Damage detection is an important area with growing interest in mechanical and structural engineering.One of the critical issues in damage detection is how to determine indices sensitive to the structural damage and in...Damage detection is an important area with growing interest in mechanical and structural engineering.One of the critical issues in damage detection is how to determine indices sensitive to the structural damage and insensitive to the surrounding environmental variations.Current damage identification indices commonly focus on structural dynamic characteristics such as natural frequencies,mode shapes,and frequency responses.This study aimed at developing a technique based on energy Curvature Difference,power spectrum density,correlation-based index,load distribution factor,and neutral axis shift to assess the bridge deck condition.In addition to tracking energy and frequency over time using wavelet packet transform,in order to further demonstrate the feasibility and validity of the proposed technique for bridge condition assessment,experimental strain data measured from two stages of a bridge in the different intervals were used.The comparative analysis results of the bridge in first and second stage show changes in the proposed feature values.It is concluded,these changes in the values of the proposed features can be used to assess the bridge deck performance.展开更多
The dynamic finite element model （FEM） of a prestressed concrete continuous box-girder bridge, called the Tongyang Canal Bridge, is built and updated based on the results of ambient vibration testing （AVT） using a...The dynamic finite element model （FEM） of a prestressed concrete continuous box-girder bridge, called the Tongyang Canal Bridge, is built and updated based on the results of ambient vibration testing （AVT） using a real-coded accelerating genetic algorithm （RAGA）. The objective functions are defined based on natural frequency and modal assurance criterion （MAC） metrics to evaluate the updated FEM. Two objective functions are defined to fully account for the relative errors and standard deviations of the natural frequencies and MAC between the AVT results and the updated FEM predictions. The dynamically updated FEM of the bridge can better represent its structural dynamics and serve as a baseline in long-term health monitoring, condition assessment and damage identification over the service life of the bridge .展开更多
The electrochemical degradation of reed pulp black liquor containing lignin pretreated by acidification method was investigated using a three-dimensional electrode reactor. Using activated carbon as particle electrode...The electrochemical degradation of reed pulp black liquor containing lignin pretreated by acidification method was investigated using a three-dimensional electrode reactor. Using activated carbon as particle electrode, the effects of p H value, reaction temperature, electrolysis time and current on residual concentration of total organic carbon(TOC) were discussed in detail. The optimal conditions were obtained: pH 2.5, influent flow rate of 200 mL/min, 25 °C, 300 mA and 2h of electrolysis time, and the removal efficiency of TOC maintains at 35.57 %. The results of the electrochemical method indicate that ·OH radicals are produced in activated carbon anode in the electrolysis process and then adsorbed on the activated carbon surface. Microcell consists of ·OH radicals and the absorbed lignin. With the microcell reaction, the lignin is degraded, while the anodic polarized curve illustrates that the lignin is obviously oxidized in the anode. The contributions of direct and indirect electrolyses to the TOC removal ratio are about 50%, respectively.展开更多
Signal reconstruction is a significantly important theoretical issue for compressed sensing.Considering the situation of signal reconstruction with unknown sparsity,the conventional signal reconstruction algorithms us...Signal reconstruction is a significantly important theoretical issue for compressed sensing.Considering the situation of signal reconstruction with unknown sparsity,the conventional signal reconstruction algorithms usually perform low accuracy.In this work,a sparsity adaptive signal reconstruction algorithm using sensing dictionary is proposed to achieve a lower reconstruction error.The sparsity estimation method is combined with the construction of the support set based on sensing dictionary.Using the adaptive sparsity method,an iterative signal reconstruction algorithm is proposed.The sufficient conditions for the exact signal reconstruction of the algorithm also is proved by theory.According to a series of simulations,the results show that the proposed method has higher precision compared with other state-of-the-art signal reconstruction algorithms especially in a high compression ratio scenarios.展开更多
According to the results of accelerated tests of acidification corrosion depth and compressive strength of concretes subjected to sulfuric acid environments,the acidification depth laws of concretes were predicted bas...According to the results of accelerated tests of acidification corrosion depth and compressive strength of concretes subjected to sulfuric acid environments,the acidification depth laws of concretes were predicted based on the grey system theory.Thus,the remaining compressive strength was calculated when the acidification depth reached the protection layer thickness of concrete structures,which indicates that the limit state of durability failure can be defined based on strength degradation,and the calculation process was illustrated by an example.The calculated results show that the remaining compressive strength values in the durability failure limit state for the concrete structures exposed to p H=2 and 3 sulfuric acid water environments and wet-dry cyclic sulfuric acid environment with p H=2 are 74%,72%,and 80% of initialstrength,respectively.The method provides references for the durability evaluation of concrete structure design under the acidic environments.展开更多
An experimental research was conducted to determine the corrosion and bearing capacity of a reinforced concrete（RC） slab at different ages in a marine environment.Results show that the development of corrosion-induc...An experimental research was conducted to determine the corrosion and bearing capacity of a reinforced concrete（RC） slab at different ages in a marine environment.Results show that the development of corrosion-induced cracks on a slab in a marine environment can be divided into three stages according to crack morphology at the bottom of the slab.In the first stage,cracks appear.In the second stage,cracks develop from the edges to the middle of the slab.In the third stage,longitudinal and transverse corrosion-induced cracks coexist.The corrosion ratio of reinforcements nonlinearly increases with the age,and the relationship between the corrosion ratio of the reinforcements and the corrosion-induced crack width of the concrete is established.The flexural capacity of the corroded RC slab nonlinearly decreases with the age,and the model for the bearing capacity factor of the corroded RC slab is established.The mid-span deflection of the corroded RC slab that corresponds to the yield of the reinforcements linearly increases with the increase in corrosion ratio.Finally,the mechanisms of corrosion morphology and the degradation of the mechanical properties of an RC slab in a marine environment are discussed on the basis of the basic theories of steel corrosion in concrete and concrete structure design.展开更多
In order to realize information construction on settlement of pile-group foundation of Sutong Bridge, the monitoring instruments of high-precision micro-pressure sensor and hydrostatic leveling and settlement profiler...In order to realize information construction on settlement of pile-group foundation of Sutong Bridge, the monitoring instruments of high-precision micro-pressure sensor and hydrostatic leveling and settlement profiler were integrated synthetically. A set of practical multi-scale monitoring system on settlement of super-large pile-group foundation in deep water was put forward. The reliable settlement results are obtained by means of multi-sensor data fusion. Finite element model of pile-group foundation is established. By analysis of finite element simulated calculation of pile-group foundation, rules of settlement and uneven settlement obtained by monitoring and calculation results are coincident and the absolute error of settlement between them is 4.7 mm. The research shows that it is reasonable and feasible to monitor settlement of pile-group foundation with the system, and it can provide a method for the same type pile-group foundation in deep water.展开更多
Flow characteristics of thermally stratified shear flow in braided rivers are particularly complicated and poorly understood. In this study, a series of typical flow patterns was examined and their critical criteria w...Flow characteristics of thermally stratified shear flow in braided rivers are particularly complicated and poorly understood. In this study, a series of typical flow patterns was examined and their critical criteria were determined. Four flow patterns were identified: mixed, locally unstable, continuously stratified, and two-layer flow. Temperature distributions of the four types of flow patterns were analyzed and compared.The critical Froude numbers for unstable flow, FDcr1, and stable flow, FDcr2, were determined to be 6 and 1, respectively, and comparison of FDcr1 and FDcr2 to the peak Froude numbers, FD1 at the outer bank and FD2 at the inner bank along the anabranch, allowed the flow patterns to be assessed. Then, a discriminant based on initial Jeffreys-Keulegan stability parameters was established to distinguish the flow stages from twolayer flow to completely mixed flow. It is indicated that the three critical Jeffreys-Keulegan parameters increased with the diversion angle of braided rivers. Results also show that, compared to the stratified flow in straight and curved channels, it was more difficult for braided stratified flow to maintain as two-layer flow, and it more easily became mixed flow. Consequently, empirical expressions for stability criteria of the thermally stratified shear flow in braided rivers are presented.展开更多
Due to the existence of the attached mortar,the performance of the recycled concrete aggregate(RCA)is inferior to the natural aggregate,which significantly limits its wide application in industry.In this study,five ki...Due to the existence of the attached mortar,the performance of the recycled concrete aggregate(RCA)is inferior to the natural aggregate,which significantly limits its wide application in industry.In this study,five kinds of modified solutions were used to modify the surface of RCA,and the modification effects were compared.The results showed that sodium silicate,nano-silica(NS),Bacillus pasteurii and soybean powder had relatively good modification effects on RCA,which could reduce the crushing value and water absorption,and increase apparent density.The composite solution(15%sodium silicate and 2%NS)and soybean powder solution had better modification effect.The 28 d compressive strength and splitting tensile strength of recycled aggregate concrete(RAC)prepared by RCA modified by soybean powder solution were 4.6%and 5.2%higher than those prepared by RCA modified by composite solution,respectively.This indicates that among the five kinds of modified solutions,soybean powder solution has the best modification effect on RCA,and the optimal soaking time of soybean powder solution is 8 h.At this time,the crushing value,water absorption and apparent density of RCA are 12.8%,5.3%,and 2653 kg/m^(3),respectively.The research results of this study provide a reference for the modification of RCA and its efficient utilization.展开更多
Multi-pylon multi-span suspension bridge is a new type super flexible structure system, and the rigidity design of middle pylon is one of the main difficult technical issues. Due to the requirements of longitudinal ri...Multi-pylon multi-span suspension bridge is a new type super flexible structure system, and the rigidity design of middle pylon is one of the main difficult technical issues. Due to the requirements of longitudinal rigidity, the structural form and the corresponding foundation type of middle pylon are different from those of the ordinary steel pylon, and the complicated dynamic characteristics make the calculation quite difficult. In this article, exploration has been made in selection of similarity ratio and model materials, section simulation, restriction conditions simulation, fixing of mass blocks, fabrication scheme and testing method by taking into account different construction and working conditions such as restriction conditions and working environment of a three-pylon suspension bridge, to conduct the test experimental design of the dynamic behavior of the middle pylon, with the purpose to reveal its dynamic characteristics and make comparison and analysis with theoretical assumptions, to provide basis for anti-wind and anti-seismic design and reference for the design and research of three-pylon two-span suspension bridges in the future.展开更多
The rock permeability is an important parameter in the studies of seepage and stress coupling.The micro-cracks and pores can initiate and grow on a small scale and coalesce to form large-scale fractures and faults und...The rock permeability is an important parameter in the studies of seepage and stress coupling.The micro-cracks and pores can initiate and grow on a small scale and coalesce to form large-scale fractures and faults under compressive stresses,which would change the hydraulic conductivity of the rock,and therefore,the rock permeability.The rock permeability is,therefore,closely rela-ted with the micro-cracking growing,coalescence,and macro new fracture formation.This article proposes a conceptual model of rock permeability evolution and a micro kinematics mechanism of micro-cracking on the basis of the basic theory of micromechanics.The applicability of the established model is verified through numerical simulations of in situ tests and laboratory tests.The simu-lation results show that the model can accurately forecast the peak permeability evolution of brittle rock,and can well describe the macro-experimental phenomenon before the peak permeability evolution of brittle rock on a macro-scale.展开更多
As a cable-stayed bridge with the longest main span, the Sutong Bridge faces the threat of typhoons every year. Based on field measured data measured at the top of the tower and at the mid-span by anemometers, Typhoon...As a cable-stayed bridge with the longest main span, the Sutong Bridge faces the threat of typhoons every year. Based on field measured data measured at the top of the tower and at the mid-span by anemometers, Typhoon Muifa is analyzed in detail to obtain the wind characteristics, including the mean wind speed and direction, turbulence intensity and gust factor, power spectral density and integral scale of turbulence, etc. The correlated mean wind speeds at the two heights show the reliability of recorded wind data as well as the variation of wind speed with height. Turbulence inten- sities and gust factors fluctuate in a similar way. The values of inte- gral scales are sensitive in different case. The measured power spec- tra are particularly compared with Kaimal spectrum, Teunissen spectrum, Harris spectrum, and Davenport spectrum. The results show that the measured spectra cannot fit the code-suggested spectra very well, which exhibits the demand of more accurate spectra. Conclusions obtained in this article can provide references for wind resistance desima of suoer-long-soan cable-staved brides.展开更多
文摘Damage detection is an important area with growing interest in mechanical and structural engineering.One of the critical issues in damage detection is how to determine indices sensitive to the structural damage and insensitive to the surrounding environmental variations.Current damage identification indices commonly focus on structural dynamic characteristics such as natural frequencies,mode shapes,and frequency responses.This study aimed at developing a technique based on energy Curvature Difference,power spectrum density,correlation-based index,load distribution factor,and neutral axis shift to assess the bridge deck condition.In addition to tracking energy and frequency over time using wavelet packet transform,in order to further demonstrate the feasibility and validity of the proposed technique for bridge condition assessment,experimental strain data measured from two stages of a bridge in the different intervals were used.The comparative analysis results of the bridge in first and second stage show changes in the proposed feature values.It is concluded,these changes in the values of the proposed features can be used to assess the bridge deck performance.
基金National Natural Science Foundation of China Under Grant No.50575101Transportation Science Research Item of Jiangsu Province Under Grant No.06Y20
文摘The dynamic finite element model （FEM） of a prestressed concrete continuous box-girder bridge, called the Tongyang Canal Bridge, is built and updated based on the results of ambient vibration testing （AVT） using a real-coded accelerating genetic algorithm （RAGA）. The objective functions are defined based on natural frequency and modal assurance criterion （MAC） metrics to evaluate the updated FEM. Two objective functions are defined to fully account for the relative errors and standard deviations of the natural frequencies and MAC between the AVT results and the updated FEM predictions. The dynamically updated FEM of the bridge can better represent its structural dynamics and serve as a baseline in long-term health monitoring, condition assessment and damage identification over the service life of the bridge .
基金Project(50925417)supported by the National Natureal Science Foundation for Distinguished Young Scholar of ChinaProject(51074191)supported by the National Natural Science Foundation of China
文摘The electrochemical degradation of reed pulp black liquor containing lignin pretreated by acidification method was investigated using a three-dimensional electrode reactor. Using activated carbon as particle electrode, the effects of p H value, reaction temperature, electrolysis time and current on residual concentration of total organic carbon(TOC) were discussed in detail. The optimal conditions were obtained: pH 2.5, influent flow rate of 200 mL/min, 25 °C, 300 mA and 2h of electrolysis time, and the removal efficiency of TOC maintains at 35.57 %. The results of the electrochemical method indicate that ·OH radicals are produced in activated carbon anode in the electrolysis process and then adsorbed on the activated carbon surface. Microcell consists of ·OH radicals and the absorbed lignin. With the microcell reaction, the lignin is degraded, while the anodic polarized curve illustrates that the lignin is obviously oxidized in the anode. The contributions of direct and indirect electrolyses to the TOC removal ratio are about 50%, respectively.
基金supported by the National Natural Science Foundation of China(61773202,71874081)the Special Financial Grant from China Postdoctoral Science Foundation(2017T100366)+2 种基金the Key Laboratory of Avionics System Integrated Technology for National Defense Science and Technology,China Institute of Avionics Radio Electronics(6142505180407)the Open Fund of CAAC Key laboratory of General Aviation Operation,Civil Aviation Management Institute of China(CAMICKFJJ-2019-04)the Innovation Project of the Civil Aviation Administration of China(EAB19001)。
文摘Signal reconstruction is a significantly important theoretical issue for compressed sensing.Considering the situation of signal reconstruction with unknown sparsity,the conventional signal reconstruction algorithms usually perform low accuracy.In this work,a sparsity adaptive signal reconstruction algorithm using sensing dictionary is proposed to achieve a lower reconstruction error.The sparsity estimation method is combined with the construction of the support set based on sensing dictionary.Using the adaptive sparsity method,an iterative signal reconstruction algorithm is proposed.The sufficient conditions for the exact signal reconstruction of the algorithm also is proved by theory.According to a series of simulations,the results show that the proposed method has higher precision compared with other state-of-the-art signal reconstruction algorithms especially in a high compression ratio scenarios.
基金Funded by the Nnational Natural Science Foundation of China(51372185)
文摘According to the results of accelerated tests of acidification corrosion depth and compressive strength of concretes subjected to sulfuric acid environments,the acidification depth laws of concretes were predicted based on the grey system theory.Thus,the remaining compressive strength was calculated when the acidification depth reached the protection layer thickness of concrete structures,which indicates that the limit state of durability failure can be defined based on strength degradation,and the calculation process was illustrated by an example.The calculated results show that the remaining compressive strength values in the durability failure limit state for the concrete structures exposed to p H=2 and 3 sulfuric acid water environments and wet-dry cyclic sulfuric acid environment with p H=2 are 74%,72%,and 80% of initialstrength,respectively.The method provides references for the durability evaluation of concrete structure design under the acidic environments.
基金financially supported by the National Natural Science Foundation of China(Grant No.50079002)
文摘An experimental research was conducted to determine the corrosion and bearing capacity of a reinforced concrete（RC） slab at different ages in a marine environment.Results show that the development of corrosion-induced cracks on a slab in a marine environment can be divided into three stages according to crack morphology at the bottom of the slab.In the first stage,cracks appear.In the second stage,cracks develop from the edges to the middle of the slab.In the third stage,longitudinal and transverse corrosion-induced cracks coexist.The corrosion ratio of reinforcements nonlinearly increases with the age,and the relationship between the corrosion ratio of the reinforcements and the corrosion-induced crack width of the concrete is established.The flexural capacity of the corroded RC slab nonlinearly decreases with the age,and the model for the bearing capacity factor of the corroded RC slab is established.The mid-span deflection of the corroded RC slab that corresponds to the yield of the reinforcements linearly increases with the increase in corrosion ratio.Finally,the mechanisms of corrosion morphology and the degradation of the mechanical properties of an RC slab in a marine environment are discussed on the basis of the basic theories of steel corrosion in concrete and concrete structure design.
基金Project(2002CB412707) supported by the National Basic Research Program of ChinaProject(2006BAG04B05) supported by the National Science and Technology Pillar Program during the 11th Five-Year Plan of ChinaProject(2010B14414) supported by the Scientific Research Program of Center University in China
文摘In order to realize information construction on settlement of pile-group foundation of Sutong Bridge, the monitoring instruments of high-precision micro-pressure sensor and hydrostatic leveling and settlement profiler were integrated synthetically. A set of practical multi-scale monitoring system on settlement of super-large pile-group foundation in deep water was put forward. The reliable settlement results are obtained by means of multi-sensor data fusion. Finite element model of pile-group foundation is established. By analysis of finite element simulated calculation of pile-group foundation, rules of settlement and uneven settlement obtained by monitoring and calculation results are coincident and the absolute error of settlement between them is 4.7 mm. The research shows that it is reasonable and feasible to monitor settlement of pile-group foundation with the system, and it can provide a method for the same type pile-group foundation in deep water.
基金supported by the National Natural Science Foundation of China(Grants No.51379058,51379060,and 51479064)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD Project)the Fundamental Research Funds for the Central Universities(Grants No.2016B06714 and 2014B07814)
文摘Flow characteristics of thermally stratified shear flow in braided rivers are particularly complicated and poorly understood. In this study, a series of typical flow patterns was examined and their critical criteria were determined. Four flow patterns were identified: mixed, locally unstable, continuously stratified, and two-layer flow. Temperature distributions of the four types of flow patterns were analyzed and compared.The critical Froude numbers for unstable flow, FDcr1, and stable flow, FDcr2, were determined to be 6 and 1, respectively, and comparison of FDcr1 and FDcr2 to the peak Froude numbers, FD1 at the outer bank and FD2 at the inner bank along the anabranch, allowed the flow patterns to be assessed. Then, a discriminant based on initial Jeffreys-Keulegan stability parameters was established to distinguish the flow stages from twolayer flow to completely mixed flow. It is indicated that the three critical Jeffreys-Keulegan parameters increased with the diversion angle of braided rivers. Results also show that, compared to the stratified flow in straight and curved channels, it was more difficult for braided stratified flow to maintain as two-layer flow, and it more easily became mixed flow. Consequently, empirical expressions for stability criteria of the thermally stratified shear flow in braided rivers are presented.
基金the financial support of National Key R&D Program of China(No.2019YFC1906200)the National Natural Science Foundation of China(Nos.51879093,51009057 and 52108206)+1 种基金Jiangsu Science and Technology Department of China(No.BE2015706)Science and Technology Project of Nanjing Water Authority(No.201802).
文摘Due to the existence of the attached mortar,the performance of the recycled concrete aggregate(RCA)is inferior to the natural aggregate,which significantly limits its wide application in industry.In this study,five kinds of modified solutions were used to modify the surface of RCA,and the modification effects were compared.The results showed that sodium silicate,nano-silica(NS),Bacillus pasteurii and soybean powder had relatively good modification effects on RCA,which could reduce the crushing value and water absorption,and increase apparent density.The composite solution(15%sodium silicate and 2%NS)and soybean powder solution had better modification effect.The 28 d compressive strength and splitting tensile strength of recycled aggregate concrete(RAC)prepared by RCA modified by soybean powder solution were 4.6%and 5.2%higher than those prepared by RCA modified by composite solution,respectively.This indicates that among the five kinds of modified solutions,soybean powder solution has the best modification effect on RCA,and the optimal soaking time of soybean powder solution is 8 h.At this time,the crushing value,water absorption and apparent density of RCA are 12.8%,5.3%,and 2653 kg/m^(3),respectively.The research results of this study provide a reference for the modification of RCA and its efficient utilization.
文摘Multi-pylon multi-span suspension bridge is a new type super flexible structure system, and the rigidity design of middle pylon is one of the main difficult technical issues. Due to the requirements of longitudinal rigidity, the structural form and the corresponding foundation type of middle pylon are different from those of the ordinary steel pylon, and the complicated dynamic characteristics make the calculation quite difficult. In this article, exploration has been made in selection of similarity ratio and model materials, section simulation, restriction conditions simulation, fixing of mass blocks, fabrication scheme and testing method by taking into account different construction and working conditions such as restriction conditions and working environment of a three-pylon suspension bridge, to conduct the test experimental design of the dynamic behavior of the middle pylon, with the purpose to reveal its dynamic characteristics and make comparison and analysis with theoretical assumptions, to provide basis for anti-wind and anti-seismic design and reference for the design and research of three-pylon two-span suspension bridges in the future.
基金supported by the Natural National Science Foundation of China(Grant Nos.51009052,11172090)the Three Gorge Research Center for Geo-Hazards,the Ministry of Education(Grant No.TGRC201026)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.2010B02514)the Key Laboratory of Coastal Disasters and Defence of Ministry of Education,Hohai University(Grant No.2010016)
文摘The rock permeability is an important parameter in the studies of seepage and stress coupling.The micro-cracks and pores can initiate and grow on a small scale and coalesce to form large-scale fractures and faults under compressive stresses,which would change the hydraulic conductivity of the rock,and therefore,the rock permeability.The rock permeability is,therefore,closely rela-ted with the micro-cracking growing,coalescence,and macro new fracture formation.This article proposes a conceptual model of rock permeability evolution and a micro kinematics mechanism of micro-cracking on the basis of the basic theory of micromechanics.The applicability of the established model is verified through numerical simulations of in situ tests and laboratory tests.The simu-lation results show that the model can accurately forecast the peak permeability evolution of brittle rock,and can well describe the macro-experimental phenomenon before the peak permeability evolution of brittle rock on a macro-scale.
基金Supported by the National Natural Science Foundation of China(50908046,50978056)the Teaching and Scientific Research Fund for Excellent Young Teachers of Southeast University(3205001101)+1 种基金the Basic Scientific andResearch Fund of Southeast University(Seucx-201106)the Priority Academic Program Development Foundation of Jiangsu Higher Education Institutions,China
文摘As a cable-stayed bridge with the longest main span, the Sutong Bridge faces the threat of typhoons every year. Based on field measured data measured at the top of the tower and at the mid-span by anemometers, Typhoon Muifa is analyzed in detail to obtain the wind characteristics, including the mean wind speed and direction, turbulence intensity and gust factor, power spectral density and integral scale of turbulence, etc. The correlated mean wind speeds at the two heights show the reliability of recorded wind data as well as the variation of wind speed with height. Turbulence inten- sities and gust factors fluctuate in a similar way. The values of inte- gral scales are sensitive in different case. The measured power spec- tra are particularly compared with Kaimal spectrum, Teunissen spectrum, Harris spectrum, and Davenport spectrum. The results show that the measured spectra cannot fit the code-suggested spectra very well, which exhibits the demand of more accurate spectra. Conclusions obtained in this article can provide references for wind resistance desima of suoer-long-soan cable-staved brides.
