08-10-2014, 04:06 PM
Current seismic code specifications for design of buildings use a design base shear spectrum based on single-degree-of-freedom (SDOF) systems and specify the lateral force profile using an assumed fundamental mode shape. The present study proposes an improvement to the above method, which is known as the Equivalent Lateral Force (ELF) Method, by incorporating the effects of deformation type and higher modes. The study idealizes buildings as uniform vertical cantilevers which; being continuum systems, have infinite number of deformation modes of which the significant modes are included in the analysis. A shear factor ÃŜò is used to characterize the relative contributions of flexural and shear deformations, ÃŜò = 0 implying pure flexural behaviour andÃŜò = âÃâ à Ÿ , pure shear. Closed form solutions of the governing differential equation of cantilevers subjected to ground motion are obtained and time history analyses are performed. The base shear response spectra and lateral force distributions obtained from the study are compared with code provisions.