A new unified strength criterion in the principal stress space has been proposed for use with normal strength concrete （NC） and high strength concrete （HSC） in compressioncompression-tension, compression-tension-t...A new unified strength criterion in the principal stress space has been proposed for use with normal strength concrete （NC） and high strength concrete （HSC） in compressioncompression-tension, compression-tension-tension, triaxial tension, and biaxial stress states. The study covers concrete with strengths ranging from 20 to 130 MPa. The conception of damage Poisson＇s ratio is defined and the expression for damage Poisson＇s ratio is determined basically. The failure mechanism of concrete is illustrated, which points out that damage Poisson＇s ratio is the key to determining the failure of concrete. Furthermore, for the concrete under biaxial stress conditions, the unified strength criterion is simplified and a simplified strength criterion in the form of curves is also proposed. The strength criterion is physically meaningful and easy to calculate, which can be applied to analytic solution and numerical solution of concrete structures.展开更多
With the development of high-speed railway in China, composite foundation with rigid piles has become a stamdard solution of meeting the high requirements of stability and post-construction settlement of embankment on...With the development of high-speed railway in China, composite foundation with rigid piles has become a stamdard solution of meeting the high requirements of stability and post-construction settlement of embankment on soft subgrade. Among several im- provement pattems, plain concrete piles have been extensively used to treat soft ground supported embankment. To investigate the deformation and failure modes of unimproved soft ground and soft ground reinforced by sub-embankment plain concrete piles, and to learn the influences of track and vehicle load, the effect of pile spacing, as well as the compression moduli of soil layers and upper load condition on the failure modes, a series of centrifuge model tests were performed. Test results indicate that the dis- placement of unimproved soft ground under the embankment increases continuously as embankment, track and train loading, and slip circle failure takes place. The deformation law of soft ground reinforced by sub-embankment plain concrete piles depends on pile spacing, compression modulus of the soft ground, and loading conditions. It was also found that plain concrete piles show displacement and failure patterns depending on its location, compression modulus of soft soil around the pile, and loading condi- tions. Furthermore, the evaluation of improved ground stability as well as the model test procedure is also presented.展开更多
Some of the current concrete damage plasticity models in the literature employ a single damage variable for both the tension and compression regimes,while a few more advanced models employ two damage variables.Models ...Some of the current concrete damage plasticity models in the literature employ a single damage variable for both the tension and compression regimes,while a few more advanced models employ two damage variables.Models with a single variable have an inherent dificulty in accounting for the damage accrued due to tensile and compressive actions in appropriately different manners,and their mutual dependencies.In the current models that adopt two damage variables,the independence of these damage variables during cyclic loading results in the failure to capture the effects of tensile damage on the compressive behavior of concrete and vice-versa.This study presents a cyclic model established by extending an existing monotonic constitutive model.The model describes the cyclic behavior of concrete under multiaxial loading conditions and considers the influence of tensile/compressive damage on the compressive/tensile response.The proposed model,dubbed the enhanced concrete damage plasticity model(ECDPM),is an extension of an existing model that combines the theories of classical plasticity and continuum damage mechanics.Unlike most prior studies on models in the same category,the performance of the proposed ECDPM is evaluated using experimental data on concrete specimens at the material level obtained under cyclic multiaxial loading conditions including uniaxial tension and confined compression.The performance of the model is observed to be satisfactory.Furthermore,the superiority of ECDPM over three previously proposed constitutive models is demonstrated through comparisons with the results of a uniaxial tension-compression test and a virtual test.展开更多
The recent increase in blast/bombing incidents all over the world has pushed the development of effective strengthening approaches to enhance the blast resistance of existing civil infrastructures.Engineered geopolyme...The recent increase in blast/bombing incidents all over the world has pushed the development of effective strengthening approaches to enhance the blast resistance of existing civil infrastructures.Engineered geopolymer composite(EGC)is a promising material featured by eco-friendly,fast-setting and strain-hardening characteristics for emergent strengthening and construction.However,the fiber optimization for preparing EGC and its protective effect on structural elements under blast scenarios are uncertain.In this study,laboratory tests were firstly conducted to evaluate the effects of fiber types on the properties of EGC in terms of workability,dry shrinkage,and mechanical properties in compression,tension and flexure.The experimental results showed that EGC containing PE fiber exhibited suitable workability,acceptable dry shrinkage and superior mechanical properties compared with other types of fibers.After that,a series of field tests were carried out to evaluate the effectiveness of EGC retrofitting layer on the enhancement of blast performance of typical elements.The tests include autoclaved aerated concrete(AAC)masonry walls subjected to vented gas explosion,reinforced AAC panels subjected to TNT explosion and plain concrete slabs subjected to contact explosion.It was found that EGC could effectively enhance the blast resistance of structural elements in different scenarios.For AAC masonry walls and panels,with the existence of EGC,the integrity of specimens could be maintained,and their deflections and damage were significantly reduced.For plain concrete slabs,the EGC overlay could reduce the diameter and depth of the crater and spallation of specimens.展开更多
In this study, finite element （FE）-based primary pavement response models are employed for investigating the early-age deformation characteristics of jointed plain concrete pavements （JPCP） under environmental eff...In this study, finite element （FE）-based primary pavement response models are employed for investigating the early-age deformation characteristics of jointed plain concrete pavements （JPCP） under environmental effects. The FE-based ISLAB （two-and-one-half-dimensional） and EverFE （three-dimensional） software were used to conduct the response analysis. Sensitivity analyses of input parameters used in ISLAB and EverFE were conducted based on field and laboratory test data collected from instrumented pavements on highway US-34 near Burlington, Iowa. Based on the combination of input parameters and equivalent temperatures established from preliminary studies, FE analyses were performed and compared with the field measurements. Comparisons between field measured and computed deformations showed that both FE programs could produce reasonably accurate estimates of actual slab deformations due to environmental effects using the equivalent temperature difference concept.展开更多
The effect of size on the biaxial flexural strength(BFS)of Portland cement mortar was investigated by using the recently proposed triangular plate method(TPM).An experimental program was conceived to study the size ef...The effect of size on the biaxial flexural strength(BFS)of Portland cement mortar was investigated by using the recently proposed triangular plate method(TPM).An experimental program was conceived to study the size effect by keeping a constant water-cement ratio of 0.485,cement-sand ratio of 1:2.75,and using unreinforced triangular mortar plates of five different thicknesses and seven different side lengths.The BFS of the produced specimens was tested,and variations of BFS depending on specimen thickness and side length were determined.The results indicated that increases in triangular plate specimen side length and specimen thickness led to a decrease in the BFS of Portland cement mortar.The effect of specimen length increase on BFS was more significant than on the effect of the specimen thickness.The variations in specimens’thickness indicated a deterministic Type I size effect,while the variations in specimens’length showed an energetic-statistical Type I size effect.展开更多
基金Project supported by the National Natural Science Foundation of China (Nos. 50438020 and 50578162).
文摘A new unified strength criterion in the principal stress space has been proposed for use with normal strength concrete （NC） and high strength concrete （HSC） in compressioncompression-tension, compression-tension-tension, triaxial tension, and biaxial stress states. The study covers concrete with strengths ranging from 20 to 130 MPa. The conception of damage Poisson＇s ratio is defined and the expression for damage Poisson＇s ratio is determined basically. The failure mechanism of concrete is illustrated, which points out that damage Poisson＇s ratio is the key to determining the failure of concrete. Furthermore, for the concrete under biaxial stress conditions, the unified strength criterion is simplified and a simplified strength criterion in the form of curves is also proposed. The strength criterion is physically meaningful and easy to calculate, which can be applied to analytic solution and numerical solution of concrete structures.
基金supported by Program for New Century Excellent Talents in University of China (Grant No.NCET-12-0941)the Fundamental Research Funds for the Central Universities of China (Grant No.A0920502051206-3)
文摘With the development of high-speed railway in China, composite foundation with rigid piles has become a stamdard solution of meeting the high requirements of stability and post-construction settlement of embankment on soft subgrade. Among several im- provement pattems, plain concrete piles have been extensively used to treat soft ground supported embankment. To investigate the deformation and failure modes of unimproved soft ground and soft ground reinforced by sub-embankment plain concrete piles, and to learn the influences of track and vehicle load, the effect of pile spacing, as well as the compression moduli of soil layers and upper load condition on the failure modes, a series of centrifuge model tests were performed. Test results indicate that the dis- placement of unimproved soft ground under the embankment increases continuously as embankment, track and train loading, and slip circle failure takes place. The deformation law of soft ground reinforced by sub-embankment plain concrete piles depends on pile spacing, compression modulus of the soft ground, and loading conditions. It was also found that plain concrete piles show displacement and failure patterns depending on its location, compression modulus of soft soil around the pile, and loading condi- tions. Furthermore, the evaluation of improved ground stability as well as the model test procedure is also presented.
基金The authors acknowledge the financial support of this study by the Austrian Marshall Plan Foundation,which funded the first author's short-term visit to UCLA during the course of this study.
文摘Some of the current concrete damage plasticity models in the literature employ a single damage variable for both the tension and compression regimes,while a few more advanced models employ two damage variables.Models with a single variable have an inherent dificulty in accounting for the damage accrued due to tensile and compressive actions in appropriately different manners,and their mutual dependencies.In the current models that adopt two damage variables,the independence of these damage variables during cyclic loading results in the failure to capture the effects of tensile damage on the compressive behavior of concrete and vice-versa.This study presents a cyclic model established by extending an existing monotonic constitutive model.The model describes the cyclic behavior of concrete under multiaxial loading conditions and considers the influence of tensile/compressive damage on the compressive/tensile response.The proposed model,dubbed the enhanced concrete damage plasticity model(ECDPM),is an extension of an existing model that combines the theories of classical plasticity and continuum damage mechanics.Unlike most prior studies on models in the same category,the performance of the proposed ECDPM is evaluated using experimental data on concrete specimens at the material level obtained under cyclic multiaxial loading conditions including uniaxial tension and confined compression.The performance of the model is observed to be satisfactory.Furthermore,the superiority of ECDPM over three previously proposed constitutive models is demonstrated through comparisons with the results of a uniaxial tension-compression test and a virtual test.
基金National Natural Science Foundation of China(Grant Nos.51908188 and 51938011).
文摘The recent increase in blast/bombing incidents all over the world has pushed the development of effective strengthening approaches to enhance the blast resistance of existing civil infrastructures.Engineered geopolymer composite(EGC)is a promising material featured by eco-friendly,fast-setting and strain-hardening characteristics for emergent strengthening and construction.However,the fiber optimization for preparing EGC and its protective effect on structural elements under blast scenarios are uncertain.In this study,laboratory tests were firstly conducted to evaluate the effects of fiber types on the properties of EGC in terms of workability,dry shrinkage,and mechanical properties in compression,tension and flexure.The experimental results showed that EGC containing PE fiber exhibited suitable workability,acceptable dry shrinkage and superior mechanical properties compared with other types of fibers.After that,a series of field tests were carried out to evaluate the effectiveness of EGC retrofitting layer on the enhancement of blast performance of typical elements.The tests include autoclaved aerated concrete(AAC)masonry walls subjected to vented gas explosion,reinforced AAC panels subjected to TNT explosion and plain concrete slabs subjected to contact explosion.It was found that EGC could effectively enhance the blast resistance of structural elements in different scenarios.For AAC masonry walls and panels,with the existence of EGC,the integrity of specimens could be maintained,and their deflections and damage were significantly reduced.For plain concrete slabs,the EGC overlay could reduce the diameter and depth of the crater and spallation of specimens.
文摘In this study, finite element （FE）-based primary pavement response models are employed for investigating the early-age deformation characteristics of jointed plain concrete pavements （JPCP） under environmental effects. The FE-based ISLAB （two-and-one-half-dimensional） and EverFE （three-dimensional） software were used to conduct the response analysis. Sensitivity analyses of input parameters used in ISLAB and EverFE were conducted based on field and laboratory test data collected from instrumented pavements on highway US-34 near Burlington, Iowa. Based on the combination of input parameters and equivalent temperatures established from preliminary studies, FE analyses were performed and compared with the field measurements. Comparisons between field measured and computed deformations showed that both FE programs could produce reasonably accurate estimates of actual slab deformations due to environmental effects using the equivalent temperature difference concept.
文摘The effect of size on the biaxial flexural strength(BFS)of Portland cement mortar was investigated by using the recently proposed triangular plate method(TPM).An experimental program was conceived to study the size effect by keeping a constant water-cement ratio of 0.485,cement-sand ratio of 1:2.75,and using unreinforced triangular mortar plates of five different thicknesses and seven different side lengths.The BFS of the produced specimens was tested,and variations of BFS depending on specimen thickness and side length were determined.The results indicated that increases in triangular plate specimen side length and specimen thickness led to a decrease in the BFS of Portland cement mortar.The effect of specimen length increase on BFS was more significant than on the effect of the specimen thickness.The variations in specimens’thickness indicated a deterministic Type I size effect,while the variations in specimens’length showed an energetic-statistical Type I size effect.
