The method for estimating the ultimate strength of outer columns in multi-story frame under earth-quakes is not established yet. It yields an underestimate of the buckling strength of outer column to take the column length for buckling length as is applied expediently, because outer column buckling under earthquakes is considered to be a phenomenon which takes place under the controlled horizontal displacement. The authors investigate experimentally and analytically the relation between horizontal displacement and buckling strength of outer columns in multi-story frame, and, using these results, propose a design formula for outer columns subjected to the over-turning moment under earthquakes.
