• Title/Summary/Keyword: flexural failure

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Application of Acoustic Emission for Assessing Deterioration in Reinforced Concrete Beams (철근 콘크리트 빔의 노화도 평가를 위한 음향방출 기술의 응용)

  • Yoon, Dong-Jin;Park, Phi-Lip;Lee, Seung-Seok
    • Journal of the Korean Society for Nondestructive Testing
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    • v.20 no.4
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    • pp.276-284
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    • 2000
  • The acoustic emission (AE) behavior of reinforced concrete beams tested under flexural loading was investigated to characterize and identify the source of damage. This research was aimed at identifying the characteristic AE response associated with micro-crack development, localized crack propagation, corrosion, and debonding of the reinforcing steel. Concrete beams were prepared to isolate the damage mechanisms by using plain, notched-plain, reinforced, and corroded-reinforced specimens. The beams were tested using four-point cyclic step-loading. The AE response was analyzed to obtain key parameters such as the time history of AE events, the total number and rate of AE events, and the characteristic features of the waveform. Initial analysis of the AE signal has shown that a clear difference in the AE response is observed depending on the source of the damage. The Felicity ratio exhibited a correlation with the overall damage level, while the number of AE events during unloading can be an effective criterion to estimate the level of corrosion distress in reinforced concrete structures. Consequently, AE measurement characterization appears to provide a promising approach for estimating the level of deterioration in reinforced concrete structure.

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The Investigation of the Effects on Bent-up Bars within Beam-Column Joint Core with High-Strength Concrete (고강도 콘크리트 보-기둥접합부의 역학적 거동에 대한 연구 -구부림 철근을 중심으로-)

  • 이광수;오정근;신성우;최문식
    • Magazine of the Korea Concrete Institute
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    • v.3 no.2
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    • pp.123-132
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    • 1991
  • The purpose of this study was to Investigate the effects of bent - up bar Within beam - column 1lint core with High - Strength Concrete up to 800kg/$cm^2$. To achieve these objectives, 5 specimens were designed and tested under monotoric loading and reversed cyclic loadings. The primary variables were the number of bent-up bars, compressive strength of concrete and loading patterns. The results showed that the load capacity of specimen subjected to monotonic loading had more large than that of specirnn subjected to reversed cyclic loadings and the bent - up bar within joint core could prevented the crack at the joint face from propagating into the pint core but the failure was concentrated at the face of beam - column pint. Thus the study on flexural strength ratio should be accomplished before using bent - up bars within the joint core.

An Indeterminate Strut-Tie Model and Load Distribution Ratio for Reinforced Concrete Corbels (철근콘크리트 코벨의 부정정 스트럿-타이 모델 및 하중분배율)

  • Chae, Hyun Soo;Yun, Young Mook
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.34 no.4
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    • pp.1065-1079
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    • 2014
  • The ultimate behavior of reinforced concrete corbel is complicated due to the primary design variables including the shear span-to-effective depth ratio a/d, flexural reinforcement ratio, load condition, and material properties. In this study, a simple indeterminate strut-tie model reflecting all characteristics of the ultimate strength and complicated structural behavior is proposed for the design of the reinforced concrete corbels with shear span-to-effective depth ratio of $a/d{\leq}1$. A load distribution ratio, defined as the fraction of applied load transferred by horizontal truss mechanism, is also proposed to help structural designers perform the design of reinforced concrete corbels by using the strut-tie model approaches of current design codes. For the development of the load distribution ratio, numerous material nonlinear finite element analyses of the proposed indeterminate strut-tie model were conducted by changing primary design variables. The ultimate strengths of reinforced concrete corbels tested to failure were evaluated by incorporating the proposed strut-tie model and load distribution ratio into the ACI 318-11's strut-tie model method. The validity of the proposed model and load distribution ratio was examined by comparing the strength analysis results with those by the ACI 318-11's conventional design method and strut-tie model methods of current design codes.

Quantitative Damage Evaluation of Fiber-Reinforced Cement Composite Using Acoustic Emission Technique (음향방출 기법을 이용한 섬유보강 시멘트 복합체의 정량적 손상평가)

  • Lee, Young-Oh;Yun, Yeo-Jin;Yun, Hyun-Do
    • Journal of the Korea Concrete Institute
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    • v.21 no.4
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    • pp.457-464
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    • 2009
  • Fiber is an important ingredient in fiber-reinforced cement composite (FRCC) which can control fracture of cement composite by bridging action. In compliance with the action of the fiber and the aggregate size, it also showed a different failure mechanism. For practical application, it is needed to investigate the fracture behavior of the FRCC and to understand the micro-mechanism of cement matrix with reinforcing fiber. In order to evaluate a characteristics of fracture process in the FRCC, acoustic emission (AE) technique was used for the analysis and evaluation of FRCC damage by acoustic emission under flexural and cyclic compressive loadings. The AE signals were monitored by AMSY4 AE instrument during the entire loading period. The specimens are reinforced with 0, 1.0, 1.5 and 2.0% (by volume) Polyvinyl alcohol (PVA) fiber. The test results showed that the damage progress of the FRCC was characteristic for the fiber replacement ratio. As a result of analyzing the felicity ratio (FR) values, it is shown that this values can be used for evaluating the degree of FRCC damage. On the whole the felicity ratio values of FRCC are shown between 0.4 and 1.1. And, the AE kaiser effect was shown in the all FRCC specimen. In addition, the damage behavior and the microscopic fracture process of the FRCC are evaluated using the AE parameters, such as calm ratio, b-value and felicity ratio. The purpose of this reserch was to advance the state of knowledge regarding the applicability of acoustic emission as an evaluation method for FRCC.

Mechanical Characteristics of Recycled PET Polymer Concrete with Demolished Concrete Aggregates (PET와 재생골재를 이용한 폴리머콘크리트의 역학적 특성)

  • Jo Byung-Wan;Lee Du-Wha;Park Seung-Kook
    • Journal of the Korea Concrete Institute
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    • v.17 no.3 s.87
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    • pp.335-342
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    • 2005
  • In this paper, fundamental properties of Polymer Concrete(PC), made from unsaturated polyester resin based on recycled PET and recycled aggregate were investigated. Mechanical properties include strength, modulus of elasticity, and chemical resistance. Resins based on recycled PET and recycled aggregate offer the possibility of low source cost for forming useful products, and would also help alleviate an environmental problem and save energy. The results of test for resin contents and recycled aggregate ratio we, first, the strength of Polymer Concrete made with resin based on recycled PET and recycled aggregate increases with resin contents relatively, however beyond a certain resin contents the strength does not change appreciably, Second, the relationship between the compressive strength and recycled aggregate ratio at resin $9\%$ has a close correlation linearly whereas there is no correlation between the compressive strength and the flexural strength of RPC with recycled aggregate ratio. Third, the effect of acid resistance at resin $9\%$ was found to be nearly unaffected by HCI, whereas the PC with $100\%$ recycled aggregate showed poor acid resistance. Unlike acid, alkali nearly does not seem to attack the RPC as is evident from the weight change and compressive strength. And last, In case of stress-strain curve of polymer concrete with $100\%$ of natural aggregate and $100\%$ recycled aggregate it is observed the exceptional behavior resulting in different failure mechanisms of the material under compression.

An Experimental Study on Bond Strength of High-Strength Reinforcing Bars with High Relative Rib Area (높은 마디면적 고강도 철근의 부착강도에 관한 실험적 연구)

  • Hong Geon-Ho;Choi Dong-Uk;Choi Oan-Chul;Hong Gi-Suop
    • Journal of the Korea Concrete Institute
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    • v.17 no.3 s.87
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    • pp.375-384
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    • 2005
  • The effects of bar deformation properties on bond of steel reinforcing bars to concrete are experimentally studied to predict the bond strength. Based on the previous research about high relative rib area, bond strength between reinforcing bars and concrete can be improved by the control of rib height and spacing. But, the equations in Korean code provisions to estimate development and splice length do not include these specifications of reinforcing bars. So the purpose of this paper is to determine the effect of relative rib area to the bond strength. This paper describes 2 kinds of experimental researches. Thirty beam-end specimens were tested to investigate the effects of bar size and relative rib areas ranging from 0.112 to 0.162. And, twelve lap-splice beam specimens were tested to the same variables. Each test results are normalized and compared with the proposed equations of ACI 408 committee. The results show that bond strength is increased as bar size and the relative rib area(Rr) increase. The distribution of flexural cracks and failure aspect do not appear to be affected by $R_r$.

Ebaluation of Ultimate Stress of Unbonded Tendon in Prestressed Concrete Members(I)-Considereateon of ACI code and the State-of -the Art- (프리스트레스트 콘크리트 부재에서 비부착 긴장재의 극한응력 평가에 관한 연구(I)-기존연구 및 ACI 규준식의 고찰-)

  • 임재형;문정호;음성우;이리형
    • Magazine of the Korea Concrete Institute
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    • v.9 no.4
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    • pp.167-176
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    • 1997
  • The current study is a part of series of research about the evaluation method of the unbonded tendon stress in prestressed concrete member at flexural failure. As the first part. previous design equations were examined in oder to find whether any modifications may be needed. A total of 167 experimental results tested for more than 40 years were gathered to build D/B and then previous proposed and codified equations were evaluated with the experimental relsults. The ACI Code equation and Naaman, Harajli, and Chakrabarti's equations were chosen for the purpose of examination. Then, the followings were obtained from the analytical examination. It is desirable to compute the tendon stress with the member analysis method instead of the sectional analysis method which has been used in the current ACI Code. The tendon stress may also be influenced significantly by the amount of ordinary bonded reinforcements and the loading types. And the current ACI Code overestimated the effect of span/depth ratio. As results, it was concluded that the revision of the ACi Code equation should be considered positively. Then, a new design has to be proposed with the reasonable and comprehensive investigation about influential factors on the tendon stress variation.

Fracture Strength of All-Ceramic 3-Unit Fixed Partial Dentures Manufactured by CAD/CAM and Copy-Milling Systems (CAD/CAM 및 카피밀링 시스템을 이용하여 제작한 구치부 3-유닛 고정성 국소의치의 파절강도)

  • Kang, Hoo-Won;Kim, Hee-Jin;Kim, Jang-Ju;Ko, Myung-Won
    • Journal of Technologic Dentistry
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    • v.34 no.2
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    • pp.95-103
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    • 2012
  • Purpose: Fracture strength of all-ceramic 3-unit fixed partial dentures manufactured by CAD/CAM and copy-milling systems were evaluated. Methods: Zirconia cores were made by milling the pre-sintered zirconia block by CAD/CAM or copy milling method followed by subsequent sintering. By building-up the corresponding porcelains on the core, all-ceramic bridges were fabricated, and those were evaluated in comparison with PFM fixed partial denture. Results: During the flexural test of the 3-unit PFM bridge, the porcelain started to chip or break at 507.28(${\pm}62.82$)kgf and the metal framework did not break until the maximum load level of 800kgf which was set in the testing instrument of this study. However, among all-ceramic restoration test groups, Everest(EV) group showed a peeling off or breakage of the porcelain from 365.64(${\pm}64.96$)kgf and the core was broken at 491.77(${\pm}55.62$)kgf. Those values of Zirkonzahn(ZR) were 431.03(${\pm}58.47$)kgf and 602.74(${\pm}48.44$)kgf, respectively. The break strength of the porcelain of PFM(PM) group was significantly higher than that of EV (p<0.05) group and there was no significant difference when comparing to that of ZR (p>0.05). ZR group showed higher break strength than that of EV group however there was no significant difference (p>0.05). The break strength of cores were in the increasing order of EV < ZR < PM (p<0.05). Conclusion: We could find that even though the PM group fractured at much higher value than all-ceramic cores, the breakage values of the porcelain of PM group with crack formation or delamination, which will be regarded as clinical failure, was significantly higher than that of EV group and not significantly higher than that of ZR group at p-values of 0.05. The break strength of ZR group was higher than that of EV group at an insignificant level(p>0.05).

Comparison of Mechanical and Interfacial Properties on Chemical Structures of Acrylic and Epoxy Adhesives (아크릴 및 에폭시 접착제의 화학적 구조에 따른 유리섬유 복합재료의 기계적 및 계면 물성 변화 평가)

  • Shin, Pyeong-Su;Kim, Jong-Hyun;Choi, Jin-Yeong;Kwon, Dong-Jun;Lee, Sang-Il;Park, Joung-Man
    • Composites Research
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    • v.29 no.2
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    • pp.79-84
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    • 2016
  • An adhesive can be used to connect two different materials in structures. In comparing with other connecting methods, such as bolt, rivet, and hot melting, the adhesive does not need to use them. It leads to reduce the weight and decrease the stress concentration along the connecting line. This work studied the comparison of mechanical and interfacial properties of commonly-used two adhesives, acrylic type and bisphenol-A epoxy type. Tensile and flexural strength of neat adhesives were also compared. Lap shear test of two adhesives was deduced from the measurement of tensile and fatigue tests. After testing, the failure patterns of adhesive surfaces were observed by a microscope. Tensile strength and mechanical fatigue resistance at using bisphenol-A epoxy adhesive were better than acrylic adhesive. Also adding CNT reinforcement in epoxy adhesive can anticipate mechanical improvement.

An Experimental Study on the Shear Behavior of Reinforced Concrete Beams Strengthened by Slit Type Steel Plates with Anchor Bolt (앵커볼트 체결 Slit형 강판 보강 RC보의 전단거동에 관한 실험적 연구)

  • Lee, Choon-Ho;Jeong, Woo-Dong;Shim, Jong-Seok
    • Journal of the Korea Concrete Institute
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    • v.22 no.5
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    • pp.703-710
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    • 2010
  • Reinforced concrete beams of existing structure often encounter insufficient shear problems for various reasons. Application of steel plates is one of widely used methods for shear strengthening of reinforced concrete beams that are insufficient of shear capacity. This study presents test results on strengthening shear deficient RC beams by external bonding of vertical and diagonal slit type steel plates with anchor bolt. Test parameters are width, interval, angle and length of slits with anchor bolt. The purpose was to evaluate the failure modes and shear capacities for RC beams strengthened by various slit type steel plates with anchor bolt. The results showed that the slit type steel plate specimens strengthened by adhesive bonding and bolting failed in shear fracture modes at maximum load. Flexural crack first occurred on the tension face of beam and then inclined cracks occurred on the shear span. Finally, slit type steel plates strengthened by adhesive bonding and fastening bolts managed to delay abrupt debonding and didn't detach fully from main body of RC beam.