• Title/Summary/Keyword: cracking resistance

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Study on the Utilization of Steel Fiber Reinforced Concrete for Efficient Structural Behavior in Slab System (슬래브의 효율적인 구조 거동을 위한 강섬유보강 콘크리트의 부분적 활용에 관한 실험적 연구)

  • 윤영수;데니스미첼;최응규;박성균
    • Proceedings of the Korea Concrete Institute Conference
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    • 1998.04b
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    • pp.469-474
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    • 1998
  • To overcome the common deficiencies found in two-way slabs, such as excessive cracking around columns, excessive deflections and low punching shear strength, it was proposed to investigate the strategic use of steel fiber-reinforced concrete. Providing fiber-reinforced concrete results in an increase in the punching shear resistance, a significant increase in the ductility, greater post-cracking stiffness and better crack control.

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Proposed Detailing of Reinforcement to Enhance the Structural Performance in Two-way Slab System (이방향 슬래브의 구조성능 향상을 위한 배근상세의 제안)

  • ;Denis Mitchell
    • Proceedings of the Korea Concrete Institute Conference
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    • 1998.04a
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    • pp.379-384
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    • 1998
  • To overcome the common deficiencies found in such two-way slabs, such as excessive cracking around columns, excessive deflections and low punching shear strength, it was proposed to investigate the strategic reinforcing steel distribution detailings. Concentration of the top mat of flexural reinforcement result in a higher punching shear resistance, higher post cracking stiffness, a more uniform distribution of strains in the top bars and smaller cracks at all levels of loading.

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A Study on the Mechanical Properties of HPC Pile Using Steel Fiber (강섬유를 혼입한 HPC Pile의 역학적 특성에 관한 연구)

  • 박승범;신동기;박병철;권혁준
    • Proceedings of the Korea Concrete Institute Conference
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    • 1997.04a
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    • pp.365-372
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    • 1997
  • This study is aimed for manufacturing a High performance Concrete(HPC) Pile as using steel fibers, investigation the mechanical properties of HPC Pile and proposition the potential application. At this study. We found that mechanical properties(cracking moment and fracture moment) of Pretensioned spun High strength Concrete (PHC) Pile using steel fibers is much superior to without steel fibers. Therefore. we think that using steel fibers in Concrete Pile is to progress flexural strength energy absorption capacity and post-cracking resistance.

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A study of the sulfide stress corrosion cracking characteristic of A106 Gr B steep pipe weldment (황화수소환경에서 A106 Gr-B 강 용접부의 응력부식균열 특성 평가)

  • Lee, Gyu-Young;Park, Kwang-Jin;Bae, Dong-Ho
    • Proceedings of the KSME Conference
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    • 2007.05a
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    • pp.114-119
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    • 2007
  • Sulfide stress cracking (SSC) of materials exposed to oilfield environment containing hydrogen sulfide $(H_{2}S)$ has been recognized as a materials failure problem. Laboratory data and field experience have demonstrated that extremely low concentration of $H_{2}S$ may be sufficient to lead to SSC failure of susceptible materials. In some cases, $(H_{2}S)$ can act synergistically with chlorides to produce corrosion and cracking failures. SSC is a form of hydrogen embrittlement that occurs in high strength steels and in localized hard zones in weldment of susceptible materials. In the heat-affected zones adjacent to welds, there are often very narrow hard zones combined with regions of high residual stress that may become embrittled to such an extent by dissolved atomic hydrogen. On the base of understanding on sulfide stress cracking and its mechanism, SSC resistance for the several materials, those are ASTM A106 Gr B using in the oil industries, are evaluated.

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Stress Corrosion Cracking Characteristics of Shot-peened Stainless Steel Containing Ti (Shot-peening 표면처리된 Ti 함유 스테인리스강의 응력균열부식)

  • Choe Han-Cheol
    • Journal of the Korean institute of surface engineering
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    • v.37 no.6
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    • pp.350-359
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    • 2004
  • Stress corrosion cracking(SCC) characteristics of shot-peened stainless steel containing Ti (0.09 wt%-0.92 wt%) fabricated by the vacuum furnace were investigated using SCC tester and potentiostat. The homogenization and the sensitization treatment were carried out at $1050^{\circ}C$ for 1hr and $650^{\circ}C$ for 5 hr. The samples for SCC were shot-peened using $\Phi$0.6 mm steel ball for 4 min and 10 min. Intergranular and pitting corrosion characteristics were investigated by using EPR and CPPT. SCC test was carried out at the condition of$ 288^{\circ}C$, 90 kgf pressure, water with 8 ppm dissolved oxygen, and $8.3xl0^{-7}$/s strain rate. After the corrosion and see test, the surface of the tested specimen was observed by the optical microscope, TEM and SEM. Specimen with Ti/C ratio of 6.14 showed high tensile strength at the sensitization treatment. The tensile strength decreased with the increase of the Ti/C ratio. Pitting and intergranular corrosion resistance increased with the increase of Ti/C ratio. Stress corrosion cracking strength of shot-peened specimen was higher than that of non shot- peened specimen. Stress corrosion cracking strength decreased with the increase of the Ti/C ratio.

Crack growth and cracking behavior of Alloy 600/182 and Alloy 690/152 welds in simulated PWR primary water

  • Lim, Yun Soo;Kim, Dong Jin;Kim, Sung Woo;Kim, Hong Pyo
    • Nuclear Engineering and Technology
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    • v.51 no.1
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    • pp.228-237
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    • 2019
  • The crack growth responses of as-received and as-welded Alloy 600/182 and Alloy 690/152 welds to constant loading were measured by a direct current potential drop method using compact tension specimens in primary water at $325^{\circ}C$ simulating the normal operating conditions of a nuclear power plant. The as-received Alloy 600 showed crack growth rates (CGRs) between $9.6{\times}10^{-9}mm/s$ and $3.8{\times}10^{-8}mm/s$, and the as-welded Alloy 182 had CGRs between $7.9{\times}10^{-8}mm/s$ and $7.5{\times}10^{-7}mm/s$ within the range of the applied loadings. These results indicate that Alloys 600 and 182 are susceptible to cracking. The average CGR of the as-welded Alloy 152 was found to be $2.8{\times}10^{-9}mm/s$. Therefore, Alloy 152 was proven to be highly resistant to cracking. The as-received Alloy 690 showed no crack growth even with an inhomogeneous banded microstructure. The cracking mode of Alloys 600 and 182 was an intergranular cracking; however, Alloy 152 was revealed to have a mixed (intergranular + transgranular) cracking mode. It appears that the Cr concentration and the microstructural features significantly affect the cracking resistance and the cracking behavior of Ni-base alloys in PWR primary water.

An Evaluation on the Weldability of Al-Li Alloys by Varestraint Testing Method (Varestraint Test법에 의한 Al-Li합금의 용접성 평가)

  • 김형태;이창배;신현식;서창제
    • Journal of Welding and Joining
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    • v.14 no.6
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    • pp.48-57
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    • 1996
  • The weldability of high purity aluminum-lithium binary alloys has been investigated using the Varestraint test. Autogenous GTAW (gas-tungsten-arc-welds) were run along specimens of different lithium concentration using three sets of welding parameters. Welding voltage was held constant at 10 volts. Welding current (70∼100 amps) and travel speed (23∼33 cm/min) were the parameter varied. Hot-tearing susceptibility varied with lithium content and exhibited a steep peak at 2.6 weight percent lithium. Depth of penetration increased with increasing heat input and lithium concentration. The susceptibility is influenced by the wettability of dendrites by the interdendritic eutectic liquid as well as the time available for back-Siting by eutectic liquid. The welding condition of welding current 70A and travel speed 23 cm/min was showed good resistance to cracking in aluminum-lithium alloys. Suggestions for improving weld cracking resistance are also provided.

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A Study on Laboratory Performance Characteristics of Modified Asphalt Cements and Mixtures (다양한 개질 아스팔트 시멘트와 혼합물의 실험적 공용 특성 평가에 관한 연구)

  • Kim, Nak-seok;Im, Jung-Soon;Park, Hyun-SIk;Lee, Jong-Man
    • Journal of the Society of Disaster Information
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    • v.3 no.1
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    • pp.21-35
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    • 2007
  • The principal objective of this research is to evaluate the laboratory mechanical characteristics of color asphalt binders and mixtures. The dynamic shear rheometer (DSR) tests were performed to analyze the viscous and elastic behavior of asphalt binders. Various tests were also conducted to investigate the laboratory performance characteristics of color asphalt mixtures. The test results revealed that the values of $G^*$ and ${\delta}$ of modified color binders were higher than those of the conventional binders at low temperatures. These results are expected to increase the thermal cracking resistance of asphalt mixtures at low temperatures. It should be noted that the color asphalt mixtures with modified asphalt binder can be widely used as a common pavement material with a proper mix design.

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Effects of tensile softening on the cracking resistance of FRP reinforced concrete under thermal loads

  • Panedpojaman, Pattamad;Pothisiri, Thanyawat
    • Structural Engineering and Mechanics
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    • v.36 no.4
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    • pp.447-461
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    • 2010
  • Fiber reinforced polymer (FRP) bars have been widely used as reinforcement for concrete structures. However, under elevated temperatures, the difference between the transverse coefficients of thermal expansion of FRP rebars and concrete may cause the splitting cracks of the concrete cover. As a result, the bonding of FRP-reinforced concrete may not sustain its function to transfer load between the FRP rebar and the surrounding concrete. The current study investigates the cracking resistance of FRP reinforced concrete against the thermal expansion based on a mechanical model that accounts for the tensile softening behavior of concrete. To evaluate the efficacy of the proposed model, the critical temperature increments at which the splitting failure of the concrete cover occurs and the internal crack radii estimated are compared with the results obtained from the previous studies. Simplified equations for estimating the critical temperature increments and the minimum concrete cover required to prevent concrete splitting failure for a designated temperature increment are also derived for design purpose.

Monitoring Failure Behaviour of Pultruded CFRP Composites by Electrical Resistance Measurement

  • Mao, Yaqin;Yu, Yunhua;Wu, Dezhen;Yang, Xiaoping
    • Carbon letters
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    • v.5 no.1
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    • pp.18-22
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    • 2004
  • The failure behaviours of unidirectional pultruded carbon fiber reinforced polymer (CFRP) composites were monitored by the electrical resistance measurement during tensile loading, three-point-bending, interlaminar shear loading. The tensile failure behaviour of carbon fiber tows was also investigated by the electrical resistance measurement. Infrared thermography non-destructive evaluation was performed in real time during tensile test of CFRP composites to validate the change of microdamage in the materials. Experiment results demonstrated that the CFRP composites and carbon fiber tows were damaged by different damage mechinsms during tensile loading, for the CFRP composites, mainly being in the forms of matrix damage and the debonding between matrix and fibers, while for the carbon fiber tows, mainly being in the forms of fiber fracture. The correlation between the infrared thermographs and the change in the electrical resistance could be regarded as an evidence of the damage mechanisms of the CFRP composites. During three-point-bending loading, the main damage forms were the simultaneity fracture of matrix and fibers firstly, then matrix cracking and the debonding between matrix and fiber were carried out. This results can be shown in Fig. 9(a) and (b). During interlaminar shear loading, the change in the electrical resistance was related to the damage degree of interlaminar structure. Electrical resistance measurement was more sensitive to the damage behaviour of the CFRP composites than the stress/time curve.

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