Braces in steel structures are one of the most important element for earthquake proofing. This paper deal with, therefore, one procedure to estimate effective cross section area statistically with multiple regression analysis. Some explanatory variables are decided in this estimation by full scale static experiment of steel braces. Furthermore, scatter in these cross section areas to nominal cross section area, and scatter in yield ratio of steel materials are investigated in order to introduce some conditions for ultimate resistance design in which influences of dynamic effects are considered for earthquake proof design.
