• Title/Summary/Keyword: Reinforcement Cracking

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Effect of fiber reinforcing on instantaneous deflection of self-compacting concrete one-way slabs under early-age loading

  • Vakhshouri, Behnam;Nejadi, Shami
    • Structural Engineering and Mechanics
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    • v.67 no.2
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    • pp.155-163
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    • 2018
  • The Early-age construction loading and changing properties of concrete, especially in the multi-story structures can affect the slab deflection, significantly. Based on previously conducted experiment on eight simply-supported one-way slabs this paper investigates the effect of concrete type, fiber type and content, loading value, cracking moment, ultimate moment and applied moment on the instantaneous deflection of Self-Compacting Concrete (SCC) slabs. Two distinct loading levels equal to 30% and 40% of the ultimate capacity of the slab section were applied on the slabs at the age of 14 days. A wide range of the existing models of the effective moment of inertia which are mainly developed for conventional concrete elements, were investigated. Comparison of the experimental deflection values with predictions of the existing models shows considerable differences between the recorded and estimated instantaneous deflection of SCC slabs. Calculated elastic deflection of slabs at the ages of 14 and 28 days were also compared with the experimental deflection of slabs. Based on sensitivity analysis of the effective parameters, a new model is proposed and verified to predict the effective moment of inertia in SCC slabs with and without fiber reinforcing under two different loading levels at the age of 14 days.

Behavior of reinforced sustainable concrete hollow-core slabs

  • Al-Azzawi, Adel A.;Shallal, Mustafa S.
    • Advances in concrete construction
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    • v.11 no.4
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    • pp.271-284
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    • 2021
  • This study aims to trace the response of twelve one-way sustainable concrete hollow-core slabs made by reducing cement content and using replacement of coarse aggregate by plastic aggregate. The trial mixes comprise the 25, 50, 75, and 100% replacement of natural coarse aggregate. The compressive strength of the resulting lightweight concrete with full replacement of coarse aggregate by plastic aggregate was 28 MPa. These slabs are considered to have a reduced dead weight due to using lightweight aggregate and due to reducing cross-section through using voids. The samples are tested under two verticals line loads. Several parameters are varied in this study such as; nature of coarse aggregate (natural or recycled), slab line load location, the shape of the core, core diameter, flexural reinforcement ratio, and thickness of the slab. Strain gauges are used in the present study to measure the strain of steel in each slab. The test samples were fourteen one-way reinforced concrete slabs. The slab's dimensions are (1000 mm), (600 mm), (200 mm), (length, width, and thickness). The change in the shape of the core from circular to square and the use of (100 mm) side length led to reducing the weight by about (46%). The cracking and ultimate strength is reduced by about (5%-6%) respectively. With similar values of deflection. The mode of failure will remain flexural. It is recognized that when the thickness of the slab changed from (200 mm to 175 mm) the result shows a reduction in cracking and ultimate strength by about (6% and 7%) respectively.

Experimental and Analytical Study on the Surface Strain and Internal Pressure Due to Corrosion of Reinforcement (철근부식에 의한 콘크리트의 표면변형률과 내부팽창압에 대한 실험 및 해석연구)

  • 오병환;김기현;강의영;장승엽;김지상;서정문
    • Proceedings of the Korea Concrete Institute Conference
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    • 2001.11a
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    • pp.777-780
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    • 2001
  • Corrosion products of reinforcement in the concrete exerts pressure to the adjacent concrete that the concrete is subject to tensile stress. If the tensile strength exceeds the tensile strength, cracks are initiated around steel and propagates through concrete cover. Cracking of the cover means that the lifetime of the structure is ended. So the amount of corrosion which introduces crack in the concrete cover is a crucial factor in the reinforcement corrosion problem. In this study, relation between internal pressure and amount of corrosion are pursued by way of corrosion experiment and finite element analysis.

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Flexural Behavior of Concrete Beams Reinforced with GFRP Bars (GFRP 보강근을 사용한 콘크리트 보의 휨파괴 거동)

  • Ha Sang Hoon;Kim Jung Kyu;Hwang Keum Sik;Eo Seok Hong
    • Proceedings of the Korea Concrete Institute Conference
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    • 2005.11a
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    • pp.339-342
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    • 2005
  • This paper presents flexural test results of concrete beams reinforced with GFRP and conventional steel reinforcement for comparison. The beams were tested under static loading to investigate the effects of reinforcement ratio and compressive ,strength of concrete on cracking, deflection, ultimate capacity and mode of failure, This study attempts to establish a theoretical basis for the development of simple and rational design guideline. Test results show that ultimate capacity increases as the reinforcement ratio and concrete strength increase. The ultimate capacity increased up to $8\%-25\%$ by using high strength concrete. The deflection at maximum load of GFRP reinforced beams was about three times that of steel reinforced beams. For GFRP-reinforced beams, the ACI code 440 design method resulted in conservative flexural strength -estimates.

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Flexural Behavior of Prestressed Concrete Beams with CFRP(Carbon Fiber Reinforced Plastic) Tendons (CFRP 긴장재를 이용한 프리스트레스트 콘크리트 보의 휨거동)

  • 조병완;태기호;최용환
    • Proceedings of the Korea Concrete Institute Conference
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    • 2000.04a
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    • pp.639-644
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    • 2000
  • Prestressing steels are susceptible to corrosion, which is considered the major reason in the deterioration of prestressed concrete structures. To solve this problem, many research have been made to utilize new type of tendons. FRP tendons have many advantages compared to steel tendons. However, FRP tendons have some disadvantages, such as no plastic behavior. This study focused on the flexural behavior of prestresssed concrete beams which is fabricated by post-tensioning method with CFRP (Carbon Fiber Reinforced Plastic) tendons. Th results drawn from the study, prestressed concrete beams with CFRP tendons have higher flexural cracking load, flexural yielding load, and flexural fracture load. While displacement at the fracture stage is lower compared to prestressed concrete beams with steel tendon. Excessive steel reinforcement lead lower ductility index. So, appropriate reinforcement guideline is needed. Further more, prestressed concrete beams with CFRP tendons can have sufficient ductility index when ruptured by crushing of concrete or used unbonded tendon. Therefore, the best design method for prestressed concrete beams with CFRP tendons is over-reinforcement, and use of unbonded tendon.

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Computationally efficient 3D finite element modeling of RC structures

  • Markou, George;Papadrakakis, Manolis
    • Computers and Concrete
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    • v.12 no.4
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    • pp.443-498
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    • 2013
  • A detailed finite element modeling is presented for the simulation of the nonlinear behavior of reinforced concrete structures which manages to predict the nonlinear behavior of four different experimental setups with computational efficiency, robustness and accuracy. The proposed modeling method uses 8-node hexahedral isoparametric elements for the discretization of concrete. Steel rebars may have any orientation inside the solid concrete elements allowing the simulation of longitudinal as well as transverse reinforcement. Concrete cracking is treated with the smeared crack approach, while steel reinforcement is modeled with the natural beam-column flexibility-based element that takes into consideration shear and bending stiffness. The performance of the proposed modeling is demonstrated by comparing the numerical predictions with existing experimental and numerical results in the literature as well as with those of a commercial code. The results show that the proposed refined simulation predicts accurately the nonlinear inelastic behavior of reinforced concrete structures achieving numerical robustness and computational efficiency.

Time-dependent bond transfer length under pure tension in one way slabs

  • Vakhshouri, Behnam
    • Structural Engineering and Mechanics
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    • v.60 no.2
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    • pp.301-312
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    • 2016
  • In a concrete member under pure tension, the stress in concrete is uniformly distributed over the whole concrete section. It is supposed that a local bond failure occurs at each crack, and there is a relative slip between steel and surrounding concrete. The compatibility of deformation between the concrete and reinforcement is thus not maintained. The bond transfer length is a length of reinforcement adjacent to the crack where the compatibility of strain between the steel and concrete is not maintained because of partially bond breakdown and slip. It is an empirical measure of the bond characteristics of the reinforcement, incorporating bar diameter and surface characteristics such as texture. Based on results from a series of previously conducted long-term tests on eight restrained reinforced concrete slab specimens and material properties including creep and shrinkage of two concrete batches, the ratio of final bond transfer length after all shrinkage cracking, to THE initial bond transfer length is presented.

Effects of Shear Span-to-depth Ratio and Tensile Longitudinal Reinforcement Ratio on Minimum Shear Reinforcement Ratio of RC Beams (전단경간비와 주인장철근비가 철근콘크리트 보의 최소전단철근비에 미치는 영향)

  • Lee Jung-Yoon;Kim Wook-Yeon;Kim Sang-Woo;Lee Bum-Sik
    • Journal of the Korea Concrete Institute
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    • v.16 no.6 s.84
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    • pp.795-803
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    • 2004
  • To prevent the shear failure that occurs abruptly with no sufficient warning, the minimum amount of shear reinforcement should be provided to reinforced concrete(RC) beams. The minimum amount of shear reinforcement of RC beams is influenced by not only compressive strength of concrete but also shear span-to-depth ratio and ratio of tensile longitudinal reinforcement. In this paper, 14 RC beams were tested in order to observe the influences of shear span-to-depth ratio, ratio of tensile longitudinal reinforcement, and compressive strength of concrete. The test results indicated that the rate of shear strength to the diagonal cracking strength of RC beams with the same amount of shear reinforcement increased as the ratio of tensile longitudinal reinforcement increased, while it decreased as the shear span-to-depth ratio increased. The observed test results were compared with the calculated results by the current ACI 318-02 Building Code and the proposed equation.

Steel Fibers Efficiency as Shear Reinforcement in Concrete Beams (섬유보강콘크리트 보의 전단거동에 미치는 강섬유의 효과)

  • 문제길;홍익표
    • Magazine of the Korea Concrete Institute
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    • v.6 no.2
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    • pp.118-128
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    • 1994
  • There have been conducted a lot of works on shear behavior of steel fiber reinforced concrete beams. Fiber reinforced concrete beams without shear reinforcement were tested to determine their cracking shear strengths and ultimate shear capacities. Results of tests on 14 reinforced concrete beams (including 11 containing steel fibers) are reported. Two parameters were varied in the study, namely, the volume fraction of fibers and shear span-to-depth ratio.The effects of fiber incorporation on failure modes, deflections, cracking shear strength, and ul~imate shear strength have been examined. Resistance to shear stresses have been found to be improved by the inclusion of fibers, The mode of failure changed from shear to flexure when the shear span-to-depth ratio exceeds 3.4. Based on these investigations, a method of computing the shear strength of steel fiber reinforced concrete beam is suggested. The comparisons between computed values and expenmentally observed values are shown to verify the proposed theoretical treatment and steel fibers efficiency.

Performance of Geogrids for Retarding Reflection Crack of Asphalt Overlay Pavement (아스팔트 덧씌우기의 반사균열 지연을 위한 지오그리드의 적용성 연구)

  • Kim, Kwang-Woo;Doh, Young-Soo;Kim, Bun-Chang;Lee, Moon-Sup
    • International Journal of Highway Engineering
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    • v.7 no.2 s.24
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    • pp.1-12
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    • 2005
  • This study was conducted to evaluate effect of geogrid and fabric, which are used underneath the overlaid asphalt pavement for retarding reflection cracking by simulated laboratory test. In this study, an interlayer at the interface between old concrete pavement surface and overlaid asphalt mixture, and polymer-modifier were used as an effort of retarding reflection crack initiation and for strengthening mixture. Five products were used in preparation of asphalt concrete beam specimen which was tack coated on top of jointed concrete block. Simulated Mode I and II fracture test were conducted under wheel loading and results were compared among those products. From the test results, several material and reinforcement combinations were observed to have a significant retardation effect against reflection cracking. The most effectively strengthened pavement against reflection cracking was found to be the LDPE-modifier asphalt mixture with a grid reinforcement at the bottom.

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