Evaluating the effect of masonry infills on natural period of buildings with moment‐resisting frame

Building design codes generally provide empirical formulas for estimating the fundamental period. These formulas are developed on the basis of observed periods of real buildings during ground motion, and the period is generally expressed as a function of building height, type (frame or shear wall), etc. In this study, the fundamental period of vibration of a series of regular steel-framed buildings is studied using finite element modelling and modal eigenvalue analysis including the effect of infill. It has been found that when the models do not include infill, the period given by the analysis is significantly longer than that predicted by the codes equation. However, when the effect of infill is included in the models, the time periods determined from eigenvalue analysis were remarkably close to those predicted by the code formulas. The finding of the study has shown us a practical way to determine the fundamental period of steel frames using rational approaches like modal analysis. After an evaluation of the results, a modified formula has been proposed for estimation of natural period of steel buildings with moment-resisting frame system having infill. Using the proposed formula, we can estimate natural period of this kind of structural systems more accurately than the one approximated by code formula. Copyright © 2009 John Wiley & Sons, Ltd.