This paper presents the effect of column-to-beam strength ratio on the maximum story drift angles of steel frames subjected to bi-directional ground motions. Analyses were carried out using bi-directional ground motions as directions of a strong axis and a weak axis. Followings were deduced; Maximum value of story drift angles given out of calculated results in arbitrary directions can be almost approximated by maximum story drift angles obtained responses when ground motion of strong axis is applied in the direction of parallel to the structural plane or in the direction of a half of right angle to it in cases where column-to-beam strength ratio is over√2.
