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FRP-UHPC 복합 보강기법으로 보강된 RC 슬라브의 휨 파괴를 위한 설계 조건
김정중,노혁천,마흐무드 레다 타하,Kim, Jung Joong,Noh, Hyuk-Chun,Reda Taha, Mahmoud M. 한국복합신소재구조학회 2012 복합신소재구조학회논문집 Vol.3 No.2
This study proposes flexural failure design criteria of continuous slabs enhanced by a hybrid system of fiber reinforced polymer (FRP) and ultra high performance concrete (UHPC). The proposed hybrid retrofit system is designed to be placed at the top surface of the slabs for flexural strengthening of the sections in both positive and negative moment zones. The enhancing mechanisms of the proposed system for both positive and negative moment regions are presented. The neutral axis of the enhanced sections in positive moment zone at flexural failure is enforced to be in UHPC overlay for preventing the compression in FRP. From this condition, a relationship between design parameters of FRP and UHPC is established. Although the capacity of the proposed retrofit system to enhance flexural strength and ductility is confirmed through experiments of one-way RC slabs having two continuous spans, the retrofitted slabs failed in shear. To prevent this shear failure, a design criteria of flexural failure is proposed.
나노 실리카를 사용한 콘크리트의 시멘트 매트릭스 미세구조 분석
김정중(Jung Joong Kim),문지호(Jiho Moon),염광수(Kwang-Soo Youm),이학은(Hak-Eun Lee),임남형(Nam-Hyoung Lim) 한국철도학회 2014 한국철도학회 학술발표대회논문집 Vol.2014 No.5
콘크리트의 배합에 있어서 포졸란 물질의 사용은 수화된 시멘트내의 칼슘실리케이트 수화물을 증가시키고 미세 공극을 채워줌으로써 콘크리트의 투수성을 감소시킨다. 또한 콘크리트내의 전체 염기량을 낮추어 알카리 골재반응에 의한 균열의 방지에도 효과가 있다. 본 연구에서는 포졸란 물질 중 반응성이 가장 우수한 나노실리카를 사용한 콘크리트 시멘트의 미세구조를 분석할 것이다. 향후 콘크리트의 동결융해 실험, 알카리 골재 반응, 프리스트레스 강선과의 접착력 실험과 연계하여 균열에 대한 높은 내구성을 요구하는 콘크리트 침목의 제작에 최적화된 나노실리카의 배합비를 산출하는데 기초연구로 사용될 것이다. The incorporation of pozzolanic materials in concrete has many beneficial effects to enhance the mechanical properties of concrete. The calcium silicate hydrates in cement matrix of concrete increase by pozzolanic reactions. The fine pozzolanic particles fill spaces between clinker grains, thereby resulting in a denser cement matrix and interfacial transition zone between cement matrix and aggregates; this lowers the permeability and increases the compressive strength of concrete. Moreover, the total alkali contents in concrete are reduced by replacing cement with pozzolanic materials; this prevents cracks due to alkaliaggregate reaction (AAR). In this study, nanosilica, which is the most reactive pozzolanic materials, is incorporated in cement pastes. The differences of microstructural compositions between the hydrated cements with and without nanosilica are examined using several techniques. The results can be used for a basic research to manufacture concrete railway sleepers that is durable and has high resistance to AAR using the optimum contents of nanosilica.
손상과 크리프의 상호작용에 의한 조적조 기둥의 복합거동
김정중 ( Jung Joong Kim ) 한국복합신소재구조학회 2014 복합신소재학회논문집 Vol.5 No.2
Since the collapse of historical masonry structures in Europe in the late 1990’s, the interests in understanding the long-term effect of masonry under sustained compressive stresses have increased. That requires combining the significance of time-dependent effects of creep with the effect of damage due to overstress to realize the evolution of cracks and then failure in masonry. Meanwhile, composite analysis of masonry columns was proven effective for realizing ultimate strength capacity of masonry column. In this study, a simplified mechanical model with step-by-step in time analysis was proposed to incorporate the interaction of damage and creep to estimate the maximum stress occurred in masonry. It was examined that the interaction of creep and damage in masonry can accelerate the failure of masonry.
김정중(Kim Jung-Joong),손장열(Sohn Jang-Yeul) 한국생활환경학회 2009 한국생활환경학회지 Vol.16 No.2
Recently sports stadiums have been built not only for athletic sports but also for various events such as live concerts and recitals. The number of the stadiums which are covered by a half dome have been increasing. Therefore it is very important to solve the sound obstacle problem caused by the half dome. But sound designs of most of stadiums, with only a few as an exception, have not been planned properly and the proper sound absorption materials have not been used. This study investigates four World Cup stadiums (Seoul, Incheon, Daegu, Busan). First, sound factors according to the location in the stadium were compared by the design standard through field measurement. Then architectural sound absorption structure was analyzed and in turn the sound factors were considered totally for obtaining the proper reverberation time, RASTI, and sound pressure level. The average reverberation time for dome stadiums Busan were 6.03 seconds, longer than arch(Daegu) stadiums which were 3.8 seconds. However, the variance of the reverberation time at low frequencies(125 ㎐ and 250 ㎐) between the lower tiers(tier 1, 2) and the higher tiers(tier 4, 5) was larger in arch stadiums Daegu by about 2 seconds. The RASTI values for shield kite stadiums Seoul and dome stadiums Busan were between 0.38 and 0.50 indicating that audibility was ‘Poor’ to ‘Fair’. But otherwise, cone stadiums incheon achieved a RASTI value of 0.50 for all spectator seats and arch stadiums Daegu satisfy audibility standards for all areas except the playing field.