• Fire Science and Engineering
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• v.26 no.6
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• pp.78-84
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• 2012

In this study, we have conducted a fire resistance experiment under loading condition on standard fire to evaluate the fire resistance performance according to applying reinforcement of methods for reinforcing the lateral confinement of reinforced bars (Wire Rope) and fire resistance reinforcement (Fiber-Cocktail) for 100 MPa high strength concrete column. In the result of the experiment, in case of the test objects applied by hoop, it has been shown as not possible to be applied as the fire resistance structure after satisfying the fire resistance performance for 43 minutes. In case of applying the wire rope as lateral confinement of reinforced bar, instead of hoop in identical volume ratio, it has been shown as possible to apply it to the buildings with under 4 floors after satisfying the fire resistance performance fro 69 minutes with any separate fire resistance process. Also, in case of applying with mixing wire rope method, instead of hoop, and Fiber-Cocktail mix method to prevent spall, it has been shown as possible to apply to the buildings with over 12 floors after satisfying the fire resistance performance for 180 minutes.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.469-483
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• 2018

Steel bars have been widely used as the primary reinforcement for Precast Segmental Concrete Lining for TBM Tunnels. Previously, studies have been carried out to gauge the potential for steel fiber reinforcement to replace the use of steel bar reinforcements in the segmental lining to reduce the amount of the steel bar reinforcement. Steel fiber reinforcements have been investigated and widely applied to SFRC TBM linings to improve the constructability of SFRC TBM linings worldwide. However, the steel fiber reinforcement often caused punctures to the water membranes inside tunnel lining and had long-term durability deterioration issues caused by steel corrosion, as well as cosmetic problems. Therefore, this paper sought to gauge the potential of synthetic fiber reinforcements, which have proven to be very attractive substitutes for steel fiber reinforcements. This study analyzed the performance of both steel and synthetic fiber reinforcements in segmental linings and evaluated the applicability of the fiber reinforcements to the TBM Precast Concrete Segmental Linings of TBM tunnels. As a conclusion, this study demonstrates that the potential use of steel and synthetic fibers in various combination, can substitute the rebar reinforcement in the concrete mix for segmental concrete linings.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.4
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• pp.30-38
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• 2017

Recently, research on the development of a composite slab system for shorting the construction period by simplifying the process by omitting the form work and the reinforcement placing is underway. The purpose of this study is to evaluate the long-term behavior of a simplified slab system that replaces the form work and tensile reinforcement using structural deck-plate and replaces the temperature reinforcement using steel fiber reinforced concrete. In the conventional composite deck-plate slab method, w.w.f is generally used for crack control by drying shrinkage. But previous research results by various researchers were pointed out it is not effective to control the shrinkage and temperature cracking. In this study, the long-term cracking and structural behavior of steel fiber reinforced deck plate slab specimen with two continuous spans constructed under typical load conditions were evaluated. Experimental results showed that the number and width of long-term cracks decreased remarkably in the simplified slab specimen, and the deflection was also decreased compared with conventional RC slab specimen. However, in the continuous end of the slab where the negative moment is applied, it is analyzed that reinforced details are necessary to control the crack width in the service load and to recover deflection at load removal.

• Journal of the Korea Concrete Institute
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• v.25 no.2
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• pp.187-194
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• 2013

Fiber reinforced polymer (FRP) has been gathering interest from designers and engineers for its possible usage as a replacement reinforcement of a steel reinforcing bar due to its advantageous characteristics such as high tensile strength, non-corrosive material, etc. Since it is manufactured with various contents ratios, fiber types, and shapes without any general specification, test results for concrete members reinforced with these FRP reinforcing bars could not be systematically used. Moreover, since investigations for FRP reinforced members have mainly focused on short-term behavior, the purpose of this study is to evaluate long-term behaviors of glass FRP (GFRP) reinforcing bar and concrete beams reinforced with GFRP. In this paper, test results of tensile and bond performance of GFRP reinforcing bar and creep behavior are presented. In the creep tests, results showed that 100 years of service time can be secured when sustained load level is below 55% of tensile strength of GFRP reinforcing bar. A modification factor of 0.73 used to calculate long-term deflection of GFRP reinforced beams was acquired from the creep tests for GFRP reinforced concrete beams. It is expected that these test results would give more useful information for design of FRP reinforced members.

• 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.24 no.1
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• pp.25-35
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• 2012

For a member subjected to direct shear forces, forces are transferred across interface concrete area and resisted by shear transfer capacity. Shear-friction equations in recent concrete structural design provisions are derived from experimental test results where shear-friction capacity is defined as a function of steel reinforcement area contained in the interface. This empirical equation gave too conservative values for concrete members with large amounts of reinforcement. This paper presents a method to evaluate shear transfer strengths and to define ultimate conditions which result in crushing of concrete struts after yielding of longitudinal reinforcement perpendicular to the interface concrete. This method is based on the bi-axial stress field theory where different constitutive laws are applied in various means to gain accurate shear strengths by considering softening effects of concrete struts based on the modified compression-field theory and the softened truss model. The validity of the proposed method is examined by applying to some selected test specimens in literatures and results are compared with recent design code provisions. A general agreement is observed between predicted and measured values at ultimate loading stages in initially uncracked normal-strength concrete test.

• Journal of the Korea Concrete Institute
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• v.25 no.3
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• pp.261-269
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• 2013

In this study, it was developed eco-friendly inorganic binding material concrete using ground granulated blast furnace slag and alkali activator (water glass, sodium hydroxides). Eight reinforced concrete beam using inoganic binding material concrete were constructed and tested under monotonic loading. The major variables were mixture ratio of alkali activator, type of admixture and admixture. Experimental programs were carried out to improve and evaluate the flexural performance of such test specimens, such as the load-displacement, the failure mode, the maximum load carrying capacity, and ductility capacity. All the specimens were modeled in scale-down size. The eco-friendly concrete using inorganic binding material encouraged alkali activation reaction was rapidly hardening speed and showed possibility as a high strength concrete. Also, the RC beams using new materials showed similar behavior and failed similarly with RC beam used portland cement. It is thought that eco-friendly inorganic binding material concrete can be used with construction material and product as a basic research to replace cement concrete. If there is application to structures in PC member as well as production of 2nd concrete product, it could be improved the productivity and reduction of construction duration etc.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.313-316
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• 2008

Corrosion of steel in the reinforced concrete structures is one of the main reason of degradation. It causes that lifetime of structures is shortened and maintenance cost is increased. And it also causes degradation of structures like bridges which are under repeated load. So, many research have been performed about FRP rebar. But there are few research about FRP rebar under fatigue. This study is to examine flexural characteristic of concrete beam reinforced with FRP(CFRP, GFRP) rebar under static and fatigue for considering the application. The specimens that used in this study are designed by ACI 440.1R-06 and reinforced with CFRP(CR) or GFRP(GR) overly. In the result of static bending test, all specimens were failed at compression phase. In fatigue test, the fatigue stress level was 60%, 70% or 80% of the static bending strength. Most of the specimens seemed to be compressive failure, but CR-60 and CR-70 specimens were failed with rupturing of tension bar.

• KIEAE Journal
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• v.8 no.3
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• pp.69-76
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• 2008

This is an experimental study on the maximum load value and structural behavior of reinforced concrete columns containing shells as a substitute fine aggregate of concrete, through making reinforced concrete test columns with shells. In this study, the main factors consist of the grain sizes and the percentage of substitution of shells to fine aggregate in two kinds of water cement ratio. The results of the study showed as followed. The maximum load value decreased with increased the rate of substitution about shells and as the grain size of shells became smaller, the load values of them were somewhat changed higher but it is important that we must consider absorption rate of shells sufficiently. If we have a proper water cement ratio in column productions containing the shells, we can meet the requirement of the percentage of substitution until 30%. The deflection and deformation properties of reinforced concrete columns with shells represented typical curves like that of normal reinforced concrete. But as the failture types, they are able to make some change without being out of the fundamental graph forms. After the analyzing structural behaviors and the properties of reinforced concrete test columns containing shells, the most excellent grain size of shells represented 3.0mm and less with taking uniformly, and the percentage of practicable substitution of them to fine aggregate was about 30%.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.6
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• pp.238-245
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• 2010

Progressive collapse is defined as a collapse caused by sectional destruction of a structural member which links to other surrounding structures. Currently the design guidelines for the prevention of progressive collapse is not available in Korea. So, structural engineers have a difficulty in evaluating progressive collapse. In this study, the static and dynamic analysis to evaluate the methods and procedures are conducted using commercial analysis program for RC moment resisting frames. According to the study, DCR value of RC moment resisting frame system based on code in Korea is over 2 and it shows that it can't provide alternate load paths due to the progressive collapse. And additional reinforcement should be considered for the progressive collapse resistance. As a result of vertical deflection and DCR value of linear static analysis and linear dynamic analysis, the results of dynamic analysis were underestimated more than the result of static analysis. Thus, the dynamic coefficient value of 2 provides conservative estimation.