Collapse analysis of high-rise steel moment frames incorporating deterioration effects of column axial force - bending moment interaction

Existing high-rise steel moment resisting frames (SMRF) in Japan sustained severe damage under the background of Tohoku earthquake and face collapse risks if great ocean ridge earthquakes occur in the near future. This paper presents a numerical study on collapse analysis of existing high-rise SMRFs under long period ground motions over the design levels. A finite element model based on fiber discretized layers was employed to incorporate the deterioration effects in bending strength of beams and axial force-bending moment (N-M) interaction of columns. Parameters for the numerical model were validated by a series of component tests, and a shaking table test on a high-rise SMRF substructure. Simulation results shown reasonable accuracy for predicting the low-cycle fatigue of steel beams, post-local buckling of steel columns and side-sway collapse mode of high-rise SMRFs. Then, parametric analyses were conducted to evaluate the dominant factors controlling the collapse capacity of high-rise SMRFs with various story and degradation levels. It indicated that a beam-to-column strength deterioration factor (SDF) plays an important role on collapse behavior characterized by asymmetric sway deformation concentrated at lower stories. Finally, design recommendation in terms of critical buckling strength of columns is proposed to define the collapse capacity of critical columns in high-rise SMRFs.