• Hip & pelvis
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• 제36권2호
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• pp.120-128
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• 2024

Purpose: The purpose of this study was to compare the clinical and radiographic outcomes with use of short-curved stems versus standard-length single wedged stems over a minimum follow-up period of five years. Materials and Methods: A retrospective study of primary total hip arthroplasties performed using the Fitmore^® stem (127 hips, 122 patients) and the M/L taper^® stem (195 hips, 187 patients) between October 2012 and June 2014 was conducted. The clinical and radiographic outcomes were obtained for evaluation over a minimum follow-up period of five years. Results: In both the Fitmore^® and M/L taper^® groups, the mean Harris hip score improved from 52.4 and 48.9 preoperatively to 93.3 and 94.5 at the final follow-up, respectively (P=0.980). The mean Western Ontario and McMaster Universities Osteoarthritis Index scores also improved from 73.3 and 76.8 preoperatively to 22.9 and 25.6 at the final follow-up, respectively (P=0.465). Fifteen hips (Fitmore^®: 14 hips; M/L taper^®: one hip, P<0.001) developed intraoperative cracks and were treated simultaneously with cerclage wiring. Radiography showed a radiolucent line in 24 hips in the Fitmore^® group and 12 hips in the M/L taper^® group (P=0.125). Cortical hypertrophy was detected in 29 hips (Fitmore^® group: 28 hips; M/L taper^® group: one hip, P<0.001). Conclusion: Similarly favorable clinical and radiographic outcomes were achieved with use of both short-curved stems and standard-length single wedged stems. However, higher cortical hypertrophy and a higher rate of femoral crack were observed with use of Fitmore^® stems.

• Journal of Korean Neurosurgical Society
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• 제37권3호
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• pp.217-222
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• 2005

Objective: To achieve optimal fit of implant, it is necessary to bend the implant during spine surgery. Bending procedure may decrease stiffness of plate especially made of titanium and stainless steel. Typically titanium suffers adverse effects including early crack propagation when it is bent. We investigate whether 6 degree bending of titanium plates would decrease the stiffness after full cyclic loading by comparing with non-bending titanium plates group. Methods: Authors experimented 40 titanium alloy plates of 57mm in length, manufactured by 5 different companies. Total 40 plates were divided into two groups (20 bent plates for experimental group and 20 non-bent plates for control group). Twenty plates of experimental group were bent to 6 degree with 3-point bending technique and verified with image analyzer. Using the electron microscope, we sought for a initial crack before and after 3-point bending. Mechanical testing by means of 6000 cyclic axial-compression loading of 35N in compression with moment arm of 35mm-1.1 Nm was conducted on each plate and followed by the electron microscopic examination to detect crack or fissure on plates. Results: The stiffness was decreased after 6000 cyclic loading, but there was no statistically significant difference in stiffness between experimental and control group. There was no evidence of change in grain structure on the electron microscopic magnification. Conclusion: The titanium cervical plates can be bent to 6 degree without any crack or weakness of plate. We also assume that minimal bending may increase the resistance to fatigue fracture in cervical flexion-extension movement.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.481-486
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• 1999

According to results of this research Fly-ash Cement permanent-form production was found to be possible by fly-ash mortal. The compress strength 350kg/$\textrm{cm}^2$, banding strength 120kg/$\textrm{cm}^2$ were possible material separting and bleeding by excessive W/C rate was decreased permanent-form made by polymer solved high price of polymer by fly-ash. Model material was made by result of first research. There were no minute-crack on beam form and out surface of form was very smooth, So filling degree seemed desirable length of form after steaming curing was maintained as expected. with these results production of form seemed possible. In the banding load test, fly-ash showed increase of maxim load 12% than RC. in the case of minute-crack, comparing with RC, fly-ash showed no crack at connect. at the first stage under continuing loading size of crack increased. These phenomena seemed to be based on contribution of stress of inner bars in permanent-form. in the test of defection, fly-ash shower about 10% beam load increase than RC. in the case of beam defection, RC showed sudden decrease of tolerance at maxim load and total breaking, but permanent-form showed breaking of bending maintaining defection with contribution of steel stress ($\Phi$6 wire-mash). There phenomenic seemed to be attributed to increase of surface and steel tolerance of form. According to construction explacemaion, it was guessed that each panel was constructed by conner-steels in form edge. so cohesiveness was small. on these bases. keeping width of horizontal band 30cm, form-panel of 20mm width was found to be of use. Permanent-form was found to be efficient in compressibleness, defection, safety and use of Fly-ash mortal.

• Architectural research
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• 제22권1호
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• pp.33-39
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• 2020

In this study, side-face blowout failure strength of high strength headed reinforcing bar, which is vertically anchoring between RC or SFRC members, is evaluated throughout pullout test. The major test parameters are content ratio of high strength steel fibers, strength of rebar, length of anchorage, presence of shear reinforcement, and the side concrete cover thickness planned to be 1.3 times of the rebar. In pullout test, tensile force was applied to the headed reinforcing bar with the hinged supports positioned 1.5 and 0.7 times the anchorage length on both sides of the headed reinforcing bar. As a result, the cone-shaped crack occurred where the headed reinforcing bar embedded and finally side-face blowout failure caused by bearing pressure of the headed reinforcing bar. The tensile strength of specimens increased by 13.0 ~26.2% with shear reinforcement. The pullout strength of the specimens increased by 3.6 ~15.4% according to steel fiber reinforcement. Increasing the anchoring length and shear reinforcement were evaluated to reduce the stress bearing ration of the total stress.

• Structural Engineering and Mechanics
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• 제87권4호
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• pp.375-389
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• 2023

In many fiber concrete beams with Carbon Fiber Reinforced Polymer (CFRP), debonding occurs between the carbon sheets and the concrete due to the low strength of the bonding resin. A total of 42 fiber concrete beams with a cross-section of 10×10 cm with a span length of 50 cm are fabricated and retrofitted with CFRP and subjected to a 4-point bending test. Graphene Oxide (GO) at 1, 2, and 3 wt% of the resin is used to improve the mechanical properties of the bonding resins, and the effect of length, width, and the number of layers of CFRP and resin material are investigated. The crack pattern, failure mode, and stress-strain curve are analyzed and compared in each case. The results showed that adding GO to polyamine resin could improve the bonding between the resin and the fiber concrete beam. Furthermore, the optimum amount of nanomaterials is equal to 2% by the weight of the resin. Using 2% nanomaterials showed that by increasing the length, width, and number of layers, the bearing and stiffness of fiber concrete beams increased significantly.

• 대한기계학회논문집
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• 제12권1호
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• pp.123-130
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• 1988

본 연구에서는 비교적 데이터 처리속도가 빠른 80286계의 CPU를 사용한 16bit 퍼스널 컴퓨터를 이용하는 경우보다, 가격면에서는 훨씬 유리하면서도, 성능은 거의 뒤지지 않는 피로시험 자동화 및 피로거동 고정밀 측정을 위한 시스템을 완성하였다. 본 연구에서 사용한 방법 및 작성한 소프트웨어등은 사용시험기, 피로연구 대상등에 거의 관계없이 이용이 가능하나, 여기서는 편의상, 시험기로서는 폐루우프(closed-loop)유압서어보 피로시험기를 사용하였으며, 피로거동의 측정에 대해서는 주로 피로균열지전을 대상으로 하였다.

• Computers and Concrete
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• 제33권6호
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• pp.659-670
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• 2024

The mechanical behaviour of layered concrete samples containing an internal crack was numerically studied by modelling the geo-mechanical specimens in the particle flow code in two dimensions (PFC2D). The numerical modelling software was calibrated with the experimental results of the Brazilian tensile strengths gained from the laboratory disc-type specimens. Then, the samples with the bedding layers and internal notch were numerically simulated with PFC2D under uniaxial compressive loading. In each specimen, the layers' thickness was 10 mm but the layer's inclination angle was changed to 0°, 30°, 60°, 90°, 120° and 150°. Of course, the layers'interfaces are considered to have very low strengths. The internal notch was kept at 3 cm in length however, its inclination angle was changed to 0°, 40°, 60° and 90°. Therefore, a total, of 24 numerical models were made to study the failure mechanism of the layered concrete samples. Considering these results, it has been concluded that the inclination angles of both internal crack and bedding layers affect the failure mechanism and uniaxial compressive strength of the concrete.

• 한국강구조학회 논문집
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• 제15권6호통권67호
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• pp.629-637
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• 2003

본 논문은 강교량에서 큰 응력범위가 발생하는 위치에 불가피하게 존재하는 가장 일반적인 피로 취약 상세인 면내 거셋 용접부에 대한 3단계에 걸친 피로 시험 결과를 분석 평가 하였다. 플랜지 및 부착물의 두께, 부착물의 길이와 적용강재를 변화시킨 총 57개의 피로 시험편이 제작되어 인장피로시험이 수행되었으며, 1단계 시험에서는 실물크기 및 시험체에 대한 피로 실험도 수행되었다. 실험 결과로부터 현 설계기준에 제시된 대상상세에 대한 피로강도 기준의 적정성을 평가하고, 플랜지와 용접 연결된 부착물의 두께, 길이 등의 기하학적 형상 및 적용강재의 강도가 피로강도에 미치는 영향과 균열의 발생 및 진전 거동 특성을 규명하였다. 외국의 피로실험 자료와 비교 분석한 결과 강재가 서로 달라도 유사한 피로강도를 갖는 것으로 나타났으며, 이는 강종 보다는 기하학적 형상 및 용접관련사항이 피로강도에 미치는 영향이 크다는 것을 나타내며, 형상에 따라 응력집중계수의 차이가 매우 커서 거셋 부착부의 변화부 반경, 길이 및 플랜지의 폭에 따라 상세분류를 좀더 세분화 할 필요가 있는 것으로 나타났다.

• Advances in concrete construction
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• 제14권5호
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• pp.299-307
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• 2022

Cement-based matrixes have low tensile strength and negligible ductility. Adding fibres to these matrixes will improve their mechanical properties and make these composites suitable for structural applications. Post-cracking tensile strength of steel fibers-reinforced cementitious composite materials is directly related to the number of transverse fibers passing through the crack width and the pulling-out behavior of each of the fibers. Therefore, the exact recognition of the pullout behavior of single fibers is necessary to understand the uniaxial tensile and bending behavior of steel fiber-reinforced concrete. In this paper, an experimental study has been carried out on the pullout behavior of 3D (steel fibers with totally two hooks at both ends), 4D (steel fibers with a total of four hooks at both ends), and 5D (steel fibers with totally six hooks at both ends) in which the fibers have been located either perpendicular to the crack width or in an inclined manner. The pullout behavior of the mentioned steel fibers at an inclination angle of 0, 15, 30, 45, and 60 degrees and with embedded lengths of 10, 15, 20, 25, and 30 millimetres is studied in order to explore the simultaneous effect of the inclination angle of the fibers relative to the alongside loading and the embedded length of fibers on the pullout response in each case, including the maximal pullout force, the slip of the maximum point of pullout force, pullout energy, fiber rupture, and concrete matrix spalling. The results showed that the maximum pullout energy in 3D, 4D, and 5D steel fibers with different embedded lengths occurs at 0 to 30° inclination angles. In 5D fibers, maximum pullout energy occurs at a 30° angle with a 25 mm embedded length.

• 한국건설순환자원학회논문집
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• 제8권2호
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• pp.175-182
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• 2020

철근 부식으로 인한 철근 콘크리트 구조물의 내구성능 저하를 방지하는 방법 중 하나인 에폭시 도막 철근의 사용이 증가하고 있으나, 에폭시 도막으로 인한 콘크리트와 철근의 부착성능 부족으로 정착길이 및 겹침이음길이를 증가시켜야하는 것이 문제가 된다. 이 논문은 에폭시 도막 철근의 부착성능을 개선하여 직접인발시험에서 확인한 기본정착길이의 감소 가능성을 실제 휨부재의 이음길이 산정에 반영할 수 있는지를 확인하기 위하여 수행한 실험연구를 정리한 것이다. 휨부재에서 일반철근과 에폭시 도막 철근의 겹침이음 특성을 비교하기 위하여 철근지름 및 겹침이음길이를 변수로 하여 36개의 시험체로 보-단부 실험을 통해 겹침 이음 성능평가를 하였다. 실험결과에 의하면 현행설계기준에 따라 이음길이에 보정계수 1.2를 사용한 에폭시 도막 철근 부착강도와 일반철근 부착강도를 비교한 결과 파괴 양상, 처짐특성 및 균열폭 등을 고려할 때 현행 설계기준에 따른 보정계수의 필요성을 확인하였다.