The utilization of high-strength steel bars(HSSB)within concrete structures demonstrates significant advantages in material conservation and mechanical performance enhancement.Nevertheless,existing design codes exhibi...The utilization of high-strength steel bars(HSSB)within concrete structures demonstrates significant advantages in material conservation and mechanical performance enhancement.Nevertheless,existing design codes exhibit limitations in addressing the distinct statistical characteristics of HSSB,particularly regarding strength design parameters.For instance,GB50010-2010 fails to specify design strength values for reinforcement exceeding 600 MPa,creating technical barriers for advancing HSSB implementation.This study systematically investigates the reliability of eccentric compression concrete columns reinforced with 600 MPa-grade HSSB through high-order moment method analysis.Material partial factors were calibrated against target reliability indices prescribed by GB50068-2018,incorporating critical variables including live-to-dead load ratios,design methodologies,and service conditions.The findings show that the value of k significantly affects the calibration of material partial factors,impacting the reliability of bearing capacity.Considering various k values and target reliability indices,it is recommended that the material partialfactorbe setat1.15,implyingthatthedesignstrengthfor600MPahigh-strengthsteelbars shouldbe considered as 522 MPa.For safety levels I and II,load adjustment factors of 1.1 and 0.9,respectively,may be applied.展开更多
Based on the Canadian Standards Association (CSA) criteria,105 pullout specimens were tested to investigate the effect of different rib geometries on bond strength of glass fiber reinforced polymer (GFRP) rebars embed...Based on the Canadian Standards Association (CSA) criteria,105 pullout specimens were tested to investigate the effect of different rib geometries on bond strength of glass fiber reinforced polymer (GFRP) rebars embedded in concrete. Two kinds of conventional reinforcing rebars were also studied for comparison. Each rebar was embedded in a 150 mm concrete cube,with the embedded length being four times the rebar diameter. The experimental parameters were the rebar type,rebar component,rebar diameter,rebar surface texture,rib height,rib spacing and rib width. Theoretical analysis was also carried out to explain the experimental phenomena and results. The experimental and theoretical results indicated that the bond strength of GFRP rebars was about 13%～35% lower than that of steel rebars. The bond strength and bond-slip behavior of the specially machined rebars varied with the rebar type,rebar diameter,rebar surface texture,rib height,rib spacing and rib width. Using the results,design recom-mendations were made concerning optimum rib geometries of GFRP ribbed rebars with superior bond-slip characteristics,which concluded that the optimal rib spacing of ribbed rebars is the same as the rebar diameter,and that the optimal rib height is 6% of the rebar diameter.展开更多
Based on the Canadian Standards Association(CSA) criterion,experiments on 30 pull-out specimens were conducted to study the bond strength of deformed GFRP rebars with 8 different surface configurations.Each rebar was ...Based on the Canadian Standards Association(CSA) criterion,experiments on 30 pull-out specimens were conducted to study the bond strength of deformed GFRP rebars with 8 different surface configurations.Each rebar was embedded in a 150 mm concrete cube,and the test embedded length was four times of the rebar diameter.Relationship between the mode of failure,the average bond strength and the average bond strength-slip for each rebar was analyzed.Results show that the failure mode of all specimens is the shearing off or desquamation of ribs,no splitting cracks appear on the cube specimens.The bond stress of deformed GFRP rebars mainly depends on the mechanical interaction between the ribs of the bar and the surrounding concrete,and the bond strength of deformed GFRP rebars is improved obviously.The optimal rib spacing is less than 2.5 times of the rebar diameter,and the rib height is more than 3% of the rebar diameter.展开更多
It is well known that the strengthening mechanisms of Nb microalloying on low carbon flat product have been widely studied and recognized since microalloying 75, but the application research and strengthening effects...It is well known that the strengthening mechanisms of Nb microalloying on low carbon flat product have been widely studied and recognized since microalloying 75, but the application research and strengthening effects of niobium on middle carbon steel like rebars have been incomplete and under argument due to some factors like limited solubility of Nb（CN） in reheating stage, dominant application of vanadium in rebars, as well as uncertain strengthening effect resulted from high rolling temperature and fast rolling speed in finishing rolling stage. Combining with new version of GB1499.2-2018： Steel for the reinforcement of concrete-Part 2： Hot rolled ribbed bars, it is very necessary to clarify the strengthening effects of niobium on high strength rebars for cost saving. In this paper, some new phenomena have been presented and discussed based on industrial trial results of Nb-bearing HRB400E, HRB500E and HRB600（E）, and then strengthening effects of niobium on high strength rebars were discussed.展开更多
The influence of alloying elements and cooling conditions after rolling on the microstructures and mechanical properties of a series of medium carbon Si-Mn-Mo-V high-strength precision-formed rebars were investigated....The influence of alloying elements and cooling conditions after rolling on the microstructures and mechanical properties of a series of medium carbon Si-Mn-Mo-V high-strength precision-formed rebars were investigated.It is found that steel with combined addition of Mo and V appears to be the most promising one than those containing V and Nb or containing V alone under the same pro- cessing conditions.From CCT curve of the steel and the cooling curve of the bar determined by sim- ulating the cooling rate in mill practice,the reason why 40Si2MnMoV bar has excellent combination of strength and ductility is clarified.展开更多
Kinked rebar is a special type of steel material,which is installed in beam column nodes and frame beams.It effectively enhances the blast resilience,seismic collapse resistance,and progressive collapse resistance of ...Kinked rebar is a special type of steel material,which is installed in beam column nodes and frame beams.It effectively enhances the blast resilience,seismic collapse resistance,and progressive collapse resistance of reinforced concrete(RC)structures without imposing substantial cost burdens,thereby emerging as a focal point of recent research endeavors.On the basis of explaining the working principle of kinked rebars,this paper reviews the research status of kinked rebars at home and abroad from three core domains:the tensile mechanical properties of kinked rebars,beam column nodes with kinked rebars,and concrete frame structures with kinked rebars.The analysis underscores that the straightening process of kinked rebars does not compromise their ultimate strength but significantly bolsters structural ductility and enhances energy dissipation capabilities.In beam-column joints,the incorporation of kinked rebars facilitates the seamless transfer of plastic hinges,adhering to the design principle of“strong columns and weak beams.”In addition,kinked rebars can greatly improve the resistance of the beam;The seismic resistance,internal explosion resistance,and progressive collapse resistance of reinforced concrete frame structures with kinked rebar have significantly improved.Beyond its primary application,the principle of kinked rebar was extended to other applications of kinked materials such as corrugated steel plates and origami structures,and the stress characteristics of related components and structures were studied.Intriguingly,this paper also proposes the application of kinked rebars in bridge engineering,aiming to address the challenges of localized damage concentration and excessive residual displacement in RC bridge piers.The introduction of kinked rebars in piers is envisioned to mitigate these issues,with the paper outlining its advantages and feasibility,thereby offering valuable insights for future research on kinked reinforcement and seismic design strategies for bridges.展开更多
The influence mechanism of trace Nb on the corrosion resistance of surface corrosion products of high-strength anti-seismic rebar in the simulated marine environment was studied by combining first-principles calculati...The influence mechanism of trace Nb on the corrosion resistance of surface corrosion products of high-strength anti-seismic rebar in the simulated marine environment was studied by combining first-principles calculations with corrosion mass loss method,surface analysis,cross-sectional analysis,quantitative analysis,and electrochemical test.The results demonstrated that the addition of trace Nb effectively improved the compactness and stability of surface corrosion layer of rebar,and the corrosion resistance of corrosion layer increased with the increase in Nb content.The beneficial effect of Nb content on the corrosion layer summarized two important key points.Firstly,the addition of Nb was beneficial to promoting the improvement in the structural stability of α-FeOOH,and α-FeOOH structure of solid solution Nb atoms was beneficial to strengthening the fixation of Cl atoms,thus increasing α/(β+γ)ratio,total impedance value,and corrosion potential.Secondly,the formation of Nb oxides can not only repair the corrosion layer,but also play a role in the fixation Cl atoms,resulting in the improvement in corrosion resistance of corrosion layer.展开更多
The quality of rebar welds directly impacts the overall service performance of highway infrastructure.However,current assessments of weld appearance quality primarily rely on traditional inspection methods such as man...The quality of rebar welds directly impacts the overall service performance of highway infrastructure.However,current assessments of weld appearance quality primarily rely on traditional inspection methods such as manual visual inspection,which suffer from significant limitations in accuracy,reliability,and efficiency.Given the increasing demand for safety performance inspections of highway infrastructure in China,traditional methods struggle to meet modern rapid inspection requirements.Therefore,this study proposes the design of a portable,non-destructive inspection device for rebar weld appearance,utilizing visible light vision and line-structured light 3D scanning technology.The device is equipped with an STM32 master control chip to manage encoder reading,scanning laser control,ring fill light,industrial camera synchronization,image acquisition,and serial port command transmission.Additionally,a weld image processing and detection software system was developed to receive,store,and identify weld defects.A field inspection prototype was created and subjected to various defect weld detection experiments in a laboratory setting.Experimental results demonstrate that the device can accurately measure weld parameters by acquiring multimodal images,fulfilling defect detection requirements.The device features high detection accuracy,portability,and user-friendliness,making it significant for the objective inspection and evaluation of rebar weld appearance and welding quality.展开更多
By increasing the nitrogen content in vanadium-containing steel,the mechanical properties of the steel can be effectively improved.In order to better utilize the strengthening effect of N in vanadium-containing steel ...By increasing the nitrogen content in vanadium-containing steel,the mechanical properties of the steel can be effectively improved.In order to better utilize the strengthening effect of N in vanadium-containing steel and reduce the use of ferrosilicon,which will reduce production costs and provide a theoretical basis for adjusting the composition of steel bars,we designed three different vanadium-containing steel samples with varying N and Si contents.Through mechanical property testing,metallographic microscopy,scanning electron microscopy,transmission electron microscopy,and other test methods,the evolution of the structure and mechanical properties of HRB400e steel under different N and Si contents were studied.The results showed that increasing the nitrogen content in steel can improve the yield strength of threaded steel.Before nitrogen addition,the yield strength of S1 steel exceeds the national standard at 29 MPa.After increasing the N content by 0.0056%,the yield strength of the steel exceeds the national standard of 64.4 MPa.Thermodynamic calculations revealed the presence of VN,V(C,N),Si_(3)N_(4),Fe_(3)C,and M_(7)C_(3)phases in the steel,and VN,Fe_(3)C,and M_(7)C_(3)phases were found in the test steel through the transmission electron microscope and high resolution transmission electron microscope.Increasing the N content can also increase the precipitation temperature of the precipitates,allowing them to better anchor the austenite grain boundaries during hot rolling and prevent the growth of austenite grains.This conclusion was also confirmed through high-temperature coagulation experiments.After refinement of the austenite grain size,the final ferrite and pearlite structure is further refined,and their distribution becomes more uniform.展开更多
A new type of corrosion-resistant alloyed-steel rebar,Cr10MoV,was researched using techniques such as corrosion electrochemistry,X-ray computed tomography,and zero resistance ammeter to systematically study the macro-...A new type of corrosion-resistant alloyed-steel rebar,Cr10MoV,was researched using techniques such as corrosion electrochemistry,X-ray computed tomography,and zero resistance ammeter to systematically study the macro-cell corrosion behavior and corrosion resistance of alloyed-steel rebar in mortar and concrete samples induced by chloride ion concentration in the marine environment.The macro-cell corrosion characteristics and development patterns induced by chloride ion concentration in alloyed-steel rebar were preliminarily revealed.In the macro-cell corrosion system of rebar mortar samples induced by 29 times chloride ion concentration,the corrosion current density of the alloyed-steel rebar combination stabilizes at 1.6–2.4μA/cm^(2),which is only one-third of that of the carbon-steel rebar combination,while the dissimilar steel rebar combination stabilizes at 0–0.4μA/cm^(2).Alloyed-steel rebar and carbon-steel rebar are configured in high concentration and low concentration chlorine salt areas,respectively.With the help of high corrosion resistance,the long-term stable corrosion resistance of alloyed-steel rebar is ensured.The potential difference between carbon-steel rebar and alloyed-steel rebar is reduced to weaken the driving force of macro-cell corrosion.It is a useful way to inhibit the macro-cell corrosion of dissimilar steel rebar and ensure the high corrosion resistance and durability of marine reinforced concrete structures.展开更多
Fiber reinforced plastics (i. e. FRP) rebars are one kind of high-performance composite materi- als used in concrete structures of civil engineering. Compared with ordinary steel rebars, FRP rebars have the characteri...Fiber reinforced plastics (i. e. FRP) rebars are one kind of high-performance composite materi- als used in concrete structures of civil engineering. Compared with ordinary steel rebars, FRP rebars have the characteristics of high tensile strength, an- tisepsis, light weight, low elastics modulus and low shear strength, et al. At present time, FRP re- bars have been studied and applied in Europe, America and Japan Since 2000, in the Fund of NS- FC, we systematically carried out experimental and theoretical studies on FRP rebars The progress of our research is briefly introduced in this paper.展开更多
Chloride-induced corrosion of steel reinforcement is the key factor leading to the degradation of reinforced concrete building durability.Improving the corrosion resistance of oxide scale of rebar has always been a re...Chloride-induced corrosion of steel reinforcement is the key factor leading to the degradation of reinforced concrete building durability.Improving the corrosion resistance of oxide scale of rebar has always been a research hotspot in the field of civil engineering materials.A ZIF-8 modified Ce-Sol-gel(ZCS)film was prepared on oxide scale of plain steel rebars by sol-gel method.It is observed that the|Z|_(0.01 Hz)value of the ZCS film reached 320 kΩcm^(2),which is about 29 times higher than that of blank rebar in simulated concrete pore(SCP)solution with 0.1 M NaCl.Then,they were inserted into mortar block and curing them in a curing box at T=20±2℃and RH=95±2%for 28 days.Subsequently,these samples were subject to electrochemical impedance spectroscopy in 3.5 wt%NaCl.The|Z|_(0.01 Hz)value of the rebar with the ZCS film was six times higher than that of the blank rebar after immersing for 20 days,resulting in an overall increase in corrosion resistance for rebar.The results indicated that the modification by ZIF-8 could reduce the porosity of Ce-sol-gel(CS)film and improved the“labyrinth effect”of the film.Additionally,the negative charge on the surface of ZIF-8 in alkaline condition increased the repulsion effect with Cl−,significantly reducing the sensitivity of rebar to Cl−.展开更多
This paper presents an easily installed improved perfobond connector (PBL) designed to reduce the shearconcentration of PBL. The improvement of PBL lies in changing the straight penetrating rebar to the Z-typepenetrat...This paper presents an easily installed improved perfobond connector (PBL) designed to reduce the shearconcentration of PBL. The improvement of PBL lies in changing the straight penetrating rebar to the Z-typepenetrating rebar. To study the shear performance of improved PBL, two PBL test specimens which containstraight penetrating rebar and six improved PBL test specimens which contain Z-type penetrating rebars weredesigned and fabricated, and push-out tests of these eight test specimens were carried out to investigate andcompare the shear behavior of PBL. Additionally, Finite Element Analysis (FEA) models of the PBL specimenswere established and validated against the test results. Through FEA, the effects of concrete grade, perforatedplate’s aperture, Z-type penetrating rebar’s diameter, Z-type penetrating rebar’s bending angle, and bending lengthon shear behaviors were discussed. The results indicate that (1) Compared with PBL specimens with straightpenetrating rebars, Z-type penetrating rebar can significantly improve the shear resistance and shear stiffnessof the specimens. This enhanced performance can be mainly attributed to the increased adhesion of the transverserebar. (2) By comparing the load-slip curve, the slip of PBL test specimens which contain straight penetratingrebar increases rapidly and the bearing capacity decreases rapidly after concrete craking, while the bearingcapacity of Z-type penetrating rebar specimens decreases first and then increases gradually, showing betterductility. (3) The stress of the PBL shear connector with Z-type penetrating rebar is more uniform than thePBL shear connector with straight penetrating rebar, and the overall deformation is more uniform. (4) The higherthe concrete grade, the higher the shear bearing capacity and the better ductility of the new PBL. Increasing theaperture of the perforated plate or the diameter of the rebar has a very limited effect on the improvement of theshear capacity of PBL. Through the systematic analysis of the mechanical properties of Z-type penetrating rebarPBL specimen, the experimental reference is provided for improving the structure and design of new type PBL.展开更多
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
基金supported by grants from the Natural Science Foundation of Fujian Province(Grant No.2022J05184).
文摘The utilization of high-strength steel bars(HSSB)within concrete structures demonstrates significant advantages in material conservation and mechanical performance enhancement.Nevertheless,existing design codes exhibit limitations in addressing the distinct statistical characteristics of HSSB,particularly regarding strength design parameters.For instance,GB50010-2010 fails to specify design strength values for reinforcement exceeding 600 MPa,creating technical barriers for advancing HSSB implementation.This study systematically investigates the reliability of eccentric compression concrete columns reinforced with 600 MPa-grade HSSB through high-order moment method analysis.Material partial factors were calibrated against target reliability indices prescribed by GB50068-2018,incorporating critical variables including live-to-dead load ratios,design methodologies,and service conditions.The findings show that the value of k significantly affects the calibration of material partial factors,impacting the reliability of bearing capacity.Considering various k values and target reliability indices,it is recommended that the material partialfactorbe setat1.15,implyingthatthedesignstrengthfor600MPahigh-strengthsteelbars shouldbe considered as 522 MPa.For safety levels I and II,load adjustment factors of 1.1 and 0.9,respectively,may be applied.
基金Project (No. 200431882021) supported by the Western Communi-cation Construction and Science & Technological Project,China
文摘Based on the Canadian Standards Association (CSA) criteria,105 pullout specimens were tested to investigate the effect of different rib geometries on bond strength of glass fiber reinforced polymer (GFRP) rebars embedded in concrete. Two kinds of conventional reinforcing rebars were also studied for comparison. Each rebar was embedded in a 150 mm concrete cube,with the embedded length being four times the rebar diameter. The experimental parameters were the rebar type,rebar component,rebar diameter,rebar surface texture,rib height,rib spacing and rib width. Theoretical analysis was also carried out to explain the experimental phenomena and results. The experimental and theoretical results indicated that the bond strength of GFRP rebars was about 13%～35% lower than that of steel rebars. The bond strength and bond-slip behavior of the specially machined rebars varied with the rebar type,rebar diameter,rebar surface texture,rib height,rib spacing and rib width. Using the results,design recom-mendations were made concerning optimum rib geometries of GFRP ribbed rebars with superior bond-slip characteristics,which concluded that the optimal rib spacing of ribbed rebars is the same as the rebar diameter,and that the optimal rib height is 6% of the rebar diameter.
基金Sponsored by the Western Communication Construction and Science & Technological Project(Grant No.200431882021)the National Science Fundfor Distinguished Young Scholars (Grant No.50525823)
文摘Based on the Canadian Standards Association(CSA) criterion,experiments on 30 pull-out specimens were conducted to study the bond strength of deformed GFRP rebars with 8 different surface configurations.Each rebar was embedded in a 150 mm concrete cube,and the test embedded length was four times of the rebar diameter.Relationship between the mode of failure,the average bond strength and the average bond strength-slip for each rebar was analyzed.Results show that the failure mode of all specimens is the shearing off or desquamation of ribs,no splitting cracks appear on the cube specimens.The bond stress of deformed GFRP rebars mainly depends on the mechanical interaction between the ribs of the bar and the surrounding concrete,and the bond strength of deformed GFRP rebars is improved obviously.The optimal rib spacing is less than 2.5 times of the rebar diameter,and the rib height is more than 3% of the rebar diameter.
文摘It is well known that the strengthening mechanisms of Nb microalloying on low carbon flat product have been widely studied and recognized since microalloying 75, but the application research and strengthening effects of niobium on middle carbon steel like rebars have been incomplete and under argument due to some factors like limited solubility of Nb（CN） in reheating stage, dominant application of vanadium in rebars, as well as uncertain strengthening effect resulted from high rolling temperature and fast rolling speed in finishing rolling stage. Combining with new version of GB1499.2-2018： Steel for the reinforcement of concrete-Part 2： Hot rolled ribbed bars, it is very necessary to clarify the strengthening effects of niobium on high strength rebars for cost saving. In this paper, some new phenomena have been presented and discussed based on industrial trial results of Nb-bearing HRB400E, HRB500E and HRB600（E）, and then strengthening effects of niobium on high strength rebars were discussed.
文摘The influence of alloying elements and cooling conditions after rolling on the microstructures and mechanical properties of a series of medium carbon Si-Mn-Mo-V high-strength precision-formed rebars were investigated.It is found that steel with combined addition of Mo and V appears to be the most promising one than those containing V and Nb or containing V alone under the same pro- cessing conditions.From CCT curve of the steel and the cooling curve of the bar determined by sim- ulating the cooling rate in mill practice,the reason why 40Si2MnMoV bar has excellent combination of strength and ductility is clarified.
基金supported by the Zhejiang Provincial Natural Science Foundation of China under Grant No.LTGG23E080001Zhejiang Engineering Research Center of Intelligent Urban Infrastructure under Grant No.IUI2022-ZD-01.
文摘Kinked rebar is a special type of steel material,which is installed in beam column nodes and frame beams.It effectively enhances the blast resilience,seismic collapse resistance,and progressive collapse resistance of reinforced concrete(RC)structures without imposing substantial cost burdens,thereby emerging as a focal point of recent research endeavors.On the basis of explaining the working principle of kinked rebars,this paper reviews the research status of kinked rebars at home and abroad from three core domains:the tensile mechanical properties of kinked rebars,beam column nodes with kinked rebars,and concrete frame structures with kinked rebars.The analysis underscores that the straightening process of kinked rebars does not compromise their ultimate strength but significantly bolsters structural ductility and enhances energy dissipation capabilities.In beam-column joints,the incorporation of kinked rebars facilitates the seamless transfer of plastic hinges,adhering to the design principle of“strong columns and weak beams.”In addition,kinked rebars can greatly improve the resistance of the beam;The seismic resistance,internal explosion resistance,and progressive collapse resistance of reinforced concrete frame structures with kinked rebar have significantly improved.Beyond its primary application,the principle of kinked rebar was extended to other applications of kinked materials such as corrugated steel plates and origami structures,and the stress characteristics of related components and structures were studied.Intriguingly,this paper also proposes the application of kinked rebars in bridge engineering,aiming to address the challenges of localized damage concentration and excessive residual displacement in RC bridge piers.The introduction of kinked rebars in piers is envisioned to mitigate these issues,with the paper outlining its advantages and feasibility,thereby offering valuable insights for future research on kinked reinforcement and seismic design strategies for bridges.
基金supported by National Natural Science Foundation of China(Grant No.52074095)Guizhou Provincial Basic Research Program(Natural Science)(Grant No.QKHJC-ZK[2023]YB072)+2 种基金Guizhou Provincial Key Technology R&D Program(Grant No.QKHZC[2023]YB404)Guizhou Provincial Key Technology R&D Program(Grant No.QKHZC[2022]YB053)The numerical calculation of the first-principles was supported and assisted by the High-Performance Computing Center of Guizhou University.
文摘The influence mechanism of trace Nb on the corrosion resistance of surface corrosion products of high-strength anti-seismic rebar in the simulated marine environment was studied by combining first-principles calculations with corrosion mass loss method,surface analysis,cross-sectional analysis,quantitative analysis,and electrochemical test.The results demonstrated that the addition of trace Nb effectively improved the compactness and stability of surface corrosion layer of rebar,and the corrosion resistance of corrosion layer increased with the increase in Nb content.The beneficial effect of Nb content on the corrosion layer summarized two important key points.Firstly,the addition of Nb was beneficial to promoting the improvement in the structural stability of α-FeOOH,and α-FeOOH structure of solid solution Nb atoms was beneficial to strengthening the fixation of Cl atoms,thus increasing α/(β+γ)ratio,total impedance value,and corrosion potential.Secondly,the formation of Nb oxides can not only repair the corrosion layer,but also play a role in the fixation Cl atoms,resulting in the improvement in corrosion resistance of corrosion layer.
基金Supported by the Central Public-Interest Scientific Institution Basal Research Fund(2023-9062)the Transport Power Pilot Project(2021-C334)。
文摘The quality of rebar welds directly impacts the overall service performance of highway infrastructure.However,current assessments of weld appearance quality primarily rely on traditional inspection methods such as manual visual inspection,which suffer from significant limitations in accuracy,reliability,and efficiency.Given the increasing demand for safety performance inspections of highway infrastructure in China,traditional methods struggle to meet modern rapid inspection requirements.Therefore,this study proposes the design of a portable,non-destructive inspection device for rebar weld appearance,utilizing visible light vision and line-structured light 3D scanning technology.The device is equipped with an STM32 master control chip to manage encoder reading,scanning laser control,ring fill light,industrial camera synchronization,image acquisition,and serial port command transmission.Additionally,a weld image processing and detection software system was developed to receive,store,and identify weld defects.A field inspection prototype was created and subjected to various defect weld detection experiments in a laboratory setting.Experimental results demonstrate that the device can accurately measure weld parameters by acquiring multimodal images,fulfilling defect detection requirements.The device features high detection accuracy,portability,and user-friendliness,making it significant for the objective inspection and evaluation of rebar weld appearance and welding quality.
基金support from the Open Competition Scientific and Technological Research Projects of Heilongjiang Province(2022ZXJ03A02)Key Research and Development Project of School-local Cooperation in Lvliang City(No.2023XDHZ05).
文摘By increasing the nitrogen content in vanadium-containing steel,the mechanical properties of the steel can be effectively improved.In order to better utilize the strengthening effect of N in vanadium-containing steel and reduce the use of ferrosilicon,which will reduce production costs and provide a theoretical basis for adjusting the composition of steel bars,we designed three different vanadium-containing steel samples with varying N and Si contents.Through mechanical property testing,metallographic microscopy,scanning electron microscopy,transmission electron microscopy,and other test methods,the evolution of the structure and mechanical properties of HRB400e steel under different N and Si contents were studied.The results showed that increasing the nitrogen content in steel can improve the yield strength of threaded steel.Before nitrogen addition,the yield strength of S1 steel exceeds the national standard at 29 MPa.After increasing the N content by 0.0056%,the yield strength of the steel exceeds the national standard of 64.4 MPa.Thermodynamic calculations revealed the presence of VN,V(C,N),Si_(3)N_(4),Fe_(3)C,and M_(7)C_(3)phases in the steel,and VN,Fe_(3)C,and M_(7)C_(3)phases were found in the test steel through the transmission electron microscope and high resolution transmission electron microscope.Increasing the N content can also increase the precipitation temperature of the precipitates,allowing them to better anchor the austenite grain boundaries during hot rolling and prevent the growth of austenite grains.This conclusion was also confirmed through high-temperature coagulation experiments.After refinement of the austenite grain size,the final ferrite and pearlite structure is further refined,and their distribution becomes more uniform.
基金the financial support from National Natural Science Foundation of China(Grant Nos.52278255 and 51878246)Postgraduate Research&Practice Innovation Program of Jiangsu Province(SJCX24_0195).
文摘A new type of corrosion-resistant alloyed-steel rebar,Cr10MoV,was researched using techniques such as corrosion electrochemistry,X-ray computed tomography,and zero resistance ammeter to systematically study the macro-cell corrosion behavior and corrosion resistance of alloyed-steel rebar in mortar and concrete samples induced by chloride ion concentration in the marine environment.The macro-cell corrosion characteristics and development patterns induced by chloride ion concentration in alloyed-steel rebar were preliminarily revealed.In the macro-cell corrosion system of rebar mortar samples induced by 29 times chloride ion concentration,the corrosion current density of the alloyed-steel rebar combination stabilizes at 1.6–2.4μA/cm^(2),which is only one-third of that of the carbon-steel rebar combination,while the dissimilar steel rebar combination stabilizes at 0–0.4μA/cm^(2).Alloyed-steel rebar and carbon-steel rebar are configured in high concentration and low concentration chlorine salt areas,respectively.With the help of high corrosion resistance,the long-term stable corrosion resistance of alloyed-steel rebar is ensured.The potential difference between carbon-steel rebar and alloyed-steel rebar is reduced to weaken the driving force of macro-cell corrosion.It is a useful way to inhibit the macro-cell corrosion of dissimilar steel rebar and ensure the high corrosion resistance and durability of marine reinforced concrete structures.
基金Support for this research by the Fund of Rising-Star Plan of Shanghai Scientific and Technical Committee(No.02QF14047)the Fund of National Natural Science Foundation of China(No.50008012)is gratefully acknowledged.
文摘Fiber reinforced plastics (i. e. FRP) rebars are one kind of high-performance composite materi- als used in concrete structures of civil engineering. Compared with ordinary steel rebars, FRP rebars have the characteristics of high tensile strength, an- tisepsis, light weight, low elastics modulus and low shear strength, et al. At present time, FRP re- bars have been studied and applied in Europe, America and Japan Since 2000, in the Fund of NS- FC, we systematically carried out experimental and theoretical studies on FRP rebars The progress of our research is briefly introduced in this paper.
基金support from the National Key R&D Program of China(No.2019YFE0111000)the National Natural Science Foundation of China(Nos.52171093,51771061 and U20A20233).
文摘Chloride-induced corrosion of steel reinforcement is the key factor leading to the degradation of reinforced concrete building durability.Improving the corrosion resistance of oxide scale of rebar has always been a research hotspot in the field of civil engineering materials.A ZIF-8 modified Ce-Sol-gel(ZCS)film was prepared on oxide scale of plain steel rebars by sol-gel method.It is observed that the|Z|_(0.01 Hz)value of the ZCS film reached 320 kΩcm^(2),which is about 29 times higher than that of blank rebar in simulated concrete pore(SCP)solution with 0.1 M NaCl.Then,they were inserted into mortar block and curing them in a curing box at T=20±2℃and RH=95±2%for 28 days.Subsequently,these samples were subject to electrochemical impedance spectroscopy in 3.5 wt%NaCl.The|Z|_(0.01 Hz)value of the rebar with the ZCS film was six times higher than that of the blank rebar after immersing for 20 days,resulting in an overall increase in corrosion resistance for rebar.The results indicated that the modification by ZIF-8 could reduce the porosity of Ce-sol-gel(CS)film and improved the“labyrinth effect”of the film.Additionally,the negative charge on the surface of ZIF-8 in alkaline condition increased the repulsion effect with Cl−,significantly reducing the sensitivity of rebar to Cl−.
文摘This paper presents an easily installed improved perfobond connector (PBL) designed to reduce the shearconcentration of PBL. The improvement of PBL lies in changing the straight penetrating rebar to the Z-typepenetrating rebar. To study the shear performance of improved PBL, two PBL test specimens which containstraight penetrating rebar and six improved PBL test specimens which contain Z-type penetrating rebars weredesigned and fabricated, and push-out tests of these eight test specimens were carried out to investigate andcompare the shear behavior of PBL. Additionally, Finite Element Analysis (FEA) models of the PBL specimenswere established and validated against the test results. Through FEA, the effects of concrete grade, perforatedplate’s aperture, Z-type penetrating rebar’s diameter, Z-type penetrating rebar’s bending angle, and bending lengthon shear behaviors were discussed. The results indicate that (1) Compared with PBL specimens with straightpenetrating rebars, Z-type penetrating rebar can significantly improve the shear resistance and shear stiffnessof the specimens. This enhanced performance can be mainly attributed to the increased adhesion of the transverserebar. (2) By comparing the load-slip curve, the slip of PBL test specimens which contain straight penetratingrebar increases rapidly and the bearing capacity decreases rapidly after concrete craking, while the bearingcapacity of Z-type penetrating rebar specimens decreases first and then increases gradually, showing betterductility. (3) The stress of the PBL shear connector with Z-type penetrating rebar is more uniform than thePBL shear connector with straight penetrating rebar, and the overall deformation is more uniform. (4) The higherthe concrete grade, the higher the shear bearing capacity and the better ductility of the new PBL. Increasing theaperture of the perforated plate or the diameter of the rebar has a very limited effect on the improvement of theshear capacity of PBL. Through the systematic analysis of the mechanical properties of Z-type penetrating rebarPBL specimen, the experimental reference is provided for improving the structure and design of new type PBL.
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.
