• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.3A
• /
• pp.421-428
• /
• 2006

This study was performed by using experiment to minimize behavior difference of Monolithic and segmental Girder and to prove the design concept of the PSI (Precast PSC-Segmental I Grider). A full scale girder test was performed in four different cases, the monolithic girder, the segmental girder type-1, the segmental girder type-2 and the segmental girder type-3. The monolithic girder that was produced in one body 25 m span and the segmental girder that was jointed 5-sliced 5 m segment. The girder was built by as one body prestressing the tendons after manufacturing the segmental girder, and second prestressing after the casting of the slab concrete. The test result shows that the measured values were almost same or slightly bigger than the theoretical values which means that the PSI girder bridges concept came out to be reliable.

• Smart Structures and Systems
• /
• v.32 no.4
• /
• pp.253-266
• /
• 2023

The time-reversal method is employed to improve the ability of pipeline defect detection, and a new approach of identifying the pipeline defect depth is proposed in this research. When the L(0,2) mode ultrasonic guided wave excited through a lead zirconate titinate (PZT) transduce array propagates along the pipeline with a defect, it will interact with the defect and be partially converted to flexural F(n, m) modes and longitudinal L(0,1) mode. Using a receiving PZT array attached axisymmetrically around the pipeline, the L(0,2) reflection signal as well as the mode conversion signals at the defect are obtained. An appropriate rectangle window is used to intercept the L(0,2) reflection signal and the mode conversion signals from the obtained direct detection signals. The intercepted signals are time reversed and re-excited in the pipeline again, result in the guided wave energy focusing on the pipeline defect, the L(0,2) reflection and the L(0,1) mode conversion signals being enhanced to a higher level, especially for the small defect in the early crack stage. Besides the L(0,2) reflection signal, the L(0,1) mode conversion signal also contains useful pipeline defect information. It is possible to identify the pipeline defect depth by monitoring the variation trend of L(0,2) and L(0,1) reflection coefficients. The finite element method (FEM) simulation and experiment results are given in the paper, the enhancement of pipeline defect reflection signals by time-reversal method is obvious, and the way to identify pipeline defect depth is demonstrated to be effective.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.13 no.1 s.53
• /
• pp.161-168
• /
• 2009

In this study, the concrete, in which the steel fiber(SF) with different volume-surface ratios and lengths was intermixed in High flowing Self-Compacting Concrete(HSCC), was produced to compare with steel fiber reinforced concrete as a part of plan to improve the workability and the quality of steel fiber reinforced concrete. As the result of experiment, the flowing and passing characteristics of HSCC intermixed with SF was highly improved as there was no fiber ball phenomenon due to the effect of high flowability and the viscosity, and in the identical range of compressive strength, it showed the tendency that the splitting and flexural strength was increasing as the length was getting longer regardless of volume-surface ratio when compared with HSCC which was intermixed with SF. It is estimated that in case of application of HSCC intermixed with steel fiber to work sites, it would be possible to improve the workability and the quality which would be better than that of steel fiber reinforced concrete which has been used.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.6
• /
• pp.262-269
• /
• 2021

This paper conducts an evaluation of the structural performance of the lap splice detail of SD700 headed bar experiment for developing an RC beam with different depths joint details. The experiment variable is lap splice length, yield strength, and end anchorage of main reinforcements. For all specimens, a headed bar was applied to the main reinforcement of the beam with low depth (B2), and the beam with high depth (B1) was applied to the main reinforcement with two splice methods: straight headed bar and 90° hooked-headed bar. The experimental results were that specimens of applying SD500 and SD600 had the results of flexural fracture at the lap splice location, which maximum load was similar. For specimens of appling SD500, the 90° hooked-headed bar of B1, suppressed horizontal cracks in the lap splice section compared to the straight headed bar. Specimens of applying an SD 700 headed bar had the results of brittle anchorage failure. In addition, maximum load was increased with the lap splice length increasing. For specimens of applying SD700 headed bar, test for test maximum load/theoretical load for test development length/design development length were estimated to be 1.30~1.48 for the ACI 318-19 equation, and 1.14~1.30 for the KDS-2021 equation. Thus, ACI 318-19 equation had conservatively greater safety factors as estimated development lengththened.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.33 no.2
• /
• pp.71-79
• /
• 2017

Purpose: Ni-Cr alloy does not contain Beryllium, causing the metal compound to form oxides in the furnace but by using Titanium as a chemical catalyst the forming of the oxides can be controlled, and by controlling the impurities formed on the metal surface, the possibility of the Ni-Cr alloy bond strength being increased can be analysed. Materials and Methods: Titanium was used as a chemical catalyst in the porcelain for the oxidation of beryllium-free metal (Ni-Cr) alloy. The T1 group, which does not use Titanium power as a chemical catalyst is a reference model for comparison. The T2 group and T3 group used 10 g and 20 g of Titanium power, respectively. They are fabricated to observe the shear bond strength and surface properties. There was no significance when One-way ANOVA analysis/Tukey Honestly Significant Difference Test was conducted for statistical analysis among groups (P > 0.05). Results: Results of measuring the three-point flexural bond strength of the Ni-Cr alloy and thickness of the oxide film. Experiment T3 using 20 g Titanium chemical catalyst: $39.22{\pm}3.41MPa$ and $6.66{\mu}m$, having the highest bond strength and thinness of oxide film. Experiment T2 using 10 g Titanium chemical catalyst: $34.65{\pm}1.39MPa$ and $13.22{\mu}m$. Experiment T1 using no Titanium chemical catalyst: $32.37{\pm}1.91MPa$ and $22.22{\mu}m$. Conclusion: The T2 and T3 experiments using Titanium chemical catalyst showed higher bond strength for the Ni-Cr alloy and lower thickness of oxide film than experiment T1, and the titanium catalyst being able to increase bond strength was observed.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.18 no.4
• /
• pp.50-58
• /
• 2014

Due to the cost burden of new construction, the necessity of repair and retrofitting of aged structures is sharply increasing as the domain of repair and retrofitting construction is expanding. Because of the necessity, new technologies for repair and retrofitting are continuously studied in Korea and foreign countries. Steel adhesive method, fiber reinforced plastic (FRP) surface adhesive method, and external prestressing method are used to perform the repair and retrofitting works in Korea. In order to consider a repair method using steel mesh reinforced cement mortar (SMCM), 3-point flexural member test was conducted considering repair area and layer number of SMCM. Five types of specimens including ordinary reinforced concrete (RC) specimen with dimensions of $1400{\times}500{\times}200$ (mm) were cast for testing the deflection measurement, a LVDT was installed at the top center of the specimens. Also, a steel strain gauge and a concrete strain gauge were placed at the center of the specimens. A steel strain gauge was also installed on the shear reinforcement. The 3 point flexural member test results showed that the maximum load of SMCM reinforced specimen was higher than that of basic RC specimen in all of the load-displacement curves. Also, the results showed that, when the whole lower part of the basic RC specimen was reinforced, the maximum load and strain were 1.18 and 1.37 times higher than that of the basic RC specimen, respectively. Each specimen showed a slightly different failure behavior where the difference of the results was caused by the difference in the adhesive level between SMCM and RC. Particularly, in SM-B1 specimen, SMCM spalled off during the experiment. This failure behavior showed that the adhesive performance for RC must be improved in order to utilize SMCM as repair and retrofitting material.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.34 no.1
• /
• pp.1-12
• /
• 2007

The purpose of this study was to evaluate the effect that various concentration and application time of hydrogen peroxide had on tooth whitening and physical properties. The hydroxyapatite (HA) discs of $12mm({\Phi}){\times}1.2mm(t)$ in dimensions were made by compression $(100kg/cm^2)$ and sintering (at $1350^{\circ}C$ for 2 hours) All specimens were polished sequentially with '240 through '2000 emery paper and one side of each specimen was polished finally with $0.3{\mu}m$ alumina paste. The discs were placed in sterile whole stimulated saliva overnight at $37^{\circ}C$ in order to form an in vitro pellicle layer. Then the discs were rinsed with distilled water and soaked into staining broth at $37^{\circ}C$ for 7 days. These stained specimens were bleached with hydrogen peroxide according to the change of concentration $(3{\sim}30%)$ and application time ($3{\sim}10$ days). The specimens were analyzed with a spectrophotometer, X-ray diffractometer (XRD), scanning electron microscope (SEM), surface roughness tester, microhardness tester and biaxial flexural strength. The results of present study can be summarized as follows : 1. The bleaching effect was increased with the increased concentration and the extended application time of hydrogen peroxide. 2. The surface roughness was significantly increased from the specimen bleached with 15% hydrogen peroxide for 10 days and with 30% for 7 and 10 days respectively (p<0.05). 3. The changes of crystal phase observed by XRD between before and after bleaching weren't shown of any difference, but microporous structure of surface observed by SEM was shown of increase with the increased concentration and the extended application. 4. The biaxial flexural strength was significantly decreased from bleaching of specimen with 30% hydrogen peroxide for 7 and 10 days respectively (p<0.05) 5. Microhardness was significantly decreased from bleaching with 15% hydrogen peroxide for 10 days and with 30% for 3, 7 and 10 days respectively (p<0.05). Although the tooth bleaching effect was greater when the high concentration was applied, further in vivo experiment will be needed to prove it's safety.

• Journal of Korean Society of Steel Construction
• /
• v.21 no.2
• /
• pp.165-173
• /
• 2009

Hanger cables in suspension bridges are constrained by the horizontal clamp. So, the accuracy of estimated tension of hange cable using existing methods based on the simple mathematical model of singel cable decreases as the length of cable decreases because of the flexural rigidity. Therefore, back analysis and system identification techniques based on the finite element model are proposed recently. In this paper, the applicability of the back analysis and system identification techniques are compared using the hanger cable of Gang-An Bridge. The experimental results show that the back analysis and system identification techniques are more reliable than the existing string theory and linear regression method in the view point of the error of natural frequencies. However, the estimation error of tension can be varied according to the accuracy of finite element model in the model based methods. Especially, the boundary condition is more affective when the length of cable is short, so it is important to identify the boundary condition through experiment if it is possible. The tension estimation method using system identification technique is more attractive because it can easily consider the boundary condition and it is not sensitive to the number of input measured natural frequencies.

• Journal of the Korea Concrete Institute
• /
• v.25 no.4
• /
• pp.457-465
• /
• 2013

This study discussed the influence of mixtures and curing conditions on the development of strength and microstructure of RPC using ternary pozzolanic materials. Through pilot experiment, various RPC was manufactured by adding single or mixed ternary pozzolanic materials such as silica fume, blast furnace slag and fly ash by mass of cement, up to 0~65%, and cured by using 4 types of method which are water and air-dried curing at $20^{\circ}C$, steam and hot-water curing at $90^{\circ}C$. The results show that the use of ternary pozzolanic materials and a suitable curing method are an effective method for improving development of strength and microstructure of RPC. The unit volume of cement was greatly reduced in RPC with ternary pozzolanic materials and unlike hydration reaction in cement, the pozzolanic reaction noticeably contributes to a reduction in hydration heat and dry shrinkage. A considerable improvement was found in the flexural strength of RPC using ternary pozzolanic materials, and then the utilization of a structural member subjected to bending was expected. The X-ray diffractometer (XRD) analysis and Scanning Electronic Microscope (SEM) revealed that the microstructure of RPC was denser by using the ternary pozzolanic materials than the original RPC containing silica fume only.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.7
• /
• pp.4357-4363
• /
• 2015

This study is to compare the differences of bonding strength based on the Degassing temperatures and various opaque materials for Ni-Cr alloy specimen which does not contain beryllium(Be). Numerous comparison tests have been performed to measure the bonding strength by experimenting 3-point flexural rigidity tests in order to find out ways of stabilization and enhancement of bonding strength between metal and porcelain. AVOVA, surface component observation experiment by SAM/EDS, and Tukey's HSAD posteriori tests results are as follows: First, The bonding strength in all groups has exceeded the minimum (25MPa) of ISO9693 bonding strength regulation for dental mental-porcelain specimen. Second, The bonding strength of Group V1 was $32.37{\pm}1.91MPa$, $38.25{\pm}1.38MPa$ in Group V2, $46.43{\pm}2.14MPa$ in Group V3 and $47.21{\pm}1.72MPa$ Group V4. The difference has been statistically meaningful. Tukey's HSAD posteriori tests results have shown that the bonding strength in Group V4 was higher than that of Group V1. Third, the bonding strength between metal and porcelain without degassing process was higher than that of with degassing process, and the bonding strength of powder opaque was higher than that of paste opaque. Fourth, Group V4 has ranked the highest on the comparison table of metal and porcelain bonding strength.