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Title |
Fatigue Strength of High Strength Reinforcing Bars Having Yield Strength of 700 MPa
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Authors |
이재훈(Jae-Hoon Lee) ; 이선호(Seon-Ho Lee) ; 김호영(Ho-Young Kim) |
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DOI |
https://doi.org/10.4334/JKCI.2018.30.3.269 |
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Keywords |
피로 ; 피로강도 ; 철근 ; SD700 고강도철근 ; 피로한계 fatigue ; fatigue strength ; reinforcing bar ; SD700 high strength steel ; fatigue limit |
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Abstract |
The purpose of this study is to investigate the fatigue strength of high strength reinforcing steel with yield strength higher than or equal to 700 MPa, which is specified as SD700 in the Korean Standard, KS D 3504. Before conducting the fatigue test, a material test was performed for the SD700 reinforcing steel in order to determine minimum stress and stress ranges. The actual yield strength was 801 MPa and the ultimate strength was 888 MPa. The fatigue test was performed for twelve specimens by setting the minimum stress as 10 % of the yield strength and the stress ranges between 40 % and 80 % of the yield strength. The test was stopped when the specimens were fractured or when the number of load cycles exceeded 5 million times, which was presumed to be a long-life region. From the test results, it is found that the fatigue strength of SD700 reinforcing bars is 1.68 times higher than that of SD 300 steel and 1.47 times higher than that of SD400 steel in the finite-life region at 100,000 cycles. The fatigue limit of the SD700 steel is 245 MPa, which is 1.25 times higher than that of SD300 steel reported by the previous researchers. The fatigue strength equation proposed by Helgason et al. and which is adopted by AASHTO LRFD shows 70 % and Eurocode 2 (2005) shows 55 % of the expected fatigue strength of SD700 steel at 100,000 cycles in the finite-life region. The Helgason equation and Eurocode 2 equation provide 41 % and 65 % of the expected limit fatigue strength of SD700 steel at the 2 million long-life region. These results show that the currently applied equations provide highly underestimated fatigue strength for high strength steel compared with the test result SD700 steel.
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