Effect of Difference of Yield Ratio of Steel on Ductility of Steel Structures

1990 Fiscal Year Final Research Report Summary

• Project/Area Number: 01550443
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: Building structures/materials
• Research Institution: Kyushu Univ.
• Principal Investigator: MATUI Chiaki Kyushu University, Professor, 工学部, 教授 (00037756)
• Co-Investigator(Kenkyū-buntansha): SAKAI Junichi Kyushu University, Research Assistant, 工学部, 助手 (30215587) ; YOSHIZUMI Takashi Kurume Institute of Technology, Associate Professor, 工学部, 助教授 (60112314) ; TUDA Keigo Kyushu University, Research Assistant, 工学部, 助手 (50112305) ; KAWANO Akihiko Kyushu University, Associate Professor, 工学部, 助教授 (60136520)
• Project Period (FY): 1989 – 1990
• Keywords: Yield ratio / Ductility / Steel beam-column / Steel frame

Research Abstract

Quality of steel used in structures is specified by JIS. As for the yield stress the lower limit is only described in the standard. However, strength and ductility of structures under large external force are affected by the yield ratio, rather than the yield stress, Where the yield ratio is the ratio of the yield stress to the ultimate stress of steel.
Objectives of this study are to investigate the effect of the difference of values of the yield ratio on ductility of steel structures, and to make clear how much value of yield ratio is allowable from the view point of earthquake resistant properties of steel frames. Two series of tests are examined. The test of the first series is the experimental work of H-section cantilever beam-column specimens subjected to constant vertical and alternately repeated horizontal loads. Experimental parameters are the value of yield ratio (0.62, 0.82), width-to-thickness ratio of flange element (8.3, 12.5), and axial load ratio N/NO (0.1, 0.3, 0,6), wh ere N is the axial load on the specimen, and NO is the compressive strength of the cross section. Twelve specimens are tested. The test of the second series is the experimental work of steel portal frame specimens with scallop at beam end, subjected to a alternately repeated horizontal load. The experimental parameter is the value of yield ratio (0.62, 0.82). Two specimens are tested.
From the test results of the first series, it has become clear that : 1) In specimens with a large width-to-thickness ratio, the effect of the difference of the yield ratio on the ductility is small, because ductility is mainly affected by local buckling of plate elements. 2) In specimens with a small width-to-thickness ratio, the smaller the value of the yield ratio becomes, the larger the ductility becomes. On the other hand, the larger the value of axial load ratio becomes , the smaller the effect of the difference of the yield ratio on the ductility becomes. From the test results of the second series, it has become clear that : In the specimen with steel of yield ratio 0.82, the ductility factor mu is 30, in one of 0.62, mu is 41. Steel structure has large ductility and show a good earthquake resistant properties even if steel of Y=0.82 are used in structures with scallop at beam end.