• Journal of Dental Rehabilitation and Applied Science
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• v.18 no.3
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• pp.145-155
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• 2002

The results of the present feasibility study are summarized as follows, 1. The three unit bridge of knitted material and UD fibre reinforcement has both the rigidity and the strength against a vertical occlusal load of 75N. 2. Stress concentration at the junctional area between the bridge and the abutments, i.e. between the pontic and the knitted caps was observed. In the case of the bridge with reinforcement straps, it was partly shown that the concentration problem could be improved by simply increasing the fillet size at the area. Further refining in the surface of the junctional area will be needed to ensure a further improvement in the stress distribution. This will require some trade off in the level of the stress and the available space. A parametric study will help to decide the appropriate size of the fillet. 3. Design refinement is a must to improve the stress distribution and realize the most favourable shape in terms of fabrication. The current straight bar with a constant cross section area can be redesigned to a tapered shape. The curve from the dental arch should also be placed on the pontic design. In accordance with design refinement, the resistance of the bridge frame to other load cases should be evaluated. 4. Although not included in the present feasibility study, it is estimated that bridges of the anterior teeth can be made strong enough with the knitted material without further reinforcement using unidirectional materials. In this regard, a feasibility study on design concepts and stress analysis for 3, 4, 5 unit bridge is suggested. 5. Two types of bridge were analysed in terms of fatigue. The safe life design concept, i.e. fatigue design concept, looks reasonable for the bridge where if cracks should form and propagate there is virtually nothing a dentist to do. The bridge must be designed so that no crack will be initiated during the life span. In the case of crowns, however, if constructed with composite resin with knitted materials, it might be possible to repair them, which in general is impossible for crowns of PFM or of metal. Therefore for composite resin crowns, a damage tolerance design concept can be applied and reasonably higher operational stresses can be allowed. In this case, of course, a periodic inspection program should be established in parallel. 6. Parts of future works in terms of structural viewpoint which need to be addressed are summarized as the following: 1) To develop processing technology to accommodate design concepts; 2) More realistic modelling of the bridge and analysis-geometry and loading condition. Thickness variation in the knitted material, taper in the pontic, design for anterior tooth bridge, the effect of combined loads, etc, will need to be included; 3) To develop appropriate design concepts and design goals for the fibre composite FPD aiming at taking the best advantage of knitted materials, including the damage tolerance design concept; 4) To develop testing method and perform test such as static ultimate load test, fatigue test, repair test, etc, as necessary.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1379-1385
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• 2007

In domestic transitional zone design, there is regulation to prevent generation of irregular substructure behaviors that negatively influence in prevention of plasticity settlement on approach section and contact section as well as relieve overall track rigidity by reducing sectional foundation and track stiffness difference, but design guideline that considers dynamic behavior of transitional track in actual service line is very insignificant. Therefore in this study, characteristics of transitional track dynamic behaviors by substructure stiffness are researched and measured dynamic response of transitional track by substructure stiffness in order to prove correlation between substructure and track and calculate elasticity(stiffness) and track load of transitional track by using measurement and formula to provide basic information for developing design guideline considering dynamic behavior of service line transitional track.

• International Journal of Highway Engineering
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• v.8 no.2 s.28
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• pp.55-62
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• 2006

Transverse cracks in continuously reinforced concrete pavement (CRCP) occur at early ages due to temperature and moisture variations. The width and spacing of transverse cracks have a significant effect on pavement performance such as load transfer efficiency and punchout development. Also, crack widths in CRCP depend on 'zero-stress temperature,' which is defined as a temperature where initial concrete stresses become zero, as well as drying shrinkage of concrete. For good long-term performance of CRCP, transverse cracks need to be kept tight. To keep the crack widths tight throughout the pavement life, zero-stress temperature must be as low as practically possible. Thus, temperature control at early ages is a key component In ensuring good CRCP performance. In this study, concrete temperatures were predicted using PavePro, a concrete temperature prediction program, for a CRCP construction project, and those values were compared with actual measured temperatures obtained from field testing. The cracks were also surveyed for 12 days after concrete placement. Findings from this study can be summarized as follows. First, the actual maximum temperatures are greater than the predicted maximum temperature in the ranges of 0.2 to 4.5$^{\circ}C$. For accurate temperature predictions, hydration properties of cementitious materials such as activation energy and adiabatic constants, should be evaluated and accurate values be obtained for use as input values. Second, within 24 hours of concrete placement, temperatures of concrete placed in the morning are higher than those placed in the afternoon, and the maximum concrete temperature occurred in the concrete placed at noon. Finally, from the 12 days of condition survey, it was noted that the rate of crack occurrence in the morning placed section was 25 percent greater than that in the afternoon placed section. Based on these findings, it is concluded that maximum concrete temperature has a significant effect on crack development, and boner concrete temperature control is needed to ensure adequate CRCP performance.

• International Journal of Highway Engineering
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• v.11 no.3
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• pp.97-109
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• 2009

One of the main causes of asphalt rutting is high temperature of the pavement. Nevertheless, there has been few research on lowering the pavement temperature for reducing rutting. This study investigated the performance characteristics of moisture-retaining porous asphalt pavement, which is known to have a temperature reducing effect. The purpose of this study is to quantify the temperature reducing effect of moisture-retaining porous asphalt pavement and its effect of reducing rutting through Accelerated Pavement Testing(APT). Additionally, the possibility of reducing the thickness of the pavement in comparison to general dense grade pavement by analyzing structural layer coefficient of moisture retaining pavement. A total of three test sections consisting of two moisture-retaining porous asphalt pavement sections and one general dense-grade porous asphalt pavement section were constructed for this study. Heating and spraying of water were carried out in a regular cycle. The loading condition was 8.2 ton of wheel load, the tire pressure of $7.03kgf/cm^2$, and the contact area of $610cm^2$. The result of this experiment revealed that the temperature reducing effect of the pavement was about $6.6{\sim}7.9^{\circ}C$(average of $7.4^{\circ}C$) for the middle layer and $7.9{\sim}9.8^{\circ}C$(average of $8.8^{\circ}C$) for surface course, resulting in a rutting reduction of 26% at the pavement surface. Additionally, the structural layer coefficient of moisture retaining pavement measured from a laboratory test was 0.173, about 1.2 times that of general dense grade pavement. The general dense-grade porous asphalt pavement test section exhibited rutting at all layers of surface course, middle layer, and base layer, while the test sections of moisture-retaining porous asphalt pavement manifested rutting mostly at surface course only.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.2
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• pp.169-177
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• 2016

Sliding slab track system, which consists of low friction sliding layer between track slab and bridge deck, is recently devised to reduce track-bridge interaction effect of continuously welded rail(CWR) without applying special devices such as rail expansion joint(REJ). In this study, a series of track-bridge interaction analyses of a long-span bridge with sliding slab track and REJ are performed respectively and the results are compared. The bridge model includes PSC box girder bridge with 9 continuous spans, and steel-concrete composite girder bridge with 2 continuous spans. The total length of the bridge model is 1,205m, and the maximum spacing between the two fixed supports is 825m. Analyses results showed that the sliding slab track system is highly effective on interaction reduction since lower rail additional axial stress is resulted than REJ application. Additionally, horizontal reaction forces in fixed supports were also reduced compared to the results of REJ application. However, higher slab axial forces were developed in the sliding slab track due to the temperature load. Therefore, track slab section of the sliding slab track system should be carefully designed against slab axial forces.

• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.1
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• pp.25-36
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• 2016

Heavy metals in the stream sediments around Shihwa Lake were studied not only to investigate the characteristics of spacio-temporal distribution but also to assess the pollution degree and ecological risk using various pollution indices. Among metals, Zn had the highest values (1,311 mg/kg) and Hg showed the lowest value (0.261 mg/kg). The order of mean concentrations (mg/kg) of metals was Zn>Cu>Pb>Cr>Ni>Co>As>Cd>Hg in stream sediments around Shihwa Lake. Metal concentrations showed different pollution pattern with industrial region, indicating that these metals originated from different sources and industrial region had higher metal concentration than rural/urban regions. The results of geoaccumulation index (Igeo) showed that the stream sediments were significantly polluted with Cd, Cu, Zn and Pb, indicating moderately to highly polluted by these metals. According to PLI consideration, industrial region was more seriously polluted by metals whereas an rural/urban region was not polluted. About 85% of sampling site for Cr, Ni, Cu, Zn and Pb from industrial regions were exceeded the PEL values. The mPELQ and SQI values derived from PEL of industrial region were classified as 'highly toxic' and 'very poor' and metal pollution level tend to be worse in wet season. This indicates that the industrial activities and stromwater runoff represents an important sources of heavy metals around Shihwa Lake.

• Journal of the Korea Concrete Institute
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• v.23 no.5
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• pp.657-665
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• 2011

LB-DECK, a precast concrete panel type, is a permanent concrete deck form used as a formwork for cast-in-place concrete pouring at bridge construction site. LB-DECK consists of 60 mm thick concrete slab and 125 mm height Lattice-girders partly embedded in the concrete slab. These decks have been applied to the bridges, which girder spacings are short enough to resist longitudinal cracking caused by construction loads. This paper presents experimental research work conducted to evaluate the cracking load of LB-DECKs designed for long span bridge decks. Twenty four non-composite beams and four composite beams are fabricated considering three design variables of thickness of concrete slab, height of lattice-girder, and diameter of top-bar. Static loads controlled by displacements are applied to test beams to obtain cracking and ultimate loads. Vertical displacements at the center of beams, strains of top-bar, crack propagation in concrete slab, and final failure modes are carefully monitored. The obtained cracking loads are compared to the analytical results obtained by elastic analyses. Long-term analyses using age-adjusted effective modulus method (AEMM) are also conducted to investigate the effects of concrete shrinkage on the cracking loads. Based on the test results, the tensile strength and the design details of LB-DECKs are discussed to prevent longitudinal cracking of long span bridge decks.

• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.569-575
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• 2007

The repair of concrete surfaces does not normally take into account structural tolerance for longer service lift and better capabilities of concrete structures. In particular, the repair of surface spelling completes as mortar is applied, which does not display additional structural performances. The use of crimped wire mesh for better construction and fracture resistance, however, expects to have some reinforcement effects. Particularly, it is also expected that the repair of bottom part in structures built between bridges like irrigation structures results in the increase of flexural resistance. Therefore, this study is intended to perform the repair using crimp wire mesh and examine strength depending on the repair section and depth. For this, a slab with 150 mm in depth, 3,000 mm in length and 600 mm in width and total 8 objects to experiment such as upper part, upper whole, bottom part, bottom whole and crimp wire mesh reinforced are manufactured to perform flexural performance. The results of the analysis show that yield strength and failure load increase as the depth of repair materials in the experiment reinforced with crimp wire mesh get bigger. In the same condition, repair of bottom part is able to increase internal force of bending force. Besides, the results show that partial repair of structures under bending force cannot produce flexural performance. Consequently, the repair method with crimp wire mesh results in the increase of flexural resistance.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.4
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• pp.405-413
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• 2015

In the US, the number of cases of subterranean water contamination from tritium leaking through a damaged buried nuclear power plant pipe continues to increase, and the degradation of the buried metal piping is emerging as a major issue. A pipe blocked from corrosion and/or degradation can lead to loss of cooling capacity in safety-related piping resulting in critical issues related to the safety and integrity of nuclear power plant operation. The ASME Boiler and Pressure Vessel Codes Committee (BPVC) has recently approved Code Case N-755 that describes the requirements for the use of polyethylene (PE) pipe for the construction of Section III, Division 1 Class 3 buried piping systems for service water applications in nuclear power plants. This paper contains tensile and slow crack growth (SCG) test results for high-density polyethylene (HDPE) pipe welds under the environmental conditions of a nuclear power plant. Based on these tests, the fracture surface of the PENT specimen was analyzed, and the fracture mechanisms of each fracture area were determined. Finally, by using 3D finite element analysis, limit loads of HDPE related to premature failure were verified.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.4
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• pp.316-322
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• 2009

This paper presents a preliminary study to monitor the lateral behavior of pile foundation using multiplexed fiber Bragg grating(FBG) sensors. In the Preliminary study, an 1.7 meter long cantilever beam with the shape of square hollow box was fabricated and tested under the static loading. Four FBG sensors were multiplexed in a single optical fiber and installed into the top and bottom of the cantilever beam. The strains are directly measured from FBG sensors followed by curvature calculations based on the plane section assumption. Vertical deflections are then estimated using the regression analyses based on the geometric relationships. It has been found that excellent correlation with conventional sensing system was observed. The success of the test encourages the use of the FBG sensing system as a monitoring system for pile foundations. However, further consideration should be given in the case of the sensor malfunction for the practical purpose.