Reza Rahgozar - Associate Professor, Department of Civil Engineering, university of Kerman, Kerman, Iran
Leila Najarzadeh - Graduate Student of Civil Engineering, Department of Civil Engineering,

In this paper a simple mathematical method based on the continuous approach, is proposed to determine the natural frequencies of braced tube systems in tall buildings. Braces are modeled as transverse springs in specific locations along height of structure that is idealized as a cantilever beam representing the structural characteristics. Initially energy method and Hamilton principle have been used to obtain the differential equations of the equivalent beam, then by applying the separation of variables on time and space and using boundary conditions, the natural frequencies of vibration have been calculated. The utility and accuracy of the proposed method is shown by a numerical example, in which this method is compared with the results of SAP2000 analysis. The proposed method is found to be simple and efficient, and provides reasonably accurate results in the preliminary analysis of tall building structures.

tall buildings, braced tube, free vibration, Hamilton principle, energy method