This paper deals with the distribution of lateral seismic forces along the height of a building. Four seismic force parameters, namely, seismic coefficient, seismic shear coefficient, seismic force and seismic shear, were defined as functions of normalized weight. After reviewing some existing distributions in seismic codes, three elastic continuous bodies - the uniform shear type, shear type with inverted triangular first mode shape, and uniform flexural type - were studied by modal analysis using a simplified response spectrum. Five-mass model structures of shear, shear-flexural and flexural types with six different mass-stiffness distributions were analyzed by the same method. The distributions obtained by the analyses were compared to the existing distributions in seismic codes. As a result of the analysis a new expression for the distribution of seismic force parameters is proposed. The proposed distribution was compared with a time history analysis of the same series of model structures subjected to recorded earthquake ground motions.

^*1 Head, Building Engineering Division, International Institute of Seismology and Earthquake Engineering, Building Research Institute, Ministry of Construction.