Abstract
The maximum strength of steel frames caused by inelastic instability is discussed. The frames with various geometries and loading conditions (see Table-1 and Table-2) are analyzed by previously proposed method (see Trans. of A.I.J. Vol.110, 113, and 116) From analytical results the critical load formula is discussed and following formula is proposed, [chemical formula] where parameters K_1 and K_2 depend on frame geometry and loading condition. For portal frame with column thrust and increasing horizontal loading, K_1, K_2 -values are respectively 0.54 and 0.46. q_<cr>/q_R is ratio of failure load to rigid plastic collapse load considered the reduction of plastic moment by axial stress and p_e is elastic buckling load. The relations between q_<cr>/q_R-value and natural period of frames are also discussed in this paper and, following expressions are obtained as critical load formula for elasto-plastic steel frames subjected to column thrust and increasing horizontal loads. For portal frame ; q_<cr>/q_R=1.0-2.3T_0-13.5T_0^2 For multi-story frame ; q_<cr>/q_R=1.0-2.63T_0-17.6T_0^2 [chemical formula] T : natural period of frame with vertical load. h_0 : height of standard story of frame (in cm).
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