• Journal of Technologic Dentistry
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• v.34 no.2
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• pp.95-103
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• 2012

Purpose: Fracture strength of all-ceramic 3-unit fixed partial dentures manufactured by CAD/CAM and copy-milling systems were evaluated. Methods: Zirconia cores were made by milling the pre-sintered zirconia block by CAD/CAM or copy milling method followed by subsequent sintering. By building-up the corresponding porcelains on the core, all-ceramic bridges were fabricated, and those were evaluated in comparison with PFM fixed partial denture. Results: During the flexural test of the 3-unit PFM bridge, the porcelain started to chip or break at 507.28(${\pm}62.82$)kgf and the metal framework did not break until the maximum load level of 800kgf which was set in the testing instrument of this study. However, among all-ceramic restoration test groups, Everest(EV) group showed a peeling off or breakage of the porcelain from 365.64(${\pm}64.96$)kgf and the core was broken at 491.77(${\pm}55.62$)kgf. Those values of Zirkonzahn(ZR) were 431.03(${\pm}58.47$)kgf and 602.74(${\pm}48.44$)kgf, respectively. The break strength of the porcelain of PFM(PM) group was significantly higher than that of EV (p<0.05) group and there was no significant difference when comparing to that of ZR (p>0.05). ZR group showed higher break strength than that of EV group however there was no significant difference (p>0.05). The break strength of cores were in the increasing order of EV < ZR < PM (p<0.05). Conclusion: We could find that even though the PM group fractured at much higher value than all-ceramic cores, the breakage values of the porcelain of PM group with crack formation or delamination, which will be regarded as clinical failure, was significantly higher than that of EV group and not significantly higher than that of ZR group at p-values of 0.05. The break strength of ZR group was higher than that of EV group at an insignificant level(p>0.05).

• Composites Research
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• v.29 no.2
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• pp.79-84
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• 2016

An adhesive can be used to connect two different materials in structures. In comparing with other connecting methods, such as bolt, rivet, and hot melting, the adhesive does not need to use them. It leads to reduce the weight and decrease the stress concentration along the connecting line. This work studied the comparison of mechanical and interfacial properties of commonly-used two adhesives, acrylic type and bisphenol-A epoxy type. Tensile and flexural strength of neat adhesives were also compared. Lap shear test of two adhesives was deduced from the measurement of tensile and fatigue tests. After testing, the failure patterns of adhesive surfaces were observed by a microscope. Tensile strength and mechanical fatigue resistance at using bisphenol-A epoxy adhesive were better than acrylic adhesive. Also adding CNT reinforcement in epoxy adhesive can anticipate mechanical improvement.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.703-710
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• 2010

Reinforced concrete beams of existing structure often encounter insufficient shear problems for various reasons. Application of steel plates is one of widely used methods for shear strengthening of reinforced concrete beams that are insufficient of shear capacity. This study presents test results on strengthening shear deficient RC beams by external bonding of vertical and diagonal slit type steel plates with anchor bolt. Test parameters are width, interval, angle and length of slits with anchor bolt. The purpose was to evaluate the failure modes and shear capacities for RC beams strengthened by various slit type steel plates with anchor bolt. The results showed that the slit type steel plate specimens strengthened by adhesive bonding and bolting failed in shear fracture modes at maximum load. Flexural crack first occurred on the tension face of beam and then inclined cracks occurred on the shear span. Finally, slit type steel plates strengthened by adhesive bonding and fastening bolts managed to delay abrupt debonding and didn't detach fully from main body of RC beam.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.6
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• pp.155-162
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• 2012

When RC (Reinforced Concrete) structures are exposed to sea water, steel corrosion can occur and this leads a degradation of structural performance. Referring the electro-deposition system with sea water from the 1st step research, durability and structural performance are evaluated in coated steel and RC members containing it in the 2nd research. In the durability performance test, Half Cell Potential test is performed and the coated steel is evaluated to have the high resistance to corrosion, which shows only 35% of corrosion velocity in normal (bare) steel. In the structural performance test, tensile strength, adhesive strength, and flexural/shear in RC member are performed. For the electro-deposit coated steel, increasing ratios of 3.2% and 8.8% are evaluated in the test of tensile strength and adhesive strength, respectively. For the structural test in RC member, there is no big difference between RC members with coated and non-coated steel in ultimate load and failure pattern It is evaluated that the chemical compound with $CaCO_3$ and $Mg(OH)_2$ from electro-deposition causes slightly increased structural performance. The electro-deposit coated steel can be more widely applied after performance verification from several tests like fatigue, resistance to impact, and long term-submerging test.

• Journal of Conservation Science
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• v.27 no.4
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• pp.395-401
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• 2011

After pressurized impregnation treatment, which has been proposed as an effective conservation method for stone cultural property, was executed with methyl metacrylate (MMA), MMA-butyl acrylate (PMB73) mixture and MMA-vinyl trimethoxy silane (PMV5) co-monomer mixture, the physical-chemical properties on the sand stone and the granite impregnated were evaluated. Compared to the case of granite, the impregnation ratios of sand stone showed larger values in the range of 3.2 to 3.7 wt% and these were increased up to 32% when the decompression process was applied to autoclave. The physical properties of sand stone such as anti-moisture property, flexural strength, impact property and ultrasonic velocity were also higher values than those of granite, which can be interpreted by high impregnation ratio resulted in many void within sand stone. The impact failure energy was 1.22 J for PMMA, 1.84 J for PMB73, and 2.8 J for PMV5, respectively. Since the inorganic affinity of treatment agent is more effective than the molecular structure of acrylic agent, PMV5 improved inorganic property indicates the optimum impact property.

• Journal of the Korea Concrete Institute
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• v.18 no.4 s.94
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• pp.527-534
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• 2006

This paper outlines a new strengthening technique for concrete beams using externally unbended high-strength bars. The advantages of proposed method lie in speed and simplicity of construction compared to the alternative strengthening method. Externally unbended reinforcement retains many of the advantages over external unbended prestressed tendons. It eliminates time consuming stressing operations. Clearance requirements around anchorages are reduced as access is not required for prestressing jacks. Test results of eight specimens on reinforced concrete beams using different reinforcement materials such as carbon fiber sheet, steel plate and high-tension bar are reported. The beam strengthened by carbon fiber sheet showed a brittle failure mode due to the separation of fiber. As a result of draped profile of external bar, the maximum strength of the beam were increased by up to 212 percent and the deflections were reduced by up to 65 percent. Test results show that the beams reinforced with high-tension bar are superior to reference specimens, especially for the strength and deformation capacity.

• Journal of Korean Society of Steel Construction
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• v.15 no.3
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• pp.261-269
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• 2003

The length of the links in an eccentrically braced frame will dictate the behavior of the frame. Link length controls the yielding mechanism and the ultimate failure mode. For short links, the links' shear forces reach the plastic shear capacity before the end moments reach the plastic moment capacity, and the links yields in the shear, forming a shear hinges. These links are termed "shear links." For long links, the end moments reach the plastic moment capacity before the links' shear forces reach the plastic shear capacity, forming moment hinges. These links are termed moment links." In long links, flexural yielding dominates the response, and very high bending strains are required at the link ends to produce large link deformations. In a shear links, the shear force is constant along the length of the links, and the inelastic shear strain are is uniformly distributed over the length of the links. This permits the development of large inelastic link deformations without the development of excessively high local strains. However, The use of eccentrically braced steel frames for the purpose of architectural cionsiderations such as openings and doors, areis dictating the use of longer links, though. Little data areis available on the behavior of long links under cyclic loading conditions. In This paper documents the results of an experimental program is that was conducted to assess the response of moment links in eccentrically braced frames. Sixteen specimens awere tested using a cyclic load.

• Journal of Korean Society of Steel Construction
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• v.22 no.3
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• pp.271-280
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• 2010

This study was programmed to fabricate a beam-to-column connection that is limited to a steel-welded moment connection with full-scale members, using SN steel. A cyclic seismic test was conducted of the nine specimens that were fabricated by choosing the test variable for the weld access hole geometry, connection design method, and RBS. From the test results, failure modes, the moment-drift behavior, and the strain distribution were provided. From the specimen material properties, the beam's nominal plastic flexural capacity and classified qualified connection as a special moment flame were calculated. By analyzing the skeleton part and the baushinger part, a range of strength-raising effects, and deformation ratios were provided, with which the seismic performance of the specimens were evaluated. The test results showed that the specimens eliminated their weld access holes that demonstrated higher seismic performance than the specimens' existing weld access holes, and that the WUF-W connection that was reinforced by the supplemental fillet weld around the shear tap that was fastened by five bolts demonstrated superior seismic performance.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.119-127
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• 2014

The application of sulfur polymer emulsion (SPE) as an acrylate substitute for semi-rigid pavement grout was evaluated, and the performance improvement by employing PVA fibers were also evaluated. The result indicated that the filling ratio of semi-rigid pavement material decreased as the fiber content increased, but it was measured to be 92~94% in every mixing condition, which satisfies the target performance, 90%. The maximum Marshall stability value of semi-rigid pavement material was measured to be 25.4 kN, which is about 4.7 times higher than the Korean Standard required for semi-rigid pavement material, 5.0 kN. The dynamic stability evaluation of semi-rigid pavement material indicated that the resistance to deformation from the wheel tracking test was improved by an SPE substitution, and in every mixing condition, the deformation converged to a constant value after 45 minutes with the same dynamic stability of 31,500 times/mm. The strain at the flexural failure was about 0.53%, which shows superior rigidity to asphalt pavements. The examination of abrasion resistance and impact resistance showed that the loss ratio was 9.8~6.0% in every mixing condition, which indicates a good abrasion resistance. Also, when fiber content ratio was 0.3%, the impact resistance was 2.82 times higher compared to plain (i.e., when fibers were not added). In the limited range of this study, an SPE substitution ratio of 30% was found to be an optimal level considering the mechanical and durability performance. In addition, it is thought that semi-rigid pavement material with superior performance could be manufactured if fiber content ratio up to 0.3% is applied depending on the purpose of use.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.5
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• pp.82-90
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• 2018

The nuclear structures are composed of large diameter bars over No.36. If the hooked bars are used for anchorage of large diameter bars, too long length of the tail extension of the hook plus bend create congestion and make an element difficult to construct. To address those problems, headed bars were developed. Provisions of ACI 318-08 specify the development length of headed bars and ignore the effect of transverse reinforcement based on the background researches. However, if headed bars are used at the cut-off or lap splice, longitudinal reinforcements, which are deformed in flexural members, induce tensile stress in cover concrete and increase the tensile force in the transverse reinforcement. The object of this research is to evaluate the effects of transverse reinforcement on the anchorage capacity of headed bar so anchorage test with variable of transverse rebar spacing was conducted. Specimens, which can consider the behavior at the cut-off, were tested. Test results show that failure of specimen without transverse reinforcement was sudden and brittle with concrete cover lifted and developed stress of headed bars was less than half of yield strength of headed bars. On the other hand, in the specimen with transverse reinforcement, transverse rebar directly resist the load of free-end so capacity of specimens highly increased.