• Title/Summary/Keyword: steel reinforcement strain

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Application of Concentrated FRP Bars to Enhance the Capacity of Two-Way Slabs (2방향 슬래브의 성능 향상을 위한 집중 배근된 FRP 바의 적용)

  • Lee, Joo-Ha;Yang, Jun-Mo;Yoon, Young-Soo
    • Journal of the Korea Concrete Institute
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    • v.19 no.6
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    • pp.727-734
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    • 2007
  • The influence of the differences in the physical and mechanical properties between fiber-reinforced polymer (FRP) and conventional steel, concentrated reinforcement in the immediate column region, as well as using steel fiber-reinforced concrete (SFRC) in the slab near the column faces, on the punching behavior of two-way slabs were investigated. The punching shear capacity, stiffness, ductility, strain distribution, and crack control were investigated. Concentrating of the slab reinforcement and the use of SFRC in the slab enhanced the punching behavior of the slabs reinforced with glass fiber-reinforced polymer (GFRP) bars. In addition the test results of the slabs with concentrated reinforcement were compared with various code equations and the predictions proposed in the literature specifically for FRP-reinforced slabs. An appropriate method for determining the reinforcement ratio of slabs with a banded distribution was also investigated to allow predictions to properly reflect the benefit of the slab reinforcement concentration.

Prediction of residual mechanical behavior of heat-exposed LWAC short column: a NLFE model

  • Obaidat, Yasmeen T.;Haddad, Rami H.
    • Structural Engineering and Mechanics
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    • v.57 no.2
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    • pp.265-280
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    • 2016
  • A NLFE model was proposed to investigate the mechanical behavior of short columns, cast using plain or fibrous lightweight aggregate concrete (LWAC), and subjected to elevated temperatures of up to $700^{\circ}C$. The model was validated, before its predictions were extended to study the effect of other variables, not studied experimentally. The three-dimensional NLFE model was developed using ANSYS software and involved rational simulation of thermal mechanical behavior of plain and fibrous LWAC as well as longitudinal and lateral steel reinforcement. The prediction from the NLFE model of columns' mechanical behavior, as represented by the stress-strain diagram and its characteristics, compared well with the experimental results. The predictions of the proposed models, considering wide range of lateral reinforcement ratios, confirmed the behaviors observed experimentally and stipulated the importance of steel confinement in preserving post-heating mechanical properties of plain and fibrous LWAC columns, being subjected to high temperature.

Earthquake resistance of structural walls confined by conventional tie hoops and steel fiber reinforced concrete

  • Eom, Taesung;Kang, Sumin;Kim, Okkyue
    • Earthquakes and Structures
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    • v.7 no.5
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    • pp.843-859
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    • 2014
  • In the present study, the seismic performance of structural walls with boundary elements confined by conventional tie hoops and steel fiber concrete (SFC) was investigated. Cyclic lateral loading tests on four wall specimens under constant axial load were performed. The primary test parameters considered were the spacing of boundary element transverse reinforcement and the use of steel fiber concrete. Test results showed that the wall specimen with boundary elements complying with ACI 318-11 21.9.6 failed at a high drift ratio of 4.5% due to concrete crushing and re-bar buckling. For the specimens where SFC was selectively used in the plastic hinge region, the spalling and crushing of concrete were substantially alleviated. However, sliding shear failure occurred at the interface of SFC and plain concrete at a moderate drift ratio of 3.0% as tensile plastic strains of longitudinal bars were accumulated during cyclic loading. The behaviors of wall specimens were examined through nonlinear section analysis adopting the stress-strain relationships of confined concrete and SFC.

Effect of cover depth and rebar diameter on shrinkage behavior of ultra-high-performance fiber-reinforced concrete slabs

  • Yoo, Doo-Yeol;Kwon, Ki-Yeon;Yang, Jun-Mo;Yoon, Young-Soo
    • Structural Engineering and Mechanics
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    • v.61 no.6
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    • pp.711-719
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    • 2017
  • This study investigates the effects of reinforcing bar diameter and cover depth on the shrinkage behavior of restrained ultra-high-performance fiber-reinforced concrete (UHPFRC) slabs. For this, twelve large-sized UHPFRC slabs with three different rebar diameters ($d_b=9.5$, 15.9, and 22.2 mm) and four different cover depths (h=5, 10, 20, and 30 mm) were fabricated. In addition, a large-sized UHPFRC slab without steel rebar was fabricated for evaluating degree of restraint. Test results revealed that the uses of steel rebar with a large diameter, leading to a larger reinforcement ratio, and a low cover depth are unfavorable regarding the restrained shrinkage performance of UHPFRC slabs, since a larger rebar diameter and a lower cover depth result in a higher degree of restraint. The shrinkage strain near the exposed surface was high because of water evaporation. However, below a depth of 18 mm, the shrinkage strain was seldom influenced by the cover depth; this was because of the very dense microstructure of UHPFRC. Finally, owing to their superior tensile strength, all UHPFRC slabs with steel rebars tested in this study showed no shrinkage cracks until 30 days.

Experimental Study and Confinement Analysis on RC Stub Columns Strengthened with Circular CFST Under Axial Load

  • Liang, Hongjun;Lu, Yiyan;Hu, Jiyue;Xue, Jifeng
    • International journal of steel structures
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    • v.18 no.5
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    • pp.1577-1588
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    • 2018
  • As the excellent mechanical performance and easy construction of concrete filled steel tubes (CFST) composite structure, it has the potential to be used to strengthen RC pier columns. Therefore, tests were conducted on 2 reinforcement concrete (RC) stub columns and 9 RC columns strengthened with circular CFST under axial loading. The test results show that the circular CFST strengthening method is effective since the mean bearing capacity of the RC columns is increased at least 3.69 times and the ductility index is significantly improved more than 30%. One of the reasons for enhancement is obvious confinement provided by steel tube besides the additional bearing capacity supplied by the strengthening materials. From the analysis of the enhancement ratio, the strengthening structure has at least an extra 20% amplification except for taking full advantage of the strength of the strengthening material. Through the analysis of confining stress provided by steel tube and the stress-strain relationship of confined concrete, it is found that the strength of the core concrete can be increased by 21-33% and the ultimate strain can be enhanced to beyond $15,000{\mu}{\varepsilon}$.

Study on the Strength Characteristics and Flexural Toughness of Steel Fiber Reinforced Polymer Concrete (강섬유 보강 폴리머 콘크리트의 강도특성 및 휨인성에 관한 연구)

  • 김기락;연규석;이윤수
    • Journal of the Korea Concrete Institute
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    • v.11 no.4
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    • pp.137-145
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    • 1999
  • The use of steel fiber reinforced to improve the strength and flexural toughness of concrete is well known, but reinforcement of polymer concrete with steel fibers has been hardly reported till now. Polymer concrete has high strength, durability and freeze-thaw resistance than that of cement concrete, but it has disadvantage such as low flexural toughness. In this paper, the strength characteristics and flexural toughness of steel fiber reinforced polymer concrete are investigated experimentally with various steel fiber aspect ratios($\ell$/d), and contents(vol.%). As the result, the flexural and splitting tensile strengths and flexural toughness were increased aspect ratio, and reach the maximums at a aspect ratio of 50. The relationship between the compressive, flexural and splitting tensile strength were high. And the relationship between flexural strength and strain energy was approximately linear.

Deformation Characteristics of Reinforced Polymer Concrete Beams (철근보강 폴리마 콘크리트보의 변형특성)

  • 연규석
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.30 no.1
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    • pp.63-72
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    • 1988
  • The primary objective of the study was to find the deformation characteristics of reinforced polymer concrete beams. A test program was carried out to compare the behavior in deformation of polyester and MMA concrete beams with cement concrete beams but with varying ratios of tensile reinforcement. From the results the following conclusions can be made. 1.The various strengths of polymer concrete ware very high compared to the strengths for cement concrete. Also, compared to conventional concrete beams, flexural strength of reinforced polymer concrete beams was distinctly higher for the same section and steel ratios. 2.The polymer concrete beams exhibit large deflections accompanied by relatively high strengths as compared to cement concrete beams. 3.The average ultimate strain at the extreme compression fiber of polymer concrete beams was 0.01 1 cm / cm, and this value was about three to four times as large as that of cement concrete beams, 4.The polymer concrete beams developed more cracks which were more wide crack distribution spacing than the cement concrete beams, and the beams failed in a more ductile manner. 5.The reinforcing steel ratio has a significant effect on the beam strength, load-deflection response, stress-strain curve, and crack pattern of polymer concrete beams.

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Cracking Behavior of RC Panels under Biaxial Tension (이축인장을 받는 철근콘크리트 패널의 균열 거동)

  • 곽효경;김도연
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2003.10a
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    • pp.599-606
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    • 2003
  • An analytical model which can simulate the post-cracking nonlinear behavior of reinforced concrete (RC) members such as bars and panels subjected to uniaxial and biaxial tensile stresses is presented. The proposed model includes the description of biaxial failure criteria and the average stress-strain relation of reinforcing steel. Based on strain distribution functions of steel and concrete after cracking, average response of an embedded reinforcement, a criterion to consider the tension-stiffening effect is proposed using the concept of average stresses and strains. The validity of the introduced model is established by comparing the analytical predictions for reinforced concrete tension members with results from experimental studies. Finally, correlation studies between analytical results and experimental data from biaxial tension test are conducted with the objective to establish the validity of the proposed models and identify the significance of various effects on the response of biaxially loaded reinforced concrete panels.

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A Experimental Study for Stress-Strain Behavior and Energy Capacity of Confinement Steel (심부구속철근의 응력-변형률 거동 및 에너지 성능에 관한 실험적 연구)

  • Lee, Jae-Hoon;Ko, Seong-Hyun;Hwang, Jung-Kil;Son, Hyun-A
    • Proceedings of the Korea Concrete Institute Conference
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    • 2006.11a
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    • pp.77-80
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    • 2006
  • Longitudinal reinforcements of the plastic hinge region were behaved tensile deformation and compressional deformation by direction of lateral loading. However Confinement steels were behaved only tensile deformation by lateral loading. Transverse steels were laid the state of tension in the lateral loading of time, and they were laid state that stress is zero when it was removed lateral load. Nine specimens were tested under cyclic stresses(tension and zero). The purpose of this research is to investigate the strain behavior and capacity of energy for confinement steel. The selected test variables are $L/d_b(L/d_b=6)$, size of reinforcement and specified yielding strength(300, 400, 500 MPa).

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Shape Extraction of Stiffeners of H-beam using Topologically Structural Optimization (위상최적설계를 이용한 H형강 부재의 스티프너 형상탐색)

  • Jung, Wonsik;Banh, Thien Thanh;Lee, Dongkyu
    • Journal of Korean Association for Spatial Structures
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    • v.23 no.1
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    • pp.15-23
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    • 2023
  • In this work, we deal with the feasibility of structural topology optimization for beam designs using retrofits that optimally allocates the reinforcement to the web under the condition that designers set bolt regions for H-beams of different dimensions. Mean compliance or minimal strain energy is considered for the optimization. Volume fraction is given to the design space to assign appropriate steel material quantities. The purpose of this study is to evaluate optimal shapes of stiffeners with the maximum rigidity that improves the axial and shear performance of the H-beam and to satisfy a given safety design standard of H-beam and stiffeners in case arbitrary load effect and resistances. Finally, the effectiveness of stiffness-based topology optimization on stiffeners is verified with several practical applicable examples.