Estimating Periods of Vibration of Tall Buildings

A hand method of estimating the period of free vibration of building structures, for use in determining the minimum base shear for their earthquake design, is presented. The method is for structures that have uniform properties through their height, and that are symmetrical in plan and symmetrically loaded so that they do not twist. The structures may consist of rigid frames, coupled walls, wallframes and braced frames, or any combination of these. The basis of the method is that all of the above described types of bent behave as members of a family of shearflexure structures whose static deflections can be predicted by coupled wall theory. A method of decoupling the static deflection into a flexural component and a shear plus flexure wallframe type of component is extended to dynamic behavior of a corresponding decoupled eigenvalue approach, to determine the periods of free vibration. The derivation of the method, an assessment of its accuracy, and a worked example to illustrate its application are presented.