이 연구는 한국산업규격 KS D 3504에 따라 생산된 700 MPa 이상의 항복강도를 가진 고강도 철근의 피로강도를 파악하기 위한 것이다. 피로실험을 수행하기 이전에 SD700철근에 작용할 최소응력수준과 응력범위를 정하기 위해 재료실험을 수행한 결과 항복강도는 801 MPa, 인장강도는 888 MPa로 측정되었다. 피로실험은 항복강도의 10 % 수준의 최소응력수준을 사용하여, 항복강도의 40 %에서 80 %인 응력범위로 12개의 시편을 대상으로 수행하였다. 피로실험 도중에 시편이 파단 되거나 하중반복횟수가 500만 회를 넘어서면 장기수명구간으로 판단하고 실험을 중단하였다. 피로실험결과 유한수명구간에서 SD700 철근의 피로강도는 10만 회를 기준으로 SD300보다 1.68배, SD400보다 1.47배 뛰어난 성능을 발휘하였다. SD700의 피로한계는 245 MPa로 측정되었으며 선행연구 된 SD300의 피로한계에 1.25배 정도 크게 나타났다. 하중반복횟수 10만 회 기준의 유한수명구간에서 AASHTO, LRFD(2017)가 적용하고 있는 Helgason 등의 피로강도식이 실제 SD700 철근의 피로강도의 70 %, Eurocode 2(2005)는 실제피로강도의 55 %를 나타내었다. 200만 회인 장기수명구간에서는 Helgason 등의 식이 실제 피로한계의 41 %, Eurocode 2(2005)는 65 %를 나타내었다. 이러한 결과는 현재 적용하고 있는 피로강도 식이 SD700 고강도 철근의 피로강도를 과소평가하고 있음을 나타낸다.
이 연구는 한국산업규격 KS D 3504에 따라 생산된 700 MPa 이상의 항복강도를 가진 고강도 철근의 피로강도를 파악하기 위한 것이다. 피로실험을 수행하기 이전에 SD700철근에 작용할 최소응력수준과 응력범위를 정하기 위해 재료실험을 수행한 결과 항복강도는 801 MPa, 인장강도는 888 MPa로 측정되었다. 피로실험은 항복강도의 10 % 수준의 최소응력수준을 사용하여, 항복강도의 40 %에서 80 %인 응력범위로 12개의 시편을 대상으로 수행하였다. 피로실험 도중에 시편이 파단 되거나 하중반복횟수가 500만 회를 넘어서면 장기수명구간으로 판단하고 실험을 중단하였다. 피로실험결과 유한수명구간에서 SD700 철근의 피로강도는 10만 회를 기준으로 SD300보다 1.68배, SD400보다 1.47배 뛰어난 성능을 발휘하였다. SD700의 피로한계는 245 MPa로 측정되었으며 선행연구 된 SD300의 피로한계에 1.25배 정도 크게 나타났다. 하중반복횟수 10만 회 기준의 유한수명구간에서 AASHTO, LRFD(2017)가 적용하고 있는 Helgason 등의 피로강도식이 실제 SD700 철근의 피로강도의 70 %, Eurocode 2(2005)는 실제피로강도의 55 %를 나타내었다. 200만 회인 장기수명구간에서는 Helgason 등의 식이 실제 피로한계의 41 %, Eurocode 2(2005)는 65 %를 나타내었다. 이러한 결과는 현재 적용하고 있는 피로강도 식이 SD700 고강도 철근의 피로강도를 과소평가하고 있음을 나타낸다.
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 rein...
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.
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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