In general,the material properties,loads,resistance of the prestressed concrete continuous rigid frame bridge in different construction stages are time-varying.So,it is essential to monitor the internal force state wh...In general,the material properties,loads,resistance of the prestressed concrete continuous rigid frame bridge in different construction stages are time-varying.So,it is essential to monitor the internal force state when the bridge is in construction.Among them,how to assess the safety is one of the challenges.As the continuous monitoring over a long-term period can increase the reliability of the assessment,so,based on a large number of monitored strain data collected from the structural health monitoring system(SHMS)during construction,a calculation method of the punctiform time-varying reliability is proposed in this paper to evaluate the stress state of this type bridge in cantilever construction stage by using the basic reliability theory.At the same time,the optimal stress distribution function in the bridge mid-span base plate is determined when the bridge is closed.This method can provide basis and direction for the internal force control of this type bridge in construction process.So,it can reduce the bridge safety and quality accidents in construction stages.展开更多
Although coal swelling/shrinking during coal seam gas extraction has been studied for decades,its impacts on the evolution of permeability are still not well understood.This has long been recognized,but no satisfactor...Although coal swelling/shrinking during coal seam gas extraction has been studied for decades,its impacts on the evolution of permeability are still not well understood.This has long been recognized,but no satisfactory solutions have been found.In previous studies,it is normally assumed that the matrix swelling/shrinking strain can be split between the fracture and the bulk coal and that the splitting coefficient remains unchanged during gas sorption.In this study,we defined the fracture strain as a function of permeability change ratio and back-calculated the fracture strains at different states.In the equilibrium state,the gas pressure is steady within the coal;in the non-equilibrium state,the gas pressure changes with time.For equilibrium states,the back-calculated fracture strains are extremely large and may be physically impossible in some case.For non-equilibrium states,two experiments were conducted:one for a natural coal sample and the other for a reconstructed one.For the fractured coal,the evolution of permeability is primarily controlled by the transition of coal fracture strain or permeability from local matrix swelling effect to global effect.For the reconstituted coal,the evolution of pore strain or permeability is primarily controlled by the global effect.展开更多
According to the well-known models for rubberlike elasticity with strain- stii^ening effects, the unbounded strain energy is generated with the unlimitedly growing stress when the stretch approaches certain limits. To...According to the well-known models for rubberlike elasticity with strain- stii^ening effects, the unbounded strain energy is generated with the unlimitedly growing stress when the stretch approaches certain limits. Toward a solution to this issue, an explicit approach is proposed to derive the multi-axial elastic potentials directly from the uniaxial potentials. Then, a new multi-axial potential is presented to characterize the strain-stiffening effect by prescribing suitable forms of uniaxia] potentials so that the strain energy is always bounded as the stress grows to infinity. Numerical examples show good agreement with a number of test data.展开更多
Optical full-field measurement methods are now widely applied in various domains. In general,the displacement fields can be directly obtained from the measurement,however in mechanical analysis strain fields are prefe...Optical full-field measurement methods are now widely applied in various domains. In general,the displacement fields can be directly obtained from the measurement,however in mechanical analysis strain fields are preferred.To extract strain fields from noisy displacement fields is always a challenging topic.In this study,a finite element method for smoothing displacement fields and calculating strain fields is proposed.An experimental test case on a holed aluminum specimen under tension is applied to validate this method.The heterogeneous displacement fields are measured by digital image correlation(DIC).By this proposed method,the result shows that the measuring noise on experimental displacement fields can be successfully removed,and strain fields can be reconstructed in the arbitrary area.展开更多
Based on the principle formula for the four-component strainmeters, we can directly obtain the specific plane strain, shear strain and azimuthal angle of the principal strain, and the maximum and minimum principal str...Based on the principle formula for the four-component strainmeters, we can directly obtain the specific plane strain, shear strain and azimuthal angle of the principal strain, and the maximum and minimum principal strains calculated afterwards are the indirect result. The problems of practicality of the sensitivity coefficients A and B of plane strain and shear strain are then discussed. Based on this idea, we analyzed the observation data of several four-component borehole strainmeters near the epicenter of the Yiliang M_S5.7 earthquake in 2012 and the Ludian M_S6.5 earthquake in 2014 in the Zhaotong area, Yunnan Province. The results show that the analysis based on the perspective of plane strain and shear strain has an obviously better effect than that based on the component readings, and can directly peel off the respective abnormality of the plane strain and shear strain. In addition, the correlation coefficient curves between measured data of two plane strains show significant anomalies which often occur several days before and during the earthquake.展开更多
Based on pseudo strain energy density (PSED) and grey relation coefficient (GRC), an index is proposed to locate the damage of beam-type structures in time-domain. The genetic algorithm (GA) is utilized to identify th...Based on pseudo strain energy density (PSED) and grey relation coefficient (GRC), an index is proposed to locate the damage of beam-type structures in time-domain. The genetic algorithm (GA) is utilized to identify the structural damage severity of confirmed damaged locations. Furthermore, a systematic damage identification program based on GA is developed on MATLAB platform. ANSYS is employed to conduct the finite element analysis of complicated civil engineering structures, which is embedded with interface technique. The two-step damage identification is verified by a finite element model of Xinxingtang Highway Bridge and a laboratory beam model based on polyvinylidens fluoride (PVDF). The bridge model was constructed with 57 girder segments, and simulated with 58 measurement points. The damaged segments were located accurately by GRC index regardless of damage extents and noise levels. With stiffness reduction factors of detected segments as variables, the GA program evolved for 150 generations in 6 h and identified the damage extent with the maximum errors of 1% and 3% corresponding to the noise to signal ratios of 0 and 5%, respectively. In contrast, the common GA-based method without using GRC index evolved for 600 generations in 24 h, but failed to obtain satisfactory results. In the laboratory test, PVDF patches were used as dynamic strain sensors, and the damage locations were identified due to the fact that GRC indexes of points near damaged elements were smaller than 0.6 while those of others were larger than 0.6. The GA-based damage quantification was also consistent with the value of crack depth in the beam model.展开更多
In order to achieve an access to strain sensor data with wireless transmission in bridge engineering structure testing, a wireless strain test system is presented based on the resistance strain sensor of networks. The...In order to achieve an access to strain sensor data with wireless transmission in bridge engineering structure testing, a wireless strain test system is presented based on the resistance strain sensor of networks. The wireless bridge strain test system composed of master station and substation adopts the wireless method to realize the high accuracy data acquisition between the master station and the substation under a reliable communication protocol. The system has been tested in contrast with the present strain apparatus. Results show that the wireless system is high-reliable, and has many characteristics such as high efficiency, good precision, high stability with low cost, and good flexibility, without using the present communication network.展开更多
The fatigue of concrete structures will gradually appear after being subjected to alternating loads for a long time,and the accidents caused by fatigue failure of bridge structures also appear from time to time.Aiming...The fatigue of concrete structures will gradually appear after being subjected to alternating loads for a long time,and the accidents caused by fatigue failure of bridge structures also appear from time to time.Aiming at the problem of degradation of long-span continuous rigid frame bridges due to fatigue and environmental effects,this paper suggests a method to analyze the fatigue degradation mechanism of this type of bridge,which combines long-term in-site monitoring data collected by the health monitoring system(HMS)and fatigue theory.In the paper,the authors mainly carry out the research work in the following aspects:First of all,a long-span continuous rigid frame bridge installed with HMS is used as an example,and a large amount of health monitoring data have been acquired,which can provide efficient information for fatigue in terms of equivalent stress range and cumulative number of stress cycles;next,for calculating the cumulative fatigue damage of the bridge structure,fatigue stress spectrum got by rain flow counting method,S-N curves and damage criteria are used for fatigue damage analysis.Moreover,it was considered a linear accumulation damage through the Palmgren-Miner rule for the counting of stress cycles.The health monitoring data are adopted to obtain fatigue stress data and the rain flow counting method is used to count the amplitude varying fatigue stress.The proposed fatigue reliability approach in the paper can estimate the fatigue damage degree and its evolution law of bridge structures well,and also can help bridge engineers do the assessment of future service duration.展开更多
In order to research contemporary crustal movement of Antarctica, China has constructed the deformation monitoring network in the Fildes Strait region,West Antarctica, monitored the network by using DI 20 geodimeter...In order to research contemporary crustal movement of Antarctica, China has constructed the deformation monitoring network in the Fildes Strait region,West Antarctica, monitored the network by using DI 20 geodimeter and GPS instruments, and participated the Antarctic GPS Campaign Observation organized by SCAR as well. During mathematics processing of crustal horizontal deformation observations,a method to bring deformation parameters into the error equations of observations is discussed in this paper. Several classical deformation models,such as rigid body displacement and strain,are introduced. By analyzing the reference datum of static and dynamic geodetic network,the method is developed to set up different additional weight matrix for every different kind of parameter. A series of programs are developed to implementing the method mentioned above and the analysis of West Antarctic Fildes Strait deformation monitoring network. Discussion is also made of GPS monitoring data by using the principle of monitoring network strain analysis in the paper. The research results indicate that the displacement did occur in Fildes rift region,but the displacement was not large,just a slight rift shear movement.展开更多
The Zipingpu Concrete Faced Rockfill Dam （CFRD） was subjected to significant local damage in the ＂5.12＂ Wenchuan earthquake. It is the first rockfill dam of more than one hundred meters high to encounter a strong ...The Zipingpu Concrete Faced Rockfill Dam （CFRD） was subjected to significant local damage in the ＂5.12＂ Wenchuan earthquake. It is the first rockfill dam of more than one hundred meters high to encounter a strong earthquake anywhere in the world. Based on the finite element smoothing method, the residual strains at a typical cross-section and a downstream slope of the dam were obtained by processing the dam monitored displacement data. The position of and reason for the dam settlement and deformation ofrockfill dilatancy in the earthquake were analyzed according to the section residual strain. The results show that the maximum settlement ratio on the dam body approximately occurs at 2/3 of the dam height; dilatancy occurs from the dam crest to 25-30 m in the upstream and downstream slope; the immediate cause of the face slabs horizontal construction joint dislocation is excessive residual shear strain. Meanwhile, the position of and reason for the dam fissure in the earthquake were analyzed according to the dam slope residual strain.展开更多
We analyzed 360 permanent and campaign GPS data from 1999 to 2017 in the southern Sichuan-Yunan block, and obtained crustal horizontal deformation in this region.Then, we derived the strain rate using a multi-scale sp...We analyzed 360 permanent and campaign GPS data from 1999 to 2017 in the southern Sichuan-Yunan block, and obtained crustal horizontal deformation in this region.Then, we derived the strain rate using a multi-scale spherical wavelet method.Results reveal a complex pattern of tectonic movement in the southern Sichuan-Yunnan block.Compared to the stable Eurasian plate, the maximum rate of the horizontal deformation in the southern Sichuan-Yunnan block is approximately 22 mm/a.The Xiaojiang fault shows a significantly lower deformation—a left-lateral strike-slip movement of 9.5 mm/a.The Honghe fault clearly shows a complex segmental deformation from the north to south.The northern Honghe fault shows 4.3 mm/a right strike-slip with 6.7 mm/a extension; the southern Honghe fault shows 1.9 mm/a right strike-slip with 1.9 mm/a extension; the junction zone in the Honghe and Lijiang–Xiaojinhe faults shows an obvious clockwise-rotation deformation.The strain calculation results reveal that the maximum shear-strain rate in this region reaches 70 nstrain/a, concentrated around the Xiaojiang fault and at the junction of the Honghe and Lijiang–Xiaojinhe faults.We note that most of the earthquakes with magnitudes of 4 and above that occurred in this region were within the high shear strain-rate zones and the strain rate gradient boundary zone, which indicates that the magnitude of strain accumulation is closely related to the seismic activities.Comparison of the fast shear-wave polarization direction of the upper-crust with the upper-mantle anisotropy and the direction of the surface principal compressive strain rate obtained from the inversion of the GPS data reveals that the direction of the surface principal compressive strain is basically consistent with the fast shear-wave polarization direction of the upper crust anisotropy, but different from the polarization direction of the upper mantle.Our results support the hypothesis that the principal elements of the deformation mechanism in the southern Sichuan-Yunnan block are decoupling between the upper and lower crust and ductile flow in the lower crust.展开更多
文摘In general,the material properties,loads,resistance of the prestressed concrete continuous rigid frame bridge in different construction stages are time-varying.So,it is essential to monitor the internal force state when the bridge is in construction.Among them,how to assess the safety is one of the challenges.As the continuous monitoring over a long-term period can increase the reliability of the assessment,so,based on a large number of monitored strain data collected from the structural health monitoring system(SHMS)during construction,a calculation method of the punctiform time-varying reliability is proposed in this paper to evaluate the stress state of this type bridge in cantilever construction stage by using the basic reliability theory.At the same time,the optimal stress distribution function in the bridge mid-span base plate is determined when the bridge is closed.This method can provide basis and direction for the internal force control of this type bridge in construction process.So,it can reduce the bridge safety and quality accidents in construction stages.
基金supported by the State Key Research Development Program of China(Grant No.2017YFC0804203)Key Research Program of Frontier Sciences,Chinese Academy of Sciences(Grant No.QYZDB-SSW-DQC029)the Australian Research Council under Grant DP200101293.
文摘Although coal swelling/shrinking during coal seam gas extraction has been studied for decades,its impacts on the evolution of permeability are still not well understood.This has long been recognized,but no satisfactory solutions have been found.In previous studies,it is normally assumed that the matrix swelling/shrinking strain can be split between the fracture and the bulk coal and that the splitting coefficient remains unchanged during gas sorption.In this study,we defined the fracture strain as a function of permeability change ratio and back-calculated the fracture strains at different states.In the equilibrium state,the gas pressure is steady within the coal;in the non-equilibrium state,the gas pressure changes with time.For equilibrium states,the back-calculated fracture strains are extremely large and may be physically impossible in some case.For non-equilibrium states,two experiments were conducted:one for a natural coal sample and the other for a reconstructed one.For the fractured coal,the evolution of permeability is primarily controlled by the transition of coal fracture strain or permeability from local matrix swelling effect to global effect.For the reconstituted coal,the evolution of pore strain or permeability is primarily controlled by the global effect.
基金supported by the National Natural Science Foundation of China(No.11372172)the Start-up Fund from the 211-Project of the Education Committee of China(No.S.15-B002-09-032)the Research Innovation Fund of Shanghai University(No.S.10-0401-12-001)
文摘According to the well-known models for rubberlike elasticity with strain- stii^ening effects, the unbounded strain energy is generated with the unlimitedly growing stress when the stretch approaches certain limits. Toward a solution to this issue, an explicit approach is proposed to derive the multi-axial elastic potentials directly from the uniaxial potentials. Then, a new multi-axial potential is presented to characterize the strain-stiffening effect by prescribing suitable forms of uniaxia] potentials so that the strain energy is always bounded as the stress grows to infinity. Numerical examples show good agreement with a number of test data.
基金supported by the National Basic Research Program of China("973"Project, Grant No.2010CB631005,2011CB606105)the National Natural Science Foundation of China(Grant No.10625209, 10732080,90916010)+2 种基金China Postdoctoral Science Foundation (Grant No.20090460335)Specialized Research Fund for the Doctoral Program of Higher Education(Grant No.20090002110048)the opening funds from the State Key Laboratory of Explosion Science and Technology (KFJJ10-18Y)
文摘Optical full-field measurement methods are now widely applied in various domains. In general,the displacement fields can be directly obtained from the measurement,however in mechanical analysis strain fields are preferred.To extract strain fields from noisy displacement fields is always a challenging topic.In this study,a finite element method for smoothing displacement fields and calculating strain fields is proposed.An experimental test case on a holed aluminum specimen under tension is applied to validate this method.The heterogeneous displacement fields are measured by digital image correlation(DIC).By this proposed method,the result shows that the measuring noise on experimental displacement fields can be successfully removed,and strain fields can be reconstructed in the arbitrary area.
基金sponsored by the Central Level Scientific Research Institutes of Basic R&D Special Fund Business of the Institute of Crustal Dynamics,CEA(ZDJ2017-25)
文摘Based on the principle formula for the four-component strainmeters, we can directly obtain the specific plane strain, shear strain and azimuthal angle of the principal strain, and the maximum and minimum principal strains calculated afterwards are the indirect result. The problems of practicality of the sensitivity coefficients A and B of plane strain and shear strain are then discussed. Based on this idea, we analyzed the observation data of several four-component borehole strainmeters near the epicenter of the Yiliang M_S5.7 earthquake in 2012 and the Ludian M_S6.5 earthquake in 2014 in the Zhaotong area, Yunnan Province. The results show that the analysis based on the perspective of plane strain and shear strain has an obviously better effect than that based on the component readings, and can directly peel off the respective abnormality of the plane strain and shear strain. In addition, the correlation coefficient curves between measured data of two plane strains show significant anomalies which often occur several days before and during the earthquake.
基金Supported by National Natural Science Foundation of China (No. 50778077 and No. 50608036)
文摘Based on pseudo strain energy density (PSED) and grey relation coefficient (GRC), an index is proposed to locate the damage of beam-type structures in time-domain. The genetic algorithm (GA) is utilized to identify the structural damage severity of confirmed damaged locations. Furthermore, a systematic damage identification program based on GA is developed on MATLAB platform. ANSYS is employed to conduct the finite element analysis of complicated civil engineering structures, which is embedded with interface technique. The two-step damage identification is verified by a finite element model of Xinxingtang Highway Bridge and a laboratory beam model based on polyvinylidens fluoride (PVDF). The bridge model was constructed with 57 girder segments, and simulated with 58 measurement points. The damaged segments were located accurately by GRC index regardless of damage extents and noise levels. With stiffness reduction factors of detected segments as variables, the GA program evolved for 150 generations in 6 h and identified the damage extent with the maximum errors of 1% and 3% corresponding to the noise to signal ratios of 0 and 5%, respectively. In contrast, the common GA-based method without using GRC index evolved for 600 generations in 24 h, but failed to obtain satisfactory results. In the laboratory test, PVDF patches were used as dynamic strain sensors, and the damage locations were identified due to the fact that GRC indexes of points near damaged elements were smaller than 0.6 while those of others were larger than 0.6. The GA-based damage quantification was also consistent with the value of crack depth in the beam model.
基金Sponsored by the Multidisciline Scientific Research Foundation of Harbin Institute of Technology(Grant No.HIT.MD2003.14)the Scientific Research Foundation of Liaoning Provincial Communication Department(Grant No.200516)
文摘In order to achieve an access to strain sensor data with wireless transmission in bridge engineering structure testing, a wireless strain test system is presented based on the resistance strain sensor of networks. The wireless bridge strain test system composed of master station and substation adopts the wireless method to realize the high accuracy data acquisition between the master station and the substation under a reliable communication protocol. The system has been tested in contrast with the present strain apparatus. Results show that the wireless system is high-reliable, and has many characteristics such as high efficiency, good precision, high stability with low cost, and good flexibility, without using the present communication network.
文摘The fatigue of concrete structures will gradually appear after being subjected to alternating loads for a long time,and the accidents caused by fatigue failure of bridge structures also appear from time to time.Aiming at the problem of degradation of long-span continuous rigid frame bridges due to fatigue and environmental effects,this paper suggests a method to analyze the fatigue degradation mechanism of this type of bridge,which combines long-term in-site monitoring data collected by the health monitoring system(HMS)and fatigue theory.In the paper,the authors mainly carry out the research work in the following aspects:First of all,a long-span continuous rigid frame bridge installed with HMS is used as an example,and a large amount of health monitoring data have been acquired,which can provide efficient information for fatigue in terms of equivalent stress range and cumulative number of stress cycles;next,for calculating the cumulative fatigue damage of the bridge structure,fatigue stress spectrum got by rain flow counting method,S-N curves and damage criteria are used for fatigue damage analysis.Moreover,it was considered a linear accumulation damage through the Palmgren-Miner rule for the counting of stress cycles.The health monitoring data are adopted to obtain fatigue stress data and the rain flow counting method is used to count the amplitude varying fatigue stress.The proposed fatigue reliability approach in the paper can estimate the fatigue damage degree and its evolution law of bridge structures well,and also can help bridge engineers do the assessment of future service duration.
文摘In order to research contemporary crustal movement of Antarctica, China has constructed the deformation monitoring network in the Fildes Strait region,West Antarctica, monitored the network by using DI 20 geodimeter and GPS instruments, and participated the Antarctic GPS Campaign Observation organized by SCAR as well. During mathematics processing of crustal horizontal deformation observations,a method to bring deformation parameters into the error equations of observations is discussed in this paper. Several classical deformation models,such as rigid body displacement and strain,are introduced. By analyzing the reference datum of static and dynamic geodetic network,the method is developed to set up different additional weight matrix for every different kind of parameter. A series of programs are developed to implementing the method mentioned above and the analysis of West Antarctic Fildes Strait deformation monitoring network. Discussion is also made of GPS monitoring data by using the principle of monitoring network strain analysis in the paper. The research results indicate that the displacement did occur in Fildes rift region,but the displacement was not large,just a slight rift shear movement.
基金National Natural Science Foundation of China under Grant No. 50979014, 51179024China Higher School Specialized Research Funds for Doctors under Grant No. 20090041110016
文摘The Zipingpu Concrete Faced Rockfill Dam （CFRD） was subjected to significant local damage in the ＂5.12＂ Wenchuan earthquake. It is the first rockfill dam of more than one hundred meters high to encounter a strong earthquake anywhere in the world. Based on the finite element smoothing method, the residual strains at a typical cross-section and a downstream slope of the dam were obtained by processing the dam monitored displacement data. The position of and reason for the dam settlement and deformation ofrockfill dilatancy in the earthquake were analyzed according to the section residual strain. The results show that the maximum settlement ratio on the dam body approximately occurs at 2/3 of the dam height; dilatancy occurs from the dam crest to 25-30 m in the upstream and downstream slope; the immediate cause of the face slabs horizontal construction joint dislocation is excessive residual shear strain. Meanwhile, the position of and reason for the dam fissure in the earthquake were analyzed according to the dam slope residual strain.
基金supported by the National Natural Science Foundation of China (Project 41730212)the Basic Research Project of the Institute of Earthquake Forecasting, China Earthquake Administration (Grant No.2017IES0102, 2016IES0201)
文摘We analyzed 360 permanent and campaign GPS data from 1999 to 2017 in the southern Sichuan-Yunan block, and obtained crustal horizontal deformation in this region.Then, we derived the strain rate using a multi-scale spherical wavelet method.Results reveal a complex pattern of tectonic movement in the southern Sichuan-Yunnan block.Compared to the stable Eurasian plate, the maximum rate of the horizontal deformation in the southern Sichuan-Yunnan block is approximately 22 mm/a.The Xiaojiang fault shows a significantly lower deformation—a left-lateral strike-slip movement of 9.5 mm/a.The Honghe fault clearly shows a complex segmental deformation from the north to south.The northern Honghe fault shows 4.3 mm/a right strike-slip with 6.7 mm/a extension; the southern Honghe fault shows 1.9 mm/a right strike-slip with 1.9 mm/a extension; the junction zone in the Honghe and Lijiang–Xiaojinhe faults shows an obvious clockwise-rotation deformation.The strain calculation results reveal that the maximum shear-strain rate in this region reaches 70 nstrain/a, concentrated around the Xiaojiang fault and at the junction of the Honghe and Lijiang–Xiaojinhe faults.We note that most of the earthquakes with magnitudes of 4 and above that occurred in this region were within the high shear strain-rate zones and the strain rate gradient boundary zone, which indicates that the magnitude of strain accumulation is closely related to the seismic activities.Comparison of the fast shear-wave polarization direction of the upper-crust with the upper-mantle anisotropy and the direction of the surface principal compressive strain rate obtained from the inversion of the GPS data reveals that the direction of the surface principal compressive strain is basically consistent with the fast shear-wave polarization direction of the upper crust anisotropy, but different from the polarization direction of the upper mantle.Our results support the hypothesis that the principal elements of the deformation mechanism in the southern Sichuan-Yunnan block are decoupling between the upper and lower crust and ductile flow in the lower crust.
