SIMPLIFIED ANALYSES OF MULTI-STOREYED FRAMES UNDER LATERAL LOADS

Abstract

The Draft Indian Standard (BDC-38(984) )l) for design of multistoreyed buildings suggests simplified methods of analyses under static lateral loads. The suggested clau-ses 10.2.5 and 3.2.1 (A-3) pertaining to storey reduction and simplified ,lateral displacement computation' respectively are examined here. It is found that the method of reduction in number of storeys is too erroneous to be adopted for design purposes. The simplified method for lateral displace-ment gives very, high values at two to three bottom storeys while it gives nearly correct values at all other storeys. In dynanic analysis of large elastic systems, eigenvalue solution becomes expensive. From this point reduction of mass and stiffness matrices is desirable. The [2] C31 reduction method developed by Guyan and later Irons is applied to multistoreyed frames in this work. The masses are lumped at floors, neglecting rotatory inertia. It is found that the use of reduction (eigenvalue eco.nomisation) gives very good fundamental frequency . The fundamental frequency is also found to increase with the decrease in the number of 'master' deflections..