繰返し水平力を受ける高張力鋼骨組の弾塑性性状に関する研究

抄録

The behavior of high strength portal frames under constant vertical loads and alternating horizontal force was studied experimentally. Test frames were made by using welded wide flange sections of mild steel SM 41 and high strength steel SM 50, SM 58, respectively. Some obervations from the test results are as follows; (1) When vertical loads are large, the maximum restoring force at each cycle increases up to a certain value as the number of loading cycles increases, even in a region past the point of frame instability. The maximum restoring force depends on the magnitude of the ratios σ_y/σ_u of yield stress σ_y to tensile strength σ_u and P/P_y of column load P to column axial yield load P_y. The value of σ_y/σ_u becomes large, the ratio of the maximum restoring force to the theoretical plastic collapse load becomes small. (2) Both of the dimensionless accumulated plastic energy absorption capacity and dimensionless accumulated plastic deformation capacity of high strength steel frames were very small in comparison with the ones of mild steel frames. (3) High strength steel frames have not much advantage from the point of view of energy absoption capacity of a structure under alternating repeated loads. Experimental hysteretic behavior is fairly well predicted by elastic-plastic analysis based on the moment-curvature relations that take account of the effect of ratio σ_y/σ_u. The maximum restoring force and the limit value of average axial strain under repeated horizontal force are predicted by simple analytical method taking account of the effect of ratio σ_y/σ_u.