ABSTRACT

This work developed a numerical model for determining the dynamic response of a concert high-rise flexible frames (tall frame) subjected to wind load in Nigeria. The model was based on the finite element idealization for flexible frames, static condensation and lumped mass parameters. A MATLAB program was developed for the model and two investigations were carried out. Firstly, an investigation was carried out to determine the level of significance of the dynamic response for design purposes in Nigeria. To this end, the developed MATLAB program was used to determine the dynamic and static responses of four structures, of various heights (29.2m to 72.4m) and floors (8 to 20) respectively. An assumed wind velocity of 15m/s was considered for safety reasons since the actual maximum wind velocity in Nigeria is less than 10m/s. The responses considered included floor translations, axial force, bending moment and shear force. The percentage difference between static and dynamic response as well as their level of significance were determined. Based on the results it was inferred that dynamic analysis of tall building below 72.4m in height and width not exceeding 13m, could be ignored in Nigeria provided that the static analysis is done properly, with appropriate code provisions. Secondly, the effect of increase in width and height on the fundamental natural frequency of tall frames was also investigated, requiring the addition of three frames, namely Frame 5, Frame 6, Frame 7 all of which have the same height of 29.2m but vary in width from 13m to 28m. Analysis results showed that the fundamental natural frequency increases with increase in width at constant height and decrease with increase in height at constant width.