This research is concerned with the pertinent column-to-beam strength ratio of 3D multi-storied steel moment frames. Analyses were carried out by using bidirectional ground motions transformed into the direction of strong and weak axes. The maximum value of the maximum story drift angle of the frames, which is subjected to bidirectional ground motions in arbitrary directions, is represented by the angle, which is subjected to one directional ground motion along the direction where the strength of the frame is the maximum. Based on the reasons reported above and the result of a previous study on 2D frames, the pertinent column-to-beam strength ratio of 3D steel frames can be expressed by a function of the input energy level.
