• 한국해양공학회지
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• 제21권6호
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• pp.7-15
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• 2007

A mechanical model was developed to predict the behavior of point-loaded RC slender beams (a/d > 2.5) without stirrups. It is commonly accepted by most researchers that a diagonal tension crack plays a predominant role in the failure mode of these beams, but the failure mechanism of these members is still debatable. In this paper, it was assumed that diagonal tension failure was triggered by the concrete cover splitting due to the dowel action at the initial location of diagonal tension cracks, which propagate from flexural cracks. When concrete cover splitting occurred, the shape of a diagonal tension crack was simultaneously developed, which can be determined from the principal tensile stress trajectory. This fictitious crack rotates onto the crack tip with load increase. During the rotation, all forces acting on the crack (i.e, dowel force of longitudinal bars, vertical component of concrete tensile force, shear force by aggregate interlock, shear force in compression zone) were calculated by considering the kinematical conditions such as crack width or sliding. These forces except for the shear force in the compression zone were uncoupled with respect to crack width and sliding by the proposed constitutive relations for friction along the crack. Uncoupling the shear forces along the crack was aimed at distinguishing each force from the total shear force and clarifying the failure mechanism of RC slender beams without stirrups. In addition, a proposed method deriving the dowel force of longitudinal bars made it possible to predict the secondary shear failure. The proposed model can be used to predict not only the entire behavior of point-loaded RC slender shear beams, but also the ultimate shear strength. The experiments used to validate the proposed model are reported in a companion paper.

• 콘크리트학회지
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• 제4권4호
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• pp.171-179
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• 1992

본 연구에서는 전단-스팬비가 1.5에서 2.5 범위의 고강도 콘크리트 보에 대해 기존 규준식의 안전여부를 확인하고, 사균열강도와 극한전단강도를 결정하기 위해 총 15개의 시험체를 제작하여 실험적 연구를 수행하였다. 주요변수는 전단-스팬비(a/d=1.5, 2.0, 2,5)와 수직전단철근비(Rv=0, 25, 50, 75, 100%, Rv=[$ ho$v / $\rho$v(ACI)] 100)이며, 콘크리트 압축강도(f＇c=747kg/$ extrm{cm}^2$와 인장철근비($\rho$w=0.0377)는 일정하다. 실험결과 본 연구의 전단-스팬비의 범위에서 ACI 318-89 (11-31)식은 일반적으로 수직전단철근에 의해 저항되는 전단강도를 상당히 과소평가하는 것으로 나타났다. 따라서 수직전단철근에 대한 영향이 재고되어야 할 것이다.

• Computers and Concrete
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• 제20권6호
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• pp.689-704
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• 2017

The paper presents experimental and numerical investigations of prefabricated composite structural building reinforced concrete slabs with the insulating material for a residential building construction. The building slabs were composed of concrete and expanded polystyrene. In experiments, the slabs in the full-scale 1:1 were subjected to vertical concentrated loads and failed along a diagonal shear crack. The experiments were numerically evaluated using the finite element method based on two different constitutive continuum models for concrete. First, an elasto-plastic model with the Drucker-Prager criterion defined in compression and with the Rankine criterion defined in tension was used. Second, a coupled elasto-plastic-damage formulation based on the strain equivalence hypothesis was used. In order to describe strain localization in concrete, both models were enhanced in the softening regime by a characteristic length of micro-structure by means of a non-local theory. Attention was paid to the formation of critical diagonal shear crack which was a failure precursor.

• Computers and Concrete
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• 제3권1호
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• pp.65-77
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• 2006

This study reports the details of the finite element analysis of eleven shear critical partially prestressed concrete T-beams having steel fibers over partial or full depth. Prestressed concrete T-beams having a shear span to depth ratio of 2.65 and 1.59 and failing in the shear have been analyzed using 'ANSYS'. The 'ANSYS' model accounts for the nonlinear phenomenon, such as, bond-slip of longitudinal reinforcements, post-cracking tensile stiffness of the concrete, stress transfer across the cracked blocks of the concrete and load sustenance through the bridging of steel fibers at crack interface. The concrete is modeled using 'SOLID65'-eight-node brick element, which is capable of simulating the cracking and crushing behavior of brittle materials. The reinforcements such as deformed bars, prestressing wires and steel fibers have been modeled discretely using 'LINK8' - 3D spar element. The slip between the reinforcement (rebar, fibers) and the concrete has been modeled using a 'COMBIN39'-non-linear spring element connecting the nodes of the 'LINK8' element representing the reinforcement and nodes of the 'SOLID65' elements representing the concrete. The 'ANSYS' model correctly predicted the diagonal tension failure and shear compression failure of prestressed concrete beams observed in the experiment. The capability of the model to capture the critical crack regions, loads and deflections for various types of shear failures in prestressed concrete beam has been illustrated.

• 콘크리트학회논문집
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• 제26권2호
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• pp.143-150
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• 2014

콘크리트의 압축파괴에 의한 취성적인 비틀림파괴와 사인장균열의 폭을 제한하기 위하여 콘크리트구조기준은 비틀림보강철근의 항복강도를 제한하고 있다. 2012년에 콘크리트구조기준에서는 비틀림보강철근의 항복강도를 400 MPa에서 500 MPa로 상향하였다. 그 이유는 500 MPa의 비틀림보강철근을 사용한 비틀림부재의 경우에도 전단파괴하는 부재와 유사하게 기준에서 요구하는 비틀림파괴모드, 사용성, 경제성을 만족시킬 수 있을 것으로 판단하였기 때문이다. 그러나 현재 고강도 비틀림보강철근을 사용한 비틀림부재에 대한 연구는 전단부재에 대한 연구에 비하여 부족한 실정이다. 이 연구에서는 340 MPa, 480 MPa, 667 MPa의 비틀림보강철근을 사용한 철근콘크리트 보의 비틀림거동을 실험적으로 평가하였다. 실험에 의하면 비틀림보강철근의 파괴모드는 비틀림보강철근의 항복강도와 콘크리트의 압축강도에 의하여 영향을 받았다. 비틀림보강철근의 항복강도가 400 MPa이하인 경우에는 콘크리트의 압축강도와 무관하게 한 곳 이상에서 비틀림보강철근이 항복강도에 도달하여 비틀림인장파괴하였지만, 항복강도가 480 MPa 이상인 경우에는 비틀림보강철근이 항복하지 않는 경우가 발생하여 이에 대한 추가적인 연구가 필요할 것으로 판단된다.