• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.7
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• pp.152-163
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• 2019

In this paper, effect of steel fiber inclusion, compressive strength of matrix, shear reinforcement and shear span to depth ratio on the flexural behavior of UHPFRC(Ultra High Performance Fiber Reinforced Concrete) were investigated with test of 10-UHPFRC beam specimens. All test specimens were subjected to the flexural static loading. It was shown that steel fiber significantly improve the shear strength of UHPFRC beams. 2% volume fraction of steel fiber change the mode of failure from shear failure to flexural failure and delayed the failure of compressive strut with comparatively short shear span to depth ratio. UHPFRC beams without steel fiber had a 45-degree crack angle and fiber reinforced one had lower crack angle. Shear reinforcement contribution on shear strength of beams can be calculated by 45-degree truss model with acceptable conservatism. Using test results, French and Korean UHPFRC design recommendations were evaluated. French recommendation have shown conservative results on flexural behavior but Korean recommendation have shown overestimation for flexural strength. Both recommendations have shown the conservatism on the flexural ductility and shear strength either.

• Elastomers and Composites
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• v.45 no.2
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• pp.122-128
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• 2010

We measured shear viscosity of copoly(styrene(St)/butyl methacrylate(BMA)) (co-PSB) particles, with a capillary rheometer at $170^{\circ}C$, prepared by suspension polymerization with hydrophobic silica as a stabilizer. co-PSB particles with the weight average molecular weights of lower than 74,800 g/mol displayed a Newtonian behavior at low shear rates. With the weight average molecular weight exceeding 136,800 g/mol, co-PSB particles showed shear thinning against shear rates and the absolute value of the slopes between shear viscosity vs. shear rate increased. When the ratio between St and BMA changed from 7/3 to 5/5 to 3/7, shear viscosity and glass transition decreased despite similar molecular weights. When the ratio was 1/9, it showed a large increase in initial shear viscosity despite reduced glass transition. Shear viscosity exhibited an increase in proportion to carbon black concentration. The effect of carbon black concentration on the shear viscosity of co-PSB composites was less pronounced compared to varying molecular weights and/or compositional ratio.

• Journal of Dental Rehabilitation and Applied Science
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• v.34 no.2
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• pp.89-96
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• 2018

Purpose: The aim of this study was to evaluate the effect of delayed time, surface treatment, and repair materials on repair of bis-acryl composite resin through comparison of shear bond strength and to evaluate the utility of bis-acryl composite resin repair using polymethyl methacrylate resin. Materials and Methods: A total of 90 bis-acryl composite resin specimens were fabricated and classified into 9 test groups, each of 10 pieces according to delayed time, surface treatment and repair material. The shear bond strength of each specimen was measured using a universal testing machine immediately after fabrication and analyzed using a statistical analysis program (IBM SPSS statistics 20). After the shear bond strength measurement, the fracture surface of the specimen was observed. Results: The highest shear bond strength ($17.54{\pm}3.14MPa$) was observed in the experimental group bonded immediately with a light-curing flowable composite resin using a bonding agent. Conclusion: When repairing bis-acryl composite resin, it is necessary to consider whether to remake according to the delayed time. For effective repair, it is desirable to consider appropriate materials and surface treatment methods according to the site or purpose of use.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.2
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• pp.177-184
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• 2008

In this study, in order to reduce appeals regarding vibration and noise from blasts, the optimum delay-time of the electronic detonator, which can minimize blast vibration, is found through blast-waveform composition and blasting simulation, and we have developed the full-face Sequential Blasting Method based on the studies of damping properties of full-face section blasting. The optimum delay-time of the electronic detonator and Full-face Sequential Blasting Method using electronic detonator was applied to the Gyeongbu high-speed railway construction site to test the feasibility of this method.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.4
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• pp.99-108
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• 2007

In the flat-plate slab design of the KCI and ACI building code, the punching shear strength of connections with shear reinforcement can increase one and half times to that of connections without shear reinforcement. And the ACI-ASCE committee 352 recommendations propose limiting the direct shear ratio $V_g$/$V_c$ on interior connections to 0.4 to insure adequate drift capacity. In this study, four interior column-slab connections were tested to look into the punching shear strength and the lateral displacement capacity of the flat-plate slab with and without shear reinforcement under cyclic lateral loading. Based on the test results, it is found that the provision about punching shear strength in the codes may appropriate for the gravity loading only whereas it is unconservative for the lateral loading and that the limit of ACI-ASCE committee 352 appears conservative.

• Restorative Dentistry and Endodontics
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• v.29 no.1
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• pp.30-35
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• 2004

치아 미백술은 치아의 심미성을 향상시키는 가장 보존적인 방법의 하나로 인식되어져 왔으며 최근의 심미치과에 대한 관심의 증가와 함께 그 빈도가 급격히 증가하고 있는 술식의 하나이다. 일반적으로 치아 미백술 후 바로 접착수복을 할 경우 결합력이 감소하는 것으로 알려져 있으며 이를 해소하기 위해 일정시간 경과 후 접착수복 술식을 시행할 것을 권장 하고 있다. 자가산부식형 (self-etching primer system) 접착제는 기존의 접착제와 다른 성분으로 인해 치아미백제에 의한 영향에 대해 잘 알려져 있지 않은 상태이다. 이에 본 실험에서는 미백술을 시행한 법랑질 상에서 서로 다른 세 가지의 접착 시스템을 이용하여 미백술 후의 지연 시간이 결합력에 미치는 영향을 비교하고자 하였다. 발거한 대구치 68개를 물기가 있는 상태에서 근원심으로 절단하고 치관부를 자가중합 레진에 식립하여 시편을 제작하였다. 세 가지 접착제로 $One-step^{\circledR}$, Clearfil SE Bond $primer^{\circledR}$, One-up Bond $F^{\circledR}$를 이용하였다. 각 접착제를 미백을 시행하지 않는 대조군과 미백 시행 후 바로 접착한 즉시 접착군, 그리고 2주간 생리식염수에 보관한 후에 접착한 지연군으로 나누어 총 9개의 실험군으로 나누었다. 접착제를 처리한 면에 Clearfil $AP-X^{\circledR}$ 복합레진을 2mm충전하고, 40초간 광중합을 시행하였다. 24시간 후 전단접착강도를 측정하였으며, 그 결과는 다음과 같이 나타났다. $One-step^{\circledR}$의 경우, 즉시 접착군에서 지연 접착군보다 유의성 있게 낮은 접착강도를 나타내었다. Clearfil SE $Bond^{\circledR}$의 경우, 즉시 접착군과 미백을 시행하지 않은 군간에는 접착 강도에 유의한 차가 없었으나,지연접착군에서는 낮은 강도를 나타내었다. One-Up Bond F$^{\circledR}$의 경우, 즉시 접착군에서 유의성 있게 낮은 전단접착강도를 나타내었고, 전반적인 접착 강도가 다른 두 접착제에 비해서 유의성 있게 낮은 값을 보였다. $One-step^{\circledR}$을 사용할 경우 지연접착을 하는 것이 추천되며, Clearfil SE Bond$^{\circledR}$의 경우에는 즉시 접착을 시행하더라도 영향을 적게 받는 것으로 나타났으며, One-Up Bond $F^{\circledR}$의 경우 미백술 후 접착수복 과정에 사용에 제한이 있는 것으로 나타났다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2003.10a
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• pp.325-332
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• 2003

The tube structures act like cantilevered box beams and effectively resist lateral loads. In result, they are adopted as a high-rise buildings system. However, the shear lag in tube system prevents the idealized tube behavior such as a cantilevered box beam. Therefore, the studies on shear lag phenomena are necessarily requested. The presented papers are almost studied on framed tube structures and tube in tube structures. However, the study on the shear lag in the tube structure with core wall is lack. Thus, in this paper, the shear lag of the structure is studied. The shear lag coefficient is defined to investigate shear lag phenomena. However, existing shear lag coefficients are not adequate for understanding them. Therefore, on this study, new shear lag coefficient is suggested. In addition, the shear lag in the tube structure with core wall is analyzed by changing the five structural parameters of stiffness factor in frame, stiffness factor in wall, stiffness ratio, the number of stories and the number of bays.

• 한국도로학회:학술대회논문집
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• 2004.10a
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• pp.235-238
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• 2004

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.301-304
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• 2008

This paper presented an structural efficiency of steel coupling beam jointed single plate shear connections with seat and top angle. Parameters for the test specimens were are seat and top angle, reinforcing of concrete, embedded length, section loss. Steel coupling beam with angle showed excellent strength, stiffness, energy dissipation capacity. The specimen with no reinforcement around the embedded steel plate showed slightly low deformation capacity because of early failure in the precast concrete walls. However, the specimen with reinforcement around the embedded steel plate showed good deformation capacity. Deformation capacity was not decrease despite short embedded length. The specimen with section loss showed excellent deformation capacity. Because shear strength of steel coupling beam was lesser than of connections. These results showed that for workability and cost efficiency, the proposed system is promising for one of steel coupling beam.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.10
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• pp.40-47
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• 2006

Optical performance of the mirror for satellite camera is highly dependent on the adhesive properties of its support. Therefore, in this paper, the adhesive properties of three kinds of space adhesives are investigated. For this purpose, the lap shear test is performed with Zerodur-to-metal lap shear specimen as well as metal-to-metal one. And it is also investigated whether reliable adhesive strength can be secured after the specific thermal cycle. Finally, the properties of three adhesives are compared with each other.