A tension stiffening model for analysis of RC flexural members under service load

K. A. Patel,Sandeep Chaudhary,A.K. Nagpal 사단법인 한국계산역학회 2016 Computers and Concrete, An International Journal Vol.17 No.1

Tension-stiffening is the contribution of concrete between the cracks to carry tensile stresses after cracking in Reinforced Concrete (RC) members. In this paper, a tension-stiffening model has been proposed for computationally efficient nonlinear analysis of RC flexural members subjected to service load. The proposed model has been embedded in a typical cracked span length beam element. The element is visualized to consist of at the most five zones (cracked or uncracked). Closed form expressions for flexibility and stiffness coefficients and end displacements have been obtained for the cracked span length beam element. Further, for use in everyday design, a hybrid analytical-numerical procedure has been developed for nonlinear analysis of RC flexural members using the proposed tension-stiffening model. The procedure yields deflections as well as redistributed bending moments. The proposed model (and developed procedure) has been validated by the comparison with experimental results reported elsewhere and also by comparison with the Finite Element Method (FEM) results. The procedure would lead to drastic reduction in computational time in case of large RC structures.

피복두께와 강섬유 혼입률에 따른 초고성능 콘크리트의 균열거동과 인장증강효과

주조린,이문석,손동희,최창식,최현기,배백일 대한건축학회 2024 대한건축학회논문집 Vol.40 No.1

본 연구에서는 초고성능 콘크리트와 철근의 직접인장시험을 수행하였다. 주요 변수는 강섬유 혼입률과 피복두께이다. 실험 결과는 하중-변형률 관계, 콘크리트의 인장강도, 평균 균열 간격 및 최대 균열 폭에 대해 분석하였다. 강섬유 혼입률이 증가하고 피복두께가 두꺼워질수록 콘크리트의 인장력에 대한 저항력이 현저히 향상되어 인장강화 효과가 향상되었다. 또한, 실험체의 균열 형성 단계와 안정화된 균열 단계에서의 균열 거동을 확인하였을때 향상된 균열 제어 성능을 보여주었다. 균열 형성 단계가 완료된 후 강섬유가 혼입되지 않은 콘크리트는 더 이상 추가적인 인장력을 저항할 수 없어 추가적인 미세균열이 발생하지 않았다. 그러나 초고성능 콘크리트는 균열형성단계 이후 강섬유의 가교작용에 의해 균열을 제어하여 인장증강효과가 향상되었다. This study involved conducting material tests on ultra-high-performance concrete through direct tensile tests. The key variables examined werethe volume fraction of steel fiber and the cover thickness. This analysis focused on load-strain relationships, concrete tensile strength, averagecrack spacing, and maximum crack width. The results reveal that as the volume fraction of steel fiber increases and the cover thicknessbecomes greater, the concrete's ability to withstand tensile forces significantly improves, resulting in a more robust tension-stiffening effect. Furthermore, the crack behavior during the crack formation stage and stabilized cracking stage indicates improved crack control performance. After the initial crack formation stage, the concrete appears to no longer control additional tensile forces and cracks, with the primaryresponsibility for crack control shifting to the steel fibers. This transition enhances the tension-stiffening effect by bridging actions of thesteel fibers after the initial crack formation stage.

CSA 팽창재를 혼입한 철근보강 모르타르의 인장 경화-연화 특성에 관한 실험적 연구

최세진,안중길,박기태,권성준 한국구조물진단유지관리공학회 2014 한국구조물진단유지관리공학회 논문집 Vol.18 No.1

팽창재는 콘크리트의 건조/자기수축으로 인한 균열에 매우 효과적인 혼화재료이며 콘크리트 내부 철근에 화학적 프리스트레스를 인가할수 있다. 본 논문에서는 CSA 팽창재에 의해 화학적 프리스트레스가 도입된 모르타르의 인장경화성능을 평가하였다. 철근으로 내부구속이이루어진 철근 모르타르 시편에 대하여 일축인장시험을 수행하였으며, 균열거동 특성과 인장경화 특성을 분석하였다. CSA 모르타르에서는 압축강도 및 탄성계수는 약간 감소하였으나, 화학적 압축응력이 철근에 도입되었으며, 일반 모르타르 부재에 비해 167.5% 초기균열하중이증가하였다. 높은 인장경화특성을 평가하였으며, 기존의 인장연화모델과 실험값을 비교하여 기존 제안식의 보완점을 제시하였다. Expansion agent is a very effective admixture for prevention of cracking due to autogenous/drying shrinkage and this can induce internal chemical prestress to embedded reinforcement. In this paper, tension-softening and hardening in cement mortar with steel and CSA expansion agent are experimentally evaluated. Cement mortar with steel reinforcement is prepared and tensile strength testis performed for evaluation of cracking and tensile behavior. In spite of slightly reduced strength and elasticity in CSA mortar, significantly increased tension-hardening behavior is evaluated in CSA mortar with induced chemical prestress. Furthermore previous tension softening models are compared with the test results and improvement are proposed.

냉간 박판압연공정에서 공정변수가 엣지 크랙 성장에 미치는 영향

CUIXIANGZI(X. Z. Cui),이상호(S. H. Lee),이성진(S. J. Lee),이종빈(J. B. Lee),김병민(B. M. Kim) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5

Edge cracks in cold rolling always influence to the quality of productions, while the “V” shaped cracks were propagated by passing the roll gap. We set up the sizes and shapes of initial cracks in simulation according to the references form real productions. Different to in hot rolling, the cracks in cold rolling couldn’t be reduced from propagation automatically after generate, even if these could be reduced by changing the process parameters. In this paper, we described the affections of process parameters on the propagation of edge cracks, such as reduction ration and tension. We predicted that the dependence of the cracks propagations of changing of process conditions and expected to gain the smaller edge cracks. By raising the reduction ratio, the cracks were propagated increasingly in both transverse and rolling directions. And as tension raise, the cracks became propagated in both directions in which transverse direction was less effectively.

A study on fracture behavior due to crack propagation at compact tension specimen composed of inhomogeneous metal materials with holes near crack

최계광,이정호,조재웅 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.10

This paper aims at studying on the fracture behavior due to crack propagation at compact tension specimen composed of inhomogeneous metal materials with holes near main crack. In this study, the experiments were performed for compact tension specimens produced by the mutual bonding metals of stainless steel and brass, and the simulation analyses to verify these experiments were conducted. When the preceding study results are confirmed, the design of structures with no holes near a crack becomes more durable on the strength aspect than the design of structures with holes existing near the crack. The design for highest strength is possible if no holes are pierced in inhomogeneous metal materials bonded with adhesives. On the other hand, in case the holes due to additional bolt and rivet fastening must be pierced, the most similar tendency to that of materials without holes is exhibited when the hole center is placed by about 20 mm from the crack tip. A great difference in strength occurs according to the hole position near the main crack at inhomogeneous metal materials bonded with adhesives. So, the design considering this aspect is deemed important. The data for different positions where the crack propagations occur can be confirmed at analysis and experimental results. Therefore, the changes inside the material that are actually difficult to confirm due to the crack growth characteristics at inhomogeneous materials can be expected through an analysis. The fracture behavior of inhomogeneous metal materials bonded by adhesives was investigated through the experiment and analysis. The basic data through this study could be secured at contributing to the developed design of light-weight composite materials as well as bonding the technology for mutually different materials.

변형 경화형 시멘트 복합체의 인장강성 특성

윤현도(Yun Hyun-Do),김선우(Kim Sun-Woo),이민정(Lee Min-Jung) 대한건축학회 2007 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.27 No.1

The cracking behavior and tension stiffening characteristics of normal concrete, strain-hardening cement composites (SHCCs) tension ties under short term imposed load was investigated experimentally. The purpose of this research was to investigate the influence of cement composite damage tolerance on the tension stiffening performance and cracking process of reinforced SHCC tension ties. The effect of loading scheme (monotonic and repeated loading) was also investigated. Testing was carried out on six axially loaded tension tie specimens. Each specimen had a square cross-section dimension of 110 × 110㎜ and length of 500㎜. Improved tension stiffening performance in SHCC contributes to reduced crack widths, i.e., multiple cracking.

Fracture Toughness Estimates Based on Crack Opening Displacement for Circumferential Through-Wall Cracked Pipes under Combined Tension and Bending

김윤재(Yun-Jae Kim),허남수(Nam-Su Huh),김영진(Young-Jin Kim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5

In order to apply the Leak-Before-Break (LBB) concept to nuclear piping, accurate fracture mechanics assessment on pipes with postulated circumferential through-wall crack subject to complex loading, such as combined tension and bending is crucial. In this case, one important element is determination of relevant J-resistance curve for pipes under combined loading. In this respect, this paper provides experimental J estimation method for the circumferential through-wall cracked pipe under combined tension and four-point bending, based on the load-crack opening displacement (COD) record to estimate J-resistance curve. To give confidence in the proposed method, the J results from detailed elastic-plastic finite element (FE) analysis are also compared with estimated J based not only on proposed method but also on conventional method using load-load line displacement, which shows that estimated J based on the proposed method provides reliable J estimates regardless of analysis condition, on the other hand, the conventional method using the load-load line displacement record gives erroneous results for shallow cracks.

Co-seismic Landscape Response to the 2015-Gorkha Earthquake and Their Post Modifications

( Dandapani Adhikari ),( Krishna Devkota ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2

On April 25 and May 12, 2015, two high-magnitude earthquakes (Mw 7.8 Gorkha earthquake and Mw 7.3 aftershock) struck in Nepal. These events initiated soil tension cracks, shallow landslides, rockfalls, and avalanches in the Nepal Himalaya, flattened villages, and severely damaged structures in the mountain region of the affected area. The earthquakes resulted in about 9,000 fatalities, in addition to damage, destruction, and losses of livelihoods of thousands of people. The affected areas with the mountain slopes shattered, fissured, and soil tension-cracks formed along the crest of mountains or edge of elevated landforms where communities have been settled for generations created a lot of confusions for resettlement decisions in the face of disaster recovery processes due to the fear of renewed landslide, subsidence, slope failure, and rock fall from the mountain slopes that had fissures and soil tension-cracks for kilometers. However, except some community-based tension crack sealing and surface and subsurface drainage management, no special ground treatments have undertaken in most of the earthquake affected areas, and despite that there were few or no new landslides and reactivation of earthquake-induced landslides and soil tension-cracks took place in the area in the last four years. The soil tension-cracks created during the earthquake are not seen at present. This paper gives detail pictures of co-seismic landscape response to the 2015-Gorkha Earthquake and their natural post modifications.

Effect of hybrid fibers on tension stiffening of reinforced geopolymer concrete

Ganesan, N.,Sahana, R.,Indira, P.V. Techno-Press 2017 Advances in concrete construction Vol.5 No.1

An experimental work was carried out to study the effect of hybrid fiber on the tension stiffening and cracking characteristics of geopolymer concrete (GPC). A total of 24 concentrically reinforced concrete specimens were cast and tested under uniaxial tension. The grade of concrete considered was M40. The variables mainly consist of the volume fraction of crimped steel fibers (0.5 and 1.0%) and basalt fibers (0.1, 0.2 and 0.3%). The load deformation response was recorded using LVDT's. At all the stages of loading after the first cracking, crack width and crack spacing were measured. The addition of fibers in hybrid form significantly improved the tension stiffening effect. In this study, the combination of 0.5% steel fiber and 0.2% basalt fiber gave a better comparison than the other combinations.

전단하중의 크기가 모드 Ⅱ 분기균열의 형성과 전파에 미치는 영향

이정무(J. M. Lee),송삼흥(S. H. Song) 한국정밀공학회 2004 한국정밀공학회 학술발표대회 논문집 Vol.2004 No.10월

In this paper, we investigated the characteristics of initiation and propagation behavior for fatigue crack observed by changing various shapes of initial crack and magnitudes of loading in modified compact tension shear(CTS) specimen subjected to shear loading. In the low-loading condition, the secondary fatigue crack was created in the notch root due to friction on the pre-crack face grew to a main crack. In the high-loading condition, fatigue crack under shear loading propagated branching from the pre-crack tip. Influenced by the shear loading condition, fatigue crack propagation retardation appeared in the initial propagation region due to the reduction of crack driving force and friction on crack face. In both cases, however, fatigue cracks grew in tensile mode type. The propagation path of fatigue crack under the Mode II loading was 70 degree angle from the initial crack regardless of its shape and load magnitude.