Inverse Eigenmode Modeling and Multiscale Seismic Analysis of Irregular Frame Structure by Shear Spring–Multifloor Mass System

A modeling method of an elastic shear spring–multifloor mass system (MF system) based on the fundamental eigenmode and natural circular frequency of a full‐scale structural frame is presented. MF system has plural lumped masses as representative of single floor, and the lumped masses are connected by interfloor shear springs. MF system focuses on both global and local responses of the original frame, namely, the total displacement, the non‐uniform displacements of an identical floor and the member force distributions. Therefore, the alternative use of MF system to the original full‐scale frame leads to the accurate and rapid evaluation of the responses of the frame. The introduction of the coupled shear springs to the modeling formulation provides the coupled horizontal responses in the two orthogonal directions. In addition, the interstory shear force distribution of the original frame and that of the equivalent MF system correspond. The accuracy of the proposed method is investigated through numerical examples for in‐plan irregular frames.