• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.3
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• pp.233-239
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• 2013

This study is interested in manufacturing the self-cleaning silicate concrete surface impregnant including tetra ethyl ortho silicate, lithium silicate for the repair of the exposed concrete surface and the color concrete requiring the advanced function in view of the concrete appearance. The concrete surface layer change and static contact angel was tested for the review of application. The result of this study shows that the effective silicate is tetra ethyl ortho silicate and lithium silicate. The adhesion in tension is satisfied with performance requirement of KS standard but the reinforcement of concrete substrate is slight. So, The self-cleaning silicate concrete impregnant of this study is more desirable for the improvement of durability rather than the reinforcement.

• Journal of the Korea Concrete Institute
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• v.25 no.5
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• pp.573-581
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• 2013

In this paper, an experimental investigation of bond properties between steel fiber reinforced concrete and glass fiber reinforced polymer reinforcements was performed. The experimental variables were diameter of reinforcements, volume fraction of steel fiber, cover thickness and compressive strength of concrete. Bond failure mainly occurred with splitting of concrete cover. Main factor for splitting of concrete is tension force occurred by the displacement difference between reinforcements and concrete. Therefore, in order to prevent the bond failure between reinforcements and concrete, capacity of tensile strength of concrete cover should be upgraded. As a results of test, volume fraction of steel fiber significantly increases the bond strength. Cover thickness changes the failure mode. Diameter of reinforcements also changes the failure mode. Generally, diameter of reinforcement also affects the bond properties but this effect is not significant as volume fraction of fiber. Increase of compressive strength increases the bond strength between concrete and reinforcement because compressive strength of concrete directly affects the tensile strength of concrete.

• Nuclear Engineering and Technology
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• v.53 no.5
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• pp.1686-1704
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• 2021

This study addresses the numerical simulation of the shield building of an AP1000 nuclear power plant (NPP) subjected to a large commercial aircraft impact. First, a simplified finite element model (F.E. model) of the large commercial Boeing 737 MAX 8 aircraft is established. The F.E. model of the AP1000 shield building is constructed, which is a reasonably simplified reinforced concrete structure. The effectiveness of both F.E. models is verified by the classical Riera method and the impact test of a 1/7.5 scaled GE-J79 engine model. Then, based on the verified F.E. models, the entire impact process of the aircraft on the shield building is simulated by the missile-target interaction method (coupled method) and by the ANSYS/LS-DYNA software, which is at different initial impact velocities and impact heights. Finally, the laws and characteristics of the aircraft impact force, residual velocity, kinetic energy, concrete damage, axial reinforcement stress, and perforated size are analyzed in detail. The results show that all of them increase with the addition to the initial impact velocity. The first four are not very sensitive to the impact height. The engine impact mainly contributes to the peak impact force, and the peak impact force is six times higher than that in the first stage. With increasing initial impact velocity, the maximum aircraft impact force rises linearly. The range of the tension and pressure of the reinforcement axial stress changes with the impact height. The perforated size increases with increasing impact height. The radial perforation area is almost insensitive to the initial impact velocity and impact height. The research of this study can provide help for engineers in designing AP1000 shield buildings.

• Journal of the Korea Concrete Institute
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• v.20 no.1
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• pp.23-33
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• 2008

The moment redistribution in continuous reinforced concrete beams is very feasible phenomenon, by which the efficiency and the economy in designing reinforced concrete members can be enhanced. However, to understand the structural behavior by moment redistribution phenomenon, it is desirable to verify its mechanism experimentally considering tension stiffening effect, the relationship of moment redistribution and beam deflection, crack pattern, and effective stiffness. Six reinforced concrete continuous beam specimens were fabricated, and each specimen had a dimension of 250 mm $\times$ 350 mm and 7,000 mm long. The location of de-bonding was taken as the primary test parameter to investigate tension stiffening effect. The moment redistribution ratio of the specimens was different depending on the position of de-bonding, and in particular no moment redistribution was observed when de-bonding exist at both ends, the maximum negative moment region and the maximum positive moment region.

• Journal of the Korea Concrete Institute
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• v.23 no.2
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• pp.169-176
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• 2011

In this study, the flexural test for reinforced high performance fiber reinforced cementitious composites (R/HPFRCC) members has been conducted in order to investigate the flexural behavior including the effect of an ordinary tensile reinforcing bar. Through the test, it was observed that the flexural strength increased due to the stable tensile stress transfer of HPFRCC, even up to the ultimate state. In addition, no localized crack appeared until the yielding of the reinforcement. From the layered section analysis of the tested members, it was found that the analysis with the tensile model obtained from the tension stiffening test showed better agreement with the flexural test results, whereas the analysis with direct tension test results overestimated the flexural capacity. Through the experimental and analytical studies, two flexural failure modes have been defined in this paper; concrete crushing at the top compression layer or tensile failure at the bottom tensile layer of the beam section. Based on these two flexural failure modes, a simple formula that estimates the ultimate flexural strength of the member has been proposed in this paper. The proposed equations can be useful in a design and an analysis of R/HPFRCC members.

• Journal of the Korean GEO-environmental Society
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• v.16 no.10
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• pp.15-22
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• 2015

In this study, to evaluate the long-term behavior characteristics and the loss of prestress force, the long-term measurement of the tensile anchors in the actual construction was performed and the results were analyzed comparing with the existing estimation. As the reinforcement member used for the purpose of slope stability or uplift-resisting of the permanent structure, etc, the permanent anchor should maintain the functions during the performance period of the structure differently from the temporary anchor. However, as the time passes by, since the relaxation and the creep of the anchor occur constantly, the management for the loss of tensile force is essential to perform the functions stably. So far, the loss of the tensile force has been estimated according to the reduction of the prestress using elasticity theory and using the relaxation value according to the type of tension member and the test using the long-term measurement is limited. Therefore, in this study, the site condition and the ground were investigated for the tensile anchor in the actual construction and the long-term measurement results more than 500 days was analyzed by installing the loadcell, inclinometer and the groundwater level gauge. In addition, the long-term behavior characteristics were evaluated by comparing the disposition of the measured earth retaining wall and the tension force loss of the anchor with the existing interpretation results. In the evaluation results, the most of the tension force loss occurs within 90 days and the loss was measured less than the estimated values.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.47-53
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• 2022

As the limit state design method is applied as a method of designing concrete structures, the ultimate state is considered in the analysis or design. In fact, when the reinforced concrete member bears tensile force, the force is transmitted from the rebar to the concrete, and the structure bears the tensile force to the ultimate state even after yield. Therefore, the accurate evaluation of behavior after yield, it is necessary to study the tension stiffening effect after yield of the flexural member. In this study, a 4-point bending test was conducted on the RC simple beam having a rectangular cross section of the double reinforcement, and the behavior of the member was analyzed in detail using the image analysis method. Using the analysis results, the estimation formula for the tension stiffening effect after yield was proposed, and the applicability of this was verified through the experimental results of existing study. The difference between the ultimate strain and the yield strain representing the ductile behavior of the member is similar to the experimental results. The prediction of the proposed formula is relatively accurate.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.47-56
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• 2006

The repeated loading responses of four shear-critical reinforced concrete beams with two different shear span-to-depth ratios, were studied. One series of beams was reinforced using pairs of bundled stirrups with $90^{\circ}$ standard hooks, haying free end extensions of $6d_b$. The companion beams contained shear reinforcement made with larger diameter headed bars anchored with 50mm diameter circular heads. A single headed bar had the same area as a pair of bundled stirrups and hence the two series were comparable. The test results indicate that beams containing headed bar stirrups have a superior performance to companion beams containing bundled standard stirrups with improved ductility, larger energy absorption and enhanced post-peak load carrying capability. Due to splitting of the concrete cover and local crushing, the hooks of the standard stirrups opened resulting in loss of anchorage. In contrast, the headed bar stirrups did not lose their anchorage and hence were able to develop strain hardening and also served to delay buckling of the flexural compression steel. Excellent load-deflection predictions were obtained by reducing the tension stiffening to account for repeated load effects.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.339-347
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• 2002

An in-situ experiment was performed to evaluate the pullout resistance capacity of chains which is used as a reinforcement of reinforced earth wall. It was also considered that chain was combined with a bar or L-type steel angle by the transverse reinforcement member in the experiment. About 80 pullout tests were peformed with varying the lengths of chain(2.0m, 2.5m, and 3.0m), the combination of each transverse members(chain only, chain＋bar, or chain＋angle), and the vertical placement of reinforcements. In the case that uses a chain only and a chain combined with bar, the maximum displacement was about 150mm and load continuously increased to the ultimate tensile strength of chain, and then tension failure of chains occurred. But in the case of a chain combined with angle, the displacement decreased to about 100mm and so it was expected that this combination can constrain the displacement of chain. On the other hand, comparing the yielding pullout load measured in the field to that calculated by theoretical equation, it is shown that measured values are 1.2~3.0 times greater than those of calculated values according to the length of chain, normal vertical stress, and the combination of chain with transverse members. However, the difference in the increment of yielding pullout load between bar and angle is not clear but it appears almost the same increment. It is expected that chain can be safely used as reinforcements of reinforced earth wall, although a theoretical estimation of the pullout resistance capability of chain is too conservative.

• Journal of Korean Society of Steel Construction
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• v.9 no.3 s.32
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• pp.363-375
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• 1997

This study encompasses the performance of static and fatigue test for the 8 large scale test specimens to clarify the fatigue behavior of coped stringer and the effect of the repair and strengthening on the damaged stringer of the floor system in steel railway bridges. For the purpose of the research, the actual stress wave for the existing bridge was measured, the basic stress range frequency histogram was made and the equivalent stress range was calculated. Using the result from the equivalent stress range made by adjusting the stress range, the static and fatigue test was carried out by identifying the previous rehabilitation and after. As the result of the static tests, it was revealed that the level of local stress under the S1 specimen test of the real equivalent stress range was similar to tensile strength of the test material, and it was consistent with the requirement of the initiation condition of the fatigue crack. Through the various rehabilitation methods to the damaged specimens, the effects of the repair and reinforcement were analyzed. According to the results of the repair of effect, bolting the high tension bolt over the stop hole was confirmed to be more adequate method than drilling only stop hole to delay the fatigue crack growth. Futhermore, in case of the stringer subjected by bending moment, the reinforcement over the upper flange side was determined to be a useful strengthening method, and the reinforcement to the web of the stringer was not appropriate to accomodate as a adequate strengthening method. Also it was confirmed that the category of the fatigue design for the coped stringer met with the category E specified on the fatigue design criteria of the Highway Standard Specification in Korea.