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Hong Hao - One of the best experts on this subject based on the ideXlab platform.
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blast resistance of Concrete slab reinforced with high performance fibre Material
Journal of Structural Integrity and Maintenance, 2016Co-Authors: Hong Hao, Zhongxian LiuAbstract:AbstractConcrete is now the most abundantly used Material in construction. Despite good compressive strength, Concrete is marked with brittleness and low tensile strength. A widely adopted method to enhance the Concrete Material performance especially the tensile strength and ductility is fibrous Material addition. In the present study, Concrete mix designs with different fibre additions have been developed, and high-performance polyethylene fibre and micro steel fibre are considered with varying volume fractions in the Concrete matrix. Material static properties are obtained from laboratory tests, and further study on the dynamic performance of theses fibre reinforced Concrete Materials is investigated through field blast tests. Concrete slabs with high-performance polyethylene fibre reinforcement and hybrid steel and polyethylene reinforcement are casted and tested under close-in blast scenarios. Discussion on the structural damage and Material performance is briefed based on the test results.
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influence of the Concrete dif model on the numerical predictions of rc wall responses to blast loadings
Engineering Structures, 2014Co-Authors: Yifei Hao, Hong HaoAbstract:Abstract Reliable prediction of structural responses to blast loadings requires an accurate dynamic Material model. The dynamic strength of Concrete Material is normally higher than the static strength. Based on extensive experimental data, a number of empirical DIF (dynamic increase factor) relations have been proposed to model Concrete Material strength increment at high strain rates. Most of these empirical relations are obtained by fitting the scattered dynamic testing data. It is commonly acknowledged that the induced structural effects such as lateral inertia confinement effect are inevitable in high-speed impact tests. Therefore directly fitting the laboratory testing data may not necessarily obtain the true dynamic Concrete Material properties. Some recent studies investigated the contributions of lateral inertia and end friction confinement effects on DIF of Concrete Materials in laboratory tests, and proposed relations to remove these influences to obtain the true DIF for Concrete Materials. The present study carries out numerical simulations of a reinforced Concrete wall under different blast loadings. Different DIF relations including CEB defined DIF, DIF proposed in previous studies after removing structural effect in laboratory tests, and NO DIF, i.e., neglecting dynamic strength increment, are considered in numerical simulations. Verification of the numerical model is made through the comparisons of the numerical simulation results with field test data. The results demonstrate that using the new DIF model yields the best prediction of the structural responses. The responses of a typical RC wall under blast loads with a 5 m stand-off distance but different TNT explosive charge weights are also simulated using different DIF relations. The responses of RC wall obtained from numerical models with different DIF relations of Concrete Material are compared. From the numerical simulation results, the range of scaled distance that DIF relation has significant influences on the numerical simulation results is identified.
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influence of end friction confinement on impact tests of Concrete Material at high strain rate
International Journal of Impact Engineering, 2013Co-Authors: Yifei Hao, Hong HaoAbstract:The compressive strength of Concrete Material increases with the strain rate. The dynamic compressive strength of Concrete Material is usually obtained by conducting laboratory tests such as split Hopkinson pressure bar (SHPB) test or drop-weight test. It is commonly agreed now that the dynamic increase factor (DIF) obtained from impact test is affected by lateral inertia confinement. In addition, friction at specimen-bar interfaces also constrains the lateral deformation of the specimen under high-speed impact and thus might influence the testing results as well. However, no systematic study that devotes to investigating the influence of end friction on the dynamic compression test of Concrete specimen can be found in the literature. Moreover, owing to the complication of including aggregates in Concrete specimens in high-speed impact tests, and complexity of including aggregates in numerical simulation of high-speed impact tests of Concrete Materials, coarse aggregates are usually neglected in both the laboratory tests and numerical simulations, which may not give accurate Concrete Material dynamic properties. In the present study, a mesoscale Concrete model with distinctive consideration of different components in a Concrete specimen is developed to simulate SHPB tests and to study the influence of the confinement due to end friction between specimen and pressure bars on impact tests of dynamic Concrete Material properties. The commercial software AUTODYN is used to carry out the numerical simulations of SHPB tests. The friction coefficient between steel bar and Concrete specimen is varied from 0.0 to 0.5 in the simulation. The results confirm that the end friction confinement does affect the testing results, and its influence depends on the L/D ratio (specimen length to diameter). This observation is also verified by experimental tests. The influences with L/D ratio and friction coefficient on stress and strain distributions and failure process of mesoscale Concrete specimen under different strain rates are discussed. Based on the results from numerical simulations, an empirical formula is proposed to remove the influence of end friction confinement on dynamic strength increment of Concrete Material obtained in SHPB tests.
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experimental study of dynamic compressive properties of fibre reinforced Concrete Material with different fibres
Materials & Design, 2012Co-Authors: Hong HaoAbstract:Abstract This research conducts drop weight impact tests to study the dynamic compressive properties of fibre reinforced Concrete (FRC) Material with different types of fibres. The impact tests are conducted with an instrumented drop-weight impact system consisting of a hard steel drop weight, two 180 t fast response loadcells, a high-speed video camera, and a fast response data acquisition system. Seven fibre types with different shapes and Material properties are considered in the study. They are synthetic fibres, undulated, cold rolled, flattened, hooked end, and two new spiral shape steel fibres developed in this study. A volume fraction of 1% fibre is used in all specimens. The Concrete matrix for all FRC specimens is mixed to obtain a compressive strength of 35 MPa. The drop-weight impact experiments are conducted with two different drop heights in order to study the dynamic Material properties at different strain rates. The impact forces on top and bottom of specimens are measured to investigate the axial inertia effects and the stress wave propagation effect. The high-speed video camera is used to capture the failure process, displacement and velocity responses of specimens, which are used to estimate the strain and strain rates of the specimen under impact loading. Strain gages are also used for direct strain measurements. The dynamic stress–strain relations and impact resistance of the tested specimens are compared. The influence of fibre shapes on the failure modes, strength and energy absorbing capability of FRC is discussed. The rate sensitivities of the compressive strength, Young’s modulus and toughness of FRC are also examined. The testing results demonstrate that the new spiral steel fibre proposed in this study provides better confinement to Concrete matrix and thus better bonding to Concrete Material, therefore increases the dynamic resistance and energy absorption capacity (toughness) of FRC.
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mesoscale modelling of fibre reinforced Concrete Material under compressive impact loading
Construction and Building Materials, 2012Co-Authors: Hong HaoAbstract:Abstract This paper presents a numerical simulation of dynamic impact tests on steel fibre reinforced Concrete (SFRC) specimens to study the dynamic Material properties of SFRC. In the analysis, an axisymmetric mesoscale SFRC model is developed with distinctive consideration of the fibres, aggregates and cement mortar to investigate the dynamic failure behaviour of SFRC Material under impact loading at different strain rates. The SFRC model composes of three components, i.e., the high strength coarse aggregates, cementitious mortar and steel fibres. To simplify the model, the coarse aggregates are assumed to have circular shape with randomly distributed size and location in the SFRC specimen. The hooked-end steel fibres are also randomly distributed in the specimen with random orientations. The developed model is used to numerically simulate a Split Hopkinson Pressure Bar Test (SHPB) on SFRC specimens. The model is created with commercial software ANSYS and VPG whilst the dynamic impact tests are simulated with the explicit hydrocode LS-DYNA. Numerical results are compared with available experimental data to verify the developed model. The verified numerical model is then used to perform a series of simulations of SFRC specimens with different volume fractions of steel fibres or without steel fibre under dynamic impact loads of different loading rates. From the numerical results, the influences of steel fibres on dynamic Material properties, in particular the dynamic increase factor (DIF), and on dynamic failure mechanism of SFRC are discussed. The DIF of SFRC with different steel fibre dosages are derived from the numerical results.
Yifei Hao - One of the best experts on this subject based on the ideXlab platform.
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influence of the Concrete dif model on the numerical predictions of rc wall responses to blast loadings
Engineering Structures, 2014Co-Authors: Yifei Hao, Hong HaoAbstract:Abstract Reliable prediction of structural responses to blast loadings requires an accurate dynamic Material model. The dynamic strength of Concrete Material is normally higher than the static strength. Based on extensive experimental data, a number of empirical DIF (dynamic increase factor) relations have been proposed to model Concrete Material strength increment at high strain rates. Most of these empirical relations are obtained by fitting the scattered dynamic testing data. It is commonly acknowledged that the induced structural effects such as lateral inertia confinement effect are inevitable in high-speed impact tests. Therefore directly fitting the laboratory testing data may not necessarily obtain the true dynamic Concrete Material properties. Some recent studies investigated the contributions of lateral inertia and end friction confinement effects on DIF of Concrete Materials in laboratory tests, and proposed relations to remove these influences to obtain the true DIF for Concrete Materials. The present study carries out numerical simulations of a reinforced Concrete wall under different blast loadings. Different DIF relations including CEB defined DIF, DIF proposed in previous studies after removing structural effect in laboratory tests, and NO DIF, i.e., neglecting dynamic strength increment, are considered in numerical simulations. Verification of the numerical model is made through the comparisons of the numerical simulation results with field test data. The results demonstrate that using the new DIF model yields the best prediction of the structural responses. The responses of a typical RC wall under blast loads with a 5 m stand-off distance but different TNT explosive charge weights are also simulated using different DIF relations. The responses of RC wall obtained from numerical models with different DIF relations of Concrete Material are compared. From the numerical simulation results, the range of scaled distance that DIF relation has significant influences on the numerical simulation results is identified.
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influence of end friction confinement on impact tests of Concrete Material at high strain rate
International Journal of Impact Engineering, 2013Co-Authors: Yifei Hao, Hong HaoAbstract:The compressive strength of Concrete Material increases with the strain rate. The dynamic compressive strength of Concrete Material is usually obtained by conducting laboratory tests such as split Hopkinson pressure bar (SHPB) test or drop-weight test. It is commonly agreed now that the dynamic increase factor (DIF) obtained from impact test is affected by lateral inertia confinement. In addition, friction at specimen-bar interfaces also constrains the lateral deformation of the specimen under high-speed impact and thus might influence the testing results as well. However, no systematic study that devotes to investigating the influence of end friction on the dynamic compression test of Concrete specimen can be found in the literature. Moreover, owing to the complication of including aggregates in Concrete specimens in high-speed impact tests, and complexity of including aggregates in numerical simulation of high-speed impact tests of Concrete Materials, coarse aggregates are usually neglected in both the laboratory tests and numerical simulations, which may not give accurate Concrete Material dynamic properties. In the present study, a mesoscale Concrete model with distinctive consideration of different components in a Concrete specimen is developed to simulate SHPB tests and to study the influence of the confinement due to end friction between specimen and pressure bars on impact tests of dynamic Concrete Material properties. The commercial software AUTODYN is used to carry out the numerical simulations of SHPB tests. The friction coefficient between steel bar and Concrete specimen is varied from 0.0 to 0.5 in the simulation. The results confirm that the end friction confinement does affect the testing results, and its influence depends on the L/D ratio (specimen length to diameter). This observation is also verified by experimental tests. The influences with L/D ratio and friction coefficient on stress and strain distributions and failure process of mesoscale Concrete specimen under different strain rates are discussed. Based on the results from numerical simulations, an empirical formula is proposed to remove the influence of end friction confinement on dynamic strength increment of Concrete Material obtained in SHPB tests.
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numerical analysis of Concrete Material properties at high strain rate under direct tension
International Journal of Impact Engineering, 2011Co-Authors: Yifei Hao, Xihong Zhang, Hong HaoAbstract:The tensile strength of Concrete Material increases with the strain rate. Dynamic tensile strength of Concrete Material is usually obtained by conducting laboratory tests such as direct tensile test, flexural test, spall test or splitting test (Brazilian test). Some codes of practice such as Comite Euro-International du Beton (CEB) give empirical relations of Concrete Material dynamic increase factor (DIF) based on testing data. However, the reliability of the dynamic testing and the derived DIF are under debating. It is commonly agreed now that the DIF obtained from dynamic impact test is affected by lateral inertia confinement effect. Therefore, those derived from testing data do not truly reflect the dynamic Material properties. The influence of the lateral inertia confinement, however, is not quantified. Moreover, Concrete is a heterogeneous Material with different components, but is conventionally assumed to be homogeneous, i.e. cement mortar only, in most previous experimental or numerical studies. In the present study, a mesoscale Concrete Material model consisting of cement mortar, aggregates and interfacial transition zone (ITZ) is developed to simulate direct tensile tests and to study the influences of the lateral inertia confinement and heterogeneity on tensile strength increment of Concrete Materials with respect to strain rates. The commercial software AUTODYN is used to perform the numerical simulations. The influence of lateral inertia confinement on tensile DIF of Concrete Material is examined.
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numerical analysis of lateral inertial confinement effects on impact test of Concrete compressive Material properties
International Journal of Protective Structures, 2010Co-Authors: Yifei Hao, Hong HaoAbstract:Dynamic Material properties, in particular the dynamic strength, of Concrete Material are usually obtained by conducting laboratory tests such as drop-weight test and Split Hopkinson Pressure Bar (SHPB) test. It is commonly agreed that a few parameters associated with stress wave propagation will affect the test results, including the lateral and axial inertial effect, end friction confinement and stress wave reflection and refraction. Many different measures have been proposed to eliminate or limit the influences of these effects in dynamic tests of Material properties. However, owing to the nature of dynamic loadings, especially those with high loading rates, it is very unlikely to completely eliminate these influences in physical testing. Moreover, it is also very difficult to quantify these influences from the laboratory testing data. In the present study, a refined mesoscale Concrete Material model is developed to simulate impact tests and to study the influences of lateral inertial confinement on co...
Henri Van Damme - One of the best experts on this subject based on the ideXlab platform.
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Concrete Material science past present and future innovations
Cement and Concrete Research, 2018Co-Authors: Henri Van DammeAbstract:Abstract Concrete is flying off, but it is simultaneously facing tremendous challenges in terms of environmental impact, financial needs, societal acceptance and image. Based on an historical approach of the science of Concrete and reinforced Concrete in particular, this paper calls for the exploration of radical changes in three key aspects of Concrete use: reinforcement, binder content, and implementation methods. More precisely, it is suggested that, in parallel to the introduction of robotic fabrication methods, digital technologies may be key for the introduction several innovations like (i) rebar-free reinforcement using non-convex granular media; (ii) compression-optimized Concrete structures, using topology optimization, architectural geometry, and 3D-printing or origami-patterned formworks; (iii) truly digital Concrete through the coupling of massive data collection and deep learning.
M L Hughes - One of the best experts on this subject based on the ideXlab platform.
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a strain rate dependent Concrete Material model for adina
Computers & Structures, 1997Co-Authors: Joseph W Tedesco, J C Powell, Allen C Ross, M L HughesAbstract:Abstract The analysis, design and/or evaluation of protective structures and facilities for military use demands the accurate determination of Material and structural response to high-intensity, short-duration impulse loadings. There currently exists a preponderance of data supporting increased strength characteristics in Concrete, the primary construction Material for protective facilities, at high strain rates. This paper summarizes the modification of the nonlinear Concrete Material model currently employed in the ADINA finite-element computer programs to account for high strain rate effects. The resultant strain-rate-dependent Concrete Material model encompasses the strain-rate range from 10 −7 s −1 (quasi-static) to 10 3 s −1 , in both compression and tension.
Valentina Mercuri - One of the best experts on this subject based on the ideXlab platform.
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3d printing of reinforced Concrete elements technology and design approach
Construction and Building Materials, 2018Co-Authors: Domenico Asprone, Ferdinando Auricchio, Costantino Menna, Valentina MercuriAbstract:Abstract This paper deals with a novel approach to the fabrication of reinforced Concrete (RC) members based on Concrete 3D printing technology. The approach consists in the partition of a RC member into different Concrete segments printed separately and, then, assembled into a unique element along with the steel reinforcement system. The approach is expected to facilitate the production of free-form structurally optimized RC elements with the final aim of saving Concrete Material and, at the same time, fabricating lighter structures. As case study, we report on the Material characterization and fabrication steps of a straight 3.00 m long RC beam together with the results of a full-scale three-point bending test performed on it. As a demonstration of the potentialities of this approach, the fabrication of a free-form variable cross-section RC beam is also presented.