• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.3
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• pp.287-298
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• 2014

In order to develop SFRC TBM tunnel segment, evaluating the SFRC mixture was conducted through flexural tests of SFRC beams without ordinary steel reinforcement in this study. Considered variables were compressive strengths of SFRC, aspect and mix ratio of steel fibers and total 16 specimens were fabricated and tested until failure. The load-vertical displacement results demonstrates that the effect of aspect ratio is minor when compared to results form small beam test(Moon et al, 2013). A SFRC beam resists the vertical load until the width of crack reaches to 7 mm due to steel fibers across cracked surfaces. Moreover, it is found that flexural moment estimated by equation of TR No. 63(Concrete Society, 2011) is useful for prediction of nominal strength for SFRC structure. From the investigation of fiber distribution in cracked section, it is found that dispersion improved in actual size beam compared to in standard small beam for evaluation of flexural strength.

• Journal of the Korea Concrete Institute
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• v.29 no.4
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• pp.345-351
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• 2017

This study evaluated the effectiveness of V-shaped ties as an alternative to the supplementary crossties specified in ACI 318-14 on the flexural ductility of reinforced concrete columns. From column specimens tested under constant axial loads and reversed cyclic lateral loads, the mode of failure and lateral load-lateral displacement relationship were measured according to the variation of the applied axial load levels. After the columns reached the peak lateral load capacity, the $90^{\circ}$ hooks of the crossties gradually opened, which eventually caused premature buckling of the longitudinal reinforcement and severe crushing of the core concrete, whereas no V-ties were extracted from the core concrete until the column failure. As a result, the cumulative work damage indicators up to 80% of the peak lateral load for V-tie columns under the axial load level of 0.2, 0.4, and 0.55 was as much as 2.4, 2.3, and 5.2 times higher, respectively, than those of the companion crosstie columns. The superiority of the V-ties to the conventional crossties in enhancing the flexural ductility of columns became more prominent as the axial load level increases.

• Journal of the Korea Concrete Institute
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• v.20 no.5
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• pp.601-609
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• 2008

The purpose of this study is to investigate the flexural strengthening effectiveness for the beams combined reinforced with NSM CFRP strips and EBR CFRP strips. To accomplish this objective, a total of nine concrete T beams were tested. From this study, it is found that the flexural stiffness and strength of the beams combined reinforced with NSM and EBR strips were significantly improved compared to the beams strengthened only with NSM CFRP strip. The maximum increase of flexural strength was 347% compared to the beam without CFRP strip. Failure of the beam combined reinforced with NSM and EBR strips (T shape) is initiated by debonding of EBR strips attached on the bottom face, and it was succeeded a part of separatio-n of NSM strips along the longitudinal direction and secondly failure of NSM strips was occurred, eventually sudden explosive failure with the separation of concrete cover in the shear region. This result shows that the NSM and EBR strips have good combination to resist applied load and the combined reinforcement with NSM and EBR strips can redistribute appropriately the total stress subjected concrete beam to the EBR and NSM strips.

• Journal of the Korea Concrete Institute
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• v.27 no.6
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• pp.677-685
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• 2015

In a will to subdue the brittleness as well as the low tensile and flexural strengths of ordinary concrete, researches are being actively watched worldwide on steel fiber-reinforced Ultra High Performance Concrete (UHPC) obtained by admixing steel fibers in ultra high strength concrete. For the purpose of maximizing advantage of UHPC, this study removes the upper flange of the steel girder to apply an inverted T-shape girder for the formation of the composite beam. This paper intends to evaluate the behavior of the shear connectors and the flexural characteristics of the composite beam made of the inverted T-shape girder and UHPC slab using 16 specimens considering the compressive strength of concrete, the mixing ratio of steel fiber, the spacing of shear connectors and the thickness of the slab as variables. In view of the test results, it seemed that the appropriate stud spacing should range between 100 mm and 2 or 4 times the thickness of the slab. Moreover, the relative displacement observed in the specimens showed that ductile behavior was secured to a certain extent with reference to the criteria for ductile behavior suggested in Eurocode-4. The specimens with large stud spacing exhibited larger values than given by the design formula and revealed that the shear connectors developed larger ultimate strength than predicted owing to the action of UHPC and steel after non-composite behavior. Besides, the specimens with narrow stud spacing failed suddenly through compression at the upper chord of UHPC before reaching the full capacity of the shear connectors.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.109-115
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• 2016

A demand of high bearing capacity of piles to resist heavy static loads has been increased. For this reason, the utilization of large diameter PHC piles including a range from 700 mm to 1,200 mm have been increased and applied to the construction sites in Korea recently. In this study, in order to increase the flexural strength capacity of the PHC pile, the large diameter composite PHC pile reinforced by in-filled concrete and reinforcement was developed and manufactured. All the specimens were tested under four-point bending setup and displacement control. From the strain behavior of transverse bar, it was found that the presence of transverse bar was effective against crack propagation and controlling crack width as well as prevented the web shear cracks. The flexural strength and mid-span deflection of LICPT specimens were increased by a maximum of 1.08 times and 1.19 times compared to the LICP specimens. This results indicated that the installed transverse bar is in an advantageous ductility performance of the PHC piles. A conventional layered sectional analysis for the pile specimens was performed to investigate the flexural strength according to the each used material. The calculated bending moment of conventional PHC pile and composite PHC pile, which was determined by P-M interaction curve, showed a safety factor 1.13 and 1.16 compared to the test results.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.1
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• pp.88-96
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• 2020

It were found that the heavyweight waste glass can be used as a construction materials including concrete from previous experimental studies. In this study, in order to evaluate the structural behavior of RC members using heavyweight waste glass as fine aggregate, a flexural behavior test was performed. And then, its results were compared with those obtained from non-linear finite element model analysis. From the results, when the heavyweight waste glass as fine aggregate in RC member, the area of compressive crushing and the number of cracks increased, however, the mean of cracking spacing decreased. Also it had reduced the ductility at high loading stage. For this reason, the same analysis method about the RC member using natural sand as fine aggregate did not predict the initial stiffness, yield load and maximum load on the flexural behavior of the RC members using heavyweight waste glass as fine aggregate. On the other hand, when it is analytically implemented the reduction of neutral axis depth due to developed compression crushing, the results of non-linear finite element analysis could be predicted the experimental results, relatively well.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.04a
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• pp.202-212
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• 2000

This study investigates the ductility capacity of slender-wide reinforced concrete walls under predominant flexural moment loading. The experimental work for this study aims to provide design guidelines for bar detailing in critical regions under compressive stress in particular in case of slender-wide RC walls. According to the experimental observation the Bernoulli hypothesis of linear strain distribution is no longer valid and the ultimate compressive strain of concrete is significantly reduced, It is postulated that the nonlinear strain distribution causes the concentrated compressive stressed region and hence the premature crushing failure at the toe of walls. The reduced ultimate strain and nonlinear strain distribution need transverse reinforcement for confinement and more realistic models for the strength and displacement estimation of slender-wide RC wall.

• Structural Engineering and Mechanics
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• v.28 no.1
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• pp.39-52
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• 2008

Column shear failures observed during recent earthquakes and experimental data indicate that shear deformations are typically associated with the amount of transverse reinforcement, column aspect ratio, axial load, and a few other parameters. It was shown that in some columns shear displacements can be significantly large, especially after flexural yielding. In this paper, a piecewise linear model is developed to predict an envelope of the cyclic shear response including the shear displacement and corresponding strength predictions at the first shear cracking, peak strength, onset of lateral strength degradation, and loss of axial-load-carrying capacity. Part of the proposed model is developed using the analysis results from the Modified Compression Field Theory (MCFT). The results from the proposed model, which uses simplified equations, are compared with the column test data.

• Steel and Composite Structures
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• v.18 no.1
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• pp.213-233
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• 2015

A nonlinear finite element analysis (FEA) model is presented for simulating the behaviour of recycled aggregate concrete-filled steel tube (RACFST) beam-columns subjected to constant axial compressive load and cyclically increasing flexural loading. The FEA model was developed based on ABAQUS software package and a displacement-based approach was used. The proposed engineering stress versus engineering strain relationship of core concrete with the effect of recycled coarse aggregate (RCA) replacement ratio was adopted in the FEA model. The predicted results of the FEA model were compared with the experimental results of several RACFST as well as the corresponding concrete-filled steel tube (CFST) beam-columns under cyclic loading reported in the literature. The comparison results indicated that the proposed FEA model was capable of predicting the load versus deformation relationship, lateral bearing capacity and failure pattern of RACFST beam-columns with an acceptable accuracy. A parametric study was further carried out to investigate the effect of typical parameters on the mechanism of RACFST beam-columns subjected to cyclic loading.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.53-56
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• 2002

External low-velocity impact loadings onto the composites cause reduction of stiffness and/or strength. The reductions indicate that internal(external) damages were developed within the composites. These damages could be matrix cracking, fiber/matrix debonding, or delamination between layers. In previous studies, damage evaluation have been done by applying secondary mechanical loading such as buckle-driven compressive, or fatigue, or flexural loadings. An evaluation method by applying indentation loadings on the composites was proposed. The load-displacement curves obtained from the indentation testing provided the extent of damages within the composites due to impact loadings.