• International Journal of Highway Engineering
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• v.5 no.3 s.17
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• pp.31-42
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• 2003

The KHC Test Road project was initiated on 1991 to develop Korean Pavement Design Guide. It was constructed along the Joongbu Inland Expressway line between Yeoju and Gamgok. It is two-lane wide expressway containing fifteen asphalt and twenty-five Portland cement concrete test pavement sections. Various sensors were installed in the Test Road to evaluate the behavior of test pavement sections under the influence of traffic load and environmental change. The most important issues in the sensor installation are the accurate location and long-term survivability. They are directly influenced by the sensor installation methodology. The methodology for asphalt strain gages is mainly discussed in this paper because it is the second important sensors in the KHC Test Road project. In order to find the best methodology, we evaluated existing methodology from prior experience and several conducted test installations. We have tried mound, block out, and trench cuts since 2000. Among three methods, block out was the most effective one in terms of accurate location, long-term survivability, and material homogeneity. However, this method cannot be applied to the wearing coarse so that the mound method was used as an alternative. The block out method was applied to base and intermediate layers while the mound method was used to the wearing coarse. Three hundred seventy-four asphalt strain gauges were installed on asphalt pavement sections from September 3rd to November 18th in 2002. According to the sensor measurement evaluation, 6.3% of sensor demonstrated over ranged readings for mound method installation and 2.5% did for block out method installation. We lost only two sensors during the installation. It is 99.5% survival and it is excellent survival rate according to other experience.

• Proceedings of the KACD Conference
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• 2008.05a
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• pp.235-245
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• 2008

The aim of this study was to develop a method for measuring the slumping resistance of resin composites and to relate it to the rheological characteristics. Five commercial hybrid composites (Z100. Z250. DenFil, Tetric Ceram. ClearFil) and a nanofill composite (Z350) were used to make disc-shaped specimens of 2 mm thickness. An aluminum mold with square shaped cutting surface was pressed onto the composite discs to make standardized imprints. The imprints were light-cured either immediately (non-slumped) or after waiting for 3 minutes at $25^{\circ}C$ (slumped). White stone replicas were made and then scanned for topography using a laser 3-D profilometer. Slumping resistance index (SRI) was defined as the ratio of the groove depth of the slumped specimen to that of the non-slumped specimen. The pre-cure viscoelasticity of each composite was evaluated by an oscillatory shear test and normal stress was measured by a squeeze test using a rheometer. Flow test was also performed using a flow tester. Correlation analysis was performed to investigate the relationship between the viscoelastic properties and the SRI. SRI varied between the six materials (Z100 < DenFil < Z250 < ClearFil < Tetric Ceram < Z350). The SRI was strongly correlated with the viscous (loss) shear modulus G' but not with the loss tangent. Also. slumping resistance was more closely related to the resistance to shear flow than to the normal stress. Slumping tendency could be quantified using the imprint method and SRI. The index may be applicable to evaluate the clinical handling characteristics of composites.

• Restorative Dentistry and Endodontics
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• v.33 no.3
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• pp.235-245
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• 2008

The aim of this study was to develop a method for measuring the slumping resistance of resin composites and to relate it to the rheological characteristics. Five commercial hybrid composites (Z100, Z250, DenFil, Tetric Ceram, ClearFil) and a nanofill composite (Z350) were used to make disc-shaped specimens of 2 mm thickness. An aluminum mold with square shaped cutting surface was pressed onto the composite discs to make standardized imprints. The imprints were light-cured either immediately (non-slumped) or after waiting for 3 minutes at $25{\circ}C$ (slumped). White stone replicas were made and then scanned for topography using a laser 3-D profilometer. Slumping resistance index (SRI) was defined as the ratio of the groove depth of the slumped specimen to that of the nonslumped specimen. The pre-cure viscoelasticity of each composite was evaluated by an oscillatory shear test and normal stress was measured by a squeeze test using a rheometer. Flow test was also performed using a flow tester. Correlation analysis was performed to investigate the relationship between the viscoelastic properties and the SRI. SRI varied between the six materials (Z100 < DenFil < Z250 < ClearFil < Tetric Ceram < Z350). The SRI was strongly correlated with the viscous (loss) shear modulus G' but not with the loss tangent. Also, slumping resistance was more closely related to the resistance to shear flow than to the normal stress. Slumping tendency could be quantified using the imprint method and SRI. The index may be applicable to evaluate the clinical handling characteristics of composites.

• Journal of Korean Society of Forest Science
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• v.79 no.2
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• pp.138-143
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• 1990

In mature stand of Japanese larch (Larix leptolepis(S. et Z.) Gordon) planted in 1925, heartrot damage was investigated by felling some infected trees with fruit bodies of two butt-rot fungi, Phaeolus schweinitzii and Sparassis crispa. Percentage of heartrot area on basal area of decay trees was 19.2-74.4, and the height reached by the decay was 1.2-5.5m. Percentage of decay volume was in the range of 2.2-13.4%, but the loss wood to the height reached by the decay amounted to 27.2% (range 13.1-37.1%) of whole volume, Decay damage caused by S. crispa was much greater than that caused by P. schweinitzii. Compressive strength ($52-77kg/cm^2$) and specific gravity (0.40-0.47) of rot wood was reduced to 77% and 39% respectively in maximum as compared to sound wood of healthy tree, and those of sound-looking wood close by heartrot to 42% and 26%. The current annual growth of trees with decay was fallen behind that of sound tree from eight to fourteen years after planting in D. B. H. and from twelve to twenty-one years after in volume.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.5
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• pp.399-405
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• 2016

Recently, fiber optic sensors, which have many advantages are being applied in various fields by replacing conventional electric sensors. To transmit the light signals between an interrogator and a sensor head, optical components such as an optical adaptor and optical jumper cords are generally used. When signals are transmitted using an adaptor, the end surface of each jumper cord is faced together. If alien substances exist on the core surface of an optical fiber, those can cause light transmission loss and signal disappearance. For this reason, non-contact fiber jumper cords are developed to overcome the problems that require continual attention. The light transmission performance of non-contact fiber jumper cords are also evaluated. From the test results, conventional fiber jumper cords are unable to transmit the signals over 2 mm cavity between the ends of both cords. Otherwise, non-contact fiber jumper cords can transmit the signals with stability up to the cavity of 7 mm though they have more transmission loss than the conventional ones. Consequently, non-contact fiber jumper cords that have better signal stability than conventional ones in environments are highly recommended in field applications, especially if they play a role as a cable for signal transmission between fiber optic sensors.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4C
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• pp.147-154
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• 2011

Currently NATM tunnels are designed by applying the initial ground loads caused during construction to the primary supports, conisting of shotcrete, steel ribs and rock bolts. For long term considerations, it is assumed that the primary supports lose its functionality and therefore the secondary support, i.e. concrete lining, is design to resist against the entire ground loads. But the steel ribs, usually applied to bad ground conditions, are embedded in shotcrete causing very little corrosion and therefore the assumption that the primary support will lose all of its functionality is too conservative. Also even though shotcrete carbonates in long term, excluding it from design is also too conservative. In this study, we have, through analytical and numerical analysis, set a rational level of support pressure and allowable relaxed rock mass height sustainable by the primary support for long term design. Changes in sectional forces of the concrete lining considering the calculated support pressure of the primary supports was also carried out. Shallow subway tunnels were considered in the analysis with weathered rock and soft rock ground conditions. The analysis results showed that, by considering the support pressure of steel ribs, an economical design of the concrete lining is possible.

• Journal of Biomedical Engineering Research
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• v.24 no.1
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• pp.37-44
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• 2003

This experimental study is aimed at evaluating the hydrodynamic performance of newly designed self-expandable graft stents under steady flow condition. Two graft stents with different coating materials and a bare TiNi metallic stent for comparison test were used in the experiment. Pressure variation and velocity distribution at the upstream and downstream of the stents were measured at flow rates of 5, 10, and 15 l/min, respectively. Pressure loss due to insertion of the stent increased with increasing flow rate exponentially as expected. At a flow rate of 15 l/min, pressure loss of Polyure-thane(PU)-coated graft stent was 6 times higher than that of TiNi metallic stent, while the pressure loss of a porous Polytetrafluoroethylene(PTFE)-coated graft stent was comparable to a bare TiNi metallic stent. Velocity profiles of the porous PTFE-coated graft stent were similar to those of a bare TiNi metallic stent regardless of flow rate. Furthermore, the velocity profile of PU-coated graft stent revealed an asymmetrical and relatively low central velocity at a higher flow rate than 10 1/min, expecially, where the effects resulted in increases of wall shear stress and normal stress. The worse hydrodynamic behavior of PU-coated graft stent than the other two stents might be attributed to formation of folds due to poor flexibility of coated material when inserting the graft stent into the pipe with a more smaller size, which later gave rise non-symmetry of flow area, increase of surface roughness and jet flow via the crevice between the stent and cylinder wall.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.2
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• pp.213-224
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• 2014

Recently, tunnelling with TBM is getting popular for the construction of cable tunnel in urban area. Mechanized tunnelling method using shield TBM has various advantages such as minimization of ground settlement and prevention of vibration induced by blasting that should be accompanied by conventional tunnelling. In Korea, earth pressure balance (EPB) type shield TBM has been mainly used. Despite the popularity of EPB shield TBM for cable tunnel construction, study on the mechanical behavior of cable tunnel driven by shield TBM is insufficient. Especially, the effect of backfill grout injection on the behavior of cable tunnel driven by shield TBM is investigated in this study. Tunnelling with shield TBM is simulated using 3D FEM. The distance of backfill grout injection from the end of shield skin varies. Sectional forces such as axial force, shear force and bending moment are monitored. Vertical displacement at the ground surface is measured. Futhermore, the relation between volume loss and the distance of backfill grout injection from the end of skin plate is derived. Based on the stability analysis with the results obtained from the numerical analysis, the most appropriate injection distance can be obtained.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.1
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• pp.39-53
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• 2018

Generally, the total ventilation resistance coefficient in a tunnel consists of inlet/outlet loss coefficient, wall friction coefficient, and other loss coefficient caused by sudden expansion and contraction of cross-section, etc. For the tunnel before opening, when the running ventilation fan is stopped, the wind speed in the tunnel is reduced by the total ventilation resistance drag. The velocity decay method is comparatively stable and easy to estimate the wall friction coefficient in the pre-opening tunnel. However, the existing study reported that when the converging wind speed is a negative value after the ventilation fan stops, it is difficult to estimate the wall friction coefficient according to the velocity decay method. On the other hand, for the operating tunnel in which the piston effect acts, a more complex process is performed; however, a reasonable wall friction coefficient can be estimated. This paper aims at suggesting a method to minimize the measurement variables of the piston effect and reviewing a method that can be applied to the operating tunnel. Also, in this study, a new method has been developed, which enables to calculate an variation of the piston effect if the piston effect is constant with a sudden change of external natural wind occurring while the wind speed in the tunnel decreases after the ventilation fan stops, and a programming logic has been also developed, which enables dynamic simulation analysis in order to estimate the wall friction coefficient in a tunnel.

• Journal of the Korean Magnetics Society
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• v.21 no.1
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• pp.23-31
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• 2011

From among the NDT (nondestructive testing) methods, the MFL (magnetic flux leakage) method is specially suitable for testing pipelines because pipeline has high magnetic permeability. The system applied to MFL method is called the MFL PIG. The previous MFL PIG showed high performance in detecting the metal loss and corrosions. However, MFL PIG is highly unlikely to detect the cracks which occur by exterior-interior pressure difference in pipelines and the shape of crack is long and very narrow. In MFL PIG, the magnetic field is performed axially and there is no changes of cross-sectional area at cracks that the magnetic field passes through. Cracks occur frequently in the pipelines and the risk of the accident from the cracks is higher than that from the metal loss and corrosions. Therefore, the new PIG is needed to be researched and developed for detecting the cracks. The circumferential MFL (CMFL) PIG performs magnetic fields circumferentially and can maximize the magnetic flux leakage at the cracks. In this paper, CMFL PIG is designed and the distribution of the magnetic fields is analyzed by using 3 dimensional nonlinear finite element method (FEM). In CMFL PIG, cracks, standards of NACE, are detectable. To estimate the shape of crack, the leakage of magnetic fields for many kinds of cracks is analyzed and the method is developed by signal processing.