• Title/Summary/Keyword: pre-stress concrete

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Numerical analysis of thermal and composite stresses in pre-stressed concrete pavements

  • Nejad, Fereidoon Moghadas;Ghafari, Sepehr;Afandizadeh, Shahriar
    • Computers and Concrete
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    • v.11 no.2
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    • pp.169-182
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    • 2013
  • One of the major benefits of the pre-stressed concrete pavements is the omission of tension in concrete that results in a reduction of cracks in the concrete slabs. Therefore, the life of the pavement is increased as the thickness of the slabs is reduced. One of the most important issues in dealing with the prestressed concrete pavement is determination of the magnitude of the pre-stress. Three dimensional finite element analyses are conducted in this research to study the pre-stress under various load (Boeing 777) and thermal gradient combinations. The model was also analyzed under temperature gradients without the presence of traffic loading and the induced stresses were compared with those from theoretical relationships. It was seen that the theoretical relationships result in conservative values for the stress.

Pre- and Post Processing System on Prediction Analysis of Thermal Stress in Mass Concrete Structure (매스콘크리트의 온도균열 예측해석에서의 전후처리 시스템 개발에 관한 연구)

  • 김유석;강석화;박칠림
    • Proceedings of the Korea Concrete Institute Conference
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    • 1996.04a
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    • pp.270-274
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    • 1996
  • Until recently pre & post-processing of finite element model has been heavily relied on expensive graphic peripheral devices. But today, with the aid of inexpensive microcomputers, very effective pre & postprocessor graphics has been developed. In this study, Pre & Post processor(MASSPRE, MASSPOST) of prediction analysis of thermal stress in mass concrete structure is developed. The developed pre & post processors are raise to the efficiency in making input data for the main program and analysis of the results produced by the main program. This MASSPOST presents a stress contour graph, volume slice, time-temperature history graph, time-stress history graph, etc.

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Growth of Time-Dependent Strain in Reinforced Cement Concrete and Pre-stressed Concrete Flexural Members

  • Debbarma, Swarup Rn.;Saha, Showmen
    • International Journal of Concrete Structures and Materials
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    • v.6 no.2
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    • pp.79-85
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    • 2012
  • This paper presents the differences in growth of time-dependent strain values in reinforced cement concrete (RCC) and pre-stressed concrete (PSC) flexural members through experiment. It was observed that at any particular age, the time-dependent strain values were less in RCC beams than in PSC beams of identical size and grade of concrete. Variables considered in the study were percentage area of reinforcement, span of members for RCC beams and eccentricity of applied pre-stress force for PSC beams. In RCC beams the time-dependent strain values increases with reduction in percentage area of reinforcement and in PSC beams eccentricity directly influences the growth of time-dependent strain. With increase in age, a non-uniform strain develops across the depth of beams which influence the growth of concave curvature in RCC beams and convex curvature in PSC beams. The experimentally obtained strain values were compared with predicted strain values of similar size and grade of plane concrete (PC) beam using ACI 318 Model Code and found more than RCC beams but less than PSC beams.

Influence of pre-compression on crack propagation in steel fiber reinforced concrete

  • Abubakar, Abdulhameed U.;Akcaoglu, Tulin
    • Advances in concrete construction
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    • v.11 no.3
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    • pp.261-270
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    • 2021
  • In this study, a new understanding is presented on the microcracking behavior of high strength concrete (HSC) with steel fiber addition having prior compressive loading history. Microcracking behavior at critical stress (σcr) region, using seven fiber addition volume of 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, and 2.0% was evaluated, at two aspect ratios (60 and 75). The specimens were loaded up to a specified compressive stress levels (0.70fc-0.96fc), and subsequently subjected to split tensile tests. This was followed by microscopic analyses afterwards. Four compressive stress levels as percentage of fc were selected according to the linearity end point based on stress-time (σ-t) diagram under uniaxial compression. It was seen that pre-compression has an effect on the linearity end point as well as fiber addition where it lies within 85-91% of fc. Tensile strength gain was observed in some cases with respect to the 'maiden' tensile strength as oppose to tensile strength loss due to the fiber addition with teething effect. Aggregate cracking was the dominant failure mode instead of bond cracks due to improved matrix quality. The presence of the steel fiber improved the extensive failure pattern of cracks where it changes from 'macrocracks' to a branched network of microcracks especially at higher fiber dosages. The applied pre-compression resulted in hardening effect, but the cracking process is similar to that in concrete without fiber addition.

Damage-based stress-strain model of RC cylinders wrapped with CFRP composites

  • Mesbah, Habib-Abdelhak;Benzaid, Riad
    • Advances in concrete construction
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    • v.5 no.5
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    • pp.539-561
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    • 2017
  • In this study, the effects of initial damage of concrete columns on the post-repair performance of reinforced concrete (RC) columns strengthened with carbon-fiber-reinforced polymer (CFRP) composite are investigated experimentally. Four kinds of compression-damaged RC cylinders were reinforced using external CFRP composite wraps, and the stress-strain behavior of the composite/concrete system was investigated. These concrete cylinders were compressed to four pre-damaged states including low -level, medium -level, high -level and total damage states. The percentages of the stress levels of pre-damage were, respectively, 40, 60, 80, and 100% of that of the control RC cylinder. These damaged concrete cylinders simulate bridge piers or building columns subjected to different magnitudes of stress, or at various stages in long-term behavior. Experimental data, as well as a stress-strain model proposed for the behavior of damaged and undamaged concrete strengthened by external CFRP composite sheets are presented. The experimental data shows that external confinement of concrete by CFRP composite wrap significantly improves both compressive strength and ductility of concrete, though the improvement is inversely proportional to the initial degree of damage to the concrete. The failure modes of the composite/damaged concrete systems were examined to evaluate the benefit of this reinforcing methodology. Results predicted by the model showed very good agreement with those of the current experimental program.

Analysis of actively-confined concrete columns using prestressed steel tubes

  • Nematzadeh, Mahdi;Haghinejad, Akbar
    • Computers and Concrete
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    • v.19 no.5
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    • pp.477-488
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    • 2017
  • In this paper, an innovative technique for finite element (FE) modeling of steel tube-confined concrete (STCC) columns with active confinement under axial compressive loading is presented. In this method, a new constitutive model for the stress-strain relationship of actively-confined concrete is proposed. In total, 14 series of experimental STCC stub columns having active confinement were modeled using the ABAQUS software. The results obtained from the 3D model including the compressive strength at the initial peak point and failure point, as well as the axial and lateral stress-strain curves were compared with the experimental results to verify the accuracy of the 3D model. It was found that there existed a good agreement between them. A parametric study was conducted to investigate the effect of the concrete compressive strength, steel tube wall thickness, and pre-stressing level on the behavior of STCC columns with active confinement. The results indicated that increasing the concrete core's compressive strength leads to an increase in the compressive strength of the active composite column as well as its earlier failure. Furthermore, a reduction in the tube external diameter-to-wall thickness ratio affects the axial stress-strain curve and the confining pressure, while increasing the pre-stressing level has a negligible effect on the two.

Modified Micro-Mechanical Fiber Bridging Model for Crack Plane of Fiber Rreinforced Cementitious Composite (섬유보강 복합체의 균열면 해석을 위한 수정 미세역학 모델)

  • Shin, Kyung-Joon;Park, Jong-Bum
    • Proceedings of the Korea Concrete Institute Conference
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    • 2006.05b
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    • pp.365-368
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    • 2006
  • In this paper, the post cracking stress-crack width relationship of the composite is studied from a micromechanics points of view. Cook-Gordon debonding effect is studied by more refined method with considering of chemical friction of fiber interface. As a result, fiber with pre-debonding length retards stress development and shows more wide crack width for the same force level. longer pre-debonding length and lower pre-debonding bond strength results in lower full-debonding force, but same crack width.

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Non-Stationary Stress Analysis of Repaired Concrete Structures due to Hygral Transient Condition (대기 습도변화에 따른 콘크리트 보수체의 비정상적인 습도응력 조사)

  • 윤우현
    • Magazine of the Korea Concrete Institute
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    • v.9 no.3
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    • pp.157-166
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    • 1997
  • The object of this study was invest, igat, ing the failure phenomenon in the contact zone of rcpnired concrete structures due to the external climate change(hygral transient condition). This study was carrie out by calculating the non-stationary moisture and stress distribution in the repaired concrete structures with the cement mortar. In this analysis, main variables were the overlay thickness (Do=0.5-2.5cm). and the pre-wetting time(tc= l-5days). and the cxtcrnal 1.~1ative humidity(Ho=50-80%). The results show that the minimum overlay thickness and the minimum pre-wetting time are necessary to k e ~ p compressive stresses in the contact zone for a relative humidity.

Thermal Stress Analysis and Crack Control on the Heat of Hydration of Mass Concrete (매스콘크리트의 수화열에 관한 해석 및 온도균열 제어방안 연구)

  • 조선규;서석구;홍규선;윤철균
    • Proceedings of the Korea Concrete Institute Conference
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    • 1996.04a
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    • pp.264-269
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    • 1996
  • Thermal cracks are occurred when thermal stress due to the hydration of cement exceeds the tensile strength of concrete. In this study, the thermal stresses are investigated at the massive concrete like an anchorage of suspension bridge. The thermal crack can be controlled by considering the placing height, concrete type, pre-cooling and pipe cooling in the design stage.

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Temperature Crack Control in Slab Type구s Mass Concrete Structures (슬래브형 매스콘크리트 구조물의 온도균열제어)

  • 김동석;구본창;하재담;진형하;오승제;변근주
    • Proceedings of the Korea Concrete Institute Conference
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    • 1999.10a
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    • pp.333-336
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    • 1999
  • The crack of concrete induced by the heat of hydration is a serious problem, particularly in concrete structures such as mat-slab of nuclear reactor buildings, dams or large footings, foundations of high rise buildings, etc.. As a result of the temperature rise and restriction condition of foundation, the thermal stress which may induce the cracks can occur. Therefore the various techniques of the thermal stress control in massive concrete have been widely used. One of them is prediction of the thermal stress, besides low-heat cement which mitigates the temperature rise, pre-cooling which lowers the initial temperature of fresh concrete with ice flake, pipe cooling which cools the temperature of concrete with flowing water, design change which considers steel bar reinforcement, operation control and so on. The Aim of this paper is to verify the effect of low heat blended cement in reducing thermal stress in slab type's mass concrete such as container harbor structures.

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