Effect of multi-layer leaning column on damage concentration mitigation of multi-story steel moment resisting frames with mid-story pin column base system

Steel moment-resisting frames with mid-story pin column base system previously proposed to prevent the first story column yielding is seismically upgraded by a multi-layer leaning column. Effect on the prevention of story drift and stress concentration provided by an M. L. column is quantified with respect to its flexural stiffness by theoretical formulation, static and dynamic analysis of 3 to 9-stories frames. It is shown that seismic responses of the main frame are suitably predicted by theoretical formulation with Ai distribution, while external force distribution considering the second-order mode is proposed to predict flexural demand on the M. L. column.