• 한국전산구조공학회논문집
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• 제27권1호
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• pp.45-53
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• 2014

강도 한계상태 설계에서는 균열이 일어난 이후 철근콘크리트 부재의 인장영역에서 철근이 모든 인장력을 부담하는 것으로 가정한다. 그러나 균열 사이의 콘크리트가 실제 콘크리트 부재에서는 특히 사용하중 수준에서의 어느 정도의 인장 응력을 견디는데, 일조 하는 것으로 보고 있다. 이러한 효과를 Tension stiffening 효과라 한다. 본 연구에서는 Tension stiffening 모델과 고강도 철근 콘크리트 보의 휨 실험결과의 비교를 통해 해석모델의 유효성을 평가 하고자 한다. 이를 통해 선정 된 6가지의 Tension stiffening 모델과 실험에 의한 모멘트-곡률, 하중-처짐등을 관계를 평가하였다. 실험결과 설계기준에서는 ACI 318이 Tension stiffening 모델에서는 Owen & Damjanic이 실험 값과 가장 적은 오차율을 보이며 높은 신뢰도를 보였다.

• 콘크리트학회논문집
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• 제11권4호
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• pp.83-93
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• 1999

This paper presents tension stiffening effect of Reinforced concrete members obtained from experimental results on direct tension and bending. From the direct tension test program, crack patterns were investigated with tension softening behaviors of concrete. Tension stiffening effects and losses of strain energy were, also, analyzed from the load-deflection curve with the main experimental variables such as concrete strength, yielding stress and reinforcement ratio of rebar. Tension stiffening effect of RC members increase linearly until the first crack initiate, decrease inversely with number of cracks, and then decrease rapidly when splitting cracks are happened. The tension stiffening effect is shown to be more important at the member of lower reinforcement than that of higher. Therefore, it necessitates to consider the tension stiffening effects at a nonlinear analysis. From the above analysis, a tension stiffening model of concrete is proposed and verified by applying it to bending members. From the numerical analysis by finite element approach, it is shown that the proposed model evaluates a little higher in analyzing at nonlinear region of high strength concrete, but, perform satisfactorily in general.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회논문집(II)
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• pp.737-742
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• 1998

The tension stiffening effect is defined as the increase in stiffness in reinforced concrete member due to the stiffness provided by concrete between cracks. If this is disregarded in analysis of reinforced concrete members, especially at the level of service loads, member stiffnesses may be underestimated considerably. This paper presents on the failure behavior and tension stiffening of RC tension test with main variables such as concrete strength, rebar diameter and strength. The tension stiffening was analyzed from the load-displacement relationship by ACI code and the proposed by Collins & Mitchell. In summary, the effect of tension stiffening decrease rapidly as the rebar diameter increase, rebar strength increase, and concrete strength increase. The effect of tension stiffening on RC member is the biggest near the behavior of concrete cracking and decrease as the load close to the breaking point. Thus, the tension stiffening should be considered for the precise analysis near the load of concrete cracking.

• 한국건축시공학회지
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• 제11권1호
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• pp.83-90
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• 2011

The purpose of this research is to investigate the effect of AFm formation on the stiffening process of cement paste. High and low alkali sulfate clinkers were used for the experiments. The flow and stiffening behavior of cement paste was investigated using modified ASTM C403 penetration resistance test and oscillatory shear rheology. X-ray powder diffraction (XRD) was used for phase identification associated with stiffening of the paste. It was found from the results that low alkali clinker mixture produced very strong premature stiffening whereas high alkali clinker mixture did not cause premature stiffening. This is because of the large amount of alkali sulfate present in the clinker. Addition of calcium and sodium chloride to the high alkali clinker mixture caused faster stiffening and set.

• 콘크리트학회논문집
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• 제12권1호
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• pp.13-22
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• 2000

This paper describes the results obtained from 11 direct tension tests to explore the influence of concrete strength on tension stiffening behavior in reinforced concrete axial members. Three different concrete compressive strengths, 250, 650, and 900kgf/$\textrm{cm}^2$, were included as a main variable, while the ratio of cover thickness-to-rebar diameter was kept constant to be 2.62 to prevent from splitting cracking. As the results, it was appeared that, as higher concrete strength was used, less tension stiffening effect was resulted, and the residual deformation upon unloading was larger. In addition, the spacing between adjacent transverse cracks became smaller with higher concrete strength. The major cause for those results may be attributed to the fact that nonuniform bond stress concentration at both loaded ends and crack sections becomes severer as higher concrete is used, thereby local bond failure becomes more susceptible. From these findings, it would be said the increase in flexural stiffness resulting from using high-strength concrete will be much smaller than that predicted by the conventional knowledge. Finally, a factor accunting for concrete strength was introduced to take account for the effect of HSC on tension stiffening. This proposed equation predicts well the tension stiffening for the effect of HSC on tension stiffening. This proposed equation predicts well the tension stiffening behavior of these tests.

• Architectural research
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• 제13권1호
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• pp.25-32
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• 2011

The purpose of this research is to investigate the effect of specific hydration reaction on the stiffening process of cement paste. The cement compositions are manipulated to cause specific hydration reactions (secondary gypsum and syngenite formation) responsible for false set, and the relationship between specific hydration reactions and the flow and stiffening behavior of cement paste were investigated using modified ASTM C 403 penetration resistance measurement and oscillatory shear rheology. X-ray powder diffraction (XRD) was used for the phase identification associated with premature stiffening of cement paste. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were used for verification of syngenite formation. From the results, both secondary gypsum and syngenite formation caused faster stiffening and set. The amount of syngenite produced during 1 hour hydration was approximately 1 % of total mass of the cement paste, but cement paste with syngenite formation showed significantly accelerated stiffening behavior compared to normal cement paste.

• Structural Engineering and Mechanics
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• 제34권2호
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• pp.189-211
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• 2010

The behaviour of a reinforced concrete tension member is governed by the contribution of concrete between cracks, tension stiffening effect. Under highly repeated loading, this contribution is progressively reduced and the member response approximates that given by the fully cracked member. When focusing on the unloaded state, experiments show deformations larger than those of the naked reinforcement. This has been referred to as negative tension stiffening and is due to the fact that concrete carries compressive stresses along the crack spacing, even thought the tie is subjected to an external tensile force. In this paper a cycle-dependent approach is presented to reproduce the behaviour of the axially loaded tension member, paying attention to the negative tension stiffening contribution. The interaction of cyclic bond degradation and time-dependent effects of concrete is investigated. Finally, some practical diagrams are given to account for the negative tension stiffening effect in reinforced concrete elements.

• 콘크리트학회논문집
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• 제11권6호
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• pp.35-46
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• 1999

The steel fiber reinforced concrete may affect substantially to the tension stiffening at post cracking behavior. Even if several tension stiffening models exist, they are for plain and normal strength concrete. Thus, the development of tension stiffening models for steel fibrous high strength RC members are necessary at this time when steel fiber reinforced and high strength concretes are common in use. This paper presents tension stiffening effects from experimental results on direct tension members with the main variables such as concrete strength, concrete cover depth, steel fiber quantity and aspect ratio. The comparison of existing models against experimental results indicated that linear reduced model closely estimated the test results at normal strength level but overestimated at high strength level. Discontinuity stress reduced model underestimated at both strength levels. These existing models were not valid enough in applying at steel fibrous high strength concrete because they couldn't consider the concrete strength nor section area. Thus, new tension stiffening models for high strength and steel fiber reinforced concrete were proposed from the analysis of experimental results, considering concrete strength, rebar diameter, concrete cover depth, and steel fiber reinforcement.

• 한국농공학회지
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• 제40권4호
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• pp.120-129
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• 1998

The tension stiffening in reinforced concrete member means increase of stiffness caused by the effective tensile stress between cracks and the tension softening behavior of concrete. This paper presents on the tensile behavior and tension stiffening of RC tension members. Direct tension tests were performed with a main experimental variables such as concrete strength, rebar diameter and strength. The tension stiffening was analyzed from the load-displacement relationship and was compared with ACI code, CEB model and the proposed by Collins ＆ Mitchell. The results are as follows : The tension behaviors of RC members were quite different from those of bare bar and were characterized by loading and concrete cracking steps. The effect of tension stiffening decreased rapidly as the rebar diameter and strength increased, and the concrete strength increased. The proposed by Collins ＆ Mitchell described well the experimental results, regardless of rebar types and concrete. But, ACI code and CEB model described a little differently, depending on the types. The effect of tension stiffening in RC member was the biggest near at concrete cracking step and decreased gradually to the bare bar's behavior as loading closed to the breaking point. Thus, tension stiffening in RC members should be taken into account when the load-deflection characteristics of a member are required or a precise analysis near the load of concrete clacking is needed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.197-200
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• 2005

This paper presents an analytical model for evaluation of Tension Stiffening Effect by actual Bond-Slip relationships between the reinforcement and the surrounding concrete. The presence of longitudinal splitting cracks was found to significantly after the tension stiffening. The model is applied to the longitudinal splittings cracks and derived to Tension stiffening model. The predicted values are shown to be in good agreement with the experimentally measured data.