The influences of the number of stories and spans of a bracing frame on the effective length factor of a long column in atrium are examined by analysis using the buckling slope deflection method, and the calculated effective lengths are compared with that of obtained from simplified method. We call the simplified method as “Extended Sakamoto-Mitani method”. It is shown that 1) the number of stories affect significantly on the effective length factor, however, that of spans is small. 2) The effective length factors obtained from “Extended Sakamoto-Mitani method” agree with the correct values about within 5% error.
