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손상입은 철근콘크리트 보의 외적 포스트텐셔닝에 의한 휨 보강
이수헌,이희두,이창수,신경재 대한건축학회 2017 대한건축학회논문집 Vol.33 No.7
An experimental work was undertaken to observe and assess the behavior of damaged reinforced concrete (RC) beams with external post-tensioning steel rods. Six simply supported beams - two control beams and four comparable beams post-tensioned using externally steel rods - were tested in three-point bending. The main parameters are the diameter of external post-tensioning rods (<TEX>${\phi}22mm$</TEX> and <TEX>${\phi}28mm$</TEX>) and the ratio of tension steel reinforcement (<TEX>${\rho}=0.0106$</TEX> and 0.0166). For the post-tensioned beams, V-shaped profiles were used with a deviator located at the bottom of mid-span, and the post-tensioning force was applied to beams in order to overcome the low load-carrying capacity and existing deflection. The post-tensioning force acting on the steel rods was applied by tightening nuts of anchorage and its value was monitored by attached strain gauges. The initial strain of about <TEX>$2000{\mu}{\varepsilon}$</TEX> was chosen for post-tensioning force because it is about the maximum strain that two adult men can apply without struggle. Test results indicate that the externally post-tensioning increased the load-carrying capacity by about 40~101% and the flexural stiffness by about 27~43% compared to control beams. On the other hand, the larger steel reinforcements and external rods of the section disturbed the yielding of external rod at ultimate strength.
화재손상을 입은 철근콘크리트 보에서 외적 포스트텐셔닝 강봉의 전단 보강
이수헌 대한건축학회 2023 대한건축학회논문집 Vol.39 No.1
The purpose of this study is to discuss the applicability, strengthening effect and improvements when an externally post-tensioned steel rodsystem is applied to a fire-damaged reinforced concrete (RC) beam. A total of twelve specimens were prepared in three groups and tested tofail. Group one was not heated, and group two and group three were heated to 700℃ and 1,000℃, respectively. In each group, one beamwithout externally post-tensioned steel rods was designated as a control beam and three beams had the externally post-tensioned steel rods of18 mm, 22 mm or 28 mm in diameter. The initial effective tension of about 2,000 was applied to the steel rods. Test results indicated thatthis can be applied to fire-damaged RC because externally post-tensioning increased the load-carrying capacity by more than 67%. However,additional reinforcement is required in the part where the deviator and anchorage are installed since the concrete surface is weakened bymoisture evaporation at high temperatures. 이 연구는 화재손상을 입은 철근콘크리트 보에 외적 포스트텐셔닝 강봉을 적용하였을 때 적용 가능성과 보강 효과, 개선점 등을 논한다. 총 12개의 실험체가 3개의 실험군으로 구성되었고 파괴 시까지 실험하였다. 실험군 #1은 고온에 노출하지 않았고, 실험군 #2와 #3은 각각 700℃, 1,000℃에 노출하였다. 각 실험군은 포스트텐셔닝 강봉으로 보강하지 않은 기본 실험체 1개, 18mm, 22mm, 28mm 강봉으로 보강한 3개의 실험체로 디자인되었다. 강봉에는 초기 긴장력 약 2000με이 도입되었다. 실험결과를 보면, 포스트텐셔닝 강봉 보강법은 67% 이상의 강도 보강 효과를 보였기 때문에 그 보강 효과를 입증하였다. 하지만 고온에 콘크리트 표면의 손상이 발생하였기에 데비에이터와 정착구 부근에는 추가 보강이 이루어져야 할 것으로 판단한다.
이수헌,이희두,최준호,신경재 한국화재소방학회 2016 한국화재소방학회논문지 Vol.30 No.5
Steel is a structural material that is inherently noncombustible. On the other hand, it has high thermal conductivity andthe strength and stiffness of the material are reduced significantly when exposed to fire or high temperatures. Because theyield strength and modulus of elasticity of steel are reduced by 70% at 350 oC and less than 50% at 600 oC, the load-carryingcapacity of steel structure at high temperature rapidly lose. To be accepted as a fire-resisting construction, the firetest should be performed at the certificate authority. On the other hand, the fire test on a full-scale structure is limited bytime, space, and high-cost. The analytical method was verified by a comparison with the fire test of H-section columnsunder compression and thermal analysis based on a finite element method using the ABAQUS program, and the numericalanalysis method reported in this study was suggested as a complement of an actual fire test. 구조재료 중에서 강재는 불연성 재료이지만 열전도가 높고, 온도상승에 의하여 강성의 저하가 높은 편이다. 일반적으로 강재의 항복강도 및 탄성계수는 350 oC에서 70%, 600 oC에서 50% 이하로 감소하기 때문에 고온에서의 철골구조의재하능력은 급격히 감소하게 된다. 통상 내화구조로 인정받기 위해서는 공인기관으로부터의 품질시험을 거쳐야 한다. 하지만, 실물내화실험은 공간과 시간의 제약, 고비용의 문제점을 안고 있으므로, 본 연구에서는 ABAQUS 프로그램의 유한요소법을 이용한 열해석을 수행하여 압축을 받는 H-형강기둥의 내화실험과의 비교로 해석모델의 신뢰성을 입증하고,실물실험의 보완책으로의 가능성을 제시한다.
Behavior of Plate-to-Circular Hollow Section Joints of 600 MPa High-Strength Steel
이수헌,Kyung-Jae Shin,이희두,Woo-Bum Kim,양재근 한국강구조학회 2012 International Journal of Steel Structures Vol.12 No.4
While the recent high demand for high rise buildings has led to the development of high-performance and high-strength steels, the requirements for structural-performance steel for such buildings have been raised as engineers recognized the potential wreak damage that an earthquake could cause on a tall building. Many studies on high-strength steels have explored such requirements, but appropriate design equations are needed for the case of hollow structural section (HSS) due to the design equations that limit the maximum yield stress up to 360MPa in the design codes (AISC, 2011; KBC, 2009). This study investigated the behavior of 600MPa plate-to-circular hollow section joints subjected to applied moment and shear force by experiment and finite element analysis (FEA), and the results are compared with current design equations. The nominal strength of AISC (2005) (or KBC (2009)) overestimated the tested strength in the range between 105% and 137%. It is found that the nominal strength equation of AISC (2011) is reasonably revised in comparison to those of other design codes.