• Title, Summary, Keyword: ductility

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The Properties of Aluminium Alloy Powder for Aluminothermy Process with $Mn_3O_4$ Waste Dust ($Mn_3O_4$ 분진의 Al 테르밋 반응용 Al 합금분말의 특성)

  • Kim, Youn-Che;Song, Youn-Jun;Park, Young-Koo
    • Journal of the Korean Applied Science and Technology
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    • v.30 no.1
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    • pp.71-77
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    • 2013
  • Aluminium powder as reductant in aluminothermy process needs a fine particle size under 200 mesh, but it is not easy economically to make that because of its high ductility and powder production cost. In order to reduce the production cost of fine aluminum powder as reductant of $Mn_3O_4$ waste dust, therefore, the properties of aluminium alloy powder were investigated. Aluminium alloy ingot containing large amount of manganese can be crushed easily because of its intermetallic compounds having brittle properties. The manganese is also main element in ferro-manganese. We can obtain economically Al-15%Mn alloy powder by mechanical comminution process. And the result of thermite reaction using Al-15% Mn alloy powder instead of pure Al powder showed the fact that can be obtained the ferro-manganese which have a high purity in case of using pure aluminium powder as reductant. The recovery of manganese from $Mn_3O_4$ waste dust with Al-15%Mn alloy powder was higher level of about 70% than about 65% in case of using aluminium powder, that is due to lower spatter loss.

Evaluation of Flexural Performance of Eco-Friendly Alkali-Activated Slag Fiber Reinforced Concrete Beams Using Sodium Activator (나트륨계 알칼리 활성화제를 사용한 친환경 알카리활성 슬래그 섬유보강콘크리트 보의 휨성능 평가)

  • Ha, Gee-Joo;Yi, Dong-Ryul;Ha, Jae-Hoon
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.19 no.2
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    • pp.170-178
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    • 2015
  • In this study, it was developed eco-friendly alkali-activated slag fiber reinforced concrete using ground granulated blast furnace slag, alkali activator (water glass, sodium hydroxides), and steel fiber. Eight reinforced concrete beam using alkali-activated slag concrete were constructed and tested under monotonic loading. The major variables were mixture ratio of alkali activator, mixed/without of steel fiber. Experimental programs were carried out to improve and evaluate the flexural performance of such test specimens, such as the load-displacement, the failure mode, the maximum load carrying capacity, and ductility capacity. All the specimens were modeled in scale-down size. The reinforced concrete beams using the eco-friendly alkali-activated slag fiber reinforced concrete was failed by the flexure or flexure-shear in general. In addition, the maximum strength increased with the adding the mol of sodium hydroxide, and the specimen reinforced the steel fiber showed the value of maximum strength which is increased by 15.8% through 25.9%. It is thought that eco-friendly alkali-activated slag fiber reinforced concrete can be used with construction material and product to replace normal concrete. If there is applied to structures such as precast concrete member and production of 2nd concrete product, it could be improved the productivity and reduction of construction duration etc.

Improvement and Seismic Performance Evaluation of RC Exterior Beam-Column Joints Using Recycled Coarse Aggregate with Hybrid Fiber (순환굵은골재 치환과 하이브리드섬유 혼입에 따른 철근콘크리트 외부 보-기둥 접합부의 내진성능 평가 및 개선)

  • Ha, Jae-Hoon;Ha, Gee-Joo;Shin, Jong-Hak
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.19 no.2
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    • pp.160-169
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    • 2015
  • In this study, experimental research was carried out to improve the seismic performance of reinforced concrete exterior beam-column joint regions using replacing recycled coarse aggregate with hybrid fiber (steel fiber+PVA fiber) in existing reinforced concrete building. Therefore it was constructed and tested seven specimens retrofitting the beam-column joint regions using such retrofitting materials. Specimens, designed by retrofitting the beam-column joint regions of reinforced concrete building, were showed the stable failure mode and increase of load-carrying capacity due to the effect of crack control at the times of initial loading and bridge of retrofitting hybrid fiber during testing. Specimens BCJGPSR series, designed by the retrofitting of replacing recycled coarse aggregate with hybrid fiber in reinforecd beam-column joint regions were increased its maximum load carrying capacity by 1.01~1.04 times and its energy dissipation capacity by 1.06~1.29 times in comparison with standard specimen BCJS. Also, specimen $BCJGPSR_1$ were increased its energy dissipation capacity by 1.33~1.65 times in comparison with specimens BCJS, BCJP and BCJGPR series for a displacement ductility of 9.

Cracking Behavior and Flexural Performance of RC Beam with Strain Hardening Cement Composite and High-Strength Reinforcing Bar (고강도 철근과 변형경화형 시멘트복합체를 사용한 보의 균열거동 및 휨 성능)

  • Jang, Seok-Joon;Kang, Su-Won;Yun, Hyun-Do
    • Journal of the Korea Concrete Institute
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    • v.27 no.1
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    • pp.37-44
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    • 2015
  • This paper describes the effect of strain hardening cement composite (SHCC) material on structure performance of reinforced concrete (RC) beams with high-strength reinforcing bar. Also, this paper explores the structure application of SHCC in order to mitigation cracking damage and improve the ductility of flexural RC members. The prediction model for flexural strength of doubly reinforced SHCC beams are investigated in this study. To achieve the these objectives, a total of 6 rectangular beam specimens were tested under four point monotonic loading condition. The main parameters included the types of cement composite and reinforcing bar. Test results indicated that reinforced beam specimens with SHCC material were improved the structure performances and damage characteristics. Specifically, replacement of conventional high-strength concrete with SHCC materials has the potential of high-strength steel bar as flexural reinforcement on RC members. It is remarkable that suggested method of reinforced SHCC beams with high-strength reinforcing bar could be used usefully to the structure design.

Seismic Performance Evaluation of R/C Frame Apartment Strengthened with Kagome Truss Damper External Connection Method by Pseudo Dynamic Test (유사동적실험에 의한 외부접합형 카고메 트러스 제진장치가 설치된 RC 라멘조 공동주택의 내진성능 평가)

  • Heur, Moo-Won;Chun, Young-Soo;Hwang, Jae-Seung;Lee, Kang-Seok
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.19 no.1
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    • pp.23-34
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    • 2015
  • Recently a new damper system with Kogome truss structure was developed and its mechanical properties were verified based on the laboratory test. This paper presents a Kagome truss damper external connection method for seismic strengthening of RC frame structural system. The Kagome external connection method, proposed in this study, consisted of building structure, Kagome damper and support system. The method is capable of reducing earthquake energy on the basis of the dynamic interaction between external support and building structures using Kagome damper. The pseudo-dynamic test, designed using a existing RC frame apartment for pilot application of LH corporation, was carried out in order to verify the seismic strengthening effects of the proposed method in terms of the maximum load carrying capacity and response ductility. Test results revealed that the proposed Kagome damper method installed in RC frame enhanced conspicuously the strength and displacement capacities, and the method can resist markedly under the large scaled earthquake intensity level.

Static Behavior of Stud Shear Connector for UHPC Deck (초고성능 콘크리트 바닥판을 위한 스터드 전단연결재의 정적 거동)

  • Lee, Kyoung-Chan;Kwark, Jong-Won;Park, Sang-Hyeok;Kim, Jee-Sang
    • Journal of the Korea Concrete Institute
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    • v.26 no.5
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    • pp.573-579
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    • 2014
  • Typical composite girder has been composed with conventional concrete deck and steel girder. Recently, ultrahigh-performance-concrete (UHPC) deck is proposed in order to enhance durability and reduce weight of deck as well as to increase stiffness and strength of the composite girder. This study investigates that a headed stud is still compatible as a shear connector for the UHPC deck and steel girder composite beam. Twelve push-out specimens are prepared to evaluate the static strength of stud shear connectors embedded in the UHPC deck. The test program proves that the static strength of the stud shear connectors embedded in UHPC well meets with design codes described in AASHTO LRFD. Chosen experimental variables are aspect ratio of height to diameter of stud, thickness of deck and thickness of concrete cover over the head of stud. From the test program, aspect ratio and cover thickness are investigated to mitigate the regulations of the existing design codes. The minimum aspect ratio and the minimum cover thickness given in AASHTO LRFD are four and 50mm, respectively. This limitation hinders to lower the thickness of the UHPC deck. The results of the experiment program give that the aspect ratio and the cover thickness can be lower down to three and 25mm, respectively. Eurocode-4 regulates characteristic relative slip at least 6mm. However, test results show that stud shear connectors embedded in UHPC provide the characteristic relative slip only about 4mm. Therefore, another measures to increase ductility of stud should be prepared.

Experimental Study on the Confinement Effect of Headed Cross Tie in RC Column Subjected to Cycling Horizontal Load (철근콘크리트 기둥에서 반복횡력에 대한 헤드형 횡보강근의 구속효과에 대한 실험연구)

  • Seo, Soo Yeon;Ham, Ju Ho
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.16 no.5
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    • pp.1-10
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    • 2012
  • This paper presents an experimental result and suggests the confinement effect of headed cross tie in reinforced concrete(RC) columns subjected to cycling horizontal loads under constant axial load. Five RC columns specimens were manufactured, taking confined type of transverse reinforcement, whether or not using cross tie, end detail of cross tie (hooked or headed), and axial stress in column as major variables, Cyclic horizontal load applied to the columns under constant axial stress and the effect of cross tie to structural capacity of column was evaluated from the test. The column without cross tie failed showing bending deformation of hoop with crack in core concrete at low horizontal load while the column with cross tie showed quite improved strength and ductility by suppressing bending deformation of hoop as well as buckling of longitudinal bar at once even after crack in core concrete. At high lateral displacement, the column with hooked cross tie showed the failure pattern loosing the confining force of cross tie since the $90^{\circ}$ hooked part of cross tie was stretched out and the cracked core concrete lumps were came off. However, the column with headed cross tie showed very stable behavior since the head of cross tie effectively confined the hoop and longitudinal bars even at high lateral displacement.

A Study on Static and Fatigue Behavior of Restrained Concrete Decks without Rebar by Steel Strap (Steel Strap으로 횡구속된 무철근 바닥판의 정적 및 피로거동 특성 연구)

  • Jo, Byung Wan;Kim, Cheol Hwan
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.16 no.5
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    • pp.137-147
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    • 2012
  • In the steel-free bridge concrete deck, steel straps are generally used instead of conventional steel rebar while laterally restrained in the perpendicular direction to the traffic in order fir the arching effect of concrete deck. In this paper, the minimum amount of FRP bar is to be suggested based on the structural strength, crack propagation, stress level and others in order to control cracks. As a result of laboratory tests, the structural strength of deck with 0.15 percentage of steel strap showed improved structural strength including ductility. The long-term serviceability of steel strap deck with FRP bar proved to satisfy the requirements and to be structurally stable while showing the amount of crack and residual vertical displacement within the allowable limits after two million cyclic loadings. The structural failure of RC bridge deck is generally caused from the punching shear rather than moment. Therefore, the ultimate load at failure could be estimated using the shear strength formula in the two-way slab based on ACI and AASHTO criteria. However the design criteria tend to underestimate the shear strength since they don't consider the arching effects and nonlinear fracture in bridge deck with lateral confinement. In this paper, an equation to estimate the punching shear strength of steel strap deck is to be developed considering the actual failure geometries and effect of lateral confinement by strap while the results are verified in accordance with laboratory tests.

Enhancement of Impact Resistance of Layered Steel Fiber Reinforced High Strength Concrete Beam (층 구조를 갖는 강섬유 보강 고강도 콘크리트 보의 충격저항성능 향상)

  • Yoo, Doo-Yeol;Min, Kyung-Hwan;Lee, Jin-Young;Yoon, Young-Soo
    • Journal of the Korea Concrete Institute
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    • v.24 no.4
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    • pp.369-379
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    • 2012
  • The collapse of concrete structures by extreme loads such as impact, explosion, and blast from terrorist attacks causes severe property damage and human casualties. Concrete has excellent impact resistance to such extreme loads in comparison with other construction materials. Nevertheless, existing concrete structures designed without consideration of the impact or blast load with high strain rate are endangered by those unexpected extreme loads. In this study, to improve the impact resistance, the static and impact behaviors of concrete beams caste with steel fiber reinforced concrete (SFRC) with 0~1.5% (by volume) of 30 mm long hooked steel fibers were assessed. Test results indicated that the static and impact resistances, flexural strength, ductility, etc., were significantly increased when higher steel fiber volume fraction was applied. In the case of the layered concrete (LC) beams including greater steel fiber volume fraction in the tensile zone, the higher static and impact resistances were achieved than those of the normal steel fiber reinforced concrete beam with an equivalent steel fiber volume fraction. The impact test results were also compared with the analysis results obtained from the single degree of freedom (SDOF) system anaysis considering non-linear material behaviors of steel fiber reinforced concrete. The analysis results from SDOF system showed good agreement with the experimental maximum deflections.

Evaluation for Deformability of RC Members Failing in Bond after Flexural Yielding (휨항복 후 부착파괴하는 철근콘크리트 부재의 부착 연성 평가)

  • Choi, Han-Byeol;Lee, Jung-Yoon
    • Journal of the Korea Concrete Institute
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    • v.24 no.3
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    • pp.259-266
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    • 2012
  • A general earthquake resistant design philosophy of ductile frame buildings allows beams to form plastic hinges adjacent to beam-column connections. In order to carry out this design philosophy, the ultimate bond or shear strength of the beam should be greater than the flexural yielding force and should not degrade before reaching its required ductility. The behavior of RC members dominated by bond or shear action reveals a dramatic reduction of energy dissipation in the hysteretic response due to the severe pinching effects. In this study, a method was proposed to predict the deformability of reinforced concrete members with short-span-to-depth-ratios, which would result in bond failure after flexural yielding. Repeated or cyclic loading produces a progressive deterioration of bond that may lead to failure at lower cyclic bond stress levels. Accumulation of bond damage is caused by the propagation of micro-cracks and progressive crushing of concrete in front of the lugs. The proposed method takes into account bond deterioration due to the degradation of concrete in the post yield range. In order to verify bond deformability of the proposed method, the predicted results were compared with the experimental results of RC members reported in the technical literature. Comparisons between the observed and calculated bond deformability of the tested RC members showed reasonably good agreement.