• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.57-66
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• 2015

This paper is a preliminary study to apply the lightweight concrete slabs reinforced with GFRP (glass fiber reinforced polymer) bars to the bridge deck slabs or some other concrete structures. So, some different behaviors between the conventional steel reinforced concrete slab and the lightweight concrete slab reinforced with GFRP bars were investigated. For this purpose, a number of slabs were constructed and then the three point bending test and numerical analysis for these slabs were performed. The flexural test results showed that the lightweight concrete slabs reinforced with GFRP bars were failed by the shear failure due to the over-reinforced design. The weight and failure load of the GFRP bar reinforced lightweight concrete slabs were 72% and 58% of the steel reinforced concrete slab with the same dimensions, respectively. Results of the numerical analysis for these slabs using a commercial program, midas FEA, showed that the load-deflection curve could be simulated well until the shear failure of the slabs, but the applied loads and the deflections continuously increased even beyond the shear failure loads.

• Textile Coloration and Finishing
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• v.28 no.4
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• pp.246-252
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• 2016

In comparison to metal alloys, braided composite features a high impact resistance and crash energy absorption potential, and also it still remained competitive stiffness and strength properties. Braiding angle is one of the most important parameters which affect the mechanical behaviors of braided composite. This paper presents transverse low velocity impact failure behavior analysis on the carbon 3D triaxial braided composite tube with the braiding angle of $20^{\circ}$, $50^{\circ}$ and $80^{\circ}$. The flexural behaviour of 3D triaxial braided composite tube under bending loads was studied by conducting quasistatic three point bending test. Also, the low velocity impact responses of the braided composite tubes were also tested to obtain load-displacement curves and energy absorption. Consequently, the increase of the braided angle, the peak load also increases owing to the bigger bending stiffness.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.3
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• pp.99-108
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• 2012

In this paper, to intend anticorrosive effect and weight reduction of conventional reinforced concrete slab, lightweight concrete slab reinforced with glass fiber reinforced polymer(GFRP) bar was considered and some basic behaviour of the slab were investigated. Measurement of splitting tensile strength and fracture energy of the concrete, a number of flexural experiment of the slab, numerical analysis using nonlinear finite element analysis, and comparison of the experimental results to the numerical analysis, were conducted. As a result, even the weight of the lightweight concrete slab could be reduced by about 28% than the normal concrete slab, failure load of the lightweight concrete slab was 36% smaller than the normal concrete slab. Such a thing can be attributed to the lower axial stiffness and lower bond strength of GFRP bar. In the numerical analysis, to consider decreasing property of bond strength of the lightweight concrete, interface element was used between the concrete and the GFRP bar elements and this method was shown to be a better way for the numerical analysis to approach the experimental results.

• Steel and Composite Structures
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• v.15 no.6
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• pp.623-643
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• 2013

Concrete filled steel tubular members (CFST) become a popular choice for modern building construction due to their numerous structural benefits and at the same time aging of those structures and member deterioration are often reported. Therefore, actions like implement of new materials and strengthening techniques become essential to combat this problem. The application of carbon fibre reinforced polymer (CFRP) with concrete structures has been widely reported whereas researches related to strengthening of steel structures using fibre reinforced polymer (FRP) have been limited. The main objective of this study is to experimentally investigate the suitability of CFRP to strengthening of CFST members under flexure. There were three wrapping schemes such as Full wrapping at the bottom (fibre bonded throughout entire length of beam), U-wrapping (fibre bonded at the bottom throughout entire length and extended upto neutral axis) and Partial wrapping (fibre bonded in between loading points at the bottom) introduced. Beams strengthened by U-wrapping exhibited more enhancements in moment carrying capacity and stiffness compared to the beams strengthened by other wrapping schemes. The beams of partial wrapping exhibited delamination of fibre and were failed even before attaining the ultimate load of control beam. The test results showed that the presence of CFRP in the outer limits was significantly enhanced the moment carrying capacity and stiffness of the beam. Also, a non linear finite element model was developed using the software ANSYS 12.0 to validate the analytical results such as load-deformation and the corresponding failure modes.

• Journal of Korean Association for Spatial Structures
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• v.15 no.2
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• pp.69-77
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• 2015

Ultra High Performance Fiber Reinforced Concrete (UHPFRC) has a outstanding tensile hardening behaviour after a crack develops, which gives ductility to structures. Existing shear strength model for fiber reinforced concrete is entirely based on crack opening behavior(mode I) which comes from flexural-shear failure, not considering shear-slip behavior(mode II). To find out the mode I and mode II behavior on a crack in UHPFRC simultaneously, maximum shear strength of cracked UHPFRC is investigated from twenty-four push-off test results. The shear stress on a crack is derived as variable of initial crack width and fiber volume ratio. Test results show that shear slippage is proportional to crack opening, which leads to relationship between shear transfer strength and crack width. Based on the test results a hypothesis is proposed for the physical mechanics of shear transfer in UHPFRC by tensile hardening behavior in stead of aggregate interlocking in reinforced concrete. Shear transfer strength based on tensile hardening behavior in UHPFRC is suggested and this suggestion was verified by comparing direct tensile test results and push-off test results.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.3
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• pp.1-12
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• 2004

Due to the 1989 Loma Prieta, 1995 Hyogoken Nambu earthquakes, etc, a number of bridge columns  were collapsed in flexure-shear failures as a consequence of the premature termination of the column longitudinal reinforcement. Nevertheless, previous researches for the performance of bridge columns were concentrated on the flexural failure mode. It is well understood that the seismic behaviour of RC bridge piers was dependent on the performance of the plastic hinge of RC bridge piers, the ductility of which was desirable to be computed on the basis of the curvature. Experimental investigation was made to evaluate the variation of the curvature of the plastic hinge  region for the seismic performance of earthquake-damaged RC columns in flexure-shear failure mode. Seven test specimens in the aspect ratio of 2.5 were made with test parameters: confinement ratios, lap splices, and retrofitting FRP materials. They were damaged under series of artificial earthquakes that could be compatible in Korean peninsula. Directly after the pseudo-dynamic test, damaged columns were retested under inelastic reversal cyclic loading under a constant axial load, $P=0.1f_{ck}A_g$. Residual seismic capacity of damaged specimens was evaluated by analzying the moment-curvature hysteresis and the curvature ductility. Test results show that the biggest curvature was developed around 15cm above the footing, which induced the column failure. It was observed that RC bridge specimens with lap-spliced longitudinal steels appeared to fail at low curvature ductility but significant improvement was made in the curvature ductility of RC specimens with FRP straps wrapped around the plastic hinge region. Based on the experimental variation of the curvature of RC specimens, new equivalent length of the plastic hinge region was proposed by considering the lateral confinement in this study. The analytical and experimental relationship between the displacement and the curvature ductility were compared based on this proposal, which gave excellent result.

• Steel and Composite Structures
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• v.22 no.5
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• pp.937-974
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• 2016

While extensive efforts have been made in the past to develop finite element models (FEMs) for concrete-filled steel tubular columns (CFSTCs), these models may not be suitable to be used in some cases, especially in view of the utilisation of high strength steel and high strength concrete. A method is presented herein to predict the complete stress-strain curve of concrete subjected to tri-axial compressive stresses caused by axial load coupled with lateral pressure due to the confinement action in square and rectangular CFSTCs with normal and high strength materials. To evaluate the lateral pressure exerted on the concrete in square and rectangular shaped columns, an accurately developed FEM which incorporates the effects of initial local imperfections and residual stresses using the commercial program ABAQUS is adopted. Subsequently, an extensive parametric study is conducted herein to propose an empirical equation for the maximum average lateral pressure, which depends on the material and geometric properties of the columns. The analysis parameters include the concrete compressive strength ($f^{\prime}_c=20-110N/mm^2$), steel yield strength ($f_y=220-850N/mm^2$), width-to-thickness (B/t) ratios in the range of 15-52, as well as the length-to-width (L/B) ratios in the range of 2-4. The predictions of the behaviour, ultimate axial strengths, and failure modes are compared with the available experimental results to verify the accuracy of the models developed. Furthermore, a design model is proposed for short square and rectangular CFSTCs. Additionally, comparisons with the prediction of axial load capacity by using the proposed design model, Australian Standard and Eurocode 4 code provisions for box composite columns are carried out.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.68-77
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• 2012

The joint of existing steel grid composite deck is composed of lap splice of reinforcing bar with end hooks and field-placed concrete. In this study, bending tests of deck joint composed of concrete shear key and high tension bolts are carried out for the design variable, concrete shear key strengthened with steel plate or not, and test results are compared with flexural performance of the existing deck joint. Test results showed that the mechanical deck joint has about 30% ~ 60% more ultimate bending strength than the existing joint. According to analysis results of moment-curvature relationship, the initial bending stiffness of the existing deck joint is some higher than that of mechanical joint. But, after crack failure the structural performance of the existing deck joint is rapidly reduced. Furthermore, the deck joint with the strengthened shear key with steel plate has more bending moment capacity than the deck joint without strengthening. And strengthening of shear key has positive influence on the increase of bending stiffness.

• Steel and Composite Structures
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• v.46 no.1
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• pp.75-92
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• 2023

The novel composite cold-formed steel (CFS)/engineered cementitious composites (ECC) beams have been recently presented. The new composite section exhibited superior structural performance as a flexural member, benefiting from the lightweight thin-walled CFS sections with improved buckling and torsional properties due to the restraints provided by thinlayered ECC. This paper investigated the shear performance of the new composite CFS/ECC section. Twenty-eight simply supported beams, with a shear span-to-depth ratio of 1.0, were assembled back-to-back and tested under a 3-point loading scheme. Bare CFS, composite CFS/ECC utilising ECC with Polyethylene fibres (PE-ECC), composite CFS/MOR, and CFS/HSC utilising high-strength mortar (MOR) and high-strength concrete (HSC) as replacements for PE-ECC were compared. Different failure modes were observed in tests: shear buckling modes in bare CFS sections, contact shear buckling modes in composite CFS/MOR and CFS/HSC sections, and shear yielding or block shear rupture in composite CFS/ECC sections. As a result, composite CFS/ECC sections showed up to 96.0% improvement in shear capacities over bare CFS, 28.0% improvement over composite CFS/MOR and 13.0% over composite CFS/HSC sections, although MOR and HSC were with higher compressive strength than PE-ECC. Finally, shear strength prediction formulae are proposed for the new composite sections after considering the contributions from the CFS and ECC components.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.271-278
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• 2019

The corrosion of reinforcements embedded in concrete causes severe deterioration in reinforced concrete structures. As a countermeasure, epoxy coated reinforcements are used to prevent corrosion of reinforcements. When epoxy coated bars are used, the resistance of corrosion is excellent, but epoxy coating on the bars have a disadvantage of reduction in bond capacity comparing to that of normal bars. Therefore, it is necessary to confirm the bond performance of epoxy coated reinforcements through experimental and analytical methods. Bond behaviors of epoxy coated bars for various diameters of 13 and 19mm and thicknesses of cover concrete of 3 types(ratio of cover to bar diameter) are examined. As the diameters of the epoxy coated bars increase, the difference of bond strength between epoxy coated and uncoated bars also increases and damage patterns showed pull out failure. In addition, finite element analysis was performed based on the bond-slip relationship obtained by direct pullout test and compared with the flexural test results. It is considered that flexural member test is more useful than pullout test for simulating the behavior of actual structure.