• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.85-88
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• 2004

In this study, a simple moment-resisting precast concrete beam-column connection is proposed for highly seismic zone using dywidag ductile rod [DDC]. DDC is superior system for ductility, energy dissipation capacity, connection strength, and drift capacity. A study was carried out to investigate the connection behavior subjected to cyclic inelastic loading. Four Precast beam-column interior connections and one monolithic connection will be tested. The variables will be examined were the strength relationship between joint's ductile rod and beam reinforcement for gain energy dissipation capacity. The specimens will be tested only reverse cyclic loading in accordance with a prescribed displacement history. Connection performance is evaluated on the basis of ductility, energy dissipation capacity, connection strength, and drift capacity. the precast connection using DDC is capable of matching of exceeding the performance of the monolithic connection and thereby provides moment-resisting behavior.

• The Journal of Advanced Prosthodontics
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• 제15권1호
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• pp.33-43
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• 2023

PURPOSE. This study investigated the physical and mechanical changes in the titanium base of three different hybrid abutment materials after cyclic loading by estimating the post-load reverse torque value (RTV), compressive side fulcrum wear pattern of titanium base, and surface roughness. MATERIALS AND METHODS. A total of 24 dental implants were divided into three groups (n = 8 each): Group Z, LD, and P used zirconia, lithium disilicate, and polyetheretherketone, respectively, for hybrid abutment fabrication. RTV was evaluated after cyclic loading with 50 N for 1.2 × 10⁶ chewing cycles. The compressive sides of the titanium bases were analyzed using a scanning electron microscope, and the roughness of the affected areas was measured using an optical profilometer after loading. Datasets were analyzed using Kruskal-Wallis test followed by Mann-Whitney tests with the Bonferroni correction (α = .05). RESULTS. Twenty-three samples passed the test; one LD sample fractured after 770,474 cycles. Post-load RTV varied significantly depending on the hybridabutment material (P = .020). Group P had a significantly higher median of post-load RTVs than group Z (16.5 and 14.3 Ncm, respectively). Groups LD and P showed minor signs of wear, and group Z showed a more pronounced wear pattern. While evaluating compressive side affected area roughness of titanium bases, lower medians were shown in group LD (Ra 0.16 and Rq 0.22 ㎛) and group P (Ra 0.16 and Rq 0.23 ㎛) than in group Z (Ra 0.26 and Rq 0.34 ㎛); significant differences were found only among the unaffected surface and group Z. CONCLUSION. The hybrid abutment material influences the post-load RTV. Group Z had a more pronounced wear pattern on the compressive side of titanium base; however, the surface roughness was not statistically different among the hybridabutment groups.

• 대한치과보철학회지
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• 제50권2호
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• pp.128-134
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• 2012

연구 목적: 본 연구는 국내 개발된 맞춤형 임플란트 지대주와 기성 임플란트 지대주의 반복 하중 전과 후의 나사 풀림 토크 값을 측정, 비교하여 나사 결합부 안전성에 차이가 있는지를 알아보고자 하였다. 연구 재료 및 방법: 총 12개의 임플란트 고정체(Implantium, Dentium Co., Seoul, Korea)를 알루미늄 원통에 레진으로 고정하고, 그것을 각각 4개씩, 3개의 군으로 나눠서 각 군별로 기성 티타늄 지대주(Implantium, Dentium Co., Seoul, Korea), 캐드캠 맞춤형 티타늄 지대주(Myplant, Raphabio Co., Seoul, Korea), 그리고 금속 연결부가 있는 캐드캠 맞춤형 지르코니아 지대주(Zirconia Myplant, Raphabio Co., Seoul, Korea)를 제작하여 임플란트에 연결하였다. 금속관은 지대주에 맞춰서 티타늄을 밀링해서 제작한뒤 지대주에 합착하였다. 반복 하중을 가하기 전에 지대주 나사를 30 Ncm 토크로 조이고 약 30분 후 나사의 초기 풀림 토크값을 측정하였다. 그 후 반복 하중을 30 N에서 120 N의 싸인 곡선을 이루는 압축력으로 2 Hz의 빈도로 50만 싸이클을 가하고 하중 후 풀림 토크값을 측정하였으며, 풀림 토크 상실률을 구하여서 군끼리 비교하였다. 나사의 풀림 토크값의 상실률의 비교를 위해 Kruskal-Wallis test를 이용해서 유의수준 .05에서 분석하였다. 결과: 반복하중 후 나사 풀림 상실률에서 기성 티타늄 지대주 군에 비해 맞춤형 티타늄 지대주는 높은 값을 보였으나 유의성 있는 차이를 보이지 않았다($P$>.05). 반면, 맞춤형 지르코니아 지대주는 기성 티타늄 지대주에 비해 유의하게 높은 값을 보였다($P$=.014). 결론: 본 실험의 한계 내에서 캐드캠 맞춤형 티타늄 임플란트 지대주는 기성 임플란트 지대주 에 비해 나사 안정성이 떨어진다고 볼 수 없다. 반면, 캐드캠 맞춤형 지르코니아 지대주 는 기성 임플란트 지대주에 비해 나사 안정성이 다소 떨어진다고 볼 수 있다.

• Structural Engineering and Mechanics
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• 제57권3호
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• pp.507-528
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• 2016

Reduced beam section (RBS) moment resisting connections are among the most economical and practical rigid steel connections developed in the aftermath of the 1994 Northridge and the 1995 Kobe earthquakes. Although the performance of RBS connection has been widely studied, this connection has not been subject to in the skewed conditions. In this study, the seismic performance of dogbone connection was investigated at different angles. The Commercial ABAQUS software was used to simulate the samples. The numerical results are first compared with experimental results to verify the accuracy. Nonlinear static analysis with von Mises yield criterion materials and the finite elements method were used to analyze the behavior of the samples The selected Hardening Strain of materials at cyclic loading and monotonic loading were kinematics and isotropic respectively The results show that in addition to reverse twisting of columns, change in beam angle relative to the central axis of the column has little impact on hysteresis response of samples. Any increase in the angle, leads to increased non-elastic resistance. As for Weak panel zone, with increase of the angle between the beam and the column, the initial submission will take place at a later time and at a larger rotation angle in the panel zone and this represents reduced amount of perpendicular force exerted on the column flange. In balanced and strong panel zones, with increase in the angle between the beam and the central axis of the column, the reduced beam section (RBS), reaches the failure limit faster and at a lower rotation angle. In connection of skewed beam, balanced panel zone, due to its good performance in disposition of plasticity process away from connection points and high energy absorption, is the best choice for panel zone. The ratio of maximum moment developed on the column was found to be within 0.84 to 1 plastic anchor point, which shows prevention of brittle fracture in connections.

• Structural Engineering and Mechanics
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• 제30권6호
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• pp.733-761
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• 2008

The failure of reinforced concrete structures in recent earthquakes caused concern about the performance of beam column joints. Confinement of joint is one of the ways to improve the performance of beam column joints during earthquakes. This paper describes an experimental study of exterior beam-column joints with two non-conventional reinforcement arrangements. One exterior beam-column joint of a six story building in seismic zone III of India was designed for earthquake loading. The transverse reinforcement of the joint assemblages were detailed as per IS 13920:1993 and IS 456:2000 respectively. The proposed nonconventional reinforcement was provided in the form of diagonal reinforcement on the faces of the joint, as a replacement of stirrups in the joint region for joints detailed as per IS 13920 and as additional reinforcement for joints detailed as per IS 456. These newly proposed detailing have the basic advantage of reducing the reinforcement congestion at the joint region. In order to study and compare the performance of joint with different detailing, four types of one-third scale specimens were cast (two numbers in each type). The main objective of the present study is to investigate the effectiveness of the proposed reinforcement detailing. All the specimens were tested under reverse cyclic loading, with appropriate axial load. From the test results, it was found that the beam-column joint having confining reinforcement as per IS: 456 with nonconventional detailing performed well. Test results indicate that the non-conventionally detailed specimens, Type 2 and Type 4 have an improvement in average ductility of 16% and 119% than their conventionally detailed counter parts (Type1 and Type 3). Further, the joint shear capacity of the Type 2 and Type 4 specimens are improved by 8.4% and 15.6% than the corresponding specimens of Type 1 and Type 3 respectively. The present study proposes a closed form expression to compute the yield and ultimate load of the system. This is accomplished using the theory of statics and the failure pattern observed during testing. Good correlation is found between the theoretical and experimental results.

• The Journal of Advanced Prosthodontics
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• 제13권1호
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• pp.65-70
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• 2021

Purpose. Implant mechanical complications, including screw loosening, can influence dental implant success. It has been shown that torque values are affected by contamination occurred in implant-abutment (I/A) interface. This study aimed to examine the effects of blood, saliva, fluoride and chlorhexidine contamination on reverse torque values (RTVs) of abutment screws in oral conditions. Materials and Methods. 50 fixtures were mounted into the stainless-steel holders and divided into five groups (n = 10). Except control group (NC), fixture screw holes in other groups were contaminated with chlorhexidine (CG), saliva (SG), blood (BG), or fluoride (FG). Abutment screws were tightened with a digital torque meter. I/A assemblies were subjected to thermocycling and cyclic loading. The mean RTVs were recorded and data were analyzed with one-way ANOVA and Tukey test. Results. Except for specimens in SG (20.56 ± 1.33), other specimens in BG (21.11 ± 1.54), CG (22.89 ± 1.1) and FG (24.00 ± 1.12) displayed significantly higher RTVs compared to NC (19.00 ± 1.87). The highest RTVs were detected in CG and FG. Conclusion. The obtained data robustly suggest that RTVs were significantly affected by fluid contaminations. Specimens in FG and CG displayed the highest RTVs. Therefore, clinicians should have enough knowledge about probable contaminations in I/A interface in order to manage them during clinical procedure and to inform patients about using oral care products.

• Structural Engineering and Mechanics
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• 제88권5호
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• pp.481-492
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• 2023

The past earthquakes revealed the importance of the design of moment-resisting reinforced concrete framed structures with ductile behavior. Due to seismic activity, failures in framed structures are widespread in beam-column joints. Hence, the joints must be designed to possess sufficient strength and stiffness. This paper investigates the effects of fibers on the ductility of hybrid fiber reinforced self-compacting concrete (HFRSCC) when subjected to seismic actions; overcoming bottlenecks at the beam-column joints has been studied by adding low modulus sisal fiber and high modulus steel fiber. For this, the optimized dose of hooked end steel fiber content (1.5%) was kept constant, and the sisal fiber content was varied at the rate of 0.1%, up to 0.3%. The seismic performance parameters, such as load-displacement behavior, ductility, energy absorption capacity, stiffness degradation, and energy dissipation capacity, were studied. The ductility factor and the cumulative energy dissipation capacity of the hybrid fiber (steel fiber, 1.5% and sisal fiber, 0.2%) added beam-column joint specimen is 100% and 121% greater than the control specimen, respectively. And also the stiffness of the hybrid fiber reinforced specimen is 100% higher than the control specimen. Thus, the test results showed that adding hybrid fibers instead of mono fibers could significantly enhance the seismic performance parameters. Therefore, the hybrid fiber reinforced concrete with 1.5% steel and 0.2% sisal fiber can be effectively used to design structures in seismic-prone areas.

• Earthquakes and Structures
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• 제4권4호
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• pp.429-449
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• 2013

Current Design Codes for Reinforced Concrete (RC) interior beam-column joints are based on limited experimental studies on the seismic behavior of eccentric joints. To supplement existing information, an experimental study was conducted that focused on the effect of eccentricity of the deeper beams with respect to the shallow beams. A total of eight one-third scale interior joints with beams of different depths were subjected to reverse cyclic loading. The primary variables in the test specimens were the amount of joint transverse reinforcement and the cross section of the shallow beams. The overall performance of each test assembly was found to be unsatisfactory in terms of joint shear strength, stiffness, energy dissipation and shear deformation. The results indicated that the vertical eccentricity of spandrel beams in this type of joint led to lower capacity in joint shear strength and severe damage of concrete in the joint core. Increasing the joint shear reinforcement was not effective to alter the failure mode from joint shear failure to beam yielding which is favorable for earthquake resistance design, whereas it was effective to reduce the crack width at the small loading stages. Based on the observed behavior, the shear stress of the joint core was suggested to be kept as low as possible for a safe and practical design of this type of joint.

• Structural Engineering and Mechanics
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• 제14권5호
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• pp.543-563
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• 2002

The use of the epoxy pressure injection technique to rehabilitate reinforced concrete beam-column joints damaged by strong earthquakes is investigated experimentally and analytically. Two one-half-scale exterior beam-column joint specimens were exposed to reverse cyclic loading similar to that generated from strong earthquake ground motion, resulting in damage. Both specimens were typical of new structures and incorporated full seismic details in current building codes. Thus the first specimen was designed according to Eurocode 2 and Eurocode 8 and the second specimen was designed according to ACI-318 (1995) and ACI-ASCE Committee 352 (1985). The specimens were then repaired with an epoxy pressure injection technique. The repaired specimens were subjected to the same displacement history as that imposed on the original specimens. The results indicate that the epoxy pressure injection technique was effective in restoring the strength, stiffness and energy dissipation capacity of specimens representing a modem design.

• 한국산업안전학회:학술대회논문집
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• 한국안전학회 1997년도 추계 학술논문발표회 논문집
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• pp.15-24
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• 1997

최근 우리나라에도 많은 지진사례가 보고되고 있으며, 이러한 지진하중은 원전설비 및 각종 기계설비등의 가동중 파손을 유발시킬 수 있는 잠재적 위험성이 높다. 이에 지진하중에 대한 안전성 확보의 필요성이 점차 대두되고 있다. 지진하중은 종ㆍ횡파에 의한 인장ㆍ압축이 반복되는 역사이클하중(reverse cyclic loading)형태로, 현재까지는 이를 고려한 설계개념이 미흡한 실정이며 이에 대한 파괴물성치의 확보는 물론 파괴물성치 평가 절차도 확립되어 있지 않은 상태이다. 따라서 지진하중에 대한 안전성확보를 위해서는, 역사이클 하중이 재료의 파괴특성 특히, 파괴저항(J-R)곡선에 미치는 영향이 고찰되어야 할 것이다. (중략)