• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.2
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• pp.275-285
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• 2015

This experimental study presents the fatigue evaluation of a precast deck connected using Ultra-High Performance, Fiber Reinforced Concrete (UHPFRC). Four types of two identical large-scale specimens were fabricated with simplified splice rebar details which had a short splice length of ten times rebar diameter. The flexural behavior of each type of specimens until failure was investigated and fatigue behavior of the same type of specimens was then evaluated using two-million cyclic loading. In the flexural tests, tensile rebars exhibited the deformation exceeding yielding strain but failure mode related to the splice details was not observed in spite of such a short splice length. In the fatigue tests, damage was not appreciably accumulated by the cyclic loading except initial flexural cracks and the stress variations in tensile rebars was less than the allowable stress range. These experimental results demonstrate that all types of specimens exhibited acceptable fatigue performance and indicate that enhanced mechanical properties of ultra-high performance material permits to use a simplified splice details along with short joint width.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.4
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• pp.396-402
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• 2021

A cross section in RC flexural members must be designed to satisfy flexural strength and ductility requirements simultaneously. In design provisions, ductile behavior is ensured by a sufficient reinforcement ratio or depth of the neutral axis. If the reinforcement ratio is less than the balanced reinforcement ratio, ductile behavior is secured, and this value is theoretically the maximum reinforcement ratio. But for a cross section with less steel, brittle failure can occur regardless of ductile behavior because of unqualifying a cracking moment. Recently, designs with a minimum steel ratio have been increasing along with the use of high-strength material, so in design provisions, a minimum amount of reinforcement is suggested. In the KCI(2012) standard, a minimum amount of reinforcement was suggested in terms of strength of steel and concrete. But in the revised KCI(2017) standard, a minimum amount of reinforcement was suggested by a relationship between the design flexural strength and cracking moment indirectly. This code can reflect the effect of cover thickness, but a material model must be defined. Therefore, the minimum amount of reinforcement in KCI(2012) and KCI(2017) was examined, and a rational review method was studied by parametric analysis.

• Journal of the Korea Concrete Institute
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• v.21 no.4
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• pp.431-439
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• 2009

These days the amount of demolished concrete waste has been increasing due to reconstruction and redevelopment of aged buildings. So the use of recycled aggregates is recommended to solve environmental problems. Some investigations have been carried out to study the flexural behavior of reinforced concrete beams with recycled aggregates. But these have some limitation due to the use of low quality recycled aggregates and small-scale specimens in the laboratory. The purpose of this experimental study is to evaluate the flexural behavior of simply supported RC beams subjected to four-point monotonic loading and made with recycled aggregates. Seven full-scale RC beams were manufactured with different replacement level of recycled aggregates. The main parameters of the study are combination of aggregates. From the test results, the flexural behavior of the beam is described in terms of crack patterns and failure modes. And the flexural strength of RC beam with different types of recycled coarse aggregates and recycled fine aggregates is compared with the provision of KCI code.

• The Journal of Korean Academy of Prosthodontics
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• v.36 no.6
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• pp.858-866
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• 1998

Soldering is the usual method used to correct an unstable fixed partial denture framework at patient's try-in; However, presoldering base metal alloys is technique-sensitve and results are unstable because it is difficult to maintain uniform heat distribution and to prevent oxidation of an alloy. A cast-joining technique has been developed by Weiss and Munyon for repair, correction and addition to base metal framework. This joining technique eliminates the problem with presoldering of non-precious frameworks. The object of this study was to 1) compare the relative flexure strength and the joining effectiveness of Ni-Cr-Be cast in two pieces and 'pre-soldered' versus in two pieces and 'cast-joined'. 2) determine the effect of increasing the number of retentive grooves on the face of the cast and 3) determine the effect of the relative matched position of groove patterns on flexure strength. The joining effectiveness can be expressed by the ratio of the mean flexure stress of soldered or cast-joined specimens to that of one-piece cast. Resin rods 3mm in diameter were used as pattern of specimens for one-piece casted, presoldered, and cast-joined groups. Cast-joined specimens had two different patterns of retentive grooves on the joined faces. Type A had cross-shaped grooves 1mm in depth. 0.6mm in width. Type B was the same except for the addition of one more retentive groove. In the experiment connecting cast-joined specimens, half of specimens with type A pattern had their patterns on the faces of paired casts matched with each other as mirror image. With the rest pairs, it was proceeded that one of paired casts turned 45 degrees so that the patterns crossed. Half of specimens with type B pattern also had the patterns matched as mirror image; However, here, one of paired casts turned 90 degrees with the other pairs. Retentive groove in this study lacked the intentional undercuts, in contrast with the suggestion of Weiss and Munyon. The specimens were subjected to four-point flexural loading in an Instron testing machine. The midspan flexural stress was calculated at the point of initial plastic strain as determined from a strip-chart recorder or at the point of failure if this occured at a lower stress level. Within the scope of this study, the following results were obtained. 1. The presoldered group showed flexural strength at least 2 times higher than the cast-joined groups. Its joining effectiveness was 82%. 2. In cast-joined groups, the flexural strength of joints with type B patterns exhibited 1.5 times that of joints with type A patterns. Joining effectivenesses were 38% for type B patterns, 25-26% for type A patterns. 3. The relative matched position of groove patterns did not have any significant effect on flexural strength of the cast-joined specimens with either type A patterns or type B patterns(p>.05).

• Journal of the Korea Concrete Institute
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• v.19 no.4
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• pp.467-474
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• 2007

In this paper, a total of 13 beams with bonding, anchorage system, amount of prestressing and span length as variables of experiment were tested in flexural test and analyzed in finite element analysis; one control beam, two simplified FRP-boned beams, four prestressed FRP-unbonded beams and four prestressed FRP-bonded beams. Also, a nonlinear finite element analysis of beams in the flexural test is performed by DIANA program considered material nonlinear of concrete, reinforcement and the interfacial bond-slip model between concrete and CFRP plates. The failure mode of prestressed CFRP plated-beams is not debonding but FRP rupture. RC members strengthened with external bonded prestressed CFRP plates occurred 1st and 2nd debonding of the composite material. After the debonding of CFRP plates occurs in bonded system, behavior of bonded CFRP-plated beams change into that of unbonded CFRP-plated beams due to fix of the anchorage system. Also, It was compared flexural test results and analytical results of RC members strengthened with CFRF plates. The ductility of beams strengthened by CFRP plates with the anchorage system is considered high with the ductility index of above 3. Analysis results showed a good agreement with experiment results in the debonding load, yield load and ultimate load.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.6
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• pp.1677-1685
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• 2014

Short discrete fibers compounded with concrete can enhance the tensile resistance and ductility of concrete. Recently, the effectiveness of the reinforcement has increased according to the increasing length of steel fiber. However, the lengthening of steel fiber requires reducing the ratio of the fiber content to remain the workability and quality of concrete. Thus, the present study evaluated the flexural performance of fiber reinforced concrete with less than l.0% fiber volume ratios of steel fiber, 30mm and 60mm long, and polypropylene fiber, being evaluated as a good reinforcing material with chemical stability, long-term durability, and cost effectiveness. Concrete with more than 0.25% steel and 0.5% polypropylene fibers improved the brittle failure of concrete after reaching cracking strength. Concrete reinforced with polypropylene exhibited deflection-softening behavior, but that with more than 0.5% polypropylene delayed stress reduction and recovered flexural strength by 60 to 80% after cracking strength. In conclusion, concrete reinforced with more than 0.75% polypropylene could improve structural flexural performance. In particular, energy absorption capacity of reinforced concrete with 1.0% polypropylene fiber was similar to that with 0.5% and 0.7% steel fibers.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.3
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• pp.80-86
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• 2020

In the fabrication process of inverted multi-tee (IMT) slabs, concrete has to be poured twice due to its shape, which is a huge disadvantage as a precast member. To overcome this, a new technique for manufacturing IMT slabs using a slipform method has been recently developed. In this study, flexural and shear tests were carried out to investigate the structural performances of inverted multi-tee (IMT) slabs manufactured using slipform method. To this end, one flexural specimen and two shear specimens with topping concrete were fabricated, and their failure modes and crack patterns, and the slips that occurred between the precast slab and topping concrete were measured and analyzed in detail. In addition, the flexural and shear strengths of the specimens were evaluated by utilizing the structural design code, and a shear strength estimation method, which is suitable for composite IMT slabs with different concrete properties, was proposed for practical design. The IMT slab satisfied the nominal flexural strength calculated by the current design code, and the proposed method provided a good estimation of the shear strength of the specimens.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.1
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• pp.102-112
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• 2019

This paper studies impact fracture behavior under temperature variation and compressive flexural strength of cement composites using VAE(vinyl acetate ethylene) powder polymer and PVA(polyvinyl alcohol) fiber. Impact test were conducted in the temperature range selected for the $-35^{\circ}C$, $0^{\circ}C$ and $35^{\circ}C$. In this experimental study, impact test were carried out using a drop impact testing machine (Ceast 9350) to obtain such as displacement, time, and impact fracture energy of normal specimen and and cement composites specimen. As test results, the use of VAE powder polymer and PVA fiber were observed to enhance the flexural strength of mortar. The compressive strength of PVA fibers reinforced cement composites was slightly decreased at 28 days, but the flexural strength was observed to increase 24.4% of normal mortar strength. As a result of the drop impact tests, PVA fiber reinforced cement composites specimens showed microcracks due to energy dispersion and crack prevention with bridge effect of the fibers, and scabbing or perforation by impact was suppressed. On the other hand, the normal mortar and VAE powder polymer cement composites specimens were carried out to the perforation and macro crack. Most of normal mortar and the cement composites subjected to impact load on specimens shows mostly local brittle failure. The impact resistant performance of the specimen with PVA fiber was greatly improved due to the increase of flexure performance.

• Journal of the Society of Disaster Information
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• v.16 no.4
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• pp.796-805
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• 2020

Purpose: A static loading test was performed to evaluate the ultimate flexural strength of a girder in which 80MPa high-strength concrete was synthesized on the compressive flange of the I-shape steel girder. Method: This test is designed and fabricated two types of specimens with different shear-connection specifications, and evaluated their ultimate flexural behavior until reaching the extreme event limit states. In addition, the ultimate strength was evaluated by comparing the test results and the results of the strain compatibility method. Result: By confirming the displacement within 0.02mm as a result of the relative slip measurement, it was verified that the two specimens secured perfect bonding. Therefore, the difference in the shear specification does not have a great effect on the stiffness, and if the specimens are completely synthesized, there is no difference in the behavior until it reaches the extreme-event limit states. Conclusion: The girder to be tested has a working load within the elastic range and meets the usability requirements for allowable deflection. Therefore, even if a part of the casing is subjected to the tensile force at the level of cracking, the deck will first reach the compression failure due to the role of the reinforcing bar.

• Journal of the Korea Institute of Building Construction
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• v.22 no.6
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• pp.553-564
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• 2022

Concrete is a representative composite material that shows excellent performance in the construction field. However, it is a brittle and nonhomogeneous material and exhibits weak behavior against bending and tensile forces. To compensate for such weakens, fiber reinforcement has been utilized, and steel fiber has been recognized as one of the best material for such purpose. However, steel fiber can seriously affect the durability of concrete exposed to the marine environment due to the corrosion caused by chlorine ions. This study intended to evaluate the mechanical performance of steel fiber reinforce concrete during and after repeated wet/dry cycles in salt solution. According to the experimental results, there was no reduction in the relative dynamic modulus of concrete during the repeated wet/dry cycles in salt solution for 37 weeks. Flexural strength was not decreased after completion of repeated wet/dry cycles in salt solution. There was no sign of corrosion in steel fibers after visual observation of fractured surface. However, the flexural toughness was decreased, and this is because about half of the concrete specimen showed failure before reaching the maximum displacement of 3 mm. Although repeated wet/dry cycles in salt solution did not cause cracks in concrete through corrosion of steel fibers, specific attention is required because it can reduce flexural toughness of steel fiber reinforced concrete.