• Structural Engineering and Mechanics
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• v.75 no.3
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• pp.389-399
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• 2020

An infill wall made of high-performance fiber-reinforced cementitious composites (HPFRCC) was utilized in this study to strengthen the reinforced concrete (RC) frame structures that had not been designed for seismic loads. The seismic performance of the RC frame structures strengthened by the HPFRCC infill walls was investigated through the experimental tests, and the test results showed that they have improved strength and deformation capabilities compared to that strengthened by the RC infill wall. A simple numerical modeling method, called the modified longitudinal and diagonal line element model (LDLEM), was introduced to consider the seismic strengthening effect of the infill walls, in which a section aggregator approach was also utilized to reflect the effect of shear in the column members of the RC frames. The proposed model showed accurate estimations on the strength, stiffness, and failure modes of the test specimens strengthened by the infill walls with and without fibers.

• Journal of the Korea Concrete Institute
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• v.26 no.4
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• pp.491-497
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• 2014

The corrosion of steel reinforcement in reinforced concrete bridge decks significantly affects the degradation of the capacity. Due to the advantageous characteristics such as high tensile strength and non-corrosive property, fiber reinforced polymer (FRP) has been gathering much interest from designers and engineers for possible usage as a alternative reinforcement for a steel reinforcing bar. However, its application has not been widespread, because there data for short- and long-term performance data of FRP reinforced concrete members are insufficient. In this paper, seven full-scale decks with dimensions of $4000{\times}3000{\times}240mm$ were prepared and tested to failure in the laboratory. The test parameter was the bottom reinforcement ratio in transverse direction. The decks were subjected to various levels of concentrated cyclic load with a contact area of $577{\times}231mm$ to simulate the vehicle loading of DB-24 truck wheel loads acting on the center span of the deck. It was observed that the glass FRP (GFRP) reinforced deck on a restraint girder is strongly effected to the level of the applied load rather than the bottom reinforcement ratio. The study results showed that the maximum load less than 58% of the maximum static load can be applied to the deck to resist a fatigue load of 2 million cycles. The fatigue life of the GFRP decks from this study showed the lower and higher fatigue performance than that of ordinary steel and CFRP rebar reinforced concrete deck. respectively.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.94-101
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• 2023

In this study, the development performance of the head bars, which is SD700, was experimentally evaluated at the RC (reinforced concrete) or SFRC (steel fiber reinforced concrete external beam-column joint. A total of 10 specimens were tested, and variables such as steel fibers, length of settlement, effective depth of the beam, and stirrups of the column were planned. As a result of the experiment, the specimens showed side-face blowout, concrete breakout, and shear failure depending on the experimental variables. In the RC series experiments with development length as a variable, it was confirmed that the development strength increased by 26.5~42.2% as the development length increased by 25-80%, which was not proportional to the development length. JD-based experiments with twice the effective depth of beams showed concrete breakout failure, reducing the maximum strength by 31.5% to 62% compared to the reference experiment. The S-series experiment, in which the spacing of the shear reinforcement around the enlarged head reinforcement was 1/2 times that of the reference experiment, increased the maximum strength by 8.4 to 9.7%. The concrete compressive strength of SFRC was evaluated to be 29.3% smaller than the concrete compressive strength of RC, but the development strength of SFRC specimens increased by 7.3% to 12.2%. Accordingly it was confirmed that the development performance of the head bar was greatly improved by reinforcing the steel fiber. Considering the results of 92% and 99% of the experimental maximum strength of the experiment arranged with 92% and 110% of the KDS-based settlement length, it is judged that the safety rate needs to be considered even more. In addition, it is required to present a design formula that considers the effective depth of the beam compared to the development length.

• Structural Monitoring and Maintenance
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• v.7 no.3
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• pp.215-231
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• 2020

In a reinforced concrete building different shapes of column are adopted depending on the structural orientation and the architectural aspect. When there is an increase in loading due to changes in usage or revision in the design codes these columns need to be strengthened for enhanced performance during their service life. Strengthening materials such as carbon fiber and glass fiber polymer has been successfully used however, due to high cost application other alternative materials need to be explore. Galvanized steel wire mesh (GSWM) is one of the suitable materials locally available. High tensile strength, low weight, corrosion resistance, easy installation, minimum change in dimensions of the sections and cost effectives are the advantages of GSWM. Therefore, in this paper, four different shapes of column such as circular, square, rectangular and L were wrapped with different layers GSWM and jacketed with mortar. All the specimens were tested under axial compression. The objective of the study is to investigate the effectiveness of GSWM as a confining material for strengthening of column having varying shape. Test results shows that the axial strength enhanced with wrapping of GSWM jacket and a circular column presented the highest load carrying capacity and ductility as compared to the others. From the study of 22 column specimens, it is found that axial load is increased upto 20% and 19% when circular and square column are strengthened with one wrap of GSWM respectively, while a rectangular and L column required a wraps of two and three layers respectively in order to achieved the same load capacity as that of a circular column. Based on the present study, it is concluded that GSWM can be effectively used for strengthening of different shapes of concrete columns economically.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.1
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• pp.193-202
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• 2008

This paper investigates experimentally the confining effect, strengthening capacity and rebound rate of sprayed Fiber-Reinforced-Polymer (SFRP). From the method, resin and chopped fibers are sprayed separately from the nozzle with high pressure, and then they are attached to the concrete surface, so structure could be repaired. To evaluate the strengthening effect of sprayed FRP, cylindrical specimens and beam specimens were strengthening with SFRP. As main material of FRP, glass fiber and polyester resin are used. To investigate the optimum condition of sprayed FRP, the effects of fiber length, coating thickness, fiber volume ratio and concrete strength were examined. Capacities of sprayed FRP method were also compared to the FRP sheet method. In case of the sprayed FRP, rebound rate is important parameter considering economical efficiency and constructibility, so rebound rate of was discussed. From the test results, optimum conditions of sprayed FRP were determined. SFRP method showed superior strengthening capacities than FRP sheet method.

• Journal of the Korea Concrete Institute
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• v.19 no.3
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• pp.351-358
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• 2007

Unlike external bonded steel plate or carbon fiber, the external unbonded strengthening using hi-strength bar has some advantages in speed and simplicity of installation. It is not required surface preparations and not affected by environmental conditions. A set of nine laboratory tests on RC beams strengthened using the hi-tension bars are reported. Anchoring pin developed in former research is installed at the end of beam to connect the hish-tension bar to RC beam. The test results strengthened by hi-tension bars are compared with those of non-strengthened specimens. The main test parameters are the cross-sectional area of the high-tension bar, distance of stirrups and condition of supports. Test results show that the beams reinforced are superior to reference specimens, especially for the strength and deformation capacity. Also, shear resisting effect of hi-strength bar can be confirmed in the specimens which have lack of stirrups.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.1
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• pp.1-11
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• 2013

Steel fiber-reinforced concrete (SFRC) is widely used for tunnel lining structure such as shot-crete in NATM tunnel and segment in TBM tunnel. In tunnel fire accidents, structural performance of a lining is very important because the lining is the structure that directly exposed to fire. In this study, the effects of high temperatures, mix ratios and types on failure pattern, DPT tensile strength and coefficient of variation were investigated through Double Punch Tests (DPT) of SFRC subjected to high temperatures. In the results, it is confirmed that the residual DPT tensile strength increases as for SFRC and this is more in SFRC with higher mix ratio. But, the equation for evaluation of DPT tensile strength does not involve the number of failure surfaces SFRC specimens subjected to high temperatures, therefore, it is required to investigate more fracture energy in DPT tests.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.589-597
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• 2009

High Performance Fiber-reinforced Cement Composite (HPFRCC) shows the multiple crack and damage tolerance capacity due to the interfacial bonding of the fibers to the cement matrix. For practical application, it is needed to investigate the fractural behavior of HPFRCC and understand the micro-mechanism of cement matrix with reinforcing fiber. This study is devoted to the investigation of the AE signals in HPFRCC under monotonic and cyclic uniaxial compressive loading, and total four series were tested. The major experimental parameters include the type and volume fraction of fiber (PE, PVA, SC), the hybrid type and loading pattern. The test results showed that the damage progress by compressive behavior of the HPFRCC is a characteristic for the hybrid fiber type and volume fraction. It is found from acoustic emission (AE) parameter value, that the second and third compressive load cycles resulted in successive decrease of the amplitude as compared with the first compressive load cycle. Also, the AE Kaiser effect existed in HPFRCC specimens up to 80% of its ultimate strength. These observations suggested that the AE Kaiser effect has good potential to be used as a new tool to monitor the loading history of HPFRCC.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.1
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• pp.11-18
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• 2018

As the amount of polycarboxylate superplasticizer varied from 1.2% to 3.0% of the mass of binder, the change in the flowability & rheological properties, and strength of UHPFRC was investigated with experiments. The test results presented that the increase in the amount of superplasticizer was effective in improving the flowability up to 1.8%, but addition more than 1.8% was hardly beneficial for enhancing the flowability and rhelogical properties. Compressive strengths with different amounts of superplasticizer showed that the strength with 1.8% was slightly higher than that of 1.2%, but the amount more than 1.8% caused strength reduction, which was higher as the amount increased. The results in flexural strength according to the amount of superplasticizer showed a similar trend with the results in compressive strength. When the effect of compressive strength and fiber distribution characteristics on the flexural strength was analysed separately, it was found that high amount of superplasticizer caused an effect of fiber distribution in addition to the effect of compressive strength on flexural strength. This effect seems to be closely related to the results of flowability or rheological properties.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.2
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• pp.23-30
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• 2008

UHPC has high performance, high strength and excellent mechanical properties. Moreover UHPC(Ultra High Performance Cementitious Composite) has advantage to reduce cross section under the same load compared with other kinds of concrete. But silica fume which is imported from foreign country has a abundant portion in UHPC mixture in comparison with normal concrete. This is one of the main reason to raise the construction cost. Superior mechanical properties of UHPC due to the optimum filling composition can be changed by replacing the very fine ingredient. The purpose of this research is to grasp the characteristic of UHPC which silica fume and silica flour is replaced with limestone powder. This experiment can be divided into three classes according to the kinds of replacement. The compressive strength and flow of all types were measured and microstructure and hydration phenomena for comparing RPC were analyzed by SEM, XRD, NMR method. As a result, the replacement can be considered to be effective by for the decrease of the UHPC structure construction cost and improvement of the fresh UHPC.