind analysis and design, it can be observed that the joint displacements were nearly increased by 65% and 59% when the tower height changes from 30m to 40m and from 40m to 50m respectively. Moreover, the stresses at bottom legs changed by 43% and 39% when the height changes from 30m to 40m and 40m to 50m respectively. For an increase in When the wind speed changed from 35m/s to 50m/s with no change in the direction of wind, the joint displacement and stresses also increased by 46% and by 48% respectively, and the results from the response spectrum analysis indicates an increment of displacement by 22% from zone III to zone V for the 30m tower model, 36% for 40m and 45% for 50m tower model. It has been concluded that the tower model with K-bracing system has the least joint displacement, least stresses at bottom leg members, least total weight and maximum natural frequency due to the wind and seismic loads as compared to XB and XX-bracing systems. While from the second part of the analysis; mixed angle members with circular bracings have the least joint displacement and average total weight and base reactions. Therefore; towers with K bracing system and angle section as legs are considered as the most appropriate, optimum and economical towers.

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