• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.1
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• pp.165-172
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• 2006

A variety of techniques for strengthening have been developed, including pate bonding, external prestressing and overslabbing. Expecially, a strengthening technique for reinforced concrete beams using external unbonded reinforcement offers advantages in speed and simplicity of installation. The purpose of this paper is to investigate the capabilities of a new retrofitting technique, namely external prestressing(out-cable), for flexural strengthening of beams. Results of 2 physical tests (external Post-tension and out-cable system specimen) on strengthened reinforced concrete continuous beams are reported and compared. It is shown that the out-cable system can provide strength enhancement.

• Journal of Dental Rehabilitation and Applied Science
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• v.25 no.4
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• pp.375-390
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• 2009

Statement of problem: Implant supported overdenture is accepted widely as a way to restore edentulous ridge providing better retention and support of dentures. Various types of attachment for overdenture have been developed. Purpose: The purpose of this study was to investigate the influence of attachment type in implant overdentures on the biomechanical stress distribution in the surrounding bone, prosthesis and interface between implant and bone. Material and methods: Finite element analysis method was used. Average CT image of mandibular body(Digital $Korea^{(R)}$, KISTI, Korea) was used to produce a mandibular model. Overdentures were placed instead of mandibular teeth and 2mm of mucosa was inserted between the overdenture and mandible. Two implants($USII^{(R)}$, Osstem, Korea) were placed at both cuspid area and 4 types of overdenture were fabricated ; ball and socket, Locator, magnet and bar type. Load was applied on the from second premolar to second molar tooth area. 6 times of finite element analyses were performed according to the direction of the force $90^{\circ}$, $45^{\circ}$, $0^{\circ}$ and unilateral or bilateral force applied. The stress at interface between implants and bone, and prosthesis and the bone around implants ware compared using von Mises stress. The results were explained with color coded graphs based on the equivalent stress to distinguish the force distribution pattern and the site of maximum stress concentration. Results: Unilateral loading showed that connection area between implant fixture and bar generated maximum stress in bar type overdentures. Bar type produced 100 Mpa which means the most among 4 types of attachments. Bilateral loading, however, showed that bar type was more stable than other implants(magnet, ball and socket). 26 Mpa of bar type was about a half of other types on overdenture under $90^{\circ}$ bilateral loading. Conclusions: In any directions of stress, bar type was proved to be the most vulnerable type in both implants and overdentures. Interface stress did not show any significant difference in stress distribution pattern.

• Journal of the Korean Geotechnical Society
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• v.32 no.12
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• pp.23-32
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• 2016

A single particle crushing test was carried out for recycled aggregates from waste concrete while demolishing various structures. When the recycled aggregates were used for backfill or road subbase materials, load-displacement and crushing characteristics were analyzed. The recycled aggregates with hydrates and aggregates were sorted into 40 mm size (75-40 mm) and 20 mm size (40-20 mm). At initial loading, their irregular surface was closed to and then crushed by loading plate. Such first crushing stage was called 'Surface crushing'. Further loading, some hydrate was crushed and detached from aggregate, and such process repeated several times. This state is called 'hydrate crushing'. The final state is called 'aggregate crushing' in which aggregate crushed and following load suddenly dropped down. As the load increased, such crushing cycle is repeated several times. The shapes of aggregates are round or square, and triangle or long shaped. Depending on their shapes and surface conditions, they crushed in different ways. The 63% of aggregates showed more than 50% load reduction due to aggregate crushing. The 90% load reduction occurred at 15% of aggregates. The 40 mm aggregate crushed at maximum load between 3.05-4.38 kN and 70% of crushed aggregates were less than 20 mm.

• Journal of The Korean Society of Agricultural Engineers
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• v.46 no.6
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• pp.21-28
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• 2004

This study aims to investigate the effects of partially distributed loads on the dynamic behaviour of steel parabolic arches by using the elasto-plastic finite element model based on the Von Mises yield criteria and the Prandtl-Reuss How rule. For this purpose, the vertical and the radial load conditions were considered as a distributed loading and the loading range is varied from 40% to 100% of arch span. Normal arch and arch with initial deflection were studied. The initial deflection of arch was assumed by the sinusoidal motile of ${\omega}_i\;=\;{\\omega}_O$ sin ($n{\pi}x/L$). Several numerical examples were tested considering symmetric initial deflection when the maximum initial deflection at the apex is fixed as L/1000. The analysis resluts showed that the maximum deflection at the apex of arch was occurred when 70% of arch span was loaded. The maximum deflection at the quarter point of arch span was occurred when 50% of arch span was loaded. It is known that the optimal rise to span ratio between 0.2 and 0.3 when the vertical or radial distributed load is applied. It is verified that the influence of initial deflection of radial load case is more serious than that of vertical load case.

• Proceedings of the KAIS Fall Conference
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• 2011.12b
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• pp.492-495
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• 2011

본 연구는 가속수명시험을 통해 배기파이프 용접부의 수명평가에 관해 다루고 있다. 배기파이프 용접부는 실차 상태에서 열과 진동이 많이 가는 부분으로 내구에 많이 취약하다. 배기 파이프에 주기적인 하중을 가하여 가속시험하여, 배기파이프 용접부에 대한 신뢰성관련 수명특성을 빠른시간 내에 산출하기 위한 것이다. 적절한 수명분포 및 고장데이터를 수집분석하고 시험방법 과 시험결과를 활용하여 신뢰성 보증 시험시간을 단축하고 제품의 개발단계 및 일정 축소와 시험비용 감소 및 제품의 보증수명증대에 기여할 것이다.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.4
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• pp.1-9
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• 2009

This paper investigates inelastic lateral-torsional buckling of stepped beams subjected to uniformly distributed load and end moments. A three-dimensional finite-element program ABAQUS (2007) and a regression program MINITAB(2006) were used to analytically develop new design equation for singly and doubly stepped beams with simple boundary condition. The flanges of the smaller cross-section in the stepped beams were fixed at 30.48 by 2.54 cm, whereas the width and thickness of the flanges of the larger cross-section varied. The web thickness and height of the beams were kept at 1.65 cm and 88.9 cm, respectively. The ratios of the flange thickness, flange width, and stepped length of beam are considered with analytical parameters. Two groups of 27 cases and 36 cases, respectively, were analyzed for doubly and singly stepped beams in the inelastic buckling range. The combined effects of residual stresses and geometrical imperfection on inelastic lateral-torsional buckling of beams are considered. The distributions of residual stress of the cross-section is same as shown in Pi and Trahair (1995) and the initial geometric imperfection of the beam is set by central displacement equal to 0.1% of the unbraced length of beam. The comparisons between results from proposed equations and the results from finite element analyses were presented in this paper. The maximum differences of two results are of 13% for the doubly stepped beam and 10% for the singly stepped beam. The proposed equations definitely improve current design methods for the inelastic lateral-torsional buckling problem and increase efficiency in building and bridge design.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.3
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• pp.255-280
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• 2024

If there are concerns about the stability of segment lining due to section deficiency or large deformation in shield TBM tunnel, reinforcement can be done through ground grouting outside the tunnel or by using steel plate reinforcement, ring beam reinforcement, or inner double layer lining inside the tunnel. Traditional analyses of shield TBM tunnels have been conducted using a continuum method that does not consider the segmented nature of segment lining. This study investigates the reinforcement mechanism for double layer reinforced sections with internal steel linings. By improving the modeling of segment lining, this study applies Break-joint mode (BJM), which considers the segmented characteristics of segment lining, to analyze the deformation characteristics of double layer reinforced sections. The results indicate that the existing concrete segment lining functioned similarly to ground reinforcement around the tunnel, rather than distribution the load. In general, both the BJM model considering the segmentation of segment lining and the continuum rigid method were similar deformation shapes and stress distributions of the lining under load. However, in terms of deformation, when the load strength exceeded the threshold, the deformation patterns of the two models differed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1A
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• pp.105-113
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• 2008

Solar radiation induces non-uniform temperature distribution in the bridge structure depending on the shape of the structure and shadows cast on it. Especially in the case of curved steel box girder bridges, non-uniform temperature distribution caused by solar radiation may lead to unusual load effects enough to damage the support or even topple the whole curved bridge structure if not designed properly. At present, it is very difficult to design bridges in relation to solar radiation because it is not known exactly how varying temperature distribution affects bridges; at least not specific enough for adoption in design. Standard regulations related to this matter are likewise not complete. In this study, the thermal behavior of curved steel box girder bridges is analyzed while taking the solar radiation effect into consideration. For the analysis, a method of predicting the 3-dimensional temperature distribution of curved bridges was developed. It uses a theoretical solar radiation energy equation together with a commercial FEM program. The behavior of the curved steel box girder bridges was examined using the developed method, while taking into consideration the diverse range of bridge azimuth angles and radii. This study also provides reference data for the thermal design of curved steel box girder bridges under solar radiation, which can be used to develop design guidelines.

• Journal of the Korea Concrete Institute
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• v.13 no.1
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• pp.62-68
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• 2001

The purpose of this paper was to investigate the relations between the unbonded tendon stress and the influential parameters which were bonded reinforcement ratio, span/depth ratio, and loading type. To this end, first, the influence of parameters were examined with twenty eight test results obtained from references. Then, an experimental study was carried out with 21 test specimens. The investigation with previous and current tests revealed the followings; (1) The bonded reinforcement ratio and prestressing ratio were proved to be an important variables on the unbonded tendon stress. (2) The ratio of span to depth and type of loading affected partially the unbonded tendon stress although their effects varied depending on bonded reinforcement ratio. (3) AASHTO LRFD Code and Moon/Lim\`s design equation predicted the test results well with some safety margins.

• Journal of Korean Society of Steel Construction
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• v.19 no.5
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• pp.473-482
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• 2007

When the material strength and ductility of shear studs is sufficient to carry the interface shear force, the composite beam can behave safely without premature structural failure in the interface and without ultimate moment reduction. In this study, the influence of the deformation capacity of shear studs embedded in high-strength concrete on structural behavior and design condition of composite beam is analyzed using FEM. In the analysis, load type, degree of shear connection and arrangement of studs are considered as analysis parameters. According to analysis results, in the case of partial interaction,the deformation capacity of studs embedded in high-strength concrete should be considered together with material strength. Especially in the case of uniform arrangement of studs and uniformly distributed load, a minimum available degree of shear connection is restricted by the deformation capacity of studs. In this case,shear studs should be arranged in consideration of the distribution of shear force at the composite section.