• Journal of the Korean Geotechnical Society
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• v.28 no.10
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• pp.27-40
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• 2012

In the design of a piled raft, the axial resistance is offered by the raft and group piles acting on the same supporting ground soils. As a consequence, pile - soil - raft and pile - soil interactions, occurring by stress and displacement duplication with pile and raft loading conditions, act as a key element changing resistances of the raft and group piles. In this study, a series of centrifuge model tests have been performed to compare the axial behavior of group pile and raft with that of a piled raft (having 16 component piles with an array of $4{\times}4$) in sands with different relative densities. The test results revealed that the increase of settlement resistance occurs separately with settlement by group pile - soil interactions. The axial resistance of group piles (at piled raft) increases by group pile - raft (pile cap) interactions and that of raft (at piled raft) decreases by group pile - raft (pile cap) interactions.

• The Journal of Korean Academy of Prosthodontics
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• v.28 no.1
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• pp.43-61
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• 1990

The laser reflexion method is a new technique which permits precise contactless measurement and observation of tooth mobility as well as tooth movement. The purposes of this study were to clarify the reliability of the laser reflexion method in clinical application and to measure the abutment tooth movement according to clasp design. This study was designed to determine 1) How much a bending movement of the impression plate stand affects the position of the reflexion pattern and how precise the patient bites into plate 2) Which clasp design causes greater movement of the abutment tooth. Under medium and maximum bite forces, tests were performed on central loading position which was 13mm distal to terminal abutment tooth of distal extension removable partial denture. The movement in the mesiodistal and buccolingual directions was measured. The Duncan's New Multiple-Range test was used to compare the means for the four castings under each direction-load combination; and the paired sample t-test was for medium and maximum bite forces. From this experiment, the following results were obtained. 1. The Roach clasp, the combination clasp, the RPI clasp, and the Akers clasp did not significantly differ in their effects on buccolingual movement of the abutment tooth. 2. The direction of abutment tooth movement was not significantly altered by clasp design and all abutment tooth movements were oriented distobuccally. 3. Under medium bite force, the Akers clasp caused greater distal movement of the abutment tooth than did the combination clasp and the RPI clasp. Under maximum bite force, the Akers clasp caused greater distal movement of the abutment tooth than did the RPI clasp. 4. The testing apparatus and procedures used in this study(laser reflexion method) proved to be reliable in clinical application.

• Journal of Periodontal and Implant Science
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• v.26 no.1
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• pp.317-333
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• 1996

The main goal of periodontal regeneration is to be achieved by epithelial exclusion, periodontal ligament cell activation or alveolar bone regeneration. The purpose of this study was to investigate on the physico- chemical and biological characteristics of biodegradable chitosan beads. Chitosan beads were fabricated by ionic gelation with sodium tripolyphosphate and they had the size in 300um diameter. As therapeutic agent, flurbiprofen was incorporated into the beads by 10, 20% loading contents. The release of drugs from the chitosan beads was measured in vitro. Also, biological activity tests of flurbiprofen loaded chitosan beads including cytotoxicity test, ihhibition of $IL-1{\beta}$ production, suppression to $PGE_2$ production, collagenase inhibition test, the ability of total protein synthesis, and tissue response were evaluated. The amount of flurbiprofen released from chitosan was 33-50% during 7 days. Minimal cytotoxicity was observed in chitosan beads. Flurbiprofen released from chitosan beads significantly suppressed the $IL-1{\beta}$ production of monocyte, $PGE_2$ production and markedly inhibited collagenase activity. Meanwhile, flurbiprofen released from this system showed increased ability for protein synthesis. Throughout 4 -week implantation period, no significant inflammatory cell infiltrated around chitosan bead and also fibroblast like cell types at the beads - tissue interface were revealed with gradual degradation of implanted chitosan beads. From these results, it was suggested that flurbiprofen loaded chitosan beads can be effectively useful for biocompatible local delivery system in periodontal regeneration.

• Journal of the Korean Society of Safety
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• v.10 no.4
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• pp.87-96
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• 1995

It is only three(3) years since we applied brackets for scaffolding in the construction area. Unfortunately, there is no structural criteria on how to install those in the site so far, despite the fact that those brackets have been applied into the site by the firms already. It is shown that resistant capacity of each bracket type has been investigated, analyzed from this experimental study. Accident-concerning data on construction site analyzed by the Ministry of Labor, show temporary structure involves 18.6% of the total industrial accident, which the accidents from scafold-supporting brackets have rate of 42.5% of the ones occurred from the temporary structures. There are two main aspects to be observed : one is how much resistant capacity the brackets have themselves, the other is how exactly to install those without eccentricity. But practically, nobody does check of this bolt-installing conditions in the site and no check of tightening level of nut because there is no available tool to check torque amount for this kind of nut. We just have to rely on scaffolders experience of this tightening. This experiment involves just this variable of tightness at site. Eventually this insufficient tightness causes to collapse those scaffolding structures. The bracket might have less the one than its original capacity due to this insufficient tightness. Three(3) times of PIVOT tests show that fractured condition of two(2) row brackets has occurred mostly at lower bolt due to shear force. Therefore, tightness of bracket-installing bolt, tensile strength of the bolt, shear strength of the bolt, loading condition with equal two point or inequal two point loads, are mainly investigated as variables in this study.

• Journal of the Korean Geosynthetics Society
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• v.8 no.2
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• pp.55-62
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• 2009

Recently, new development projects are being carried out with the soft ground located along the West coast and the South coast. As soft grounds have complex engineering properties that the load bearing capacity is low and high compressibility, it needs to solve this problems Prior to structures are constructed by the method of improvement of soft ground. The sand mat is usually being used for improvement of soft ground as a horizontal drain material and loading base. But, as the volume is enormous and an amount of demanded sand is increased, it is state of short in supply. This paper presents the feasibility study to use of precious slag ball instead of sand mat as the replacing material through the basic soil property tests, the medium of discharge capacity test and analysis of settlement character.

• Journal of the Korean Geosynthetics Society
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• v.8 no.2
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• pp.11-20
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• 2009

This study, as basic research which was intended to develope the surface reinforcement method using reinforcement material which is applicable to very soft ground in Korea, was aimed at proposing the design parameter for the surface ground improvement method. To that end, a wide width tensile test using geotextile, geogrid and steel bar (substitute for bamboo) and 21 kinds of the laboratory model tests with the end restraint conditions of the reinforcement that comprises the constrained and partially constrained (3 types) conditions were conducted. Moreover, a new procedure was proposed to take into account the effect of the stiffness of Reinforce materials on bearing capacity theory of Surface Reinforcement Method for Soft Ground.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.3
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• pp.471-491
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• 2016

Traditional limit equilibrium method needs an assumption of the failure surface to calculate the bearing capapcity of the shallow foundation. From the viewpoint of the mechanics of granular materials, however, the failure of the soil mass is initated by the local buckling of the contact force chains. In this study we observed the directional distribution of the contact force chains in the granular assembly stacked by model particles subjected to the model shallow foundation during loading. Two sets of the assemblies with a regular structure and initially local imperfection were prepared for tests. Existence of the initial local imperfection has a significant effect on the directional distribution of the contact force chains. The bearing capacity of the assembly with local imperfection is only 67% the capacity of the assembly with the regular structure.

• Steel and Composite Structures
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• v.26 no.6
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• pp.793-808
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• 2018

In this study, the seismic performance of the connections between L-shaped columns composed of concrete-filled steel tubes (L-CFST columns) and H-beams used in high-rise steel frame structures was investigated. Seven full-scale specimens were tested under quasi-static cyclic loading. The variables studied in the tests included the joint type, the axial compression ratio, the presence of concrete, the width-to-thickness ratio and the internal extension length of the side plates. The hysteretic response, strength degradation, stiffness degradation, ductility, plastic rotation capacity, energy dissipation capacity and the strain distribution were evaluated at different load cycles. The test results indicated that both the corner and exterior joint specimens failed due to local buckling and crack within the beam flange adjacent to the end of the side plates. However, the failure modes of the interior joint specimens primarily included local buckling and crack at the end plates and curved corners of the beam flange. A design method was proposed for the flexural capacity of the end plate connection in the interior joint. Good agreement was observed between the theoretical and test results of both the yield and ultimate flexural capacity of the end plate connection.

• Advances in Computational Design
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• v.3 no.3
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• pp.233-267
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• 2018

Conventional seismic design of concentrically braced frame (CBF) structures suggests that the gusset plate connecting a steel brace to beams and/or columns should be designed as non-dissipative in earthquakes, while the steel brace members should be designed as dissipative elements. These design intentions lead to thicker and larger gusset plates in design on one hand and a potentially under-rated contribution of gusset plates in design, on the other hand. In contrast, research has shown that compact and thinner gusset plates designed in accordance with the elliptical clearance method rather than the conventional standard linear clearance method can enhance system ductility and energy dissipation capacity in concentrically braced steel frames. In order to assess the two design methods, six cyclic push-over tests on full scale models of concentric braced steel frame structures were conducted. Furthermore, a 3D finite element (FE) shell model, incorporating state-of-the-art tools and techniques in numerical simulation, was developed that successfully replicates the response of gusset plate and bracing members under fully reversed cyclic axial loading. Direct measurements from strain gauges applied to the physical models were used primarily to validate FE models, while comparisons of hysteresis load-displacement loops from physical and numerical models were used to highlight the overall performance of the FE models. The study shows the two design methods attain structural response as per the design intentions; however, the elliptical clearance method has a superiority over the standard linear method as a fact of improving detailing of the gusset plates, enhancing resisting capacity and improving deformability of a CBF structure. Considerations were proposed for improvement of guidelines for detailing gusset plates and bracing members in CBF structures.

• Geomechanics and Engineering
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• v.20 no.5
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• pp.461-474
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• 2020

Analysing the incompatible deformation and damage evolution around the tunnels in mixed strata is significant for evaluating the tunnel stability, as well as the interaction between the support system and the surrounding rock mass. To investigate this issue, confined compression tests were conducted on upper-soft and lower-hard strata specimens containing a circular hole using a rock testing system, the physical mechanical properties were then investigated. Then, the incompatible deformation and failure modes of the specimens were analysed based on the digital speckle correlation method (DSCM) and Acoustic Emission (AE) data. Finally, numerical simulations were conducted to explore the damage evolution of the mixed strata. The results indicate that at low inclination angles, the deformation and v-shaped notches inside the hole are controlled by the structure plane. Progressive spalling failure occurs at the sidewalls along the structure plane in soft rock. But the transmission of the loading force between the soft rock and hard rock are different in local. At high inclination angles, v-shaped notches are approximately perpendicular to the structure plane, and the soft and hard rock bear common loads. Incompatible deformation between the soft rock and hard rock controls the failure process. At inclination angles of 0°, 30° and 90°, incompatible deformations are closely related to rock damage. At 60°, incompatible deformations and rock damage are discordant due that the soft rock and hard rock alternately bears the major loads during the failure process. The failure trend and modes of the numerical results agree very well with those observed in the experimental results. As the inclination angles increase, the proportion of the shear or tensile damage exhibits a nonlinear increase or decrease, suggesting that the inclination angle of mixed strata may promote shear damage and restrain tensile damage.