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화재피해 콘크리트의 수열온도에 따른 강도 및 색상 변화 연구
최광호 한국건설순환자원학회 2020 한국건설순환자원학회 논문집 Vol.8 No.3
In the safety diagnosis of fire-damaged concrete structures, it is difficult to evaluate the strength and changes in materials due to high temperatures with the existing durability analysis method. In particular, the compressive strength of specimen with different damage levels by thickness is used as a representative value for reducing the compressive strength of the structural member. In this study, a heating experiment was performed with only top face heating and fully heating conditions at 400°C to 800°C. After heating, splitting tensile test and color analysis were performed to sliced specimens with a thickness of 20mm accompanied by t he c ompr essive t est of a f ully h eated specimen. As a r esult of t he e xper iment, the compressive strength reduction rate calculated from the splitting tensile strength of every sliced specimen appeared to be w ithin 10% of t he f ully h eated specimen o n aver age, a nd the h ue value a nalysis showed c onsistent color values wer e observed by red at 400°C-600°C and gray at 700°C or above. It follows that the techniques proposed in this study are reasonably assessable to estimate heated temperature and residual compressive strength and damage depth of concrete.
고온을 받은 횡방향 철근 구속 콘크리트의 역학적 특성 연구
최광호,이중원 한국구조물진단유지관리공학회 2012 한국구조물진단유지관리공학회 논문집 Vol.16 No.1
콘크리트 기둥에 사용되는 횡방향 철근은 압축콘크리트 파괴 시 횡방향 벌어짐을 구속하여 폭렬을 줄일 수 있고 콘크리트의 연성을 증가시키는 데에 유효하며 강도손실 보상효과가 있다. 이를 규명하기 위하여, 띠철근의 간격과 나선철근을 변수로 한 실험체를 제작하여 가열실험을 수행하였다. 이 때 전기로 온도를 300℃, 600℃ 및 800℃로 설정하여 13.33℃/분의 속도로 가열하고 2시간동안 그 온도를 유지시켰다. 냉각된 실험체에 대해 응력-변형률 곡선을 구하기 위한 압축실험을 수행하고, 이로부터 탄성계수, 잔존 내력 및 변형률 등의 잔존 역학적 특성을 분석하였다. 실험결과 횡방향 철근비가 높을수록 철근이 콘크리트를 구속하여 다축 응력 상태가 되기 때문에 고온을 받은 콘크리트의 잔존 최대응력이 커지고 더욱 큰 변형을 발휘할 수 있는 있는 것을 확인하였다. 이울러, 콘크리트의 잔존 탄성계수의 감소율은 횡방향 철근의 구속효과로 작아지는 것으로 분석되었다. The lateral reinforcements of concrete such as hoops and spiral bars are known to confine concrete to compensate the strength loss due to fire by reducing explosive spalling and improving the capacity of ductility. In this context, a study was conducted to investigate the residual mechanical properties of confined and unconfined concrete(fck=60MPa) after a single thermal cycle at 300, 600, 800℃. The main parameters required to establish the stress-strain relationship are the peak stress, the elastic modulus, and the strain at peak stress. The knowledge of the residual mechanical properties of concrete is necessary whenever the thermally damaged structure is required to bear a significant share of the loads, even after a severe thermal accident. Based on the results obtained in this study, the residual stress of confined concrete under thermal damage is higher according to the level of confinement and the larger strain made it to have better ductility. The decreasing ratio of elastic modulus from the relationship of stress and strain was also smaller than that of unconfined concrete.