• Journal of the Korean Society of Safety
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• v.7 no.3
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• pp.99-107
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• 1992

Weld bonding can be applied as a combined method of spot welding and adhesive to have more advantages than those. Weld bonding has many merits that enlarge the fatigue strength of spot Welding and also improve the creep of adhesive. But it has not beer proved well in the various environmental conditions. In this study, weld bonding test for fatigue properties and tensile strength is presented under such various coditions as temperatures, humidity, and etc.

• Magazine of the Korean Society of Agricultural Engineers
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• v.44 no.1
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• pp.116-124
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• 2002

Natural resources fur the construction materials such as good soil, sand, and coarse aggregates have been encountered to be short due to excessive use by human. Even though some soil has been found to be unsuitable for construction materials, soil with reinforcement can naturally be an answer to these alternatives. According to recently published papers on fiber mixed soil, fiber mixed with soil can improve shear strength, compressive strength and post-peak load strength retention. In this study, a series of tests were performed to clarify the characteristics of fiber mixed soil and to give basic data for design and construction and their engineering properties, that is, unconfined compressive strength, splitting tensile strength, shear strength, crack by drying, freeze-thaw, creep and Poisson\`s ratio, were investigated and analyzed. It has been shown that fiber mixed soil is one of good alternatives fur the civil and building construction materials.

• Restorative Dentistry and Endodontics
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• v.34 no.3
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• pp.184-191
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• 2009

The purpose of this study was to evaluate the physical properties of different self-adhesive resin cements and their shear bond strength on dentin and lithium disilicate ceramic and compare these result with that of conventional resin cement. For this study, four self-adhesive resin cements (Rely-X Unicem, Embrace Wetbond, Mexcem, BisCem), one conventional resin cement (Rely-X ARC) and one restorative resin composite (Z-350) were used. In order to evaluate the physical properties, compressive strength, diametral tensile strength and flexural strength were measured. To evaluate the shear bond strength on dentin, each cement was adhered to buccal dentinal surface of extracted human lower molars. Dentin bonding agent was applied after acid etching for groups of Rely-X ARC and Z-350. In order to evaluate the shear bond strength on ceramic, lithium disilicate glass ceramic (IPS Empress 2) disks were prepared. Only Rely-X ARC and Z-350 groups were pretreated with hydrofluoric acid and silane. And then each resin cement was adhered to ceramic surface in 2 mm diameter. Physical properties and shear bond strengths were measured using a universal testing machine. Results were as follows 1. BisCem showed the lowest compressive strength, diametral tensile strength and flexural strength. (P<0.05) 2. Self-adhesive resin cements showed significantly lower shear bond strength on the dentin and lithium disilicate ceramic than Rely-X ARC and Z-350 (P<0.05) In conclusion, self-adhesive resin cements represent the lower physical properties and shear bond strength than a conventional resin cement.

• Journal of the Korean Geotechnical Society
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• v.20 no.6
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• pp.119-126
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• 2004

Behaviour of soil nailed walls in Korea has been analysed based on a number of field measurements. The investigation has included interface shear strength development at the nail-soil interface from pull-out tests, lateral ground displacements, tensile force distributions along soil nails and mobilised interface shear stress distributions. Insights into the soil nailed wall behaviour based on the shear transfer mechanism at the soil-nail interface and partial mobilisations of the interface shear strength, governed by relative shear displacement, are reported and discussed. It is expected that results from the current research can provide relevant parameters required for preliminary design of soil nailed walls in Korea.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.4
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• pp.133-140
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• 2010

The purpose of this study is to evaluate the new eco water tank which is made of high density polyethylene and concrete with low temperature cement. The strength and failure mode of eco water tank was examined through tensile test with mixture of concrete and HDPE, temperature monitoring for various kind of concrete, admixture contains etc. The strength and failure mode were examined through tensile test with mixture of concrete and HDPE, temperature monitering for different kinds of concrete, strength test with different admixtures etc. It was found that shear connector between concrete and HDPE effects significantly contributed to the combined structures. ㄱ type shear connector results in tensile strength of up to 40% compared to that of V type shear connector. Based on test result, the new eco composite tank improved the stability and safety the old one and demonstrated the applicability and capability.

• Structural Engineering and Mechanics
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• v.74 no.5
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• pp.657-670
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• 2020

Due to the high compressive and tensile strength of ultra-high performance concrete (UHPC), UHPC used in steel concrete composite structures provided thinner concrete layer compared to ordinary concrete. This leaded to the headed stud shear connectors embedded in UHPC had a low aspect ratio. In order to systematic investigate the effect of headed stud with low aspect ratio on the structural behaviors of steel UHPC composite structure s this paper firstly carried out a test program consisted of twelve push out specimens. The effects of stud height, aspect ratio and reinforcement bars in UHPC on the structural behaviors of headed studs were investigated. The push out test results shows that the increasing of stud height did not obviously influence the structural behaviors of headed studs and the aspect ratio of 2.16 was proved enough to take full advantage of the headed stud strength. Based on the test results, the equation considering the contribution of weld collar was modified to predict the shear strength of headed stud embedded in UHPC. The modified equation could accurately predict the shear strength of headed stud by comparing with the experimental results. On the basis of push out test results, bending tests consisted of three steel UHPC composite slabs were conducted to investigate the effect of shear connection degree on the structural behaviors of composite slabs. The bending test results revealed that the shear connection degree had a significantly influence on the failure modes and ultimate resistance of composite slabs and composite slab with connection degree of 96% in s hear span exhibited a ductile failure accompanied by the tensile yield of steel plate and crushing of UHPC. Finally, analytical model based on the failure mode of composite slabs was proposed to predict the ultimate resistance of steel UHPC composite slabs with different shear connection degrees at the interface.

• Computers and Concrete
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• v.17 no.6
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• pp.739-760
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• 2016

This paper reports on punching shear behavior of reinforced concrete panels, investigated experimentally and through finite element simulation. The aim of the study was to examine the punching shear of high strength concrete panels incorporating different types of aggregate and silica fume, in order to assess the validity of the existing code models with respect to the role of compressive and tensile strength of high strength concrete. The variables in concrete mix design include three types of coarse aggregates and three water-cementitious ratios, and ten-percent replacement of silica fume. The experimental results were compared with the results produced by empirical prediction equations of a number of widely used codes of practice. The prediction of the punching shear capacity of high strength concrete using the equations listed in this study, pointed to a potential unsafe design in some of them. This may be a reflection of the overestimation of the contribution of compressive strength and the negligence of the role of flexural reinforcement. The overall findings clearly indicated that the extrapolation of the relationships that were developed for normal strength concrete are not valid for high strength concrete within the scope of this study and that finite element simulation can provide a better alternative to empirical code Equations.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.10
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• pp.141-151
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• 1999

The resistance Spot Welding is widely used in the field of assembling the plates. However we don't still have any satisfactory solution, which is non-destructive quality evaluation in real-time or on-line, against it. Moreover, even though the rate of welding under the condition of expulsion has been high until now, quality control of welding against expulsion hasn't still been established. In this paper, it was proposed on the quality assurance technique of resistance spot welding pieces using Neuro-Fuzzy algorithm. Four parameters from electrode separation signal in the case of non-expulsion, and dynamic resistance patterns in the case of expulsion are selected as fuzzy input parameters. The parameters consist of Fuzzy Inference System are determined through Neuro-Learning algorithm. And then, fuzzy Inference System is constructed. It was confirmed that the fuzzy inference values of strength have within ${\pm}$4% error specimen in comparison with real strength for the total strength range, and the specimen percent having within ${\pm}$1% error was 88.8%. According to KS(Korean Industrial Standard), tensile-shear strength limit for electric coated of zinc is 400kgf/mm2. Judging to the quality of welding is good or bad, according to this criterion and the results of inference, the probability of misjudgement that good quality is valuated into poor one was 0.43%, on contrary it was 2.59%. Finally, the proposed Neuro-Fuzzy Inference System can infer the tensile-shear strength of resistance spot welding pieces with high performance for all cases-non-expulsion and expulsion. And On-Line Welding Quality Inspection System will be realized sooner or later.

• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.168-174
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• 2001

Carbon fiber sheet(CFS) has been widely used for strengthening of the concrete building structures due to its excellent physical properties such as high strength, light weight and high durability. Bond strength or behavior, on the other hands, between carbon fiber sheet and concrete is very important in strengthening the concrete member using CFS. Therefore the bond failure mechanism between CFS and concrete should be fully verified and understood. This study is to investigate the bond strength of CFS to the concrete by the direct pull-out test and the tensile-shear test. In the direct pull-out tests, the bond strength under the various environmental conditions such as curing temperature, surface condition on concrete and water content of concrete are evaluated. Also, the effective bond length, lu and the average bond stress, $\tau$y are examined in the tensile-shear tests. Based on the test results, it is concluded that the curing temperature is the most critical element for the bond strength between CFS and concrete. And, the proper value of lu and $\tau$y is recommended with 15 cm and 9.78∼ 11.88 kgf/$\textrm{cm}^2$ respectively.

• Restorative Dentistry and Endodontics
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• v.26 no.1
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• pp.23-31
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• 2001

The purpose of this study was to search the optimal silane concentrations for filler- silanization of seven experimental composites. Silica filer was a 25micron crushed type. 0.0%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, and 3.0% silane($\gamma$-methacrylooxypropyltrimethoxysilane)were added into silica-filler with weight percentage (wt%). Mixtures(silica filler/silane)were reacted at 6$0^{\circ}C$ for 72hours, and crushed into fine particles those were used as fillers for 7 experimental composites. Monomer was a 3 : 1 mixture of Bis-GMA and TEGDMA containing 0.2% tertiary amine and 0.4% camphoroquinone for light curability. A ratio for mixing the monomer and filler was 75% and 25% respectively. Seven experimental composites was classified with the concentration of silane treated, and the specimen number for each test was 10. Specimens with 6mm diameter and 3mm height dimension for measuring the diametral tensile strength were destroyed with 1mm/min cross-head speed on Instron universal testing machine (No. 4467, USA). Shear bond strength was measured on the specimens bonded to bovine enamel etched with 37% phosphoric acid solution for 1 minute Fractured surfaces were observed by SEM (Hitachi S-3200, Japan) among that of the highest values measured from each groups. Following results were obtained: 1. Experimental composites containing silanized filter showed the significantly higher diametral tensile strength and shear bond strength than the composites containing un-silanized fillers(Group1) (p<0.05). 2. In silanized filler composite resins(Group 2~7), Diametral tensile strength of Group 3 showed the significantly higher than that of Group 2 and Group 6(p<0.05). 3. Shear bond strength was higher in Group 3 than that of Group 7 (p＜0.05)in silanized fillers composite resins. 4. Fracture surface was formed in resin matrixes on the specimens from composites containing the fillers treated with 0.5% 1.0%, and 1.5% silane. These results mean that the optimal silane concentrations are exist for each fillet with its size and surface area, and that 1.0% is a optimal value for concentration to coat the 25$\mu\textrm{m}$ filler with silane.