Since all natural forces act dynamically into the structures, structural analysis and optimizations under such loads seem difficult due to various variables, non-linear time dependent constrains and objective functions. The static loads are an appropriate substitution for the dynamic or earthquake loads because of their facilities in practical applications. Due to such facilities, most of the constructional codes are intended to use equivalent static loads (ESLs) rather than dynamic loads. They use dynamic factors and structural optimization seems to succeed for static loads with those factors (Haftka and Gurdal, 1991). However, the dynamic factors are not legitimately made based on sound mathematics. They are determined by specifications or experiences. Many researches have been carried out about the different methods figuring such loads out. Based on previous researches, two different ways had been proposed to achieve ESLs. Exact ESLs and approximated ESLs.
