An Alternative Approach For Assessing Eccentricities In Asymmetric Multistory Buildings 1. Elastic Systems

摘要

A simple hand method for assessing modal eccentricities of multistory structures with partial symmetry is presented. The concept of the modal center of rigidity is introduced and the determination of eccentricities of the first two modal shears is obtained by means of an equivalent one-story eccentric system. The method is based on Southwell's formula for calculating a lower bound of the fundamental frequency and is applicable to uniform structures composed of different types of bents, such as walls, rigid frames, coupled walls and wall-frame assemblies. These structures do not belong to the special class of proportionate buildings for which dynamic properties can be accurately obtained by analyzing two simpler systems: a multistory torsionally uncoupled counterpart of the actual structure and an associated one-story coupled system. The accuracy of the proposed method is illustrated in a parametric study that includes common types of mixed-bent-type multistory structures and comparisons are made with the results obtained by three-dimensional dynamic analyses on discrete member models.