• Journal of Korean Society of Steel Construction
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• v.27 no.3
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• pp.333-345
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• 2015

This study evaluated the static and dynamic shear strength of cast-in-place anchors reinforced with hairpin bars in uncracked and cracked concrete. The anchors 30mm in diameter reinforced with D10 hairpin bar were designed with an edge distance of 150mm and an embedment depth of 240mm. The cracked specimens consisted of the orthogonal and parallel cracks to the direction of shear loads, respectively. The dynamic strength was evaluated using seismic qualification tests based on the ACI 355.2 standard. The shear strength of the hairpin reinforced anchor was hardly correlated to the concrete cracks and the dynamic strength was similar to its static shear strength. Finally, a consideration on the design strength of hairpin reinforced anchors was presented.

• Journal of Korean Society of Steel Construction
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• v.21 no.3
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• pp.277-287
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• 2009

The objective of this study was to experimentally investigate the structural behavior of steel plate concrete walls with vertical ribs (SSC walls), to compare the experimental results with the currently applied evaluation equations, and to obtain information that would be useful in the development of design equations for SSC walls. SSC test specimens that were subjected to in plane shear forces and bending moments were fabricated and tested. The experimental results show that the effect of vertical ribs on the structural behavior of SSC walls may be neglected, and that the confinement effect of concrete on the steel plates on both sides of the walls was negligible. The comparison of the experimental results with the evaluation equations showed that the structural behavior of SSC walls under shear control is close to that of the evaluation equations, but that the behavior of SSC walls under larger bending moments is not very close to that of the evaluation equations. The current evaluation equations for USC walls may be applied to the design of SSC walls because the structural walls of nuclear power plants are not subjected to large in plane bending moments.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.1 s.53
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• pp.195-204
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• 2009

Application of steel plates is one of widely used methods for shear strengthening of reinforced concrete beams that are insufficient of shear capacity. While the existing method applying solid steel plates provides good shear rigidity, however, it is concerned by brittle bond failure patterns, inefficient material usage, and low constructability. The use of strap type steel plates has also shortcomings of low strenthening effect due to small interface bonding area and ununified behavior between plates and main body. Therefore, this study aims to introduce the shear strengthening method using slit type steel plate, which can solve out the problems aforementioned, and to verify its strengthening effects on shear capacity. A total of 13 specimens strengthened by slit type steel plates were fabricated with primary test parameters of plate width, slit spacing, and plate thickness. The test results from this study were also compared to those from the existing research on RC beams strengthened by strap type steel plates, and the strengthening effects on shear capacity of specimens having bonded slit type steel plates were quantitatively analyzed. The test results showed that the RC beams strengthened by slit type steel plates had greater shear capacities than those with strap type steel plates, which is considered to be the effects of improved composite behavior and larger interface bonding area in the RC beams strengthened by the slit type steel plates.

• Journal of the Korea Concrete Institute
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• v.29 no.3
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• pp.259-266
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• 2017

The purpose of this study was to contribute to the field application cost effectively and reasonably by developing the functional piles that reinforces shear force. CFP pile (Concrete Filled Pretensioned Spun High Strength Concrete Pile with Ring type Composite shear connectors) developed in this study increases the shear stress by placing composite shear connector and filling the concrete into hollow part of the pile. By placing the reinforcement (H13-8ea) and the reinforcement (H19-8ea) into hollow section inside of PHC piles, it also improves the shear strength due to increasing steel ratio. It reinforces shear strength effectively by dowel force that is generated by putting reinforcement (H13-8) into the holes of composite shear connectors for the composite behavior of filled concrete and PHC pile. The study was reviewed and compared the calculated result of the shear strength by limit state design method highway bridge design standards (2012) and experiment result of the shear strength by KS F 4306. We can design the shear strength reasonably as the safety ratio of 2.20, 2.15, 2.05 is shown comparing to design shear strength, according to design shear strength on each cross sections and the experiment results of the CFP pile.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.1
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• pp.25-32
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• 2016

The purpose of this study is to evaluate the performance on the compressive bonding shear strength of ultra-high strength steel fiber reinforced cementitous composites(UHSCC). As a result of compressive bonding shear strength through Direct shear test, It was found that the specimen($150{\times}150{\times}150mm$) of NC(Normal concrete) + NC showed similar compressive bonding shear strength at whole experimental level. On the other hand, the specimen of UHSCC + UHSCC showed decrease of compressive bonding shear strength from after 30 minutes of the retarded placement than 0 minute. As a result of analyzing failure mode of bonding interface, It was found that the specimen of NC + NC showed mixed failure at whole experimental level. In case of the specimen of UHSCC + UHSCC, it showed interface failure from the specimen that are 30 minutes, 60 minutes and 90 minutes of delay of concrete placing. As a result of analyzing XRD test in terms of the placement interface on the specimen of NC and UHSCC, relatively much amount of $SiO_2$ was detected from the specimen of UHSCC than that of NC. It is judged that the most of main components of coating film shown in the specimen of UHSCC is $SiO_2$. In conclusion, it is judged that UHSCC which is made from after 30 minutes of delay of concrete placing is unable to be used as structural member because of deterioration of bonding performance. From later study, it is judged that the improvement of bonding performance from the part of cold joint occurrence is necessary through the interface preparation method.

• Journal of the Korean Geotechnical Society
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• v.20 no.5
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• pp.5-16
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• 2004

This paper presents the modeling of geosynthetic-reinforced compacted soils and discusses the reinforcement effect arising from confining the dilatancy deformation of the soil by geosynthetics. A series of compressive shear tests for compacted sandy soil specimens wrapped by geosynthetics are carried out by quantitatively examining the geosynthetic-reinforcement effect, occurring from a confinement of the dilative deformation in compacted soils during shearing. In the test, the initial degree of compaction is changed for each series of sandy soil specimens so that each series has different degree of dilatancy characteristics. Herein, the axial forces working on the geosynthetics so as to prevent dilative deformation of compacted soils during shearing are measured. Furthermore, the elasto-plastic modeling of compacted soils and a rational determination procedure for input parameters needed in the elasto-plastic modeling are presented. And to describe the irreversible deformation characteristics of compacted soils during shearing, the subloading yielding surface (Hashiguchi (1989)) to the elasto-plastic modeling is introduced. Finally, the elasto-plastic finite element simulation is carried out and the geosynthetic-reinforcement effect is discussed.

• Journal of the Korea Concrete Institute
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• v.29 no.4
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• pp.353-360
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• 2017

The objective of this study is theoretical and empirical evaluation of the flexural performance of concrete filled pretensioned spun high strength concrete pile with ring type composite shear connectors (CFP pile). The specimens are comprised of standard CFP pile, PHC pile+composite shear connector+filed concrete (CFP-N-N), standard CFP pile with $1^{st}$ reinforcements (H13-8ea), and standard CFP pile with $1^{st}$ and $2^{nd}$ reinforcements(H19-8ea). Flexural performance evaluation results showed that the ductility is improved with increased steel ratio, which leads to the increased maximum load by 46.4% (with $1^{st}$ reinforcement) and 103.9% (with $1^{st}$ and $2^{nd}$ reinforcements) compared to standard CFP ( CFP-N-N). Comparing with the predicted ultimate limit state values of the CFP pile design method and the experimental results, the design method presented in this study is reasonable since safety factor of 1.23 and 1.40 times for each reinforcement step are secured.

• Journal of the Korean Geosynthetics Society
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• v.5 no.4
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• pp.19-25
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• 2006

To examine the general features of a sand-clay composite triaxial test by making specimen varying ratios of diameters (dw) of sand columns that are installed on the soft ground as drains to diameters (de) of drain zone so called drainage space ratio (n=de/dw), densities of the granular columns, and strength of soft soils round around. I also conducted a test to research the reinforcement ability and effects of the ground when the granular columns are wrapped with supplementary materials such as geotextile. The results of the triaxial compression test showed that the shear strength increase is much big when the granular columns are wrapped with supplementary materials, while the shear strength increases as the diameter and density of the granular column increase in general. Also the drainage space ratio shows a distinct increase just below 3 and a similar shear behavior to sand is appeared. The pore water pressure coefficient decreases as the drainage space ratio decreases, however, when the drainage space ratio is less than 3~4, it declines significantly as shown in the results of shear behavior.

• Magazine of the Korea Concrete Institute
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• v.10 no.5
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• pp.109-115
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• 1998

철근콘크리트 구조물이 과소설계되어 있거나 과다 하중이 작용하게 되면 그 구조물의 구조성능을 파악하여 보수.보강을 시행하게 된다. 최근에 가장 맣이 사용되는 보수.보강 재료로는 특히 휨내력을 보강하는데 탄소섬유를 들 수 있다. 탄소섬유쉬트는 내열성과 내호염성에 있어서 회재가 발생할 경우 보강재료로서 충분한 성능을 가지고 있다. 그러나 이를 접착시키는데 사용되는 에폭시는 유기계 물질로서 화재시 유독가스가 발생하고 내열성능도 30$0^{\circ}C$정도에도 지탱하기 어려워 화재 발생이 가능한 구조물에 사용하기 어렵다. 이 연구에서는 무기계 폴리머 복합재료로 접착된 탄소섬유를 고온(약 800~100$0^{\circ}C$, 1시간)으로 가열한 후 가열된 섬유판의 인장, 휨 전단내력을 검토하여 내열성능을 파악하고 이 섬유쉬트로 보강한 철근콘크리트 부재의 휨 성능을 실험적으로 규명하여 화재의 위험이 있는 구조물에 구조적인 보강재료로 사용이 가능한가를 검토하였다. 연구 결과, 개발된 무기계 폴리머 복합체는 인장강도, 휨강도 및 접착강도가 유기계 접착제와 유사하게 나타났고 800~100$0^{\circ}C$ 정도로 1시간 가열한 이후에도 상온 시험체 휨내력과 전단내력의 63%, 33% 정도를 유지하여 화재의 위험이 있는 부위에도 사용이 가능한 것으로 판단되었다.

• International Journal of Highway Engineering
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• v.7 no.2 s.24
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• pp.1-12
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• 2005

This study was conducted to evaluate effect of geogrid and fabric, which are used underneath the overlaid asphalt pavement for retarding reflection cracking by simulated laboratory test. In this study, an interlayer at the interface between old concrete pavement surface and overlaid asphalt mixture, and polymer-modifier were used as an effort of retarding reflection crack initiation and for strengthening mixture. Five products were used in preparation of asphalt concrete beam specimen which was tack coated on top of jointed concrete block. Simulated Mode I and II fracture test were conducted under wheel loading and results were compared among those products. From the test results, several material and reinforcement combinations were observed to have a significant retardation effect against reflection cracking. The most effectively strengthened pavement against reflection cracking was found to be the LDPE-modifier asphalt mixture with a grid reinforcement at the bottom.