• Journal of Korean Society of Steel Construction
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• v.24 no.4
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• pp.479-490
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• 2012

Flexural tests on full-scale H-shaped beams, built up from high-strength steels (HSB800 and HSA800) with a nominal tensile strength of 800 MPa, was carried out to study the effect of flange slenderness of high-strength steel on flexural strength and rotation capacity. The primary objective was to investigate the appropriateness of extrapolating current stability criteria (originally developed for ordinary steel) to high-strength steel. The performance of high-strength steel specimens was very satisfactory from the strength, but not from the rotation capacity, perspective. The inferior rotation capacity of high-strength steel beams was shown to be directly attributable to the absence of a distinct yield plateau and the high yield ratio of the material. Residual stress measurements reconfirmed that the magnitude of the residual stress is almost independent of the yield stress of the base metal.

• Magazine of the Korea Concrete Institute
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• v.6 no.5
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• pp.140-148
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• 1994

RCI 318-8!4 recommends that when the specified cornpresslve strength of concrete In a column is greater than 1.4 times thdt spec~f~ed for a floor svsttm. top surface of the colunm concrete shall extend 2ft(600mm) into the slab from the face of colurnn to avoid unexpected brittle failure. Six test specimens were cast arid tested on 2/3 scale frame specmiens havlng different extension distances and compressive strength of concrete as the major variables. The paper discusses the performance of the frames in terms of ductility and also presents the assessment of the ACI 318-89 provisions.The test results showed that the ductility index were incrrased with increasing of compressive strength of concrete and extension distance. And top surface of the column concrete should extend 2h(h overall depth of beam) into the beam from the face of the column to avoid unexpected brittle failure in frame.

• Journal of Korean Society of Steel Construction
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• v.29 no.4
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• pp.281-289
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• 2017

The current AASHTO LRFD and Eurocode 3 specifications have been found to underestimate the flexural strength of longitudinally reinforced plate girders. This is because the web-flange interaction is not considered appropriately when a web is reinforced. The buckling strength of compression flange increases due to the improved rotational restraint to the compression flange. Also, the compression flange and the longitudinal stiffener could constrain the web rotation, so that a certain area of the web reaches yield strength. In this study, a model for evaluating the flexural strength is proposed for plate girders reinforced with one line of longitudinal stiffeners, considering the increase of the buckling strength of the compression flange and the actual stress distribution of the web. The flexural strengths of the conventional steel(SM490) and the high-strength steel(HSB800) plate girders were evaluated from the nonlinear analysis and the applicability of the proposed model was analyzed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.4
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• pp.1081-1094
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• 2014

The strut-tie model approach has proven to be effective in the ultimate analysis and design of structural concrete with disturbed regions. For the reliable analysis and safe design of the structural concrete, however, the effective strengths of concrete struts must be determined accurately. In this study, the equations of the effective strengths of concrete struts, which are useful for the three types of determinate and indeterminate strut-tie models of reinforced concrete corbels, were proposed. The effects of shear span-to-effective depth ratio, the vertical-to-horizontal force ratio, and flexural and horizontal shear reinforcement ratios were reflected in the development of the proposed equations. To examine the appropriateness of the proposed and existing equations, the ultimate strengths of 243 reinforced concrete corbels tested to failure were evaluated by using the three types of corbel strut-tie models.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.2
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• pp.37-47
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• 2010

In order to attain enhanced seismic performance of RC bridges, premature shear failure prior to the achievement of target ductilities of the piers should be prevented. For this purpose, a reliable shear strength evaluation is required. The shear strength of an RC column subjected to a lateral force decreases with an increase in ductility. Many empirical equations for the shear strength have been proposed by many researchers. However, there are many discrepancies in the initial shear strength in the low ductility range, and in the decrease rate according to the ductility. In this study, a new empirical equation of shear strength considering the displacement ductility effect has been proposed, in which the initial shear strength equation proposed by the authors was revised on the basis of the investigation of many other researchers' test results. The resulting improvement in accuracy is confirmed by comparison with other empirical equations.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.541-544
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• 2008

Recently, due to the increase of high-rise buildings construction, many researches for making harden of concrete earlier and remove of forms faster are being performed to reduce construction period. The purpose of this study is to analysis which mixing condition and curing temperature of early strength concrete. Porperties of concrete by the different factors, such as the type of active admixtures, mineral admixtures, curing temperature, the amount of binder, etc. Through the test of concrete using the different type of admixture, PC type was more excellent than PNS type admixture. The concrete Strength remarkably will be able to confirm that decreases from temperature below 12$^{\circ}C$.

• Journal of the Korea Concrete Institute
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• v.15 no.4
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• pp.615-622
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• 2003

The purpose of this study is to propose the more reasonable equation of bond strength of grout-filled splice sleeve. To accomplish this objective, total 60 full-sized specimens were tested under monotonic loading. The experimental variables are compressive strength of mortar, embedment length and size of reinforcing bars. Following conclusions are obtained; 1) If the adequacy of existing equations which estimate the bond strength of grout-filled splice sleeve are investigated, they underestimate the bond strength of grout-filled splice sleeve by 8-18%. Also the existing equations have a tendency to underestimate with decrease in the embedment length of reinforcing bars. 2) From the test result of bond failure, the equation which estimates the confining pressure of grout-filled splice sleeve was proposed by making multiple regression analyses of which independent variables are embedment length of reinforcing bars and compressive strength of mortar. This equation predicted the measured bond capacity of this test more accurately than existing equations and eliminated the deviation according to the embedment length of reinforcing bars.

• Journal of the Korea Concrete Institute
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• v.27 no.3
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• pp.299-309
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• 2015

Ultra High Performance Fiber Reinforced Concrete (UHPFRC) is distinguished from the normal concrete by outstanding compressive and tensile strength. Cracked normal concrete resists shear by aggregate interlocking while clamped by transverse reinforcement, which is called as shear friction theory. Cracked UHPFRC is expected to have a different shear transfer mechanism due to rather smooth crack face and post-cracking behavior under tensile force. Twenty-four push-off specimens with transverse reinforcement are tested for four different fiber volume ratio and three different ratio of reinforcement along the shear plane. The shear friction strength for monolithic concrete are suggested by limit analysis of plasticity and verified by test results. Plastic analysis gives a conservative, but reasonable estimate. The suggested shear friction factor and effectiveness factor of UHPFRC can be applied for interface shear transfer design of high-strength concrete and fiber reinforced concrete with post-cracking tensile strength.

• Tunnel and Underground Space
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• v.22 no.5
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• pp.339-345
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• 2012

Information on the deformation behavior and fracture strength of rocks subjected to dynamic loadings is important to stability analyses of underground openings underground vibration due to rock blasts, earthquakes and rock bursts. In this study, Split Hopkinson Pressure Bar (SHPB) system was applied to estimate dynamic compressive and tensile fracture strengths of limestone and also examine deformation behavior of limestones under dynamic loadings. A micro-focus X-ray CT scanner was used to observe non-destructively inside the impacted limestone specimens. From the dynamic tests, it was revealed that the limestone have over 140MPa dynamic compressive strength and the strain-rate dependency of the strength. Dynamic Brazilian tensile strength of the limestone exceeds 21MPa and shows over 3 times static Brazilian tensile strength.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.414-423
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• 2020

Fiber-reinforced polymer (FRP) laminate sheets, which are lightweight with high strength, are commonly used to reinforce concrete structures. The bonding strength is vital in structural design. Therefore, experiments and analytical studies with differing variables (concrete compressive strength and tensile strength, the elastic modulus of concrete and FRP, thickness of concrete and FRP, width of concrete and FRP, bond length, effective bond length, fracture energy, maximum bond stress, maximum slip) have been conducted to obtain an accurate numerical model of the bond strength between an FRP sheet and concrete. Although many models have been proposed, no validated model has emerged that could be used easily in practice. Therefore, this study analyzed the parameters that influence the bond strength that were used in 23 of the proposed models (Khalifa model, Iso model, Maeda model, Chen model, etc.) and compared them to the test results of 188 specimens via the numerical results of each model. As a result, an easy-to-use practical model with a simple and high degree of expression was proposed based on the Iso model combined with the effective bond length model that was proposed by Holzenkӓmpfer.