With the continuous development of civil engineering,concrete crack treatment technology has become an important research field.This paper proposes treatment techniques for different types of cracks,including the prev...With the continuous development of civil engineering,concrete crack treatment technology has become an important research field.This paper proposes treatment techniques for different types of cracks,including the prevention and repair of surface cracks,the reinforcement and grouting of structural cracks,and the design and construction of controlled cracks through the analysis of the causes and classification of concrete cracks.The methods and suggestions proposed in this paper are practical and can improve the quality and safety of buildings.展开更多
Feasibility of a wave propagation-based active crack detection technique for nondestructive evaluations (NDE) of concrete structures with surface bonded and embedded piezoelectric-ceramic (PZT) patches was studied...Feasibility of a wave propagation-based active crack detection technique for nondestructive evaluations (NDE) of concrete structures with surface bonded and embedded piezoelectric-ceramic (PZT) patches was studied. At first, the wave propagation mechanisms in concrete were analyzed. Then, an active sensing system with integrated actuators/sensors was constructed. One PZT patch was used as an actuator to generate high frequency waves, and the other PZT patches were used as sensors to detect the propagating wave. Scattered wave signals from the damage can be obtained by subtracting the baseline signal of the intact structure from the recorded signal of the damaged structure. In the experimental study, progressive cracked damage inflicted artificially on the plain concrete beam is assessed by using both lateral and thickness modes of the PZT patches. The results indicate that with the increasing number and severity of cracks, the magnitude of the sensor output decreases for the surface bonded PZT patches, and increases for the embedded PZT patches.展开更多
The rapid development of science and technology puts forward higher requirements for new building construction,especially in civil engineering construction.The construction quality of construction engineering is the c...The rapid development of science and technology puts forward higher requirements for new building construction,especially in civil engineering construction.The construction quality of construction engineering is the core management and the testing link.The Concrete structure is an important safety and quality guarantee in the project and is the top priority in the civil engineering.In civil engineering,the concrete structure has an important social impact on the continuous research and development,and application of construction technology.This paper,discuss the advantage and disadvantage of using concrete in building construction.展开更多
Achievements are presented for truss models of RC structures developed in previous years: 1. Two constitutive models, biaxial and triaxial, are based on regular trusses, with bars obeying nonlinear uniaxial σ-ε laws...Achievements are presented for truss models of RC structures developed in previous years: 1. Two constitutive models, biaxial and triaxial, are based on regular trusses, with bars obeying nonlinear uniaxial σ-ε laws of material under simulation;both models have been compared with test results and show a dependence of Poisson ratio on curvature of σ-ε law. 2. A truss finite element has been used in the nonlinear static and dynamic analysis of plane RC frames;it has been compared with test results and describes, in a simple way, the formation of plastic hinges. 3. Thanks to the very simple geometry of a truss, the equilibrium equations can be easily written and the stiffness matrix can be easily updated, both with respect to the deformed truss, within each step of a static incremental loading or within each time step of a dynamic analysis, so that to take into account geometric nonlinearities. So the confinement of a RC column is interpreted as a structural stability effect of concrete. And a significant role of the transverse reinforcement is revealed, that of preventing, by its close spacing and sufficient amount, the buckling of inner longitudinal concrete struts, which would lead to a global instability of the RC column. 4. The proposed truss model is statically indeterminate, so it exhibits some features, which are not met by the “strut-and-tie” model.展开更多
Cracking in wading-concrete structures has a worse impact on structural safety compared with conventional concrete structures.The accurate and timely monitoring of crack development plays a significant role in the saf...Cracking in wading-concrete structures has a worse impact on structural safety compared with conventional concrete structures.The accurate and timely monitoring of crack development plays a significant role in the safety of wading-concrete engineering.The heat-transfer rate near a crack is related to the flow velocity of the fluid in the crack.Based on this,a novel crack-identification method for underwater concrete structures is presented.This method uses water irrigation to generate seepage at the interface of a crack;then,the heat-dissipation rate in the crack area will increase because of the convective heat-transfer effect near the crack.Crack information can be identified by monitoring the cooling law and leakage flow near cracks.The proposed mobile crack-monitoring system consists of a heating system,temperature-measurement system,and irrigation system.A series of tests was conducted on a reinforcedconcrete beam using this system.The crack-discrimination indexψwas defined,according to the subsection characteristics of the heat-source cooling curve.The effects of the crack width,leakage flow,and relative positions of the heat source and crack onψwere studied.The results showed that the distribution characteristics ofψalong the monitoring line could accurately locate the crack,but not quantify the crack width.However,the leakage flow is sensitive to the crack width and can be used to identify it.展开更多
A method of the fuzzy cross-correlation factor exponent in dynamics is researched and proposed to diagnose abnormality of cracks in the concrete dam. Moreover, the Logistic time series changing from period-doubling bi...A method of the fuzzy cross-correlation factor exponent in dynamics is researched and proposed to diagnose abnormality of cracks in the concrete dam. Moreover, the Logistic time series changing from period-doubling bifurcation to chaos is tested first using this method. Results indicate that it can distinguish inherent dynamics of time series and can detect mutations. Considering that cracks in the concrete dam constitute an open, dissipative and complex nonlinear dynamical system, a typical crack on the downstream face of a concrete gravity arch dam is analyzed with the proposed method. Two distinct mutations are discovered to indicate that the abnormality diagnosis of cracks in the concrete dam is achieved dynamically through this method. Furthermore, because it can be directly utilized in the measured crack opening displacement series to complete abnormality diagnosis, it has a good prospect for practical applications.展开更多
- The behavior of the reinforced concrete members subjected to combined torsion and shear is studied in this paper. Based on the skew bending failure pattern observed in tests, and according to the gradual increase in...- The behavior of the reinforced concrete members subjected to combined torsion and shear is studied in this paper. Based on the skew bending failure pattern observed in tests, and according to the gradual increase in strain on the concrete surface, a nonlinear full range analysis is performed for predicting the torque-twist relationship of members under combined torsion and shear for the ratio of torsion to shear is chosen bigger than 0.5 (T/ V b> 0.5). The test results are compared with the theoretical predictions.展开更多
Pulse-prepump Brillouin optical time domain analysis (PPP-BOTDA) is a novel technique for distributed strain measurements, in which a pre-pump pulse is inputted in front of the measuring pump pulse to stimulate the ph...Pulse-prepump Brillouin optical time domain analysis (PPP-BOTDA) is a novel technique for distributed strain measurements, in which a pre-pump pulse is inputted in front of the measuring pump pulse to stimulate the phonon, so that higher spatial resolution and measurement precision can be obtained. Principle, methodologies and technical parameters of the PPP-BOTDA are presented and the influence of temperature on measurements is discussed. Applications are made in the bond test of steel rebars and the bending test of concrete girders. Test results show that the PPP-BOTDA can provide a precise description on the strain distribution of steel rebar and concrete, exhibiting the ability for crack detection. Moreover, structural deformation can be obtained indirectly by accumulating the distributed strains along the optical fiber, thus the deflection curves of the concrete girder during the loading process are obtained. Suggestions with regards to the application of the PPP-BOTDA in strain measurements and crack monitoring for civil infrastructures are given.展开更多
This study proposes an algorithm of embedding cohesive elements in Abaqus and develops the computer code to model 3D complex cragk propagation in quasi-brittle materials in a relatively easy and efficient manner. The ...This study proposes an algorithm of embedding cohesive elements in Abaqus and develops the computer code to model 3D complex cragk propagation in quasi-brittle materials in a relatively easy and efficient manner. The cohesive elements with softening traction-separation relations and damage initiation and evolution laws are embedded between solid elements in regions of interest in the initial mesh to model potential cracks. The initial mesh can consist of tetrahedrons, wedges, bricks or a mixture of these elements. Neither remeshing nor objective crack propagation criteria are needed. Four examples of concrete specimens, including a wedgesplitting test, a notched beam under torsion, a pull-out test of an anchored cylinder and a notched beam under impact, were modelled and analysed. The simulated crack propagation processes and load-displacement curves agreed well with test results or other numerical simulations for all the examples using initial meshes with reasonable densities. Making use of Abaqus's rich pre/post- processing functionalities and powerful standard/explicit solvers, the developed method offers a practical tool for engineering analysts to model complex 3D fracture problems.展开更多
作为西南山区最为频发的地质灾害之一,滑坡对山区中大量存在的砖混房屋造成严重影响,尤其农村山区中受灾最为严重,给人民群众生产生活造成巨大安全隐患.研究滑坡引起的上部砖混结构变形特征,对科学指导房屋设计防护及灾后监测点布置具...作为西南山区最为频发的地质灾害之一,滑坡对山区中大量存在的砖混房屋造成严重影响,尤其农村山区中受灾最为严重,给人民群众生产生活造成巨大安全隐患.研究滑坡引起的上部砖混结构变形特征,对科学指导房屋设计防护及灾后监测点布置具有重要现实意义.本文以酉阳高园子滑坡为例,通过现场调查和裂缝参数拟合研究了滑坡区砖混结构变形破坏特征.同时基于PFC3D,构建了有限体积-离散元(Finite Volume Method-Discrete Element Method,FVM-DEM)滑坡-房屋单向耦合模型,模拟并分析了在不同工况下滑坡动态发育过程,进一步揭示了房屋裂缝产生及演化过程.结果表明:相比于普通无柱砖混结构,底框结构抵抗滑坡诱发变形破坏的能力更强,并且处于前后缘段的房屋相对中段房屋更易出现损伤破坏;房屋的长宽比不宜过小,布置房屋长边走向平行斜坡走向有利于减少滑坡对房屋造成的破坏.本文总结了在滑坡作用下,上部砖混结构的变形特征和裂缝开展规律,可为农村山区砖混结构设计和布置提供参考.展开更多
With the shield tunnel going deeper and deeper, the circumferential axial force becomes the governing factor rather than the bending moment. The hand hole acts as a weak point and initial damage in the segment joint e...With the shield tunnel going deeper and deeper, the circumferential axial force becomes the governing factor rather than the bending moment. The hand hole acts as a weak point and initial damage in the segment joint especially when the circumferential axial force is extremely high. Despite the wide application of steel fiber or synthetic fiber in t|ie tunneling, limited researches focus on the structural responses of segment joint with macro structural synthetic fiber (MSSF). In this paper, a 1:2 reduced-scale experiment was conducted to study the structural perfonnance of the segment joint with different types of hand holes under ultra-high axial force. Special attention is paid to failure mode and structural performance (bearing capacity, deformation, cracking, and toughness). Moreover, segment joints with MSSF are also tested to evaluate the effects of MSSF on the failure mode and structural performance of the segment joints. The experiment results show that the hand hole becomes the weakest point of the segment joint under ultra-high axial force. A\/-type crack pattern is always observed before the final failure of the segment joints. Different types and sizes of the hand hole have different degree of influences on the structural behavior of segment joints. The segment joint with MSSF shows higher ultimate bearing capacity and toughness compared to segment joint with common concrete. Besides, the MSSF improves the initial cracking load and anti-spallling resistance of the segment joint.展开更多
The micromechanical behaviors and mechanics-optics coupling effects of optic-fiber-concrete complex in the distributed optic-fiber sensing concrete-crack technology,which was used in health monitoring of Wu Gorge Brid...The micromechanical behaviors and mechanics-optics coupling effects of optic-fiber-concrete complex in the distributed optic-fiber sensing concrete-crack technology,which was used in health monitoring of Wu Gorge Bridge on Yangtze River and a large dam successfully,have been investigated.A micromechanical theoretical analysis method and micromechanical frictional contact bi-interface model,as well as a modified optical theoretical analysis method of the mechanics-optics coupling effects are presented.A series of verification experiments,including mechanical experiments and mechanics-optics coupling experiments,have been preformed.The results of micromechanical theoretical analysis and the analysis of the modified theory of mechanics-optics coupling along with mechanical and optical experimental data are shown to be in close agreement.Both the micromechanical theory and the modified theory of mechanics-optics coupling with their analysis methods can not only enhance credibility of this novel distributed sensing technology but also provide a way to understand its sensing mechanism and optimize its technical details and system.展开更多
文摘With the continuous development of civil engineering,concrete crack treatment technology has become an important research field.This paper proposes treatment techniques for different types of cracks,including the prevention and repair of surface cracks,the reinforcement and grouting of structural cracks,and the design and construction of controlled cracks through the analysis of the causes and classification of concrete cracks.The methods and suggestions proposed in this paper are practical and can improve the quality and safety of buildings.
基金Funded by the National Natural Science Foundation of China (51178305)the Key Projects in the Science & Technology Pillar Program of Tianjin (11ZCKFSF00300)
文摘Feasibility of a wave propagation-based active crack detection technique for nondestructive evaluations (NDE) of concrete structures with surface bonded and embedded piezoelectric-ceramic (PZT) patches was studied. At first, the wave propagation mechanisms in concrete were analyzed. Then, an active sensing system with integrated actuators/sensors was constructed. One PZT patch was used as an actuator to generate high frequency waves, and the other PZT patches were used as sensors to detect the propagating wave. Scattered wave signals from the damage can be obtained by subtracting the baseline signal of the intact structure from the recorded signal of the damaged structure. In the experimental study, progressive cracked damage inflicted artificially on the plain concrete beam is assessed by using both lateral and thickness modes of the PZT patches. The results indicate that with the increasing number and severity of cracks, the magnitude of the sensor output decreases for the surface bonded PZT patches, and increases for the embedded PZT patches.
文摘The rapid development of science and technology puts forward higher requirements for new building construction,especially in civil engineering construction.The construction quality of construction engineering is the core management and the testing link.The Concrete structure is an important safety and quality guarantee in the project and is the top priority in the civil engineering.In civil engineering,the concrete structure has an important social impact on the continuous research and development,and application of construction technology.This paper,discuss the advantage and disadvantage of using concrete in building construction.
文摘Achievements are presented for truss models of RC structures developed in previous years: 1. Two constitutive models, biaxial and triaxial, are based on regular trusses, with bars obeying nonlinear uniaxial σ-ε laws of material under simulation;both models have been compared with test results and show a dependence of Poisson ratio on curvature of σ-ε law. 2. A truss finite element has been used in the nonlinear static and dynamic analysis of plane RC frames;it has been compared with test results and describes, in a simple way, the formation of plastic hinges. 3. Thanks to the very simple geometry of a truss, the equilibrium equations can be easily written and the stiffness matrix can be easily updated, both with respect to the deformed truss, within each step of a static incremental loading or within each time step of a dynamic analysis, so that to take into account geometric nonlinearities. So the confinement of a RC column is interpreted as a structural stability effect of concrete. And a significant role of the transverse reinforcement is revealed, that of preventing, by its close spacing and sufficient amount, the buckling of inner longitudinal concrete struts, which would lead to a global instability of the RC column. 4. The proposed truss model is statically indeterminate, so it exhibits some features, which are not met by the “strut-and-tie” model.
基金This work was supported by the Natural Science Foundation of Sichuan Province(No.2022NSFSC0422)China and the Fundamental Research Funds for the Central Universities,China.
文摘Cracking in wading-concrete structures has a worse impact on structural safety compared with conventional concrete structures.The accurate and timely monitoring of crack development plays a significant role in the safety of wading-concrete engineering.The heat-transfer rate near a crack is related to the flow velocity of the fluid in the crack.Based on this,a novel crack-identification method for underwater concrete structures is presented.This method uses water irrigation to generate seepage at the interface of a crack;then,the heat-dissipation rate in the crack area will increase because of the convective heat-transfer effect near the crack.Crack information can be identified by monitoring the cooling law and leakage flow near cracks.The proposed mobile crack-monitoring system consists of a heating system,temperature-measurement system,and irrigation system.A series of tests was conducted on a reinforcedconcrete beam using this system.The crack-discrimination indexψwas defined,according to the subsection characteristics of the heat-source cooling curve.The effects of the crack width,leakage flow,and relative positions of the heat source and crack onψwere studied.The results showed that the distribution characteristics ofψalong the monitoring line could accurately locate the crack,but not quantify the crack width.However,the leakage flow is sensitive to the crack width and can be used to identify it.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51079046, 50909041, 50809025, 50879024)the National Science and Technology Support Plan (Grant Nos. 2008BAB29B03, 2008BAB29B06)+7 种基金the Special Fund of State Key Laboratory of China (Grant Nos. 2009586012, 2010585212)the Fundamental Research Funds for the Central Universities (Grant Nos. 2009B08514, 2010B20414, 2010B14114)China Hydropower Engineering Consulting Group Co. Science and Technology Support Project (Grant No. CHC-KJ-2007-02)Jiangsu Province "333 High-Level Personnel Training Project" (Grant No. 2017-B08037)the Natural Science Foundation of Hohai University (Grant No. 2008426811)Graduate Innovation Program of Universities in Jiangsu Province (Grant No. CX09B_163Z)the Science Foundation for The Excellent Youth Scholars of Ministry of Education of China (Grant No. 20070294023)Dominant Discipline Construction Program Funded Projects of Universities in Jiangsu Province
文摘A method of the fuzzy cross-correlation factor exponent in dynamics is researched and proposed to diagnose abnormality of cracks in the concrete dam. Moreover, the Logistic time series changing from period-doubling bifurcation to chaos is tested first using this method. Results indicate that it can distinguish inherent dynamics of time series and can detect mutations. Considering that cracks in the concrete dam constitute an open, dissipative and complex nonlinear dynamical system, a typical crack on the downstream face of a concrete gravity arch dam is analyzed with the proposed method. Two distinct mutations are discovered to indicate that the abnormality diagnosis of cracks in the concrete dam is achieved dynamically through this method. Furthermore, because it can be directly utilized in the measured crack opening displacement series to complete abnormality diagnosis, it has a good prospect for practical applications.
文摘- The behavior of the reinforced concrete members subjected to combined torsion and shear is studied in this paper. Based on the skew bending failure pattern observed in tests, and according to the gradual increase in strain on the concrete surface, a nonlinear full range analysis is performed for predicting the torque-twist relationship of members under combined torsion and shear for the ratio of torsion to shear is chosen bigger than 0.5 (T/ V b> 0.5). The test results are compared with the theoretical predictions.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 50608017, 50725828)
文摘Pulse-prepump Brillouin optical time domain analysis (PPP-BOTDA) is a novel technique for distributed strain measurements, in which a pre-pump pulse is inputted in front of the measuring pump pulse to stimulate the phonon, so that higher spatial resolution and measurement precision can be obtained. Principle, methodologies and technical parameters of the PPP-BOTDA are presented and the influence of temperature on measurements is discussed. Applications are made in the bond test of steel rebars and the bending test of concrete girders. Test results show that the PPP-BOTDA can provide a precise description on the strain distribution of steel rebar and concrete, exhibiting the ability for crack detection. Moreover, structural deformation can be obtained indirectly by accumulating the distributed strains along the optical fiber, thus the deflection curves of the concrete girder during the loading process are obtained. Suggestions with regards to the application of the PPP-BOTDA in strain measurements and crack monitoring for civil infrastructures are given.
基金supported by EPSRC UK(No.EP/F00656X/1)Xiangting Su's one-year visit to the University of Liverpoosupported by the China Scholarship Council and the National Natural Science Foundation of China(No.50579081).
文摘This study proposes an algorithm of embedding cohesive elements in Abaqus and develops the computer code to model 3D complex cragk propagation in quasi-brittle materials in a relatively easy and efficient manner. The cohesive elements with softening traction-separation relations and damage initiation and evolution laws are embedded between solid elements in regions of interest in the initial mesh to model potential cracks. The initial mesh can consist of tetrahedrons, wedges, bricks or a mixture of these elements. Neither remeshing nor objective crack propagation criteria are needed. Four examples of concrete specimens, including a wedgesplitting test, a notched beam under torsion, a pull-out test of an anchored cylinder and a notched beam under impact, were modelled and analysed. The simulated crack propagation processes and load-displacement curves agreed well with test results or other numerical simulations for all the examples using initial meshes with reasonable densities. Making use of Abaqus's rich pre/post- processing functionalities and powerful standard/explicit solvers, the developed method offers a practical tool for engineering analysts to model complex 3D fracture problems.
文摘作为西南山区最为频发的地质灾害之一,滑坡对山区中大量存在的砖混房屋造成严重影响,尤其农村山区中受灾最为严重,给人民群众生产生活造成巨大安全隐患.研究滑坡引起的上部砖混结构变形特征,对科学指导房屋设计防护及灾后监测点布置具有重要现实意义.本文以酉阳高园子滑坡为例,通过现场调查和裂缝参数拟合研究了滑坡区砖混结构变形破坏特征.同时基于PFC3D,构建了有限体积-离散元(Finite Volume Method-Discrete Element Method,FVM-DEM)滑坡-房屋单向耦合模型,模拟并分析了在不同工况下滑坡动态发育过程,进一步揭示了房屋裂缝产生及演化过程.结果表明:相比于普通无柱砖混结构,底框结构抵抗滑坡诱发变形破坏的能力更强,并且处于前后缘段的房屋相对中段房屋更易出现损伤破坏;房屋的长宽比不宜过小,布置房屋长边走向平行斜坡走向有利于减少滑坡对房屋造成的破坏.本文总结了在滑坡作用下,上部砖混结构的变形特征和裂缝开展规律,可为农村山区砖混结构设计和布置提供参考.
文摘With the shield tunnel going deeper and deeper, the circumferential axial force becomes the governing factor rather than the bending moment. The hand hole acts as a weak point and initial damage in the segment joint especially when the circumferential axial force is extremely high. Despite the wide application of steel fiber or synthetic fiber in t|ie tunneling, limited researches focus on the structural responses of segment joint with macro structural synthetic fiber (MSSF). In this paper, a 1:2 reduced-scale experiment was conducted to study the structural perfonnance of the segment joint with different types of hand holes under ultra-high axial force. Special attention is paid to failure mode and structural performance (bearing capacity, deformation, cracking, and toughness). Moreover, segment joints with MSSF are also tested to evaluate the effects of MSSF on the failure mode and structural performance of the segment joints. The experiment results show that the hand hole becomes the weakest point of the segment joint under ultra-high axial force. A\/-type crack pattern is always observed before the final failure of the segment joints. Different types and sizes of the hand hole have different degree of influences on the structural behavior of segment joints. The segment joint with MSSF shows higher ultimate bearing capacity and toughness compared to segment joint with common concrete. Besides, the MSSF improves the initial cracking load and anti-spallling resistance of the segment joint.
基金supported by the National Natural Science Foundation of China and the Joint Foundation of Yalong River Hydropower Development (Grant No.50579094)
文摘The micromechanical behaviors and mechanics-optics coupling effects of optic-fiber-concrete complex in the distributed optic-fiber sensing concrete-crack technology,which was used in health monitoring of Wu Gorge Bridge on Yangtze River and a large dam successfully,have been investigated.A micromechanical theoretical analysis method and micromechanical frictional contact bi-interface model,as well as a modified optical theoretical analysis method of the mechanics-optics coupling effects are presented.A series of verification experiments,including mechanical experiments and mechanics-optics coupling experiments,have been preformed.The results of micromechanical theoretical analysis and the analysis of the modified theory of mechanics-optics coupling along with mechanical and optical experimental data are shown to be in close agreement.Both the micromechanical theory and the modified theory of mechanics-optics coupling with their analysis methods can not only enhance credibility of this novel distributed sensing technology but also provide a way to understand its sensing mechanism and optimize its technical details and system.