• Imaging Science in Dentistry
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• 제44권1호
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• pp.37-41
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• 2014

Purpose: The aim of this study was to investigate the accuracy of cone-beam computed tomography (CBCT) in the diagnosis of vertical root fractures in a tooth with gutta-percha and prefabricated posts. Materials and Methods: This study selected 96 extracted molar and premolar teeth of the mandible. These teeth were divided into six groups as follows: Groups A, B, and C consisted of teeth with vertical root fractures, and groups D, E, and F had teeth without vertical root fractures; groups A and D had teeth with gutta-percha and prefabricated posts; groups B and E had teeth with gutta-percha but without prefabricated posts, and groups C and F had teeth without gutta-percha or prefabricated posts. Then, the CBCT scans were obtained and examined by three oral and maxillofacial radiologists in order to determine the presence of vertical root fractures. The data were analyzed using IBM SPSS 20.0 (IBM Corp., Armonk, NY, USA). Results: The kappa coefficient was $0.875{\pm}0.049$. Groups A and D showed a sensitivity of 81% and a specificity of 100%; groups E and B, a sensitivity of 94% and a specificity of 100%; and groups C and F, a sensitivity of 88% and a specificity of 100%. Conclusion: The CBCT scans revealed a high accuracy in the diagnosis of vertical root fractures; the accuracy did not decrease in the presence of gutta-percha. The presence of prefabricated posts also had little effect on the accuracy of the system, which was, of course, not statistically significant.

• Structural Engineering and Mechanics
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• 제56권1호
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• pp.1-25
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• 2015

The main goal of this study was to develop a convenient strengthening technique for retrofitting of reinforced concrete members. For this purpose a new retrofitting material so-called prefabricated-HSPRCC (high performance steel plate reinforced cementitious composite) panel was developed by using high performance concrete and perforated steel plate. Prefabricated-HSPRCC composes advantages of steel and high performance concrete. The prefabricated-HSPRCC panels were either only bonded on the specimens using epoxy mortar or anchored to the specimen by steel bolts as well as bonding. Effect of different variations such as prefabricated-HSPRCC panel thicknesses, steel plate thicknesses, puncture orientation of perforated steel plate, existence of anchorage etc. were studied through a simple experimental work. The behaviour of the specimens under vertical point load was also studied by using simple mechanics. The retrofitted specimens were found to exhibit much better performance both in terms of strength and deformation capability. The anchorage application was found to positively affect this improved performance. Furthermore, as a result of the tests the best parameters of prefabricated-HSPRCC plate for improving strength and deformation capacities were determined.

• Advances in concrete construction
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• 제13권 2호
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• pp.153-162
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• 2022

Prefabricated exterior wall panel is the main non-load-bearing component of assembly building, which affects the comprehensive performance of thermal insulation and durability of the building. It is of great significance to develop new prefabricated exterior wall panel with durable and lightweight characteristics for the development of energy-saving and assembly building. In the prefabricated sandwich insulation hanging wall panel, the selection of material for the outer layer and the arrangement of the connector of the inner and outer wall layers affect the mechanical performance and durability of the wall panels. In this paper, high performance cement-based composites (HPFRC) are used in the outer layer of the new type wall panel. FRP bars are used as the interface connector. Through experiments and analysis, the influence of the arrangement of connectors on the mechanical behaviors of thin-walled composite wall panel and the panel with window openings under two working conditions are investigated. The failure modes and the role of connectors of thin-walled composite wallboard are analyzed. The influence of the thickness of the wall layer and their combination on the strain growth of the control section, the initial crack resistance, the ultimate bearing capacity and the deformation of the wall panels are analyzed. The research work provides a technical reference for the engineering design of the light-weight thin-walled and durable composite sandwich wall panel.

• 한국건설관리학회논문집
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• 제4권1호
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• pp.90-96
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• 2003

도심지 건축공사가 증가하고 있는 우리나라에서 작업공간의 부족 및 자재의 적시공급에 대한 문제는 반드시 해결해야 할 과제이다. 이 중에서도 주택건설에 있어 가장 큰 비중을 차지하고 있는 아파트 시공의 경우, 초고층화로 골조공사의 중요성과 함께 친환경적 공법과 합리적 공정개선 및 원가절감을 구현할 새로운 공법이 요구되고 있다. 본 연구에서는 국내 건설현장의 사례조사를 통해 슬래브 거푸집공사와 마감공사의 프로세스에서 불필요한 요소를 최소화하고자 공업화 자재를 활용한 (골조-마감공사)통합공법을 제시한다 가치흐름분석기법(Value Stream Mapping)을 활용하여 기존 프로세스에서의 비 가치 창출작업을 가치창출작업에 통합시키거나 제거하여 슬래브 공사 내에서 공기 및 투입인력의 절감 가능성을 확인하고, 공기단축과 원가절감 효과를 측정하였다. 이와 같이 공업화 자재의 활용으로 현장작업에 따른 변이를 최소화하여 공정의 안정성 및 공정계획의 신뢰성을 확보 등 공정의 합리화를 구현하고자 한다.

• 콘크리트학회논문집
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• 제16권4호
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• pp.573-579
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• 2004

For the fast construction and replacement of bridges in urban area, a prefabricated bridge system can be an excellent alternative. Details of prefabricated slabs for PSC girders were developed and static tests on shear connections were conducted to propose design equations of the shear connection. Stirrups and stud connectors were used as shear connectors and non-shrink mortar was used for the filling material in shear pockets for shear connectors. Stirrups and studs were fabricated to insert embedded nut-type devices in PSC girders. Shear strength of the shear connection considering chemical bond, friction and mechanical connectors was evaluated and empirical equations were suggested. Due to the mechanical connectors, ultimate slip capacity of the shear connection was sufficient for shear load redistribution, and suggested details of the shear connection showed good performance in terms of strength and ductility.

• Structural Engineering and Mechanics
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• 제81권3호
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• pp.305-316
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• 2022

Externally bonded ultrahigh performance fiber-reinforced concrete (UHPFRC) is commonly used as a strengthening material for reinforced concrete (RC) structures. This study reports the results of an experimental program investigating the bonding behavior between concrete and prefabricated UHPFRC plates. The overall experimental program is consisting of five RC specimens, which are strengthened using the different lengths and widths of prefabricated UHPFRC plates. These specimens were analyzed using the pull-pull double-shear test. The performance of each strengthened specimen is presented, discussed and compared in terms of failure mode, maximum load, load-slip relationship, fracture energy and strain distribution. Specimen C-25-160-300 which bonded along the whole width of 160 mm recorded the highest maximum load (109.2 kN) among all the analysed specimens. Moreover, a 3D numerical finite element model (FEM) is proposed to simulate the bond behavior between concrete and UHPFRC plates. Moreover, this study reviews the analytical models that can predict the relationship between the maximum bond stress and slip for strengthened concrete elements. The proposed FEM is verified against the experimental program and then used to test 36 RC specimens strengthened with prefabricated UHPFRC plates with different concrete grades and UHPFRC plate widths. The obtained results together with the review of analytical models helped in the formation of a design equation for estimating the bond stress between concrete and prefabricated UHPFRC plates.

• 한국산학기술학회논문지
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• 제16권6호
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• pp.4322-4327
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• 2015

하수관거 시설은 현장 시공시 다짐 불량 및 뒤채움재의 품질관리 미흡으로 인해 하수관거의 이격 및 부등침하가 발생되고, 이음부나 관의 손상이 심화되는 경우 누수가 발생된다. 노후화로 인해 유지 및 보수, 신설 비용은 매년 증가하고, 누수로 인한 인접 매립시설물 및 지하수로의 유입으로 인해 오염사례가 보고된 바 있으며, 최근에는 싱크홀의 문제를 야기하여 사회적 관심이 증대되었다. 따라서 많은 연구자들에 의해 하수관거의 기초에 대한 채움재관련 연구가 오랫동안 연구되어 왔으며, 신재생재료에 대한 관심 수요가 증가하여 재생재료를 활용한 연구들도 활발히 진행되고 있다. 본 연구에서는 하수관거를 지지하는 기초의 안전성과 경제성을 동시에 지닌 재활용재료를 활용한 조립식 하수관거 기초에 대해 연구를 진행하였으며, 사후처방방식이 아닌, 시공단계에서 사전예방하기 위해 관경 600mm, 700mm, 800mm의 대형 하수관거를 선정하여 적절한 설계 하중을 산출하고 매립 심도별 안전성에 관한 연구를 수행하였다. 본 연구결과는 신형식 하수관거 기초의 유사연구에 널리 활용 될 수 있을 것이다.

• 대한치과보존학회:학술대회논문집
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• 대한치과보존학회 2001년도 춘계학술대회
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• pp.258-258
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• 2001

Fiber-reinforced materials have highly favorable mechanical properties. and their strength-to-weight ratios are superior to those of most alloys. When compared to metals they offer many other advantages as well. including non-corrosiveness. translucency. good bonding properties. and ease ofrepair. Fiber-reinforced materials can be categorized to pre-impregnated. impregnation required. dental laboratory products. chairside products and prefabricated posts. so it is not suprising that fiber-reinforced composites have potential for use in many applications in dentistry. Fiber-reinforced materials can be utilized in frameworks for crowns. anterior or posterior fixed prostheses. chairs ide tooth replacements. periodontal splints. customized posts. prefabricated posts. orthodontic retention. denture reinforcements and in implants dentistry. To realize the full potential of using fiber-reinforced composite restorations. it is essential that the clinician and laboratory technician understand concepts of tooth preparation and framework design. Also practitioner may appreciate the background information and other details about the materials themselves so that identify the rationale for their use in various clinical situations. select well-suited materials. and carry out related procedures. Understanding the material properties and take many attentions. fiber-reinforced materials will give more esthetic. more easy. more strong and more reliable restorations.ations.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2001년도 가을 학술발표회 논문집
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• pp.65-94
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• 2001

The use of PBD(prefabricated band drain)far ground improvement is rapidly increased due to the merit of construction period and cost, environmental preservation compared with other vertical drain method, and the development of material. This paper presents the historical review, theoretical background, design procedure and method, and typical construction example for the PBD. Also, the direction of further technical development and study is recommended.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 E
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• pp.1614-1616
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• 1998

Insulation performance of major components of prefabricated joint such as epoxy insulation unit and premolded rubber cone are guaranteed by material selection design and proper manufacturing. On the other hand insulation performance of the interfaces between the premolded rubber cone and the epoxy insulation unit and the cable insulation is maintained by keeping the premolded rubber cone to close contact with such insulation by spring. Electric characteristics of a interface depend on the contact pressure, but the required characteristics are assured so far as a proper contact pressure is maintained. In this report, the interfacial pressure by pressure sensors both in the early stage and after heating cycle were measured and the simulation by FEM program were presented. The comparison of these two results show that interfacial pressure could be controlled optimally by changing the spring length and lubricant state of the interface.