• Structural Engineering and Mechanics
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• v.86 no.1
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• pp.17-27
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• 2023

To investigate the mechanical behavior of the post-tensioned prestressed concrete lining (PPCL), the desilting tunnel of the Xiaolangdi Hydro Project in China is adopted as a case, and a detailed three-dimensional continuum model verified by the observation results is established for the PPCL. The radial stresses, longitudinal stresses, axial forces and bending moments of the PPCL under the completed cable tension condition (CCTC) and design water pressure condition (DWPC) are analyzed, respectively. The numerical results reveal that the PPCL concrete is significantly compressed in the circumferential direction by the prestress, while the prestress has a negligible influence on the radial stresses of the PPCL concrete. It should be noted that the concrete near the anchor slots has a complex and adverse stress state with stress concentration, longitudinal tensioning and large bending moment. In addition, a simplified shell model and a further simplified beam model which can take the influences of the prestress loss and the anchor slot into consideration are proposed for the PPCL. The results of the simplified models are in a good agreement with these of the three-dimensional continuum model, and they can be used as efficient approaches for the structural design and analysis of the PPCL.

• Steel and Composite Structures
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• v.45 no.4
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• pp.547-554
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• 2022

This paper studies the static stability of an axially graded column with the power-law gradient varying along the axial direction. For a nonhomogeneous column with one end linked to a rotational spring and loaded by a compressive force, respectively, an Euler problem is analyzed by solving a boundary value problem of an ordinary differential equation with varying coefficients. Buckling loads through the characteristic equation with the aid of the Bessel functions are exactly given. An alternative way to approximately determine buckling loads through the integral equation method is also presented. By comparing approximate buckling loads with the exact ones, the approximate solution is simple in form and enough accurate for varying power-law gradients. The influences of the gradient index and the rotational spring stiffness on the critical forces are elucidated. The critical force and mode shapes at buckling are presented in graph. The critical force given here may be used as a benchmark to check the accuracy and effectiveness of numerical solutions. The approximate solution provides a feasible approach to calculating the buckling loads and to assessing the loss of stability of columns in engineering.

• The Journal of the Petrological Society of Korea
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• v.6 no.3
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• pp.151-165
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• 1997

The Kyemyeongsan area of Chungju in the NE part of the Ogcheon metamorphic zone, Koera, consists mainly of the Ogcheon Supergroup(Taehyangsan Quartzite, Hyangsanri Dolomite and Kyemyeogsan Formation) and the MeSozoic Chungju granite. The Kyemyeongsan Formation is composed mainly of metamorphic rocks of various grades derived from conglomeratic, basic, acidic, pelitic and psammitic rocks. The basic and acidic rocks show alternated or interfingered appearence, indicating that they were derived form bimodal type of magmatism in rift environment. Conglomeratic rocks overlie acidic volcanic rocks in geneal, but are underlain by both acidic plutonic and volcanic rocks. This indicaties that the acidic magmatism before the formation of conglomeratic rocks was different from that during or after the formation of conglomeratic rocks in its occurrence mode. The geological structure of the Ogcheon metamorphic zone in the Kyemyeongsan area, Chungju was formed at least by three phases of deormation. The first phase deformation(D1) formed a regional-scale sheath-type fold(F1) closed into the east. Its axial phane(S1) strikes NNW to NW and dips WSW to SW. The stetching lineation(L1), related to the sheath-type fold, plunges westward. The second phase deformation (D2) formed asymmetric fold(F2) of ESE-to SE-vergence with NNE to NE striking axial plane(S2) and $20~45^{\circ}/210~230^{\circ}$ plunging axis(L2). The F2 fold reoriented the original westward plunging L1 into northwestward plunging L1 in its lower limb(overturned limb). The third phase of deformation(D3) was recognized as chevron-type fold(F3) with $45^{\circ}/265$^{\circ}$ plunging axis. The F3 fold was formed by the compression of N-S direction, resulting in the reorientation of the original $20-45^{\circ}/210~230^{\circ}$ plunging L2 into mainly $35~45^{\circ}/260~280^{\circ}$ and subsidiarily $30~45^{\circ}/135~165^{\circ}$ plunging L2. After this deformation, open fold with NS striking and steeply E or W dipping axial plane is formed by the compression of E-W direction.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.5
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• pp.674-688
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• 2003

Statement of Problem : With increasing demand of the implant-supported prosthesis, it is advantageous to use the different platform width of the fixture according to bone quantity and quality of the patients. Purpose : The purpose of this study was to assess the loading distributing characteristics of two implant designs according to each platform width of fixture, under vertical and inclined loading using finite element analysis. Material and method : The two kinds of finite element models were designed according to each platform width of future (4.1mm restorative component x 11.5mm length, 5.0mm wide-diameter restorative component x 11.5mm length). The crown for mandibular first molar was made using UCLA abutment. Each three-dimensional finite element model was created with the physical properties of the implant and surrounding bone. This study simulated loads of 200N at the central fossa in a vertical direction, 200N at the outside point of the central fossa with resin filling into screw hole in a vertical direction and 200N at the buccal cusp in a 300 transverse direction individually Von Mises stresses were recorded and compared in the supporting bone, fixture, and abutment screw. Results : The stresses were concentrated mainly at the cortex in both vertical and oblique load ing but the stresses in the cancellous bone were low in both vertical and oblique loading. Bending moments resulting from non-axial loading of dental implants caused stress concentrations on cortical bone. The magnitude of the stress was greater with the oblique loading. Increasing the platform width of the implant fixture decreased the stress in the supporting bone, future and abutment screw. Increased the platform width of fixture decreased the stress in the crown and platform. Conclusion : Conclusively, this investigation provides evidence that the platform width of the implant fixture directly affects periimplant stress. By increasing the platform width of the implant fixture, it showed tendency to decreased the supporting bone, future and screw. But, further clinical studies are necessary to determine the ideal protocol for the successful placement of wide platform implants.

• Journal of Korean Association for Spatial Structures
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• v.2 no.1 s.3
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• pp.85-92
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• 2002

Two way grid single-layer domes are of great advantage in fabrication and construction because of the simple fact that they have only four members at each junction. But, from a point of view of mechanics, the rectangular latticed pattern gives rise to a nonuniform rigidity-distribution in the circumferential direction. If the equivalent rigidity is considered in the axial direction of members, the in-plane equivalent shearing rigidity depends only on the in-plane bending rigidity of members and its value is very small in comparison to that of the in-plane equivalent stretching rigidity. It has a tendency to decrease buckling -strength of dome considerably by external force. But it is possible to increase buckling strength by the use of roofing covering materials connected to framework. In a case like this, shearing rigidity of roofing material increases buckling strength of the overall structure and can be designed economically from the viewpoint of practice. Therefore, the purpose of this paper, in Lamella dome and rectangular latticed dome that are a set of 2-way grid dome, is to clarify the effects of roofing covering materials for increasing of buckling strength of overall dome. Analysis method is based on FEM dealing with the geometrically nonlinear deflection problems. The conclusion were given as follows: 1. In case of Lamella domes which have nearly equal rigidity in the direction of circumference, the rigidity of roofing covering materials does not have a great influence on buckling-strength, but in rectangular latticed domes that has a clear periodicity of rigidity, the value of its buckling strength has a tendency to increase considerably with increasing rigidity of roofing covering materials 2. In case of rectangular latticed domes, as rise-span-ratio increases, models which is subjected to pressure -type-uniform loading than vertical-type-uniform loading are higher in the aspects of the increasing rate of buckling- strength according to the rate of shear reinforcement rigidity, but in case of Lamella dome, the condition of loading and rise-span-ratio do not have a great influence on the increasing rate of buckling strength according to the rate of shear reinforcement rigidity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.6
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• pp.565-571
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• 2016

This paper investigates macro- and microscopic fractography performed on fracture specimens from low cycle fatigue (LCF) testings through an Alloy 617 base metal and weldments. The weldment specimens were taken from gas tungsten arc welding (GTAW) pad of Alloy 617. The aim of the present study is to investigate the macro- and microscopic aspects of the low cycle fatigue fracture mode and mechanism of Alloy 617 base metal and GTAWed weldment specimens. Fully axial total strain controlled fatigue tests were conducted at room temperature with total strain ranges of 0.6, 0.9, 1.2 and 1.5%. Macroscopic fracture surfaces of Alloy 617 base metal specimens showed a flat type normal to the fatigue loading direction, whereas the GTAWed weldment specimens were of a shear/star type. The fracture surfaces of both the base metal and weldment specimens revealed obvious fatigue striations at the crack propagation regime. In addition, the fatigue crack mechanism of the base metal showed a transgranular normal to fatigue loading direction; however, the GTAWed weldment specimens showed a transgranular at approximately $45^{\circ}$ to the fatigue loading direction.

• Journal of Biomedical Engineering Research
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• v.25 no.5
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• pp.361-367
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• 2004

The axial compressive strength, relative 3-D stability and osteoconductive shape design of an intervertebral fusion cage are important biomechanical factors for successful intervertebral fusion. Changes in the stress distribution of the vertebral end plate and in cage stability due to changes in the spike shape of a newly contrived box-shaped fusion cage are investigated. In this investigation, the initial contact of the cage's spikes with the end plate and the penetration of the cage's spikes into the end plate are considered. The finite element analysis is conducted to study the effects of the cage's spike height, tip width and angle on the stress distribution of the vertebral end plate, and the micromigration of the cage in the A-P direction. The stress distribution in the end plate is examined when a normal load of 1700N is applied to the vertebra after inserting 2 cages. The micromigration of the cage is examined when a pull out load of l00N is applied in the A-P direction. The analysis results reveal that the spike tip width significantly influences the stress concentration in the end plate, but the spike height and angle do not significantly influence the stress distribution in the end plate touching the cage's spikes. In addition, the analysis results show that the micromigration of the cage can be reduced by adjusting the spike angle and spike arrangement in the A-P direction. This study proposes the optimal shape of an intervertebral fusion cage, which promotes bone fusion, reduces the stress concentration in a vertebral end plate, and increases mechanical stability.

• Restorative Dentistry and Endodontics
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• v.23 no.1
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• pp.477-486
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• 1998

Recently the development of rotary instrument makes it possible that in root canal treatment operator saves much more time, maintans original curved canal shape and easily prepares continuous tapered root canal. The purpose of this experiment was to examine the smoothness of the internal surface of prepared root canal and the effectiveness of debridement in prepared root canal by SEM for the comparison of hand and Ni-Ti rotary instrument. 25 extracted human teeth were access opened and # 10 K-type file was introduced into canal until it was appeared at the apical foramen. The working length was established by subtracting 0.5mm from this measurement. Group 1. The root canal preparation was done to # 30 with working length and then step-back until # 45 with K-Flexofile (Maillefer, Swiss). Group 2. Root canal preparation was done by Naviflex Ni-Ti file (Brasseler, USA) as the same technique with group 1. Group 3. Canal was prepared by Profile .04 (Maillefer, Swiss) taper until #30. Group 4. With use of Quantec (Tycom, USA) root canal was prepared from file number 1 to 8. In group 1 and 2, the root canal irrigant was NaOCl and the other groups, NaOCl and RC-prep (Premine Dental Products, USA) was used. The prepared teeth were notched with high-speed bur as bucco-lingual direction and fractured with chisel and mallet, then examined with SEM. Group 1 showed smooth internal surface. There were scratches mainly to the axial direction. Group 2 showed similar characteristics to those in group 1. Group 3 showed more smoother and linear cutting surface with bised scratches. Group 4 has the almost same characteristics group 3 and there was no difference in the file design. Ni-Ti rotary root canal instrument prepare the dentinal wall more smoother than hand instrument. The effectiveness of debridement was not fully affected by file design. The isthmus area and accessory canals of the root canal system were not prepared in any group. According to the result, hand and rotary type instrumentation techniques were effective in removal of major amount of tissue from root canal but it was not complete. In the direction of cutting movement there was difference between them.

• Korean Journal of Radiology
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• v.22 no.10
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• pp.1640-1649
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• 2021

Objective: Flattening in the anteroposterior direction (AP flattening) of the terminal ileum (TI) or sigmoid colon (SC) lying across the psoas muscle, on magnetic resonance enterography (MRE), might mimic bowel inflammation in the coronal view. This study investigated the prevalence of AP flattening and the factors associated with its development. Materials and Methods: A total of 364 surgery-naïve patients with Crohn's disease (CD) who had undergone MRE were retrospectively reviewed. AP flattening was defined as a luminal collapse in the anteroposterior direction, with a bowel width in the axial plane < 1/4 of the normal diameter without reduction of bowel width in coronal images. The prevalence of AP flattening of the TI and SC on MRE in patients with bowel segments lying across the psoas muscle was determined. We further compared the rate of AP flattening between MRE and computed tomography enterography (CTE) in a subcohort of patients with prior CTE. The factors associated with AP flattening were analyzed using multivariable logistic regression in a subcohort of patients with endoscopic findings of TI. Results: Three hundred and twenty-two and 363 patients, respectively, had TI and SC lying across the psoas muscle. The prevalence of AP flattening on MRE was 7.5% (24/322) in TI and 5.2% (19/363) in SC. The prevalences were significantly higher on MRE than on CTE in both the TI (7.3% [12/164] vs. 0.6% [1/164]; p = 0.003) and SC (5.8% [11/190] vs. 1.6% [3/190]; p = 0.039). AP flattening of the TI was independently and strongly associated with the absence of CD inflammation on endoscopy, with an adjusted odds ratio of 0.066 (p = 0.003) for the presence versus the absence (reference) of inflammation. Conclusion: AP flattening of the TI or SC lying across the psoas muscle was uncommon and predominantly observed on MRE of the bowel without CD inflammation.

• The Journal of the Petrological Society of Korea
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• v.27 no.3
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• pp.139-151
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• 2018

The Songgang-ri area, Cheongsong-gun, which is located in the Sobaeksan province of Yeongnam Massif near the southwestern boundary of Yeongyang subbasin of Gyeongsang Basin, consists of age unknown metamorphic rocks (banded gneiss, granitic gneiss, limesilicates) and age unknown igneous rock (granite gneiss) which intrudes them. This paper researched the geological structures of the Songgang-ri area from the geometric and kinematic features and the developing sequence of multi-deformed rock structures in the geological outcrops exposed about 170 m along the riverside of Yongjeoncheon in the eastern part of Songgang village, Songgang-ri. In the Songgang-ri geological outcrops are recognized three times (Fn, Fn+1, Fn+2) of folding, three times (Dk-I, Dk-II, Dk-III) intrusion of acidic dykes, one time of faulting, which are different in deformation and intrusion timing each other. These geological structures are at least formed by five times (Dn, Dn+1, Dn+2, Dn+3, Dn+4) of deformation. The Dn deformation is recognized by Fn fold which axial surface is parallel to the regional foliation. The Dn+1 intruded the (E)NE trending Dk-I dyke in the earlier phase and formed the NW trending Fn+1 fold in the later phase under compression of (E)NE-(W)SW direction. There are tight, isoclinal, intrafolial folds, boudinage, ${\sigma}$- or ${\delta}$-type boudins, asymmetric fold, C' shear band as the major deformed rock structures. The Dn+2 intruded the (N)NW trending Dk-II dyke in the earlier phase and formed NE trending Fn+2 fold in the later phase under compression of (N)NW-(S)SE direction. There are open fold and folded boudinage as those. The Dn+2 intruded the Dk-III dyke which cuts the Dk-I and Dk-II dykes and the axial surface of Fn+2 fold. The Dn+3 formed the left-handed reverse oblique-slip fault of NNE trend in which hanging wall moves into the SSE direction. Considering in that such five times of deformation recognized in the Songgang-ri geological outcrops are closely connected to the distribution and geological structure of the constituents in the more regional area as well as Songgang-ri area, the research result is expected to play a great data in clarifying and understanding the geological structure and its development process of the surrounding and boundary constituents of the Yeongnam Massif and Gyeongsang Basin.