Because of the facilities of static analyses, designers generally applying them in their designs instead of time history ones. Distribution of lateral loads usually is based on fundamental vibration mode in the seismic design codes. Generally, in many design codes, transformation of time-dependent loadings into equivalent static forces has been conducted by force reduction factor and first vibration mode. Here, the new method based on energy of multi degree freedom (MDF) systems, and effect of higher vibration modes has been developed. By solving a simple optimization problem using genetic algorithm technique, transformation of seismic demands into the static lateral forces is available. The first step for evaluation of the proposed method is implementing it for linear dynamic analysis of structures. The results show that the obtained seismic demands could be utilized for designing proposes. However, the authors believe that the strength of the proposed method will clearly appear in nonlinear behavior of structures.
