In our previous researches, it is shown that story drift concentration is restrained by columns in two braced frames with buckling-restrained braces. For the two story braced frames with buckled braces, it is possible for the column to distribute the shear force on each story over height and the story drift concentration may be restrained, if it keeps elastic. In this paper, the equations of the drift concentration factor for two story braced frames with buckled braces have been developed from the equilibrium conditions of the frames subjected to lateral force. This paper clarifies the mechanism of the two story braced frames and the relationship between the drift concentration factor and the ratio of column flexural stiffness. Finally, the drift concentration with seismic response analysis is estimated with the equation for static drift concentration.
