• Title/Summary/Keyword: flexural fracture behavior

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Analytical investigation of the cyclic behaviour of I-shaped steel beam with reinforced web using bonded CFRP

  • Mohabeddine, Anis I.;Eshaghi, Cyrus;Correia, Jose A.F.O.;Castro, Jose M.
    • Steel and Composite Structures
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    • v.43 no.4
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    • pp.447-456
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    • 2022
  • Recent experimental studies showed that deep steel I-shaped profiles classified as high ductility class sections in seismic design international codes exhibit low deformation capacity when subjected to cyclic loading. This paper presents an innovative retrofit solution to increase the rotation capacity of beams using bonded carbon fiber reinforced polymers (CFRP) patches validated with advanced finite element analysis. This investigation focuses on the flexural cyclic behaviour of I-shaped hot rolled steel deep section used as beams in moment-resisting frames (MRF) retrofitted with CFRP patches on the web. The main goal of this CFRP reinforcement is to increase the rotation capacity of the member without increasing the overstrength in order to avoid compromising the strong column-weak beam condition in MRF. A finite element model that simulates the cyclic plasticity behavior of the steel and the damage in the adhesive layer is developed. The damage is modelled using the cohesive zone modelling (CZM) technique that is able to capture the crack initiation and propagation. Details on the modelling techniques including the mesh sensitivity near the fracture zone are presented. The effectiveness of the retrofit solution depends strongly on the selection of the appropriate adhesive. Different adhesive types are investigated where the CZM parameters are calibrated from high fidelity fracture mechanics tests that are thoroughly validated in the literature. This includes a rigid adhesive commonly found in the construction industry and two tough adhesives used in the automotive industry. The results revealed that the CFRP patch can increase the rotation capacity of a steel member considerably when using tough adhesives.

A Numerical Study on the Behavior of Steel Fiber Reinforced Shotcrete in Consideration of Flexural Toughness (휨인성을 고려한 강섬유보강 숏크리트 거동의 수치해석적 연구)

  • Cho, Byoung-Ouk;You, Kwang-Ho;Kim, Su-Man;Lim, Doo-Chul;Lee, Sang-Don;Park, Yeon-Jun
    • Tunnel and Underground Space
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    • v.17 no.5
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    • pp.411-427
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    • 2007
  • Reliability in tunnel analysis is necessary to accomplish technically sound design and economical construction. For this, a thorough understanding of the construction procedure including the ground-support interaction has to be obtained. This paper describes a proper modelling technique to simulate the behavior of the steel fiber reinforced shotcrete (SFRS) which maintain the supporting capability in post-failure regime. The additional supporting effect of the steel support was also verified by 3-D analyses and a new load distribution factor were proposed. The use of the plastic moment limit (PML) alone can eliminate the occurrence of the awkwardly high tensile stress in the shotcrete and can successfully model the post-peak ductile behavior of the SFRS. But with this method, moment is limited whenever the stress caused by moment reaches tensile strength of the shotcrete irrespective of the stress by axial force. Therefore, it was necessary to find a more comprehensive method which can reflect the influence of the moment and axial force. This can be accomplished by the proper use of "liner element" which is the built-in model in FLAC. In this model, the peak and residual strength as well as the uniaxial compressive strength of the SFRS can be specified. Analyses were conducted with these two models on the 2-lane road tunnels excavated in class IV and V rock mass and results were compared with the conventional elastic beam model. Results showed that both models can reflect the fracture toughness of the SFRS which could not be accomplished by the elastic beam model.

A Study on Shear-Fatigue Behavior of Reinforced Concrete Beams using High Strength Concrete (고강도 콘크리트를 사용한 철근콘크리트 보의 전단피로거동에 관한 연구)

  • 곽계환;박종건
    • Journal of the Korea Concrete Institute
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    • v.11 no.5
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    • pp.119-130
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    • 1999
  • Recently, as the building structure has been larger, higher, longer and more specialized, the demand of material with high-strength concrete for building has been increasing. In this research, silica-fume was used as an admixture in order to get a high-strength concrete. From the test result, High-strength concrete with cylinder strength of 1,200kgf/$\textrm{cm}^2$ in 28-days was produced and tested. The static test was carried out to measure the ultimate load, the initial load of flexural and diagonal cracking, crack patterns and fracture modes. The load versus strain and load versus deflection relations were obtained from the static test. The relation of cycle loading to deflections on the mid-span, the crack propagation and the modes of failure according to cycle number, fatigue life and S-N curve were observed through the fatigue test. Based on the fatigue test results, high-strength reinforced concrete beams failed to 57~66 percent of the static ultimate strength. Fatigue strength about two million cycles from S-N curves was certified by 60 percent of static ultimate strength.

Structural Performance of Flexural Dominant Reinforced Concrete Beams strengthened in Beam-Column Joint with SHCC (변형경화형 시멘트 복합체(SHCC)로 보-기둥 접합부 단면이 증설된 휨항복형 철근콘크리트 보의 구조성능)

  • Song, Seon-Hwa;Jang, Gwang-Soo;Kim, Yun-Su;Kim, Sun-Woo;Kim, Yong-Cheol;Yun, Hyun-Do
    • Proceedings of the Korea Concrete Institute Conference
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    • 2008.11a
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    • pp.53-56
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    • 2008
  • Reinforced concrete rahmen structures has been required ductility as well as strength of beam-column joint in seismically hazard area. Some investigations have been presented for retrofitting and/or strengthening structural elements in structure. Strain-hardening cementitious composite(SHCC) has been expected excellent reinforcement performance in beam-column joint area. The properties of reinforcing fiber, as tensile strength, aspect ratio and elastic moudulus, have great effect on the fracture behavior of SHCC. The purpose of this experimental study is to evaluate structural performance of exterior reinforced concrete beam-column joint strengthened with SHCC under cyclic loading.

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Effect of Starting Crystallographic Phase on the Mechanical Properties of Hot-Pressed SiC Ceramics (초기분말의 결정상이 $Al_2O_3$를 소결 조제로한 고온가압 SiC 세라믹스의 기계적 특성에 미치는 영향)

  • 정동익;강을손;최원봉;백용기
    • Journal of the Korean Ceramic Society
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    • v.29 no.3
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    • pp.232-240
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    • 1992
  • Densification behavior, microstructural evolution, and mechanical properties of hot-pressed specimens using $\beta$-SiC and $\alpha$-SiC powder with Al2O3 additive were studied. Beta-SiC powder was fully densified as 205$0^{\circ}C$, but $\alpha$-SiC powder was at 210$0^{\circ}C$. The maximum flexural strength and the fracture toughness of the specimen hot-pressed using $\beta$-SiC powder were 681 MPa and 6.7 MPa{{{{ SQRT {m } }}, and thosevalues of specimen hot-pressed using $\alpha$-SiC powder were 452 MPa and 4.7 MPa{{{{ SQRT {m } }}, respectively. The strength superiority of specimen hot-pressed using $\beta$-SiC powder was due to the finer grain size, and higher density. The higher toughness of specimen hot-pressed using $\beta$-SiC powder than $\alpha$-SiC powder than $\alpha$-SiC powder was due to the crack deflection mechanism arised from the difference of thermal expansion coefficient between $\alpha$ and $\beta$-SiC phases which were co-existed in the sintered body.

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A Study on Shear-Fatigue Behavior of New Polymer Reinforced Concrete Beams (신(新)폴리머 철근(鐵筋)콘크리트보의 전단피로(剪斷疲勞) 거동(擧動)에 관(關)한 연구(研究))

  • Kwak, Kae Hwan;Park, Jong Gun;Jang, Ki Woong
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.13 no.3
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    • pp.35-44
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    • 1993
  • The objective of this study is aimed at developing a new class of polymer concrete, in which hydration of cement and curing of a thermosetting resin can take place simultaneously during the mixing of concrete components. For the selected mix-proportion of the new polymer, the physical and mechanical properties needed for designs are presented. These important properties are compressive strength, flexural strength, split tensile strength, direct strength, fatigue characteristics and fracture parameters. The observed properties are always compared with conventional concrete to serve as reference for engineer in deciding or selecting the proper materials for their projects, and shore protecting structure.

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Assessment of flexural performance of hybrid fiber reinforced concrete. (하이브리드 섬유보강 콘크리트의 휨성능 평가)

  • Kim, Hag-Youn;Kim, Nam-Ho;Park, Choon-Gun
    • Proceedings of the Korea Concrete Institute Conference
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    • 2005.05b
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    • pp.337-340
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    • 2005
  • In this study, an effect of fiber blending on material property of Hybrid Fiber Reinforced Concrete (HFRC) was evaluated. Also, Compare and evaluates collating and mechanical property by the mixing rate of fiber for HFRC was determine. Modulus of rupture and strength effectiveness of Hybrid Fiber Reinforced Concrete mixed with macro-fiber(steel fiber) and micro-fiber(glass fiber, carbon fiber, cellulose fiber). Test result shows, in the case of mono fiber reinforced concrete. As the steel fiber mixing rate increases to 1.5$\%$, the strength effectiveness promotion rate rises. However, when is 2.0$\%$, strength decreases. In the case of hybrid fiber reinforcement concrete, synergy effect of micro fiber and macro fiber happens and higher Modulus of rupture and strength effectiveness appears than mono-fiber reinforcement concrete. Use of hybrid fiber reinforcement in concrete caused a significant influence on its fracture behavior; consequently, caused increase by mixing rate of steel fiber + carbon fiber and contributed by steel fiber + glass fiber, steel fiber + celluloid fiber in reinforcement effect in order. And was expose that steel fiber(1.5$\%$) + carbon fiber(0.5$\%$) is most suitable association.

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Mechanical Properties and Impact Resistance Review of Carbon Fiber Reinforced Cement Composites with Different Fiber Contents and Fiber Lengths (섬유혼입률 및 섬유길이 변화에 따른 탄소섬유 보강시멘트 복합재료의 역학적 특성과 내충격성 검토)

  • Heo, Gwang-Hee;Song, Ki-Chang;Park, Jong-Gun;Han, Yoon-Jung;Lim, Cae-Young
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.23 no.4
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    • pp.86-95
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    • 2019
  • Recently, the applications of carbon fiber have been broader than ever when it comes to such industrials as automobiles, ships, aerospace, civil engineering and architecture because of their lightweight-ness and high mechanical properties. This study analyzed mechanical properties and flexural behavior of carbon fiber reinforced cement composites(CFRC) with different fiber contents and fiber lengths, and also impact resistance by natural drop test on mortar specimens was compared and examined. In addition, contents of carbon fiber(CF) were varied by 0.5%, 1.0%, 2.0% and 3.0%. Fiber lengths was used for 6 mm and 12 mm, respectively. As a result of the test, the flow value was very disadvantageous in terms of fluidity due to the carbon fiber ball phenomenon, and the unit weight was slightly reduced. In particular, the compressive strength was decreased with increasing carbon fiber contents. On the other hand, the flexural strength was the highest with 12 mm fiber length and 2% fiber content. As the results of the impact resistance test, the specimens of plain mortar takes about 2~3 times to final fracture, while the specimens of CFRC is somewhat different depending on the increase of the fiber contents. However, when the fiber length is 12 mm and the fiber content is 2%, the impact resistance was the highest.

Evaluation of Strengthening Performance of Stiff Type Polyurea Retrofitted RC Slab Based on Attachment Procedure (경질형 폴리우레아의 개발 및 보강 순서에 따른 RC 슬래브의 성능 평가)

  • Kim, Jang-Ho Jay;Park, Jeong-Cheon;Lee, Sang-Won;Kim, Sung-Bae
    • Journal of the Korea Concrete Institute
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    • v.23 no.4
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    • pp.511-520
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    • 2011
  • Recent studies to improve reinforcement of structures have developed stiff type Polyurea by using highly polymized compound Polyurea, but the reinforcing effect of it appears to be merely good. To find the proper usage of Polyurea as structural reinforcement, stiff type Polyurea has developed by manipulating the ratio of the components that consist flexural type Polyurea and the developed stiff type Polyurea shows higher hardness and tensile capacity. The reinforcement effect evaluation of has been performed by the polyurea applied RC slab specimens, and the reinforcement effect of the combination of fiber sheet and polyurea has been tested. The results shows that the Polyurea applied specimens have significant improvement on hardness and ductility compare to those of unreinforced. Also, the specimens that stiff type Polyurea is sprayed on fiber sheet reinforcement has higher reinforcing effect than only sheet reinforced specimens. However, the specimens that and fiber sheet attached after polyurea applied on showed that the high toughness of fiber sheet restrains the ductile behavior of Polyurea due to the high ductility, thereby the specimen suffers the concentration of load, which leads the brittle fracture behavior.

Mechanical behavior and microstructural characterization of different zirconia polycrystals in different thicknesses

  • Arcila, Laura Viviana Calvache;Ramos, Nathalia de Carvalho;Campos, Tiago Moreira Bastos;Dapieve, Kiara Serafini;Valandro, Luiz Felipe;de Melo, Renata Marques;Bottino, Marco Antonio
    • The Journal of Advanced Prosthodontics
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    • v.13 no.6
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    • pp.385-395
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    • 2021
  • PURPOSE. To characterize the microstructure of three yttria partially stabilized zirconia ceramics and to compare their hardness, indentation fracture resistance (IFR), biaxial flexural strength (BFS), and fatigue flexural strength. MATERIALS AND METHODS. Disc-shaped specimens were obtained from 3Y-TZP (Vita YZ HT), 4Y-PSZ (Vita YZ ST) and 5Y-PSZ (Vita YZ XT), following the ISO 6872/2015 guidelines for BFS testing (final dimensions of 12 mm in diameter, 0.7 and 1.2 ± 0.1 mm in thicknesses). Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were performed, and mechanical properties were assessed by Vickers hardness, IFR, quasi-static BFS and fatigue tests. RESULTS. All ceramics showed similar chemical compositions, but mainly differed in the amount of yttria, which was higher as the amount of cubic phase in the diffractogram (5Y-PSZ > 4Y-PSZ > 3Y-TZP). The 4Y- and 5Y-PSZ specimens showed surface defects under SEM, while 3Y-TZP exhibited greater grain uniformity on the surface. 5Y-PSZ and 3Y-TZP presented the highest hardness values, while 3Y-TZP was higher than 4Y- and 5Y-PSZ with regard to the IFR. The 5Y-PSZ specimen (0.7 and 1.2 mm) showed the worst mechanical performance (fatigue BFS and cycles until failure), while 3Y-TZP and 4Y-PSZ presented statistically similar values, higher than 5Y-PSZ for both thicknesses (0.7 and 1.2 mm). Moreover, 3Y-TZP showed the highest (1.2 mm group) and the lowest (0.7 mm group) degradation percentage, and 5Y-PSZ had higher strength degradation than 4Y-PSZ group. CONCLUSION. Despite the microstructural differences, 4Y-PSZ and 3Y-TZP had similar fatigue behavior regardless of thickness. 5Y-PSZ had the lowest mechanical performance.