Strength criterion of plain recycled aggregate concrete under biaxial compression

Zhen-Jun He,Gan-Wen Liu,Wan-Lin Cao,Chang-Yang Zhou,Zhang Jia-Xing 사단법인 한국계산역학회 2015 Computers and Concrete, An International Journal Vol.16 No.2

This paper presents results of biaxial compressive tests and strength criterion on two replacement percentages of recycled coarse aggregate (RPRCA) by mass for plain structural recycled aggregate concrete (RAC) at all kinds of stress ratios. The failure mode characteristic of specimens and the direction of the cracks were observed and described. The two principally static strengths in the corresponding stress state were measured. The influence of the stress ratios on the biaxial strengths of RAC was also analyzed. The experimental results showed that the ratios of the biaxial compressive strength  3f to the corresponding uniaxial compressive strength c for the two RAC are higher than that of the conventional concrete (CC), and dependent on the replacement percentages of recycled coarse aggregate, stress states and stress ratios; however, the differences of tensile-compressive ratios for the two RAC and CC are smaller. On this basis, a new failure criterion with the stress ratios is proposed for plain RAC under biaxial compressive stress states. It provides the experimental and theoretical foundations for strength analysis of RAC structures subject to complex loads.

Stress interactions between two asymmetric noncircular tunnels

La, You-Sung,Kim, Bumjoo,Jang, Yeon-Soo,Choi, Won-Hyuk Techno-Press 2018 Geomechanics & engineering Vol.15 No.3

The continually growing demand for underground space in dense urban cities is also driving the demand for underground highways. Building the underground highway tunnel, however, can involve complex design and construction considerations, particularly when there exists divergence or convergence in the tunnel. In this study, interaction between two asymmetric noncircular tunnels-that is, a larger main tunnel and a smaller tunnel diverging from the main tunnel, was investigated by examining the distributions of the principal stresses and the strength/stress ratio for varying geometric conditions between the two tunnels depending on diverging conditions using both numerical analysis and scale model test. The results of numerical analysis indicated that for the $0^{\circ}$, $30^{\circ}$, $60^{\circ}$ diverging directions, the major principal stress showed an initial gradual decrease and then a little steeper increase with the increased distance from the left main tunnel, except for $90^{\circ}$ where a continuous drop occurred, whereas the minor principal stress exhibited an opposite trend with the major principal stresses. The strength/stress ratio showed generally a bell-shaped but little skewed to left distribution over the distance increased from the left larger tunnel, similarly to the variation of the minor principal stress. For the inter-tunnel distance less than 0.5D, the lowest strength/stress ratio values were shown to be below 1.0 for all diverging directions ($0^{\circ}$, $30^{\circ}$, $60^{\circ}$ and $90^{\circ}$). The failure patterns observed from the model test were found to be reasonably consistent with the results of numerical analysis.

Uniaxial Compression Behavior of High-Strength Concrete Confined by Low-Volumetric Ratio Lateral Ties

홍기남,한상훈 한국콘크리트학회 2005 콘크리트학회논문집 Vol.17 No.5

Presently, test results and stress-strain models for poorly confined high-strength columns, more specifically for columns with a tie volumetric ratio smaller than 2.0%, are scarce. This paper presents test results loaded in axial direction for square reinforced concrete columns confined by various volumetric ratio lateral ties including low-volumetric ratio. Test variables include concrete compressive strength, tie yield strength, tie arrangement type, and tie volumetric ratio. Local strains measured using strain gages bonded to an acryl rod. For square RC columns confined by lateral ties, the confinement effect was efficiently improved by changing tie arrangement type from Type-A to Type-B. A method to compute the stress in lateral ties at the concrete peak strength and a new stress-strain model for the confined concrete are proposed. Over a wide range of confinement parameters, the model shows good agreement with stress-strain relationships established experimentally.

고강도 철근 콘크리트 보의 휨 설계 및 연성능력

신성우,유석형,안종문,이광수 한국콘크리트학회 1996 콘크리트학회지 Vol.8 No.6

동일한 인장철근배근상태($\rho$/$\rho_b$=constant)에서 휨을 받는 고강도 철근 콘크리트 보는 보통강도의 철근 콘크리트보에 비해 더욱 취성적인 거동을 하게 된다. 본 실험결과 연성적인 파괴를 유도하기 위하여 콘크리트의 강도가 830kg/$cm^2$이상일 경우 철근비를 $0.6\rho_b$이하로 배근하여야 할 것으로 나타났다. 또한 콘크리트 강도가 830kg/$cm^2$ 이상일 경우 사각형응력 블록을 사용한 ACI 휨강도식의 안전율이 감소하였으며, 삼각형에 가까운 압축응력 분포를 나타내었다. 이는 콘크리트 강도가 증가할수록 응력-변형률 곡선이 거의 선형적으로 증가하는 재료적 성질에 기인하는 것으로 사료된다. The reinforced high-strength-concrete beam subjected to flexure moment behaves more brittly than the moderate-strength-concrete beam reinforced with equal reinforcement ratio($\rho$/$\rho_b$). Test results show that when the concrete strength exceeds 830kg/$cm^2$, the maximum reinforcement ratio should be less than $0.6{\rho}_b$ for ductile behavior (${\rho}_b$=balanced steel ratio). The ratio of flexural strength between experimental results and analytical results with rectangular stress block decrease as the compressive strength of concrete increase. The shape of the compressive stress block distributed triangularly. because the ascending part of the stress-strain curve shows fairly linear response up to maximum stress in contrast to the nonlinear behavior of the medium and low strength specimens.

Correlation of the maximum shear stress with micro-mechanisms of ductile fracture for metals with high strength-to-weight ratio

Lou, Yanshan,Yoon, Jeong Whan,Huh, Hoon,Chao, Qi,Song, Jung-Han Elsevier 2018 International journal of mechanical sciences Vol.146 No.-

<P><B>Abstract</B></P> <P>Mechanisms of ductile fracture are investigated experimentally in a wide range of loading conditions from compressive upsetting to the balanced biaxial tension for two metals with high strength-to-density ratio of DP980 (t1.2) steel sheets and a bulk aluminum alloy of AA7075. Specimens are carefully designed to achieve various loading conditions from shear at low stress triaxiality to the balanced biaxial tension at high stress triaxiality for DP980, while both tensile and compressive tests are conducted for AA7075. Fractured specimen surfaces are analyzed macroscopically focusing on their relations with the maximum shear stress. It is observed that all the specimens tend to fail along the direction of the maximum shear stress in various loading states of plane strain compression, uniaxial compression, shear, uniaxial tension, plane strain tension and the balanced biaxial tension. Scanning electron microscope analyses of fracture surfaces are also conducted to explore the underlying mechanism of void coalescence since coalescence of voids is viewed as the last step of ductile fracture after nucleation and growth of voids. It is noted that fractured voids elongate along the direction of the maximum shear stress for all specimens with the stress triaxiality ranging from about −0.57 in compression to 0.67 in the balanced biaxial tension. The experiments of DP980 and AA7075 reveal that ductile fracture takes place along the direction of the maximum shear stress in the wide loading conditions of compressive upsetting, shear, uniaxial tension, plane strain tension and the balanced biaxial tension with stress triaxiality below 0.67. Thus, ductile fracture is expected to be governed by the maximum shear stress in these wide loading conditions of compression, shear and tension. It is suggested that effect of the maximum shear stress must be correctly coupled in modeling of ductile fracture in these loading conditions with uncoupled and coupled ductile fracture criteria.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mechanisms of ductile fracture is investigated experimentally in the wide range of loading conditions from compressive upsetting to the tension of notched specimens for two lightweight metals of DP980 (t1.2) steel sheets and a bulk aluminum alloy of AA7075. </LI> <LI> All the specimens tend to fail along the direction of the maximum shear stress in various loading states of plane strain compression, uniaxial compression, shear, uniaxial tension and plane strain tension. </LI> <LI> Fractured voids elongate along the direction of the maximum shear stress for all specimens with the stress triaxiality ranging from negative in compression to 0.57 in the plane strain tension. </LI> <LI> The experiments of DP980 and AA7075 reveal that ductile fracture takes place along the direction of the maximum shear stress in the wide loading conditions of compressive upsetting, shear, uniaxial tension, and plane strain tension with stress triaxiality below 0.6. </LI> <LI> Effect of the maximum shear stress must be correctly coupled in modeling of ductile fracture in these loading conditions. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Shear fracture takes place in wide loading conditions of tension, shear and compression. </P> <P>[DISPLAY OMISSION]</P>

Mechanical Properties and Modeling of Amorphous Metallic Fiber-Reinforced Concrete in Compression

Dinh, Ngoc-Hieu,Choi, Kyoung-Kyu,Kim, Hee-Seung Korea Concrete Institute 2016 International Journal of Concrete Structures and M Vol.10 No.2

The aim of this paper is to investigate the compressive behavior and characteristics of amorphous metallic fiber-reinforced concrete (AMFRC). Compressive tests were carried out for two primary parameters: fiber volume fractions ($V_f$) of 0, 0.3, 0.6 and 0.8 %; and design compressive strengths of 27, 35, and 50 MPa at the age of 28 days. Test results indicated that the addition of amorphous metallic fibers in concrete mixture enhances the toughness, strain corresponding to peak stress, and Poisson's ratio at high stress level, while the compressive strength at the 28-th day is less affected and the modulus of elasticity is reduced. Based on the experimental results, prediction equations were proposed for the modulus of elasticity and strain at peak stress as functions of fiber volume fraction and concrete compressive strength. In addition, an analytical model representing the entire stress-strain relationship of AMFRC in compression was proposed and validated with test results for each concrete mix. The comparison showed that the proposed modeling approach can properly simulate the entire stress-strain relationship of AMFRC as well as the primary mechanical properties in compression including the modulus of elasticity and strain at peak stress.

Uniaxial Compression Behavior of High-Strength Concrete Confined by Low-Volumetric Ratio Lateral Ties

Hong Ki-Nam,Han Sang-Hoon Korea Concrete Institute 2005 콘크리트학회논문집 Vol.17 No.5

Presently, test results and stress-strain models for poorly confined high-strength columns, more specifically for columns with a tie volumetric ratio smaller than $2.0\%$, are scarce. This paper presents test results loaded in axial direction for square reinforced concrete columns confined by various volumetric ratio lateral ties including low-volumetric ratio. Test variables include concrete compressive strength, tie yield strength, tie arrangement type, and tie volumetric ratio. Local strains measured using strain gages bonded to an acryl rod. For square RC columns confined by lateral ties, the confinement effect was efficiently improved by changing tie arrangement type from Type-A to Type-B. A method to compute the stress in lateral ties at the concrete peak strength and a new stress-strain model for the confined concrete are proposed. Over a wide range of confinement parameters, the model shows good agreement with stress-strain relationships established experimentally.

Study on Bond-Slip Behaviors of Self-Stressing Steel Slag Concrete-Filled Steel Tube

Feng Yu,Taiyao Chen,Kang Niu,Shilong Wang,Zhengyi Kong,Yuan Fang 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.11

The bond-slip behaviors of self-stressing steel slag concrete filled steel tubes (SSSSCFST) are investigated by carrying out the push-out tests. The influence of thickness to diameter ratio, confining parameter and expansion ratio of steel slag concrete (SSC) on bond-slip performance are analyzed. Investigations of the failure modes of each specimen indicate that the shear failure of the bond interface dominates the failure of the specimen. Further, three stages of the load-slip relationship curve of bond slip was observed, i.e., the loading stage, descending section and constant load section. In the loading section, with the increase in thickness to diameter ratio or confining parameter, the interface bonding force of specimen improves firstly and then decreases. Besides, the interfacial bond strength increases with enhancement of the expansion ratio. In the descending section, the interfacial bonding force raises with improvement of diameter-thickness ratio, while decreases as the confining parameter and expansion ratio increase. Moreover, the influence of considered parameters on the ultimate interface bond load is analyzed. Finally, a theoretical model for the bond-slip behaviors of SSSSCFST is proposed by accounting for the non-uniform distribution of interface bond strength. It indicates that the theoretical model can well capture the main features that are exhibited during the whole process of push-out test.

Mechanical Properties and Modeling of Amorphous Metallic Fiber-Reinforced Concrete in Compression

Ngoc-Hieu Dinh,Kyoung-Kyu Choi,Hee-Seung Kim 한국콘크리트학회 2016 International Journal of Concrete Structures and M Vol.10 No.2

The aim of this paper is to investigate the compressive behavior and characteristics of amorphous metallic fiberreinforced concrete (AMFRC). Compressive tests were carried out for two primary parameters: fiber volume fractions (Vf) of 0, 0.3, 0.6 and 0.8 %; and design compressive strengths of 27, 35, and 50 MPa at the age of 28 days. Test results indicated that the addition of amorphous metallic fibers in concrete mixture enhances the toughness, strain corresponding to peak stress, and Poisson’s ratio at high stress level, while the compressive strength at the 28-th day is less affected and the modulus of elasticity is reduced. Based on the experimental results, prediction equations were proposed for the modulus of elasticity and strain at peak stress as functions of fiber volume fraction and concrete compressive strength. In addition, an analytical model representing the entire stress–strain relationship of AMFRC in compression was proposed and validated with test results for each concrete mix. The comparison showed that the proposed modeling approach can properly simulate the entire stress–strain relationship of AMFRC as well as the primary mechanical properties in compression including the modulus of elasticity and strain at peak stress.

고온 강구조 압축재의 좌굴 강도에 관한 연구

최현식 한국공간구조학회 2019 한국공간구조학회지 Vol.19 No.2

The high-temperature properties of mild steels were studied by comparing the test results of Kwon and the yield strength, tangent modulus predicted by the design provisions of ASCE and Eurocode(EC3). The column strengths for steel members at high temperatures were determined by the elastic and inelastic buckling strengths according to elevated temperatures. The material properties at high temperatures should be used in the strength evaluations of high temperature members. The buckling strengths obtained from the AISC, EC3 and approximate formula proposed by Takagi et al. were compared with ones calculated by the material nonlinear analysis using the EC3 material model. The newly simplified formulas for yield stress, tangent modulus, proportional limit and buckling strength which were proposed through a comparative study of the material properties and buckling strengths. The buckling strengths of proposed formulas were approximately equivalent to ones obtained from the formulas of Takagi et al. within 4% . They were corresponded to the lower bound values among the buckling strengths calculated by the design formulas and inelastic buckling analysis.