A novel approach for analyzing coupled vibrations between vehicles and bridges is presented,taking into account spatiotemporal effects and mechanical phenomena resulting fromvehicle braking.Efficient modeling and solu...A novel approach for analyzing coupled vibrations between vehicles and bridges is presented,taking into account spatiotemporal effects and mechanical phenomena resulting fromvehicle braking.Efficient modeling and solution of bridge vibrations induced by vehicle deceleration are realized using this method.The method’s validity and reliability are substantiated through numerical examples.A simply supported beam bridge with a corrugated steel web is taken as an example and the effects of parameters such as the initial vehicle speed,braking acceleration,braking location,and road surface roughness on the mid-span displacement and impact factor of the bridge are analyzed.The results show that vehicle braking significantly amplifies mid-span displacement and impact factor responses in comparison to uniform vehicular motion across the bridge.Notably,the influence of wheelto-bridge friction forces is of particular significance and cannot be overlooked.When the vehicle initiates braking near the middle of the span,both the mid-span displacement and impact factor of the bridge exhibit substantial increases,further escalating with higher braking acceleration.Under favorable road surface conditions,the midspan displacement and the impact factor during vehicle braking may exceed the design values stipulated by codes.It is important to note that road surface roughness exerts a more pronounced effect on the impact factor of the bridge in comparison to the effects of vehicle braking.展开更多
Replaceable flexural and shear fuse-type coupling beams are used in hybrid coupled shear wall(HCSW)systems,enabling concrete buildings to be promptly recovered after severe earthquakes.This study aimed to analytically...Replaceable flexural and shear fuse-type coupling beams are used in hybrid coupled shear wall(HCSW)systems,enabling concrete buildings to be promptly recovered after severe earthquakes.This study aimed to analytically evaluate the seismic behavior of flexural and shear fuse beams situated in short-,medium-and high-rise RC buildings that have HCSWs.Three building groups hypothetically located in a high seismic hazard zone were studied.A series of 2D nonlinear time history analyses was accomplished in OpenSees,using the ground motion records scaled at the design basis earthquake level.It was found that the effectiveness of fuses in HCSWs depends on various factors such as size and scale of the building,allowable rotation value,inter-story drift ratio,residual drift quantity,energy dissipation value of the fuses,etc.The results show that shear fuses better meet the requirements of rotations and drifts.In contrast,flexural fuses dissipate more energy,but their sectional stiffness should increase to meet other requirements.It was concluded that adoption of proper fuses depends on the overall scale of the building and on how associated factors are considered.展开更多
The instability of functionally graded material(FGM)structures is one of the major threats to their service safety in engineering applications.This paper aims to clarify a long-standing controversy on the thermal inst...The instability of functionally graded material(FGM)structures is one of the major threats to their service safety in engineering applications.This paper aims to clarify a long-standing controversy on the thermal instability type of simply-supported FGM beams.First,based on the Euler-Bernoulli beam theory and von K′arm′an geometric nonlinearity,a nonlinear governing equation of simply-supported FGM beams under uniform thermal loads by Zhang’s two-variable method is formulated.Second,an approximate analytic solution to the nonlinear integro-differential boundary value problem under a thermal-induced inhomogeneous force boundary condition is obtained by using a semiinverse method when the coordinate axis is relocated to the bending axis(physical neutral plane),and then the analytical predictions are verified by the differential quadrature method(DQM).Finally,based on the free energy theorem,it is revealed that the symmetry breaking caused by the material inhomogeneity can make the simply-supported FGM beam under uniform thermal loads occur snap-through postbuckling only in odd modes;furthermore,the nonlinear critical load of thermal buckling varies non-monotonically with the functional gradient index due to the stretching-bending coupling effect.These results are expected to provide new ideas and references for the design and regulation of FGM structures.展开更多
The stability and local bifurcation of a simply-supported flexible beam (Bernoulli- Euler type) carrying a moving mass and subjected to harmonic axial excitation are investigated. In the theoretical analysis, the pa...The stability and local bifurcation of a simply-supported flexible beam (Bernoulli- Euler type) carrying a moving mass and subjected to harmonic axial excitation are investigated. In the theoretical analysis, the partial differential equation of motion with the fifth-order nonlinear term is solved using the method of multiple scales (a perturbation technique). The stability and local bifurcation of the beam are analyzed for 1/2 sub harmonic resonance. The results show that some of the parameters, especially the velocity of moving mass and external excitation, affect the local bifurcation significantly. Therefore, these parameters play important roles in the system stability.展开更多
This paper investigated the fire resistance of CSBs with various parameters under high temperature rise due to fire using finite element software ABAQUS. The mechanical parameters of CSBs are analyzed, including load-...This paper investigated the fire resistance of CSBs with various parameters under high temperature rise due to fire using finite element software ABAQUS. The mechanical parameters of CSBs are analyzed, including load-bearing capacity and the temperature distribution during the heating process. Through structural analysis simulation of the entire heating process, the structural response of the CSBs is divided into five stages: elastic stage, elastic-plastic stage, self-balancing stage, catenary stage and ultimate destruction stage. The results indicate that the opening diameter-to-height ratio, opening spacing-to-height ratio and load ratio significantly affect the structural responses of CSBs in fire, followed by opening shape as secondary effects. In all the numerical analyzes, CSBs are analyzed with a uniformly distributed load and having simply supported boundary conditions.展开更多
Electron beam welding of Ti-15-3 alloy to 304 stainless steel (STS) using a copper filler metal was carried out. The temperature fields and stress distributions in the Ti/Fe and Ti/Cu/Fe joint during the welding pro...Electron beam welding of Ti-15-3 alloy to 304 stainless steel (STS) using a copper filler metal was carried out. The temperature fields and stress distributions in the Ti/Fe and Ti/Cu/Fe joint during the welding process were numerically simulated and experimentally measured. The results show that the rotated parabola body heat source is fit for the simulation of the electron beam welding. The temperature distribution is asymmetric along the weld center and the temperature in the titanium alloy plate is higher than that in the 304 STS plate. The thermal stress also appears to be in asymmetric distribution. The residual tensile stress mainly exists in the weld at the 304 STS side. The copper filler metal decreases the peak temperature and temperature grade in the joint as well as the residual stress. The longitudinal and lateral residual tensile strengths reduce by 66 MPa and 31 MPa, respectively. From the temperature and residual stress, it is concluded that copper is a good filler metal candidate for the electron beam welding of Ti-15-3 titanium alloy to 304 stainless steel.展开更多
Electron beam welding was carried out between aluminum alloy and steel with Ag interlayer. Seam morphology, structure and mechanical properties of the joints were investigated with different action positions of the el...Electron beam welding was carried out between aluminum alloy and steel with Ag interlayer. Seam morphology, structure and mechanical properties of the joints were investigated with different action positions of the electron beam spot. The results show that with the increment of the beam offset to the silver side from the interface between silver and steel, the seam morphology was improved, and the porosity in the Ag interlayer vanished. A transition layer mainly composed of Ag2Al and Al eutectic was formed at the interface between silver and aluminum, and became thin and spiccato as the beam offset increased. When the beam offset was too large, two IMC layers composed of FeAl and FeAl3 respectively were formed at the interface between steel and Ag interlayer. The optimal beam offset was 0.2 mm, and the maximum tensile strength of the joint was 193 MPa, 88.9% that of the aluminum alloy, and the fracture occurred at the interface between steel and Ag interlayer.展开更多
Electron beam welding (EBW) of 304 stainless steel to QCr0.8 copper alloy with copper filler wire was carried out. Orthogonal experiment was performed to investigate the effects of process parameters on the tensile ...Electron beam welding (EBW) of 304 stainless steel to QCr0.8 copper alloy with copper filler wire was carried out. Orthogonal experiment was performed to investigate the effects of process parameters on the tensile strength of the joints, and the process parameters were optimized. The optimum process parameters are as follows:beam current of 30 mA, welding speed of 100 mm/min, wire feed rate of 1 m/min and beam offset of-0.3 mm. The microstructures of the optimum joint were studied. The results indicate that the weld is mainly composed of dendriticαphase with little globularεphase, and copper inhomogeneity only occurs at the top of the fusion zone. In addition, a melted region without mixing exists near the weld junction of copper side. This region with a coarser grain size is the weakest section of the joints. It is found that the microhardness of the weld decreases with the increase of the copper content in solid solution. The highest tensile strength of the joint is 276 MPa.展开更多
Based on the experimental study and inelastic theory, the ultimate flexuralcapacity of steel encased concrete composite beams are derived. The difference between steel encasedconcrete composite beams with full shear c...Based on the experimental study and inelastic theory, the ultimate flexuralcapacity of steel encased concrete composite beams are derived. The difference between steel encasedconcrete composite beams with full shear connection and beams with partial shear connection,together with the relationship between the inelastic neutral axis of steel parts and concrete parts,are considered in the formulae. The calculation results of the eight specimens with full shearconnection and the three specimens with partial shear connection are in good agreement with theexperimental data, which validates the effectiveness and efficiency of the proposed calculationmethods. Furthermore, the nonlinear finite element analysis of the ultimate flexural capacity of thesteel encased concrete composite beams is performed. Nonlinear material properties and nonlinearcontact properties are considered in the finite element analysis. The finite element analyticalresults also correlate well with the experimental data.展开更多
Based on comparative test of two transfer story models, in one of which the transfer beam and basement column is constructed of steel reinforced concrete, and the other is constructed of ordinary reinforced concrete, ...Based on comparative test of two transfer story models, in one of which the transfer beam and basement column is constructed of steel reinforced concrete, and the other is constructed of ordinary reinforced concrete, its force behavior, ductility and failure mechanism under vertical and horizontal loads are studied. The results show that loading bearing and seismic behavior of transfer story structure with steel reinforced concrete beam and basement column is good. The relative design suggestion is put forward.展开更多
Microstructure of two different 18Ni Co-free maraging specimens and their electron beam weld joints were investigated comparatively by optical microscopy and SEM. It is showing that both of the steels are typical lath...Microstructure of two different 18Ni Co-free maraging specimens and their electron beam weld joints were investigated comparatively by optical microscopy and SEM. It is showing that both of the steels are typical lath martensite, however, one grain size is about three times as another one, and XRD reveals that the amount of the retained austenitic phase in the former is less then the latter. The austenite distributes in plate form along granular and lath boundaries while some in fine particle within the matrix. The microstructural difference between two specimens led to diverse behaviors in electron beam welding. The first specimen is weldable well but the second shows obvious welding defects of pits and burn-through holes in weld face. The welding microstructure exhibits a typical dendritic morphology, and the grains in the heat-affected zone recrystallized and grew up obviously for high temperature heated by welding electron beam. The weldablity is relative to the thermal conduction performance of the base materials,which is contributed greatly for grain size and austenite content.展开更多
Electron beam welding experiments of titanium alloy to stainless steel were carried out with different filler metals, such as Ni, V, and Cu. Microstructures of the joints were examined by optical microscopy, scanning ...Electron beam welding experiments of titanium alloy to stainless steel were carried out with different filler metals, such as Ni, V, and Cu. Microstructures of the joints were examined by optical microscopy, scanning electron microscopy and X-ray diffraction analysis. Mechanical properties of the joints were evaluated according to tensile strength and microhardness. As a result, influences of filler metals on microstructures and mechanical properties of electron beam welded titanium-stainless steel joints were discussed. The results showed that all the filler metals were helpful to restrain the Ti-Fe intermetallics. The welds with different filler metals were all characterized by solid solution and interfacial intermetallics. For each type of the filler metal, the type of solid solution and interfacial intermetallics depended on the metallurgical reactions between the filler metals and base metals. The interfacial intermetallics were Fe2Ti+Ni3Ti+NiTi2, TiFe, and Cu2Ti+CuTi+CuTi2 in the joints welded with Ni, V, and Cu filler metals, respectively. The tensile strengths of the joints were dependent on the hardness of the interfacial intermetallics. The joint welded with Ag filler metal had the highest tensile strength, which is about 310 MPa.展开更多
Based on the introductions of a type of diaphragm-through connection between concrete-filled square steel tubular columns (CFSSTCs) and H-shaped steel beams,a finite element model of the connection is developed and us...Based on the introductions of a type of diaphragm-through connection between concrete-filled square steel tubular columns (CFSSTCs) and H-shaped steel beams,a finite element model of the connection is developed and used to investigate the seismic behavior of the connection.The results of the finite element model are validated by a set of cyclic loading tests.The cyclic loading tests and the finite element analyses indicate that the failure mode of the suggested connections is plastic hinge at the beam with inelastic rotation angle exceeding 0.04 rad.The suggested connections have sufficient strength,plastic deformation and energy dissipation capacity to be used in composite moment frames as beam-to-column rigid connections.展开更多
The objective of this work is to investigate the fatigue behavior of reinforced concrete(RC) beams strengthened with externally bonded carbon fiber reinforced polymer(CFRP) and steel plate. An experimental investigati...The objective of this work is to investigate the fatigue behavior of reinforced concrete(RC) beams strengthened with externally bonded carbon fiber reinforced polymer(CFRP) and steel plate. An experimental investigation and theoretical analysis were made on the law of deflection development and stiffness degradation, as well as the influence of fatigue load ranges. Test results indicate that the law of three-stage change under fatigue loading is followed by both midspan deflection and permanent deflection, which also have positive correlation with fatigue load amplitude. Fatigue stiffness of composite strengthened beams degrades gradually with the increasing of number of cycles. Based on the experimental results, a theoretical model by effective moment of inertia method is developed for calculating the sectional stiffness of such composite strengthened beams under fatigue loading, and the calculated results are in good agreement with the experimental results.展开更多
Corrugated steel web is folded along the longitudinal direction and has the mechanical properties such as axial compression stiffness corrugation effect, shear modulus corrugation effect, similar to that of an accordi...Corrugated steel web is folded along the longitudinal direction and has the mechanical properties such as axial compression stiffness corrugation effect, shear modulus corrugation effect, similar to that of an accordion. In order to study the lateral-torsional buckling of box beams with corrugated steel webs (BBCSW) under the action of bending moment load, the neutral equilibrium equation of BBCSW under the action of bending moment load is derived through the stationary value theory of total potential energy and further, along with taking Kollbrunner-Hajdin correction method and the mechanical properties of the corrugated web into consideration. The analytical calculation formula of lateral-torsional buckling critical bending moment of BBCSW is then obtained. The lateral-torsional buckling critical bending moment of 96 BBCSW test specimens with different geometry dimensions are then calculated using both the analytical calculation method and ANSYS finite element method. The results show that the analytical calculation results agree well with the numerical calculation results using ANSYS, thus proving the accuracy of the analytical calculation method and model simplification hypothesis proposed in this paper. Also, compared with the box beams with flat steel webs (BBFSW) with the same geometry dimensions as BBCSW, within the common range of web space-depth ratio and web span-depth ratio, BBCSW’s lateral-torsional buckling critical bending moment is larger than that of BBFSW. Moreover, the advantages of BBCSW’s stability are even more significant with the increase of web space-depth ratio and web depth-thickness ratio.展开更多
Electron beam welding of Ti-15-3 titanium alloy to 304 stainless steel with a copper sheet as interlayer was carried out.Microstructures of the joint were studied by optical microscopy(OM),scanning electron microscopy...Electron beam welding of Ti-15-3 titanium alloy to 304 stainless steel with a copper sheet as interlayer was carried out.Microstructures of the joint were studied by optical microscopy(OM),scanning electron microscopy(SEM) and X-ray diffractometry(XRD).In addition,the mechanical properties of the joint were evaluated by tensile test and the microhardness was measured.These two alloys were successfully welded by adding copper transition layer into the weld.Solid solution with a certain thickness was located at the interfaces between weld and base metal in both sides.Regions inside the weld and near the stainless steel were characterized by solid solution of copper with TiFe2 intermetallics dispersedly distributed in it.While weld near titanium alloy contained Ti-Cu and Ti-Fe-Cu intermetallics layer,in which the hardness of weld came to the highest value.Brittle fracture occurred in the intermetallics layer when the joint was stretched.展开更多
To study the flexural behavior and calculation model,8 coral aggregate concrete(CAC)beams with different types of steel were designed.The flexural behavior of CAC beam was tested.The failure mode,bearing capacity,the ...To study the flexural behavior and calculation model,8 coral aggregate concrete(CAC)beams with different types of steel were designed.The flexural behavior of CAC beam was tested.The failure mode,bearing capacity,the maximum crack width(ws)and average crack spacing(lm)were studied.A calculation model for the bearing capacity of CAC beam was proposed.The results indicated that with the steel strength increased,the cracking moment(Mcr)and ultimate moment(Mu)of CAC beam increased,and the development of the ws gradually slowed,which effectively inhibited the formation of cracks and improved the flexural behavior of CAC beam.For CAC structures in the ocean engineering,it is recommended to use organic new coated steel to extend its effective service life.In addition,considering the influence of steel corrosion,a calculation model for the Mcr,Mu,lm and ws of CAC beam was established.展开更多
Two post weld heat treatments (PWHT), 900 ℃ oil quenched and low temperature tempered (PWHTA) and high temperature tempered and then 900 ℃ oil quenched and low temperature tempered (PWHTB), are employed to t...Two post weld heat treatments (PWHT), 900 ℃ oil quenched and low temperature tempered (PWHTA) and high temperature tempered and then 900 ℃ oil quenched and low temperature tempered (PWHTB), are employed to treat the weldment. Then the effect of two post weld heat treatment processes on the microstructure,mechanical properties and fracture toughness of electron beam welded joints of 30CrMnSiNi2A steel have been discussed. The results show that, after two kinds of PWHT the microstructure and hardness at every zones of EBW joints are nearly same. Although the welds have good mechanical properties, fracture toughness of both weld and heat affected zone (HAZ) is low, the CTOD values of welds are comparatively higher than that of HAZ. Microstructure and fracture toughness of two EBW joints have no evident differences.展开更多
A lightweight aggregate concrete-filled steel tube(LACFST) spatial truss beam was tested under bending load. The performance was studied by the analysis of the beam deflection and strains in its chords and webs. Accor...A lightweight aggregate concrete-filled steel tube(LACFST) spatial truss beam was tested under bending load. The performance was studied by the analysis of the beam deflection and strains in its chords and webs. According to the test results, several assumptions were made to deduce the bearing capacity calculation method based on the force balance of the whole section. An optimal dimension relationship for the truss beam chords was proposed and verified by finite element analysis. Results show that the LACFST spatial truss beam failed after excessive deflection. The strain distribution agreed with Bernoulli-Euler theoretical prediction. The truss beam flexural bearing capacity calculation results matched test evidence with only a 3% difference between the two. Finite element analyses with different chord dimensions show that the ultimate bearing capacity increases as the chord dimensions increase when the chords have a diameter smaller than optimal one; otherwise, it remains almost unchanged as the chord dimensions increase.展开更多
The full-range behavior of partially bonded, together with partially prestressed concrete beams containing fiber reinforced polymer (FRP) tendons and stainless steel reinforcing bars was simulated using a simplified...The full-range behavior of partially bonded, together with partially prestressed concrete beams containing fiber reinforced polymer (FRP) tendons and stainless steel reinforcing bars was simulated using a simplified theoretical model. The model assumes that a section in the beam has a trilinear moment--curvature relationship characterized by three particular points, initial cracking of concrete, yielding of non-prestressed steel, and crushing of concrete or rupturing of prestressing tendons. Predictions from the model were compared with the limited available test data, and a reasonable agreement was obtained. A detailed parametric study of the behavior of the prestressed concrete beams with hybrid FRP and stainless steel reinforcements was conducted. It can be concluded that the deformability of the beam can be enhanced by increasing the ultimate compressive strain of concrete, unhonded length of tendon, percentage of compressive reinforcement and partial prestress ratio, and decreasing the effective prestress in tendons, and increasing in ultimate compressive strain of concrete is the most efficient one. The deformability of the beam is almost directly proportional to the concrete ultimate strain provided the failure mode is concrete crushing, even though the concrete ultimate strain has less influence on the load-carrying capacity.展开更多
基金supported by the Henan Provincial Science and Technology Research Project under Grant(152102310295).
文摘A novel approach for analyzing coupled vibrations between vehicles and bridges is presented,taking into account spatiotemporal effects and mechanical phenomena resulting fromvehicle braking.Efficient modeling and solution of bridge vibrations induced by vehicle deceleration are realized using this method.The method’s validity and reliability are substantiated through numerical examples.A simply supported beam bridge with a corrugated steel web is taken as an example and the effects of parameters such as the initial vehicle speed,braking acceleration,braking location,and road surface roughness on the mid-span displacement and impact factor of the bridge are analyzed.The results show that vehicle braking significantly amplifies mid-span displacement and impact factor responses in comparison to uniform vehicular motion across the bridge.Notably,the influence of wheelto-bridge friction forces is of particular significance and cannot be overlooked.When the vehicle initiates braking near the middle of the span,both the mid-span displacement and impact factor of the bridge exhibit substantial increases,further escalating with higher braking acceleration.Under favorable road surface conditions,the midspan displacement and the impact factor during vehicle braking may exceed the design values stipulated by codes.It is important to note that road surface roughness exerts a more pronounced effect on the impact factor of the bridge in comparison to the effects of vehicle braking.
文摘Replaceable flexural and shear fuse-type coupling beams are used in hybrid coupled shear wall(HCSW)systems,enabling concrete buildings to be promptly recovered after severe earthquakes.This study aimed to analytically evaluate the seismic behavior of flexural and shear fuse beams situated in short-,medium-and high-rise RC buildings that have HCSWs.Three building groups hypothetically located in a high seismic hazard zone were studied.A series of 2D nonlinear time history analyses was accomplished in OpenSees,using the ground motion records scaled at the design basis earthquake level.It was found that the effectiveness of fuses in HCSWs depends on various factors such as size and scale of the building,allowable rotation value,inter-story drift ratio,residual drift quantity,energy dissipation value of the fuses,etc.The results show that shear fuses better meet the requirements of rotations and drifts.In contrast,flexural fuses dissipate more energy,but their sectional stiffness should increase to meet other requirements.It was concluded that adoption of proper fuses depends on the overall scale of the building and on how associated factors are considered.
文摘The instability of functionally graded material(FGM)structures is one of the major threats to their service safety in engineering applications.This paper aims to clarify a long-standing controversy on the thermal instability type of simply-supported FGM beams.First,based on the Euler-Bernoulli beam theory and von K′arm′an geometric nonlinearity,a nonlinear governing equation of simply-supported FGM beams under uniform thermal loads by Zhang’s two-variable method is formulated.Second,an approximate analytic solution to the nonlinear integro-differential boundary value problem under a thermal-induced inhomogeneous force boundary condition is obtained by using a semiinverse method when the coordinate axis is relocated to the bending axis(physical neutral plane),and then the analytical predictions are verified by the differential quadrature method(DQM).Finally,based on the free energy theorem,it is revealed that the symmetry breaking caused by the material inhomogeneity can make the simply-supported FGM beam under uniform thermal loads occur snap-through postbuckling only in odd modes;furthermore,the nonlinear critical load of thermal buckling varies non-monotonically with the functional gradient index due to the stretching-bending coupling effect.These results are expected to provide new ideas and references for the design and regulation of FGM structures.
文摘The stability and local bifurcation of a simply-supported flexible beam (Bernoulli- Euler type) carrying a moving mass and subjected to harmonic axial excitation are investigated. In the theoretical analysis, the partial differential equation of motion with the fifth-order nonlinear term is solved using the method of multiple scales (a perturbation technique). The stability and local bifurcation of the beam are analyzed for 1/2 sub harmonic resonance. The results show that some of the parameters, especially the velocity of moving mass and external excitation, affect the local bifurcation significantly. Therefore, these parameters play important roles in the system stability.
文摘This paper investigated the fire resistance of CSBs with various parameters under high temperature rise due to fire using finite element software ABAQUS. The mechanical parameters of CSBs are analyzed, including load-bearing capacity and the temperature distribution during the heating process. Through structural analysis simulation of the entire heating process, the structural response of the CSBs is divided into five stages: elastic stage, elastic-plastic stage, self-balancing stage, catenary stage and ultimate destruction stage. The results indicate that the opening diameter-to-height ratio, opening spacing-to-height ratio and load ratio significantly affect the structural responses of CSBs in fire, followed by opening shape as secondary effects. In all the numerical analyzes, CSBs are analyzed with a uniformly distributed load and having simply supported boundary conditions.
基金Foundation item:Project (2010CB731704) supported by the National Basic Research Program of ChinaProject (51075189) supported by the National Natural Science Foundation of China
文摘Electron beam welding of Ti-15-3 alloy to 304 stainless steel (STS) using a copper filler metal was carried out. The temperature fields and stress distributions in the Ti/Fe and Ti/Cu/Fe joint during the welding process were numerically simulated and experimentally measured. The results show that the rotated parabola body heat source is fit for the simulation of the electron beam welding. The temperature distribution is asymmetric along the weld center and the temperature in the titanium alloy plate is higher than that in the 304 STS plate. The thermal stress also appears to be in asymmetric distribution. The residual tensile stress mainly exists in the weld at the 304 STS side. The copper filler metal decreases the peak temperature and temperature grade in the joint as well as the residual stress. The longitudinal and lateral residual tensile strengths reduce by 66 MPa and 31 MPa, respectively. From the temperature and residual stress, it is concluded that copper is a good filler metal candidate for the electron beam welding of Ti-15-3 titanium alloy to 304 stainless steel.
基金Project (2010CB731704) supported by the National Basic Research Program of ChinaProject (51075089) supported by the National Natural Science Foundation of china
文摘Electron beam welding was carried out between aluminum alloy and steel with Ag interlayer. Seam morphology, structure and mechanical properties of the joints were investigated with different action positions of the electron beam spot. The results show that with the increment of the beam offset to the silver side from the interface between silver and steel, the seam morphology was improved, and the porosity in the Ag interlayer vanished. A transition layer mainly composed of Ag2Al and Al eutectic was formed at the interface between silver and aluminum, and became thin and spiccato as the beam offset increased. When the beam offset was too large, two IMC layers composed of FeAl and FeAl3 respectively were formed at the interface between steel and Ag interlayer. The optimal beam offset was 0.2 mm, and the maximum tensile strength of the joint was 193 MPa, 88.9% that of the aluminum alloy, and the fracture occurred at the interface between steel and Ag interlayer.
基金Project(2010CB731704)supported by the National Basic Research Program of ChinaProject(2011DFR50760)supported by International Science&Technology Cooperation Program of China
文摘Electron beam welding (EBW) of 304 stainless steel to QCr0.8 copper alloy with copper filler wire was carried out. Orthogonal experiment was performed to investigate the effects of process parameters on the tensile strength of the joints, and the process parameters were optimized. The optimum process parameters are as follows:beam current of 30 mA, welding speed of 100 mm/min, wire feed rate of 1 m/min and beam offset of-0.3 mm. The microstructures of the optimum joint were studied. The results indicate that the weld is mainly composed of dendriticαphase with little globularεphase, and copper inhomogeneity only occurs at the top of the fusion zone. In addition, a melted region without mixing exists near the weld junction of copper side. This region with a coarser grain size is the weakest section of the joints. It is found that the microhardness of the weld decreases with the increase of the copper content in solid solution. The highest tensile strength of the joint is 276 MPa.
文摘Based on the experimental study and inelastic theory, the ultimate flexuralcapacity of steel encased concrete composite beams are derived. The difference between steel encasedconcrete composite beams with full shear connection and beams with partial shear connection,together with the relationship between the inelastic neutral axis of steel parts and concrete parts,are considered in the formulae. The calculation results of the eight specimens with full shearconnection and the three specimens with partial shear connection are in good agreement with theexperimental data, which validates the effectiveness and efficiency of the proposed calculationmethods. Furthermore, the nonlinear finite element analysis of the ultimate flexural capacity of thesteel encased concrete composite beams is performed. Nonlinear material properties and nonlinearcontact properties are considered in the finite element analysis. The finite element analyticalresults also correlate well with the experimental data.
文摘Based on comparative test of two transfer story models, in one of which the transfer beam and basement column is constructed of steel reinforced concrete, and the other is constructed of ordinary reinforced concrete, its force behavior, ductility and failure mechanism under vertical and horizontal loads are studied. The results show that loading bearing and seismic behavior of transfer story structure with steel reinforced concrete beam and basement column is good. The relative design suggestion is put forward.
文摘Microstructure of two different 18Ni Co-free maraging specimens and their electron beam weld joints were investigated comparatively by optical microscopy and SEM. It is showing that both of the steels are typical lath martensite, however, one grain size is about three times as another one, and XRD reveals that the amount of the retained austenitic phase in the former is less then the latter. The austenite distributes in plate form along granular and lath boundaries while some in fine particle within the matrix. The microstructural difference between two specimens led to diverse behaviors in electron beam welding. The first specimen is weldable well but the second shows obvious welding defects of pits and burn-through holes in weld face. The welding microstructure exhibits a typical dendritic morphology, and the grains in the heat-affected zone recrystallized and grew up obviously for high temperature heated by welding electron beam. The weldablity is relative to the thermal conduction performance of the base materials,which is contributed greatly for grain size and austenite content.
基金Project(2011DFR50760)supported by International Science&Technology Cooperation Program of China
文摘Electron beam welding experiments of titanium alloy to stainless steel were carried out with different filler metals, such as Ni, V, and Cu. Microstructures of the joints were examined by optical microscopy, scanning electron microscopy and X-ray diffraction analysis. Mechanical properties of the joints were evaluated according to tensile strength and microhardness. As a result, influences of filler metals on microstructures and mechanical properties of electron beam welded titanium-stainless steel joints were discussed. The results showed that all the filler metals were helpful to restrain the Ti-Fe intermetallics. The welds with different filler metals were all characterized by solid solution and interfacial intermetallics. For each type of the filler metal, the type of solid solution and interfacial intermetallics depended on the metallurgical reactions between the filler metals and base metals. The interfacial intermetallics were Fe2Ti+Ni3Ti+NiTi2, TiFe, and Cu2Ti+CuTi+CuTi2 in the joints welded with Ni, V, and Cu filler metals, respectively. The tensile strengths of the joints were dependent on the hardness of the interfacial intermetallics. The joint welded with Ag filler metal had the highest tensile strength, which is about 310 MPa.
基金Supported by National Natural Science Foundation of China(No.51268054)Natural Science Foundation of Tianjin(No.13JCQNJC07300)the foundation of Key Laboratory of Coast Civil Structure Safety(Tianjin University),Ministry of Education of China(No.2011-1)
文摘Based on the introductions of a type of diaphragm-through connection between concrete-filled square steel tubular columns (CFSSTCs) and H-shaped steel beams,a finite element model of the connection is developed and used to investigate the seismic behavior of the connection.The results of the finite element model are validated by a set of cyclic loading tests.The cyclic loading tests and the finite element analyses indicate that the failure mode of the suggested connections is plastic hinge at the beam with inelastic rotation angle exceeding 0.04 rad.The suggested connections have sufficient strength,plastic deformation and energy dissipation capacity to be used in composite moment frames as beam-to-column rigid connections.
基金Project(51108355)supported by the National Natural Science Foundation of ChinaProject(2011CDB269)supported by the Natural Science Foundation of Hubei Province,China
文摘The objective of this work is to investigate the fatigue behavior of reinforced concrete(RC) beams strengthened with externally bonded carbon fiber reinforced polymer(CFRP) and steel plate. An experimental investigation and theoretical analysis were made on the law of deflection development and stiffness degradation, as well as the influence of fatigue load ranges. Test results indicate that the law of three-stage change under fatigue loading is followed by both midspan deflection and permanent deflection, which also have positive correlation with fatigue load amplitude. Fatigue stiffness of composite strengthened beams degrades gradually with the increasing of number of cycles. Based on the experimental results, a theoretical model by effective moment of inertia method is developed for calculating the sectional stiffness of such composite strengthened beams under fatigue loading, and the calculated results are in good agreement with the experimental results.
基金Projects(51408449,51778630)supported by the National Natural Science Foundation of ChinaProject(2018zzts189)supported by the Fundamental Research Funds for the Central Universities,China
文摘Corrugated steel web is folded along the longitudinal direction and has the mechanical properties such as axial compression stiffness corrugation effect, shear modulus corrugation effect, similar to that of an accordion. In order to study the lateral-torsional buckling of box beams with corrugated steel webs (BBCSW) under the action of bending moment load, the neutral equilibrium equation of BBCSW under the action of bending moment load is derived through the stationary value theory of total potential energy and further, along with taking Kollbrunner-Hajdin correction method and the mechanical properties of the corrugated web into consideration. The analytical calculation formula of lateral-torsional buckling critical bending moment of BBCSW is then obtained. The lateral-torsional buckling critical bending moment of 96 BBCSW test specimens with different geometry dimensions are then calculated using both the analytical calculation method and ANSYS finite element method. The results show that the analytical calculation results agree well with the numerical calculation results using ANSYS, thus proving the accuracy of the analytical calculation method and model simplification hypothesis proposed in this paper. Also, compared with the box beams with flat steel webs (BBFSW) with the same geometry dimensions as BBCSW, within the common range of web space-depth ratio and web span-depth ratio, BBCSW’s lateral-torsional buckling critical bending moment is larger than that of BBFSW. Moreover, the advantages of BBCSW’s stability are even more significant with the increase of web space-depth ratio and web depth-thickness ratio.
文摘Electron beam welding of Ti-15-3 titanium alloy to 304 stainless steel with a copper sheet as interlayer was carried out.Microstructures of the joint were studied by optical microscopy(OM),scanning electron microscopy(SEM) and X-ray diffractometry(XRD).In addition,the mechanical properties of the joint were evaluated by tensile test and the microhardness was measured.These two alloys were successfully welded by adding copper transition layer into the weld.Solid solution with a certain thickness was located at the interfaces between weld and base metal in both sides.Regions inside the weld and near the stainless steel were characterized by solid solution of copper with TiFe2 intermetallics dispersedly distributed in it.While weld near titanium alloy contained Ti-Cu and Ti-Fe-Cu intermetallics layer,in which the hardness of weld came to the highest value.Brittle fracture occurred in the intermetallics layer when the joint was stretched.
基金Projects(11832013,51878350)supported by the National Natural Science Foundation of ChinaProject(B200201063)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(BK20180433)supported by the Natural Science Foundation of Jiangsu Province,China。
文摘To study the flexural behavior and calculation model,8 coral aggregate concrete(CAC)beams with different types of steel were designed.The flexural behavior of CAC beam was tested.The failure mode,bearing capacity,the maximum crack width(ws)and average crack spacing(lm)were studied.A calculation model for the bearing capacity of CAC beam was proposed.The results indicated that with the steel strength increased,the cracking moment(Mcr)and ultimate moment(Mu)of CAC beam increased,and the development of the ws gradually slowed,which effectively inhibited the formation of cracks and improved the flexural behavior of CAC beam.For CAC structures in the ocean engineering,it is recommended to use organic new coated steel to extend its effective service life.In addition,considering the influence of steel corrosion,a calculation model for the Mcr,Mu,lm and ws of CAC beam was established.
文摘Two post weld heat treatments (PWHT), 900 ℃ oil quenched and low temperature tempered (PWHTA) and high temperature tempered and then 900 ℃ oil quenched and low temperature tempered (PWHTB), are employed to treat the weldment. Then the effect of two post weld heat treatment processes on the microstructure,mechanical properties and fracture toughness of electron beam welded joints of 30CrMnSiNi2A steel have been discussed. The results show that, after two kinds of PWHT the microstructure and hardness at every zones of EBW joints are nearly same. Although the welds have good mechanical properties, fracture toughness of both weld and heat affected zone (HAZ) is low, the CTOD values of welds are comparatively higher than that of HAZ. Microstructure and fracture toughness of two EBW joints have no evident differences.
基金Project(51208176)supported by the National Natural Science Foundation of ChinaProjects(2012M511187,2013T60493)supported by the China Postdoctoral Science FoundationProject(2015B17414)supported by the Fundamental Research Funds for the Central Universities,China
文摘A lightweight aggregate concrete-filled steel tube(LACFST) spatial truss beam was tested under bending load. The performance was studied by the analysis of the beam deflection and strains in its chords and webs. According to the test results, several assumptions were made to deduce the bearing capacity calculation method based on the force balance of the whole section. An optimal dimension relationship for the truss beam chords was proposed and verified by finite element analysis. Results show that the LACFST spatial truss beam failed after excessive deflection. The strain distribution agreed with Bernoulli-Euler theoretical prediction. The truss beam flexural bearing capacity calculation results matched test evidence with only a 3% difference between the two. Finite element analyses with different chord dimensions show that the ultimate bearing capacity increases as the chord dimensions increase when the chords have a diameter smaller than optimal one; otherwise, it remains almost unchanged as the chord dimensions increase.
基金Project (50478502) supported by the National Natural Science Foundation of China
文摘The full-range behavior of partially bonded, together with partially prestressed concrete beams containing fiber reinforced polymer (FRP) tendons and stainless steel reinforcing bars was simulated using a simplified theoretical model. The model assumes that a section in the beam has a trilinear moment--curvature relationship characterized by three particular points, initial cracking of concrete, yielding of non-prestressed steel, and crushing of concrete or rupturing of prestressing tendons. Predictions from the model were compared with the limited available test data, and a reasonable agreement was obtained. A detailed parametric study of the behavior of the prestressed concrete beams with hybrid FRP and stainless steel reinforcements was conducted. It can be concluded that the deformability of the beam can be enhanced by increasing the ultimate compressive strain of concrete, unhonded length of tendon, percentage of compressive reinforcement and partial prestress ratio, and decreasing the effective prestress in tendons, and increasing in ultimate compressive strain of concrete is the most efficient one. The deformability of the beam is almost directly proportional to the concrete ultimate strain provided the failure mode is concrete crushing, even though the concrete ultimate strain has less influence on the load-carrying capacity.