A stochastic finite element computational methodology for probabilistic durability assessment of deteriorating reinforced concrete（RC） bridges by considering the time-and space-dependent variabilities is presented.F...A stochastic finite element computational methodology for probabilistic durability assessment of deteriorating reinforced concrete（RC） bridges by considering the time-and space-dependent variabilities is presented.First,finite element analysis with a smeared cracking approach is implemented.The time-dependent bond-slip relationship between steel and concrete,and the stress-strain relationship of corroded steel bars are considered.Secondly,a stochastic finite element-based computational framework for reliability assessment of deteriorating RC bridges is proposed.The spatial and temporal variability of several parameters affecting the reliability of RC bridges is considered.Based on the data reported by several researchers and from field investigations,the Monte Carlo simulation is used to account for the uncertainties in various parameters,including local and general corrosion in rebars,concrete cover depth,surface chloride concentration,chloride diffusion coefficient,and corrosion rate.Finally,the proposed probabilistic durability assessment approach and framework are applied to evaluate the time-dependent reliability of a girder of a RC bridge located on the Tianjin Binhai New Area in China.展开更多
Differences and similarities of durability design for concrete bridges in Chinese-code and Eurocode are identified and discussed. Exposure environment classes and regulations of the minimum concrete cover and strength...Differences and similarities of durability design for concrete bridges in Chinese-code and Eurocode are identified and discussed. Exposure environment classes and regulations of the minimum concrete cover and strength of the two codes are compared and analyzed. Numerical calculations for predicting the durable life of bridges related to carbonization and chlorides corrosion （marine and de-icing） are conducted. The results show that provisions in the two codes can satisfy the durability requirements under carbonization whereas they cannot guarantee the durability for bridges in spray and splash zones. Enhancing the waterproof capacity and reducing the frequent use of de-icing agents are vital to improving the bridge durability. Some recommendations for upgrading the durability are also included.展开更多
Bidirectional electromigration rehabilitation(BIEM)is a novel electrochemical rehabilitation method involving the injection of inhibitors into steel bar surface.The BIEM effect and hydrogen embrittlement(HE)risk depen...Bidirectional electromigration rehabilitation(BIEM)is a novel electrochemical rehabilitation method involving the injection of inhibitors into steel bar surface.The BIEM effect and hydrogen embrittlement(HE)risk depend on the electrochemical parameters(current density and duration)and operating condition(stress level and concrete cover thickness)of reinforced concrete structures.Experiments were performed in this study to investigate the relationships between the aforementioned factors.For a small current density group,a linear relationship was established between electric flux and chloride extraction.For a large current density group,the reasonable current density,stress level,and treatment time were obtained.Finally,the querying method of electrochemical parameters combined with treatment time and current density was proposed.展开更多
In order to improve the capability of the RFCC unit for heavy oil conversion, reduce the yields of coke and oil slurry, and increase the economic benefits of the unit, starting August 2007 the SINOPEC Luoyang Branch C...In order to improve the capability of the RFCC unit for heavy oil conversion, reduce the yields of coke and oil slurry, and increase the economic benefits of the unit, starting August 2007 the SINOPEC Luoyang Branch Company began to apply in its No. 2 RFCC unit the Endurance catalyst featuring strong heavy oil conversion ability, low yields of coke and oil slurry, and high total light liquid yield. The results on calibration of the Endurance catalyst conducted in November 2007 indi-cated that under the circumstances of using deteriorating feedstock quality and lower unit consump-tion of catalyst, the yields of coke, oil slurry and gas decreased by 0.28 %, 1.24 % and 0.35 %, respectively. The light distillate yield and total light liquid yield increased by 0.8 % and 1.88%, respectively.展开更多
Alloying Pt with transition metals can significantly improve the catalytic properties for the oxygen reduction reaction(ORR).However,the application of Pt-transition metal alloys in fuel cells is largely limited by po...Alloying Pt with transition metals can significantly improve the catalytic properties for the oxygen reduction reaction(ORR).However,the application of Pt-transition metal alloys in fuel cells is largely limited by poor long-term durability because transition metals can easily leach.In this study,we developed a nonmetallic doping approach and prepared a P-doped Pt catalyst with excellent durability for the ORR.Carbon-supported core-shell nanoparticles with a P-doped Pt core and Pt shell(denoted as PtPx@Pt/C)were synthesized via heat-treatment phosphorization of commercial Pt/C,followed by acid etching.Compositional analysis using electron energy loss spectroscopy and X-ray photoelectron spectroscopy clearly demonstrated that Pt was enriched in the near-surface region(approximately 1 nm)of the carbon-supported core-shell nanoparticles.Owning to P doping,the ORR specific activity and mass activity of the PtP_(1.4)@Pt/C catalyst were as high as 0.62 mA cm^(–2)and 0.31 mAμgPt–^(1),respectively,at 0.90 V,and they were enhanced by 2.8 and 2.1 times,respectively,in comparison with the Pt/C catalyst.More importantly,PtP_(1.4)@Pt/C exhibited superior stability with negligible mass activity loss(6%after 30000 potential cycles and 25%after 90000 potential cycles),while Pt/C lost 46%mass activity after 30000 potential cycles.The high ORR activity and durability were mainly attributed to the core-shell nanostructure,the electronic structure effect,and the resistance of Pt nanoparticles against aggregation,which originated from the enhanced ability of the PtP_(1.4)@Pt to anchor to the carbon support.This study provides a new approach for constructing nonmetal-doped Pt-based catalysts with excellent activity and durability for the ORR.展开更多
基金The National Natural Science Foundation of China (No.50708065)the National High Technology Research and Development Program of China (863 Program) (No. 2007AA11Z113)Specialized Research Fund for the Doctoral Program of Higher Education (No. 20070056125)
文摘A stochastic finite element computational methodology for probabilistic durability assessment of deteriorating reinforced concrete（RC） bridges by considering the time-and space-dependent variabilities is presented.First,finite element analysis with a smeared cracking approach is implemented.The time-dependent bond-slip relationship between steel and concrete,and the stress-strain relationship of corroded steel bars are considered.Secondly,a stochastic finite element-based computational framework for reliability assessment of deteriorating RC bridges is proposed.The spatial and temporal variability of several parameters affecting the reliability of RC bridges is considered.Based on the data reported by several researchers and from field investigations,the Monte Carlo simulation is used to account for the uncertainties in various parameters,including local and general corrosion in rebars,concrete cover depth,surface chloride concentration,chloride diffusion coefficient,and corrosion rate.Finally,the proposed probabilistic durability assessment approach and framework are applied to evaluate the time-dependent reliability of a girder of a RC bridge located on the Tianjin Binhai New Area in China.
文摘Differences and similarities of durability design for concrete bridges in Chinese-code and Eurocode are identified and discussed. Exposure environment classes and regulations of the minimum concrete cover and strength of the two codes are compared and analyzed. Numerical calculations for predicting the durable life of bridges related to carbonization and chlorides corrosion （marine and de-icing） are conducted. The results show that provisions in the two codes can satisfy the durability requirements under carbonization whereas they cannot guarantee the durability for bridges in spray and splash zones. Enhancing the waterproof capacity and reducing the frequent use of de-icing agents are vital to improving the bridge durability. Some recommendations for upgrading the durability are also included.
基金Projects(51908496,51878610,51820105012,51778577,51638013)supported by the National Natural Science Foundation of ChinaProjects(LY18E080003,LQ19E080011,LQ19E080012,LQ20E080001)supported by the Natural Science Foundation of Zhejiang Province,ChinaProject(2018A610359)supported by the Natural Science Foundation of Ningbo,China。
文摘Bidirectional electromigration rehabilitation(BIEM)is a novel electrochemical rehabilitation method involving the injection of inhibitors into steel bar surface.The BIEM effect and hydrogen embrittlement(HE)risk depend on the electrochemical parameters(current density and duration)and operating condition(stress level and concrete cover thickness)of reinforced concrete structures.Experiments were performed in this study to investigate the relationships between the aforementioned factors.For a small current density group,a linear relationship was established between electric flux and chloride extraction.For a large current density group,the reasonable current density,stress level,and treatment time were obtained.Finally,the querying method of electrochemical parameters combined with treatment time and current density was proposed.
文摘In order to improve the capability of the RFCC unit for heavy oil conversion, reduce the yields of coke and oil slurry, and increase the economic benefits of the unit, starting August 2007 the SINOPEC Luoyang Branch Company began to apply in its No. 2 RFCC unit the Endurance catalyst featuring strong heavy oil conversion ability, low yields of coke and oil slurry, and high total light liquid yield. The results on calibration of the Endurance catalyst conducted in November 2007 indi-cated that under the circumstances of using deteriorating feedstock quality and lower unit consump-tion of catalyst, the yields of coke, oil slurry and gas decreased by 0.28 %, 1.24 % and 0.35 %, respectively. The light distillate yield and total light liquid yield increased by 0.8 % and 1.88%, respectively.
文摘Alloying Pt with transition metals can significantly improve the catalytic properties for the oxygen reduction reaction(ORR).However,the application of Pt-transition metal alloys in fuel cells is largely limited by poor long-term durability because transition metals can easily leach.In this study,we developed a nonmetallic doping approach and prepared a P-doped Pt catalyst with excellent durability for the ORR.Carbon-supported core-shell nanoparticles with a P-doped Pt core and Pt shell(denoted as PtPx@Pt/C)were synthesized via heat-treatment phosphorization of commercial Pt/C,followed by acid etching.Compositional analysis using electron energy loss spectroscopy and X-ray photoelectron spectroscopy clearly demonstrated that Pt was enriched in the near-surface region(approximately 1 nm)of the carbon-supported core-shell nanoparticles.Owning to P doping,the ORR specific activity and mass activity of the PtP_(1.4)@Pt/C catalyst were as high as 0.62 mA cm^(–2)and 0.31 mAμgPt–^(1),respectively,at 0.90 V,and they were enhanced by 2.8 and 2.1 times,respectively,in comparison with the Pt/C catalyst.More importantly,PtP_(1.4)@Pt/C exhibited superior stability with negligible mass activity loss(6%after 30000 potential cycles and 25%after 90000 potential cycles),while Pt/C lost 46%mass activity after 30000 potential cycles.The high ORR activity and durability were mainly attributed to the core-shell nanostructure,the electronic structure effect,and the resistance of Pt nanoparticles against aggregation,which originated from the enhanced ability of the PtP_(1.4)@Pt to anchor to the carbon support.This study provides a new approach for constructing nonmetal-doped Pt-based catalysts with excellent activity and durability for the ORR.
