고온노출된 강섬유보강 콘크리트의 인장성능에 대한 실험적 연구

문도영,Moon. Do Young 한국방재학회 2013 한국방재학회논문집 Vol.13 No.1

본 논문에서는 고온 노출된 강섬유 보강콘크리트의 인장성능을 실험적 연구를 통하여 검증하고자 하였다. 실험방법은 낮은 변동성을 특징으로 하는 DPT를 이용하였다. 일반적인 후크강섬유와 트위스트 강섬유, 0.25~1.0%의 강섬유 혼입률, 섬유형상비를 변수로 하여 실험을 수행하였다. 시험체는 고온 전기로에서 <TEX>$300^{\circ}C$</TEX>, <TEX>$500^{\circ}C$</TEX> 및 <TEX>$700^{\circ}C$</TEX>의 온도에서 2시간 노출되었으며, 12시간 동안 자연냉각 된 후에 가력되었다. 실험결과, 섬유혼입률이 증가할수록, 형상비가 클수록, DPT 인장강도가 증가하는 것으로 나타났다. 섬유종류의 영향은 다른 변수에 비하여 그 영향이 미미한 것으로 판단되었다. 실험결과를 근거로 강섬유의 혼입량과 형상비의 영향을 고려할 수 있는 노출온도 수준에 따른 DPT 인장강도 예측식을 제시하였다. Tensile strength of steel fiber-reinforced concrete was investigated with experimental program. For the investigation, Double Punch Test, which is known as a test method with low validity, was used. Fiber type(hooked and twisted fiber), mix ratios by volume ranged from 0.25% to 1.0%, aspect ratio were used as variables for the tests. The specimens were exposed to the elevated temperatures(<TEX>$300^{\circ}C$</TEX>, <TEX>$500^{\circ}C$</TEX> and <TEX>$700^{\circ}C$</TEX>) for 2 hours and placed at ambient temperatures for 12 hours before testing. Results demonstrated that residual tensile strength increases as mix ratio and aspect ratio increase. The effect of fiber type was insignificant. Based on the test results, the linear equation for prediction of DPT residual tensile strength was proposed in terms of mix ratio and aspect ratio.

An evolutionary fuzzy modelling approach and comparison of different methods for shear strength prediction of high-strength concrete beams without stirrups

Mohammad Mohammadhassani,Hossein Nezamabadi-pour,Meldi Suhatril,Mahdi shariati 국제구조공학회 2014 Smart Structures and Systems, An International Jou Vol.14 No.5

In this paper, an Adaptive nerou-based inference system (ANFIS) is being used for the prediction of shear strength of high strength concrete (HSC) beams without stirrups. The input parameters comprise of tensile reinforcement ratio, concrete compressive strength and shear span to depth ratio. Additionally, 122 experimental datasets were extracted from the literature review on the HSC beams with some comparable cross sectional dimensions and loading conditions. A comparative analysis has been carried out on the predicted shear strength of HSC beams without stirrups via the ANFIS method with those from the CEB-FIP Model Code (1990), AASHTO LRFD 1994 and CSA A23.3 – 94 codes of design. The shear strength prediction with ANFIS is discovered to be superior to CEB-FIP Model Code (1990), AASHTO LRFD 1994 and CSA A23.3 – 94. The predictions obtained from the ANFIS are harmonious with the test results not accounting for the shear span to depth ratio, tensile reinforcement ratio and concrete compressive strength; the data of the average, variance, correlation coefficient and coefficient of variation (CV) of the ratio between the shear strength predicted using the ANFIS method and the real shear strength are 0.995, 0.014, 0.969 and 11.97%, respectively. Taking a look at the CV index, the shear strength prediction shows better in nonlinear iterations such as the ANFIS for shear strength prediction of HSC beams without stirrups.

An evolutionary fuzzy modelling approach and comparison of different methods for shear strength prediction of high-strength concrete beams without stirrups

Mohammadhassani, Mohammad,Nezamabadi-pour, Hossein,Suhatril, Meldi,shariati, Mahdi Techno-Press 2014 Smart Structures and Systems, An International Jou Vol.14 No.5

In this paper, an Adaptive nerou-based inference system (ANFIS) is being used for the prediction of shear strength of high strength concrete (HSC) beams without stirrups. The input parameters comprise of tensile reinforcement ratio, concrete compressive strength and shear span to depth ratio. Additionally, 122 experimental datasets were extracted from the literature review on the HSC beams with some comparable cross sectional dimensions and loading conditions. A comparative analysis has been carried out on the predicted shear strength of HSC beams without stirrups via the ANFIS method with those from the CEB-FIP Model Code (1990), AASHTO LRFD 1994 and CSA A23.3 - 94 codes of design. The shear strength prediction with ANFIS is discovered to be superior to CEB-FIP Model Code (1990), AASHTO LRFD 1994 and CSA A23.3 - 94. The predictions obtained from the ANFIS are harmonious with the test results not accounting for the shear span to depth ratio, tensile reinforcement ratio and concrete compressive strength; the data of the average, variance, correlation coefficient and coefficient of variation (CV) of the ratio between the shear strength predicted using the ANFIS method and the real shear strength are 0.995, 0.014, 0.969 and 11.97%, respectively. Taking a look at the CV index, the shear strength prediction shows better in nonlinear iterations such as the ANFIS for shear strength prediction of HSC beams without stirrups.

Reinforcing Efficiencies of Two Different Cellulose Nanocrystals in Polyvinyl Alcohol-Based Nanocomposites

Park, Byung-Dae,Causin, Valerio Institute of Agricultural Science and Technology 2013 慶北大農學誌 Vol.31 No.4

As a renewable nanomaterial, cellulose nanocrystal (CNC) isolated from wood grants excellent mechanical properties in developing high performance nanocomposites. This study was undertaken to compare the reinforcing efficiency of two different CNCs, i.e., cellulose nanowhiskers (CNWs) and cellulose nanofibrils (CNFs) from hardwood bleached kraft pulp (HW-BKP) as reinforcing agent in polyvinyl alcohol (PVA)-based nanocomposite. The CNWs were isolated by sulfuric acid hydrolysis while the CNFs were isolated by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation. Based on measurements using transmission electron microscopy, the individual CNWs were about $6.96{\pm}0.87nm$ wide and $178{\pm}55nm$ long, while CNFs were $7.07{\pm}0.99nm$ wide. The incorporation of CNWs and CNFs into the PVA matrix at 5% and 1% levels, respectively, resulted in the maximum tensile strength, indicating different efficiencies of these CNCs in the nanocomposites. Therefore, these results suggest a relationship between the reinforcing potential of CNCs and their physical characteristics, such as their morphology, dimensions, and aspect ratio.

Reinforcing Efficiencies of Two Different Cellulose Nanocrystals in Polyvinyl Alcohol-Based Nanocomposites

Byung-Dae Park,Valerio Causin 경북대학교 농업생명과학대학 2013 Current Research on Agriculture and Life Sciences Vol.31 No.4

As a renewable nanomaterial, cellulose nanocrystal (CNC) isolated from wood grants excellent mechanical properties in developing high performance nanocomposites. This study was undertaken to compare the reinforcing efficiency of two different CNCs, i.e., cellulose nanowhiskers (CNWs) and cellulose nanofibrils (CNFs) from hardwood bleached kraft pulp (HW-BKP) as reinforcing agent in polyvinyl alcohol (PVA)-based nanocomposite. The CNWs were isolated by sulfuric acid hydrolysis while the CNFs were isolated by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation. Based on measurements using transmission electron microscopy, the individual CNWs were about 6.96±0.87 nm wide and 178±55 nm long, while CNFs were 7.07±0.99 nm wide. The incorporation of CNWs and CNFs into the PVA matrix at 5% and 1% levels, respectively, resulted in the maximum tensile strength, indicating different efficiencies of these CNCs in the nanocomposites. Therefore, these results suggest a relationship between the reinforcing potential of CNCs and their physical characteristics, such as their morphology, dimensions, and aspect ratio.

철근콘크리트 휨부재의 철근 인장변형률에 따른 곡률연성도 예측

이대형,배수호 한국콘크리트학회 2024 콘크리트학회논문집 Vol.36 No.2

이 연구의 목적은 콘크리트 강도 및 철근의 항복강도, 철근량에 따른 철근콘크리트 휨부재의 연성거동을 예측하기 위한 곡률연성도 관계식을 제안하는 것이다. 철근콘크리트 구조는 극한상태에서 연성파괴를 유도하는 것이 가장 중요한 설계개념으로 이를 위해 개정된 설계기준에서는 철근의 항복강도에 따라 최소허용인장변형률 및 인장지배변형률 한계를 규정하고 있다. 따라서 배근된 철근의 압축 콘크리트 파괴시 인장변형률과 항복변형률의 비를 변수로 곡률연성도 계산식을 제시하였다. 이를 위해 콘크리트 강도 및 철근의 항복강도가 곡률연성에 미치는 영향을 조사하였다. 철근의 인장변형률을 기준으로 한 경우 콘크리트의 강도에 따른 곡률연성도의 차이는 미미하였으며 철근의 항복강도가 클 경우 곡률연성도는 감소하였다. 제안식은 기존 연구결과와 유사하였으며 보다 간편하게 곡률연성도를 예측할 수 있을 것이다. This study proposes a simplified ductility formula for predicting the ductile behavior of reinforced concrete flexural members. The formula takes into account concrete strength, rebar yield strength, and the quantity of reinforcement. In reinforced concrete structures, ensuring ductile failure at the ultimate state is a crucial design concept. To achieve this, revised design standards specify minimum allowable tensile strain and tension-controlled strain limits based on rebar yield strength. Consequently, a formula for calculating curvature ductility is presented, using the ratio of tensile strain at compressive concrete failure to yield strain as a variable. In this context, the influence of concrete strength and yield strength of reinforcement on curvature ductility was investigated. It was found that the difference in curvature ductility based on concrete strength was insignificant when considering tensile strain of rebar as a reference, and with higher yield strength of reinforcement, the curvature ductility decreased. The proposed formula aligns with previous research results and provides a more convenient means to predict curvature ductility.

탄소나노튜브 혼입 고강도 경량 시멘트 복합체의 휨강도 평가

홍세희(Se-Hee Hong),이오성(Oh-Seong Lee),이호진(Ho-Jin Lee),윤영수(Young-Soo Yoon) 한국방재학회 2023 한국방재학회논문집 Vol.23 No.4

경량 구조물에 대한 관심은 비용 효율성과 전반적인 설계 감소로 인해 많은 연구자들의 관심을 받고 있다. 시멘트 복합체는경량소재를 혼입하여 경량성을 확보할 수 있지만 경량소재는 외력에 대한 저항성이 낮다. 이러한 단점을 극복하고 경량시멘트 복합체의 고강도화를 달성하기 위해 탄소나노튜브 0.05 wt.%의 혼입을 고려하였다. 본 연구에서는 3종의 휨 철근비와 2종의 전단 경간비를 고려하여 탄소나노튜브 혼입 고강도 경량 시멘트 복합체 보의 휨 성능을 평가하였다. 휨 철근비가증가할수록 시험체의 연성은 감소하였으나, 전단 성능이 확보될 경우 최소연성지수를 만족하는 것으로 나타났다. 국내 설계기준은 탄소나노튜브 혼입 고강도 경량 시멘트 복합체의 휨강도를 보수적으로 평가하는 것으로 나타났다. Lightweight structures have garnered the attention of many researchers for their cost effectiveness and overall design reduction. Cement composites can secure their lightness by incorporating lightweight materials. However, lightweight material has low resistance to external forces. To overcome this disadvantage and achieve high-strength lightweight cement composites (HSLCC), incorporation of 0.05 wt.% carbon nanotubes was considered. In this study, we evaluate the flexural performance of reinforced HSLCC beams with carbon nanotubes considering three tensile reinforcement ratios and two shear span to depth ratios. As the flexural reinforcement ratio increased, the ductility of the specimens decreased. However, specimens 0.8-3.6, 1.3-3.6, and 1.9-3.6 satisfied the minimum ductility index and secured shear performance. The domestic design standards evaluated the flexural strength conservatively for reinforced HSLCC with carbon nanotubes.

Effect of Steel Ratio on Behavior of Continuously Reinforced Concrete Railway Track under Environmental Loads

조영교,김성민,정원석,김재철,오한진 대한토목학회 2014 KSCE Journal of Civil Engineering Vol.18 No.6

The effects of the steel ratio on the slab behaviors such as tensile stresses and crack widths of the Continuously ReinforcedConcrete Railway Track (CRCT) under environmental loads were numerically investigated in this study. Two different approacheswere considered to find the steel ratio effects. One was to use different steel bar sizes without changing steel bar locations and theother was to use different numbers of steel bars with rearranging steel bar locations. The analysis results showed that the tensilestresses and crack widths under environmental loads at a certain location of the slab were directly affected by the steel bars placednearby. As the steel ratio increased by increasing the steel bar size at the top of the slab, the maximum tensile stresses increased andthe crack widths decreased. When the steel ratio was changed by placing different numbers of steel bars, the maximum tensilestresses increased and the crack widths decreased as the localized steel ratio at the top of the slab increased regardless of the steel ratioof the entire slab. Therefore, crack occurrence that is directly related to the maximum tensile stresses and corresponding crack widthsunder environmental loads could effectively be controlled by the steel bar arrangement at the top of the slab.

Evaluation of Out-of-Plane Response of R/C Structural Wall Boundary Edges Detailed with Maximum Code-Prescribed Longitudinal Reinforcement Ratio

Theodoros A. Chrysanidis 한국콘크리트학회 2020 International Journal of Concrete Structures and M Vol.14 No.1

One type of failure of reinforced concrete seismic walls is out-of-plane buckling. This type of failure appears at the compressive cycle of loading during the cyclic seismic loading. This work is mainly experimental and tries to investigate the influence of the mechanical factor of tensile deformation on the behavior of seismic walls and particularly on the phenomenon of lateral buckling. Five test specimens are constructed simulating the confined boundary regions of structural walls. They are reinforced using the maximum longitudinal reinforcement ratio (4.02%) prescribed by modern seismic and concrete codes for boundary ends. Apart from the investigation of the factor of elongation degree, this method tries to examine if the detailing of walls using maximum allowable reinforced ratio for longitudinal reinforcement inhibits the appearance of transverse buckling. Each prism specimen was strained under different tensile deformation. Degrees of elongation used were equal to 0‰, 10‰, 20‰, 30‰ and 50‰. After the first tensile cycle of loading, a second compression loading cycle was applied on each specimen, till their failure. Thus, nine experiments were carried out in total-two for each specimen apart from the first specimen which suffered zero elongation. Empirical equations are derived trying to estimate the ultimate bearing capacity and the normalized axial deformation at failure for the different tensile degrees.

Ductility and strength assessment of HSC beams with varying of tensile reinforcement ratios

Mohammadhassani, Mohammad,Suhatril, Meldi,Shariati, Mahdi,Ghanbari, Farhad Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.48 No.6

Nine rectangular-section of High Strength Concrete(HSC) beams were designed and casted based on the American Concrete Institute (ACI) code provisons with varying of tensile reinforcement ratio as (${\rho}_{min}$, $0.2_{{\rho}b}$, $0.3_{{\rho}b}$, $0.4_{{\rho}b}$, $0.5_{{\rho}b}$, $0.75_{{\rho}b}$, $0.85_{{\rho}b}$, $_{{\rho}b}$, $1.2_{{\rho}b}$). Steel and concrete strains and deflections were measured at different points of the beam's length for every incremental load up to failure. The ductility ratios were calculated and the moment-curvature and load-deflection curves were drawn. The results showed that the ductility ratio reduced to less than 2 when the tensile reinforcement ratio increased to $0.5_{{\rho}b}$. Comparison of the theoretical ductility coefficient from CSA94, NZS95 and ACI with the experimental ones shows that the three mentioned codes exhibit conservative values for low reinforced HSC beams. For over-reinforced HSC beams, only the CSA94 provision is more valid. ACI bending provision is 10 percent conservative for assessing of ultimate bending moment in low-reinforced HSC section while its results are valid for over-reinforced HSC sections. The ACI code provision is non-conservative for the modulus of rupture and needs to be reviewed.