• Earthquakes and Structures
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• 제24권2호
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• pp.97-109
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• 2023

This experimental study investigates the effectiveness of applying carbon fiber reinforced polymer (CFRP) jackets for the retrofit of short reinforced concrete (RC) columns with inadequate transverse reinforcement and stirrup spacing to longitudinal rebar diameter equal to 12. RC columns scaled at 1/3, with round and square section, were subjected to axial compression up to failure. A damage scale is introduced for the assessment of the damage severity, which focusses on the extent of buckling of the longitudinal rebars. The damaged specimens were subsequently repaired with unidirectional CFRP jackets without any treatment of the buckled reinforcing bars and were finally re-tested to failure. Test results indicate that CFRP jackets may be effectively applied to rehabilitate RC columns (a) with inadequate transverse reinforcement constructed according to older practices so as to meet modern code requirements, and (b) with moderately buckled bars without the need of previously repairing the reinforcement bars, an application technique which may considerably facilitate the retrofit of earthquake damaged RC columns. Factors for the estimation of the reduced mechanical properties of the repaired specimens compared to the respective values for intact CFRP-jacketed specimens, in relation to the level of damage prior to retrofit, are proposed both for the compressive strength and the average modulus of elasticity. It was determined that the compressive strength of the retrofitted CFRP-jacketed columns is reduced by 90% to 65%, while the average modulus of elasticity is lower by 60% to 25% in respect to similar undamaged columns jacketed with the same layers of CFRP.

• Computers and Concrete
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• 제32권1호
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• pp.1-13
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• 2023

This paper discusses a framework for predicting the flexural strength of prestressed and non-prestressed FRP reinforced T-shaped concrete beams using soft computing techniques. An analysis of 83 tests performed on T-beams of varying widths has been conducted for this purpose with different widths of compressive face, beam depth, compressive strength of concrete, area of prestressed and non-prestressed FRP bars, elasticity modulus of prestressed and non-prestressed FRP bars, and the ultimate tensile strength of prestressed and non-prestressed FRP bars. By analyzing the data using two soft computing techniques, named artificial neural networks (ANN) and gene expression programming (GEP), the fundamental parameters affecting the flexural performance of prestressed and non-prestressed FRP reinforced T-shaped beams were identified. The results showed that although the proposed ANN model outperformed the GEP model with higher values of R and lower error values, the closed-form equation of the GEP model can provide a simple way to predict the effect of input parameters on flexural strength as the output. The sensitivity analysis results revealed the most influential input parameters in ANN and GEP models are respectively the beam depth and elasticity modulus of FRP bars.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.189-192
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• 2005

Glass fiber reinforced polymer (GFRP) bars gain increasingly more attention as a reinforcing option for concrete because of their corrosion resistance and non-magnetism. GFRP reinforcement for concrete does not have the same shape as steel reinforcement. Therefore, the bond performance of FRP bars, unlike that of steel, is dependent on their design, manufacture and mechanical properties. This paper studied the effect of high strength concrete on the bond strength of GFRP bars. Twenty-nine specimens having different compressive strength of concrete were tested in order to examine the bond behavior of GFRP bars.

• Earthquakes and Structures
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• 제7권5호
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• pp.861-875
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• 2014

This paper studies the response of seismic behavior of reinforced concrete exterior beam-column joints under reversal loading with different anchorages and joint core details. The joint core was detailed without much confinement (group-I) and/or with proposed X-cross bars in the core (group-II). The beam longitudinal reinforcement's anchorages were designed as per ACI 352 (headed bars), ACI 318 (conventional $90^{\circ}$ bent hooks) and IS 456 ($90^{\circ}$ bent hooks with extended tails). The nonlinear finite element analysis response of the beam-column joints was studied, along with initial and progressive cracks up to failure. The experimental and analytical results were compared and presented in this paper to make more scientific conclusions.

• Structural Engineering and Mechanics
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• 제90권3호
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• pp.301-311
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• 2024

Different methods have been proposed in the literature for splicing the reinforcing bars in the construction of concrete structures, which are alternatively used depending on design requirements. The most common approach is the lap splicing which is known as a cost-effective method although, its main disadvantages including congestion of bars at the lap zone and consequently, material wastage has motivated utilization of the other techniques such as mechanical splices (couplers). To better evaluate the performance of the couplers, 6 reinforced concrete (RC) beams whose difference is only the type and location of splices have been experimentally studied in this paper. Based on the results, the mechanical connection of the bars did not markedly affect the load-carrying capacity of the specimens. Moreover, it was observed that after applying the loads and failure of the specimens, none of the bars ruptured at the splice location and all couplers remained undamaged.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.120-123
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• 2004

The lap splice lengths of deformed steel reinforcing bars and GFRP bars were experimentally compared using beam specimens. The purpose was to evaluate the length required of the GFRP bar to develop strength at least equivalent to the conventional steel reinforcing bar. The main test variable was the lap splice length: 10, 20, 30 $d_b$ for the deformed steel bars and 20, 30, 40 $d_b$ for the GFRP bars. Two different types of GFRP bars were tested: (1) one with spiral-type deformation and (2) plain round bars. Elastic modulus was about 1/5 of the steel bars while the tensile strength was about 690 MPa for the GFRP bars. Nominal diameter of the GFRP bars and steel bars was 12.7 and 13 mm, respectively. Normal strength concrete (28-day $f_{cu}$ = 30 MPa) was used. For the conventional steel bars (SD400 grade), strength over 400 MPa in tension was developed using the lap splice length of 20 and 30 $f_{cu}$. Only $87\%$ of the nominal yield strength was reached with the lap splice length of 10 $d_b$. For the spiral-type deformed GFRP bars with $40-d_b$ lap splice length, 440 MPa in tension was determined. The maximum tensile strength developed of the GFRP bars with smaller lap splice lengths decreased. The plain GFRP bar was not effective in developing the tensile strength even with $40-d_b$ lap splice length. Development of the cracks on beam surface was clearly visible for the beams reinforced with the GFRP bars. Mid-span deflections, however, were significantly smaller than the comparable beams with conventional steel bars indicating potential ductility problem.

• Structural Engineering and Mechanics
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• 제87권6호
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• pp.585-599
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• 2023

Geopolymer concrete (GC) can be competently utilized as a practical replacement for cement to prevent a high carbon footprint and to give a direction toward sustainable concrete construction. Moreover, previous studies mostly focused on the axial response of glass fiber reinforced polymer (glass-FRP) concrete compressive elements without determining the effectiveness of repairing them after their partial damage. The goal of this study is to assess the structural effectiveness of partially damaged GC columns that have been restored using carbon fiber reinforced polymer (carbon-FRP). Bars made of glass-FRP and helix made of glass-FRP are used to reinforce these columns. For comparative study, six of the twelve circular specimens-each measuring 300 mm×1200 mm-are reinforced with steel bars, while the other four are axially strengthened using glass-FRP bars (referred to as GSG columns). The broken columns are repaired and strengthened using carbon-FRP sheets after the specimens have been subjected to concentric and eccentric compression until a 30% loss in axial strength is attained in the post-peak phase. The study investigates the effects of various variables on important response metrics like axial strength, axial deflection, load-deflection response, stiffness index, strength index, ductility index, and damage response. These variables include concentric and eccentric compression, helix pitch, steel bars, carbon-FRP wrapping, and glass-FRP bars. Both before and after the quick repair process, these metrics are evaluated. The results of the investigation show that the axial strengths of the reconstructed SSG and GSG columns are, respectively, 15.3% and 20.9% higher than those of their original counterparts. In addition, compared to their SSG counterparts, the repaired GSG samples exhibit an improvement in average ductility indices of 2.92% and a drop in average stiffness indices of 3.2%.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.185-188
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• 2008

FRP 보강근은 철근부식의 근본적인 대책으로서 높은 인장강도와 내부식성이 우수한 재료이다. 그러나 낮은 탄성계수로 인해 부재의 처짐 및 균열이 철근콘크리트를 사용한 부재에 비하여 크게 발생하는 문제점이 있으며, 취성적인 성질로 인하여 파괴가 급격히 발생할 우려가 있다. 이러한 FRP 보강근을 구조부재에 사용하기 위해서는 기존의 철근콘크리트 부재설계와는 다른 개념이 필요하며, 이미 구조부재에 FRP 보강근을 사용하고 있는 외국의 경우 기존의 FRP 보강근을 사용한 구조부재의 설계를 위한 제안식들은 실험에 의한 계수의 추가 등으로 철근콘크리트 구조설계식을 수정하는 형태로서 제안되어지고 있다. 그러나 이러한 방법은 설계식을 복잡하게 하며, 철근콘크리트와 다른 FRP 보강근의 특성을 적절히 반영하고 있다고 할 수 없다. 또한, 기존의 설계식의 수정된 형태에서는 하중저감계수와 같은 안전계수(safety factor)를 제안하고 있으나, 정확한 신뢰성레벨은 알지 못하며, 실험에 의한 경험적 값의 성격이 강하다. 따라서 본 연구에서는 FRP bar를 사용한 보의 불확실성을 조사하고, FRP bar를 사용한 부재의 신뢰성지수를 평가하였다.

• Steel and Composite Structures
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• 제34권1호
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• pp.17-34
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• 2020

This paper investigates the flexural behavior of concrete beams reinforced longitudinally with either steel bars, molded glass-fiber reinforced polymer (GFRP) grating mesh or pultruded glass-fiber reinforced polymer (GFRP) grating mesh, under four-point bending. The variables included in this study were the type of concrete (normal weight concrete, perlite concrete and vermiculite concrete), type of the longitudinal reinforcement (steel bars, molded and pultruded GFRP grating mesh) and the longitudinal reinforcement ratio (between 0.007 and 0.035). The influences of these variables on the load-midspan deflection curves, bending stiffness, energy absorption and failure modes were investigated. A total of fifteen beams with a cross-sectional dimension of 160 mm × 210 mm and an overall length of 2400 mm were cast and divided into three groups. The first group was constructed with normal weight concrete and served as a reference concrete. The second and third groups were constructed with perlite concrete and vermiculite concrete, respectively. An innovative type of stirrup was used as shear reinforcement for all beams. The results showed that the ultimate load of the beams reinforced with pultruded GFRP grating mesh ranged between 19% and 38% higher than the ultimate load of the beams reinforced with steel bars. The bending stiffness of all beams was influenced by the longitudinal reinforcement ratio rather than the type of concrete. Failure occurred within the pure bending region which means that the innovative stirrups showed a significant resistance to shear failure. Good agreement between the experimental and the analytical ultimate load was obtained.

• 한국공간구조학회논문집
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• 제20권2호
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• pp.31-38
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• 2020

U-flanged truss beam is composed of u-shaped upper steel flange, lower steel plate of 8mm or more thickness, and connecting lattice bars. Upper flange and lower plate are connected by the diagonal lattice bars welded on the upper and lower sides. In this study, the details of delayed buckling of lattice members were developed through reinforcement of the end section, in order to improve structural capacity of U-flanged Truss Steel Beam. To verify the effects of these details, the simple beam experiment was conducted. The maximum capacity of all the specimens were determined by the buckling of the lattice. The vertical reinforced details of the ends with steel plates, rather than the details reinforced with steel bars, are confirmed to be a valid method for enhancing the structural capacity of the U-flanged Truss beam. In addition, U-flanged Truss Steel Beam with reinforced endings with steel plates can exhibit sufficient capacity of the lattice buckling by the formulae according to Korean Building Code (KBC, 2016) and Eurocode 3.