제5회 CANMET/ACI 최신 콘크리트 기술 규제 학회

윤현도 한국콘크리트학회 2001 콘크리트학회지 Vol.13 No.6

보강섬유 종류에 따른 고인성 시멘트 복합체의 손상과정 및 음향방출특성

윤현도,김선우,전에스더 대한건축학회 2006 大韓建築學會論文集 : 構造系 Vol.22 No.9

Fiber is an important ingredient in high performance fiber-reinforced cementitious composite (HPFRCC), which can control fracture of cementitious composite by bridging action. The properties of reinforcing fiber, as tensile strength, aspect ratio and elastic modulus, have great effect on the fracture behavior of HPFRCC. Acoustic emission(AE) method was used to evaluate the characteristics of fracture process and the micro-failure mechanism of HPFRCC. This investigation of distress attempts to relate external behavior to internal signals of distress through acoustic emission. This helps to identify critical internal distress vis-a-vis external level of stress. For these purposes, three kinds of fibers were used : PP(Polypropylene), PE(Polyethylene), SC(Steel cord). In this study, the AE characteristics of HPFRCC with different fiber type(PE.15, PP2.0, SC0.75+PE0.75) distributions under four-point-bending were studied. The result show that the AE technique is a valuable tool to study the failure mechanism of HPFRCC. Moreover, there is a good relationship between AE hits and fracture energy.

섬유 혼입조건에 따른 섬유 보강 고인성 시멘트 복합체의 인장거동 특성

윤현도,김선우,전에스더 대한건축학회 2006 大韓建築學會論文集 : 構造系 Vol.22 No.12

The effect of fiber types and fiber combination on the tensile response of cement paste matrix was experimentally investigated. The fibers used included polyvinyl alcohol(PVA), high-strength high-modulus polyethylene(PE), and polypropylene(PP), and they were randomly mixed in the matrix at volume fractions below 2.5%. Tensile properties of the composites were measured by the direct tensile test under both monotonic and cyclic loading. Various cyclic testing schemes were used to examine the effect of cyclic loading on the material's tensile stress-strain envelope. Testing results identified a unique unloading and reloading response for HPFRCC, which is a consequence of fibers debonding and pulling out of the matrix. The envelope curve is shown to govern cyclic response. HPFRCC can maintain its peak stress to large strains, producing a significantly different response than traditional cementitious materials. PE fiber with high strength and elastic modulus are found to be more effective than PVA and PP fibers in improving the strength, ductility and energy absorption capacity of cement-based composites.

중심 축력을 받는 HPFRCC 기둥의 압축거동

윤현도,황선경,변장배,전수만 대한건축학회 2006 大韓建築學會論文集 : 構造系 Vol.22 No.10

This paper explores the constitutive models of HPFRCC(High Performance Fiber Reinforced Cement Composite) column using PVA(Polyvinyl alcohol) fibers and SC(Steel cord) fiber and in particular the substitutability of fibers for transverse reinforcement. An experimental program was conducted that nine square reinforced cement composite columns were tested with varying fiber content and the volumetric ratio of transverse reinforcement. One contained no fibers, four contained simple PVA fibers and four contained hybrid SC and PVA fibers. All nine columns were tested by the application of a concentric, axial compression force. Also, constitutive model, proposed by Yong, Nour, and Nawy, are applied to express the stress-strain relationships in compression of HPFRCC columns. It was found that ductility improvements were noticeable for HPFRCC columns and the addition of fibers could reduce the amount of transverse reinforcement which confine core cement composite. It was also found that Yong model could predict the compressive behavior of HPFRCC columns.

개구부의 설치에 따른 기존 실규모 철근콘크리트 전단벽의 거동에 관한 비선형 유한요소해석

윤현도,한민기 대한건축학회 2006 大韓建築學會論文集 : 構造系 Vol.22 No.7

Non-linear finite element analysis (FEA) model is developed for reinforced concrete rectangular shear walls with an opening that may be artificially introduced to provide for functional and accessibility improvements in the remodeling of residential apartments. A commercial FEA code ABAQUS has been used, which can take into account material inelasticity, concrete cracking, geometric non-linearity and bond-slip between rebar and concrete. The finite element implementation is based on the smeared crack approach with rotating cracks parallel to the principal strain directions. The proposed analytical model results agreed well with measurements from the two existing actual scale reinforced concrete rectangular walls tested at the Building Research Institute in Japan. Lastly, parametric studies on the effects of the opening position, size, and shape of artificially-introduced opening on the strength and behavior of existing rectangular reinforced concrete shear walls have been carried out. It was found that the opening being introduced in the mid and center of wall reduced the strength of wall more. An increasing in the opening size by increasing the length of rectangular opening decreased the strength and stiffness of the wall.

탄소섬유 쉬트로 보강된 철근콘크리트 보의 손상단계별 음향방출 특성

윤현도,김선우,전수만,서수연,최창식,최기봉 대한건축학회 2007 大韓建築學會論文集 : 構造系 Vol.23 No.1

In this study, the application of the acoustic emission (AE) technique to monitor damage levels in reinforced concrete beam strengthened in flexure with carbon fiber reinforced polymer (CFRP) sheet was investigated. The objective of this study is to take the first step in creating a user-friendly health monitoring system for reinforced concrete structure strengthened with CFRP sheet using AE. Five beams were 200 x 270mm in cross section and were tested under three-point bending over a span of 1,700mm. The AE signal were collected and analyzed for all specimens. The AE parameters were analyzed for damage levels(based on initial crack, crack propagation, yielding of main bars, and fracture or rip-off of CFRP sheet) of all specimens. Results from this study show that event, amplitude versus frequency, and amplitude versus duration of a signal, showed a clear difference for different loading stages depending upon the active damage mechanism.

플루오르화에 의해 표면 개질된 폴리프로필렌 섬유의 매입인발거동

윤현도,전에스더,이영석 대한건축학회 2006 大韓建築學會論文集 : 構造系 Vol.22 No.11

High performance fiber-reinforced cementitious composites(HPFRCCs) are characterized by a stress-strain response in tension that exhibits pseudo strain-hardening behavior and multiple cracking. Such behavior is contingent on three groups of variables ; fiber(type, geometry and strength), matrix(strength, toughness, modulus) and interface related parameters such as the interfacial bond strength. In this paper, the effect of embedded length on the pullout characteristics and the effect of surface treatment with fluorination on the interfacial bond between the fiber and cementitious matrix were studied. Polypropylene fibers have a weak bond with cementitious matrix because of hydrophobicity of fibers, which does not allow for sufficient friction to develop between the two. Thus, a new method(fluorination) to improve the frictional bond by means of surface treatment of fibers was also proposed. The fluorination processing, w/b ratio of the mixtures, inclination angle and embedded length influence the pullout behavior. As a result, the fluorination process improves friction bond, maximum pullout load and end slip of polypropylene fiber.

철판 보강된 섬유보강 시멘트 복합체 합성 커플링 보의 내진성능

윤현도,김선우,전에스더,박완신 대한건축학회 2006 大韓建築學會論文集 : 構造系 Vol.22 No.8

Reinforced concrete coupled shear walls in tall buildings are known as efficient structural systems to provide lateral resistance to wind and earthquake. The coupling beams connecting two shear walls are normally subjected to very high bending and shear stresses. This paper reports experimental studies to investigate the behavior and shear strength of the steel-plate reinforced concrete coupling beams under cyclic loading. In the test program, two coupling beam specimens are constructed and tested. The important variables in the test program was the use of concrete or high performance fiber-reinforced cementitious composite (HPFRCC) in coupling beams. Precast steel-plate reinforced coupling beams with concrete and HPFRCC (PCB-PC and PCB-PH specimen) were tested to evaluate their failure modes, shear behavior, multiple crack pattern, energy dissipation and bar strain. Based on the experimental results, the response of the coupling beam of specimen PCB-PH is deficient in shear, reaching a maximum shear force in the beam of 773.74kN, representing 140% of specimen PCB-PC. The relative deflection of specimen PCB-PH at ultimate was 16.6mm (Rotation angle=2.77%). Furthermore, PCB-PH represented multiple crack patterns the crack width was 0.4mm at rotation angle 2.0%, while specimen PCB-PC was 3.0mm at that. The results of these experiments demonstrate that it is possible to significantly improve the strength, stiffness, displacement capacity, energy absorption of shear deficient reinforced concrete coupling beams due to bridging of fibers in concrete.

고인성 시멘트 복합체를 사용한 끼움벽으로 보강된 비내진 상세 철근콘크리트 골조의 내진성능

윤현도,최창식,김선우,이갑원,이혜연 대한건축학회 2006 大韓建築學會論文集 : 構造系 Vol.22 No.5

The seismic behavior of the lightly reinforced concrete frames (LRCFs) was controlled by the nonductile behavior of the critical regions. These critical regions require retrofit to improve the seismic behavior of the lightly reinforced concrete frames. Critical column end regions must be retrofit to increase the global ductility capacity. The objective of this research is to evaluate structural strengthening performance of lightly reinforced concrete frame with high performance fiber-reinforced cement composites(HPFRCCs) experimentally. The experimental investigation consisted of a cyclic load tests on 1/3-scale models of one story-one bay lightly reinforced concrete frame infilled wall. Material ductility and web panel reinforcement details were variables in the experiment. The experimental results, as expected, show that the multiple crack pattern, strength, ductility and energy dissipation capacity are superior for specimen with HPFRCC infill wall due to bridging of fibers and stress redistribution in cement matrix.

Experimental studies on seismic behavior of steel coupling beams

윤현도,Wan-Shin Park,정재용,Yong-Chul Kim 국제구조공학회 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.20 No.6