When the bridge components needing maintenance are the world problem at present,and the health monitoring system is considered to be a very helpful tool for solving this problem.In this paper,a large number of s...When the bridge components needing maintenance are the world problem at present,and the health monitoring system is considered to be a very helpful tool for solving this problem.In this paper,a large number of strain data acquired from the structural health monitoring system(SHMS)installed on a continuous rigid frame bridge are adopted to do reliability assessment.Firstly,a calculation method of punctiform time-dependent reliability is proposed based on the basic reliability theory,and introduced how to calculate reliability of the bridge by using the stress data transformed from the strain data.Secondly,combined with“Three Sigma”principle and the basic pressure safety reserve requirement,the critical load effects distribution function of the bridge is defined,and then the maintenance reliability threshold for controlling the unfavorable load state which appears in the early operation stage of this type bridge is suggested,and then the combination of bridge maintenance management and health monitoring system is realized.Finally,the transformed stress distribution certifies that the load effects of concrete bridges practically have a normal distribution;as for the concrete continuous rigid frame bridge with C50 strength grade concrete,the retrofit reliability threshold should be valued at 6.13.The methodology suggested in this article can help bridge engineers do effective maintenance of bridges,which can effectively extend the service life of the bridge and bring better economic and social benefits.展开更多
Metal carbyne(M≡C)complexes have been discovered for nearly half a century,however,they gained far less study in comparison with metal-carbon single bond(M—C)and metal carbene(M=C)species in synthetic chemistry.Up t...Metal carbyne(M≡C)complexes have been discovered for nearly half a century,however,they gained far less study in comparison with metal-carbon single bond(M—C)and metal carbene(M=C)species in synthetic chemistry.Up to three sigma bonds are possibly forged on a single carbon through metal carbynes or carbyne equivalents,which holds great potentials in organic synthesis but also requires high efficiency of bond formation and precise control of reactivity and selectivity.Along this line,two systems based on stoi-chiometric transformations of manganese carbynes and ruthenium/rhodium-catalyzed reactions of diazo hypervalent iodine reagents,carbyne equivalents,have emerged recently,which will be highlighted herein.Future potentials and challenges in this intriguing area are also briefly discussed.展开更多
Due to large topography slopes in natural rivers, pollutant concentration embodies a property of three-dimensional distribution when wastewater is discharged from effluents along the bank. With the sigma coordinate al...Due to large topography slopes in natural rivers, pollutant concentration embodies a property of three-dimensional distribution when wastewater is discharged from effluents along the bank. With the sigma coordinate along the vertical dimension fitted to both the moving free surface and the bed topography, a three-dimensional numerical model was developed in the present work to address pollutant transport processes in the above-mentioned cases. To avoid the reduction in accuracy caused by spurious diffusion in the case of steep bottom slopes, a formula for horizontal diffusion in the sigma coordinate system was derived. A case study for the side discharge into a straight open-channel flow shows that numerical results are verified well by experimental data. Furthermore, the present model is also verified by the simulation of discharging wastewater from Fuling Phosphorus Factory effluent into the Three Gorges Reservoir and the agreement between the numerical simulation results and field observation data is satisfactory. The change of the mixing zone scope in the water surface versus the layers along the vertical dimension was also discussed in detail. The study shows that a more realistic calculation for pollutant discharge has been provided by the present model than by the depth-average model which predicts an unrealistically smaller mixing zone.展开更多
文摘When the bridge components needing maintenance are the world problem at present,and the health monitoring system is considered to be a very helpful tool for solving this problem.In this paper,a large number of strain data acquired from the structural health monitoring system(SHMS)installed on a continuous rigid frame bridge are adopted to do reliability assessment.Firstly,a calculation method of punctiform time-dependent reliability is proposed based on the basic reliability theory,and introduced how to calculate reliability of the bridge by using the stress data transformed from the strain data.Secondly,combined with“Three Sigma”principle and the basic pressure safety reserve requirement,the critical load effects distribution function of the bridge is defined,and then the maintenance reliability threshold for controlling the unfavorable load state which appears in the early operation stage of this type bridge is suggested,and then the combination of bridge maintenance management and health monitoring system is realized.Finally,the transformed stress distribution certifies that the load effects of concrete bridges practically have a normal distribution;as for the concrete continuous rigid frame bridge with C50 strength grade concrete,the retrofit reliability threshold should be valued at 6.13.The methodology suggested in this article can help bridge engineers do effective maintenance of bridges,which can effectively extend the service life of the bridge and bring better economic and social benefits.
基金Financial support from the National Natural Science Foundation of China(22025109,21772202)Beijing National Laboratory for Molecular Sciences(BNLMS-CXXM-201901)the K.C.Wong Education Foundation is gratefully acknowledged.
文摘Metal carbyne(M≡C)complexes have been discovered for nearly half a century,however,they gained far less study in comparison with metal-carbon single bond(M—C)and metal carbene(M=C)species in synthetic chemistry.Up to three sigma bonds are possibly forged on a single carbon through metal carbynes or carbyne equivalents,which holds great potentials in organic synthesis but also requires high efficiency of bond formation and precise control of reactivity and selectivity.Along this line,two systems based on stoi-chiometric transformations of manganese carbynes and ruthenium/rhodium-catalyzed reactions of diazo hypervalent iodine reagents,carbyne equivalents,have emerged recently,which will be highlighted herein.Future potentials and challenges in this intriguing area are also briefly discussed.
基金supported by the National Basic Research and Development Program of China (973 Program, Grant No. 2006CB403304)
文摘Due to large topography slopes in natural rivers, pollutant concentration embodies a property of three-dimensional distribution when wastewater is discharged from effluents along the bank. With the sigma coordinate along the vertical dimension fitted to both the moving free surface and the bed topography, a three-dimensional numerical model was developed in the present work to address pollutant transport processes in the above-mentioned cases. To avoid the reduction in accuracy caused by spurious diffusion in the case of steep bottom slopes, a formula for horizontal diffusion in the sigma coordinate system was derived. A case study for the side discharge into a straight open-channel flow shows that numerical results are verified well by experimental data. Furthermore, the present model is also verified by the simulation of discharging wastewater from Fuling Phosphorus Factory effluent into the Three Gorges Reservoir and the agreement between the numerical simulation results and field observation data is satisfactory. The change of the mixing zone scope in the water surface versus the layers along the vertical dimension was also discussed in detail. The study shows that a more realistic calculation for pollutant discharge has been provided by the present model than by the depth-average model which predicts an unrealistically smaller mixing zone.
