To enhance the Young’s modulus(E)and strength of titanium alloys,we designed titanium matrix composites with intercon-nected microstructure based on the Hashin-Shtrikman theory.According to the results,the in-situ re...To enhance the Young’s modulus(E)and strength of titanium alloys,we designed titanium matrix composites with intercon-nected microstructure based on the Hashin-Shtrikman theory.According to the results,the in-situ reaction yielded an interconnected microstructure composed of Ti_(2)C particles when the Ti_(2)C content reached 50vol%.With widths of 10 and 230 nm,the intraparticle Ti lamellae in the prepared composite exhibited a bimodal size distribution due to precipitation and the unreacted Ti phase within the grown Ti_(2)C particles.The composites with interconnected microstructure attained superior properties,including E of 174.3 GPa and ultimate flexural strength of 1014 GPa.Compared with that of pure Ti,the E of the composite was increased by 55% due to the high Ti_(2)C content and interconnected microstructure.The outstanding strength resulted from the strong interfacial bonding,load-bearing capacity of interconnected Ti_(2)C particles,and bimodal intraparticle Ti lamellae,which minimized the average crack driving force.Interrupted flexural tests revealed preferential crack initiation along the{001}cleavage plane and grain boundary of Ti_(2)C in the region with the highest tensile stress.In addition,the propagation can be efficiently inhibited by interparticle Ti grains,which prevented the brittle fracture of the composites.展开更多
Long-term load and flexural failure experiments are carried out on two prestressed concrete(PC) simply supported box girders. In the long-term load experiment, girder-1(G1) is in an elastic state, while girder-2(G2) i...Long-term load and flexural failure experiments are carried out on two prestressed concrete(PC) simply supported box girders. In the long-term load experiment, girder-1(G1) is in an elastic state, while girder-2(G2) is in a cracking state. To investigate the influence of cracking on the flexural behaviors of PC simply supported box beams, the experiment results are analyzed from many aspects, such as load–deflection, load–strain, and failure mode. Experiment results show the following: 1) the shrinkage and creep of concrete have considerable influences on the long-term deflection and strain of the two girders; 2) in the flexural failure experiment, the cracks and ultimate loads of the two girders are close. The rigidity degeneration of G2 is significantly faster than that of G1, and thus G2 shows nonlinear characteristics earlier; 3) to prove the validity and rationality of the current code, the cracking load and ultimate load of the two girders are calculated according to the current code.展开更多
To improve the brittleness characteristics of magnesium phosphate cement-based materials(MPC)and to promote its promotion and application in the field of structural reinforcement and repair,this study aimed to increas...To improve the brittleness characteristics of magnesium phosphate cement-based materials(MPC)and to promote its promotion and application in the field of structural reinforcement and repair,this study aimed to increase the toughness of MPC by adding jute fiber,explore the effects of different amounts of jute fiber on the working and mechanical properties of MPC,and prepare jute fiber reinforced magnesium phosphate cement-based materials(JFRMPC)to reinforce damaged beams.The improvement effect of beam performance before and after reinforcement was compared,and the strengthening and toughening mechanisms of jute fiber on MPC were explored through microscopic analysis.The experimental results show that,as the content of jute fiber(JF)increases,the fluidity and setting time of MPC decrease continuously;When the content of jute fiber is 0.8%,the compressive strength,flexural strength,and bonding strength of MPC at 28 days reach their maximum values,which are increased by 18.0%,20.5%,and 22.6%compared to those of M0,respectively.The beam strengthened with JFRMPC can withstand greater deformation,with a deflection of 2.3 times that of the unreinforced beam at failure.The strain of the steel bar is greatly reduced,and the initial crack and failure loads of the reinforced beam are increased by 192.1%and 16.1%,respectively,compared to those of the unreinforced beam.The JF added to the MPC matrix dissipates energy through tensile fracture and debonding pull-out,slowing down stress concentration and inhibiting the free development of cracks in the matrix,enabling JFRMPC to exhibit higher strength and better toughness.The JF does not cause the hydration of MPC to generate new compounds but reduces the amount of hydration products generated.展开更多
Through the flexural behavior test of coral aggregate reinforced concrete beams(CARCB) and ordinary Portland reinforced concrete beams(OPRCB), and based on the parameters of concrete types, concrete strength grades an...Through the flexural behavior test of coral aggregate reinforced concrete beams(CARCB) and ordinary Portland reinforced concrete beams(OPRCB), and based on the parameters of concrete types, concrete strength grades and reinforcement ratios, the crack development, failure mode, midspan deflection and flexural capacity were studied, the relationships of bending moment-midspan deflection, load-longitudinal tensile reinforcement strain, load-maximum crack width were established, and a calculation model for the flexural capacity of CARCB was suggested. The results showed that with the increase in the reinforcement ratio and concrete strength grade, the crack bending moment(Mcr)and ultimate bending moment(Mu) of CARCB gradually increased. The characteristics of CARCB and OPRCB are basically the same. Furthermore, through increasing the concrete strength grade and reinforcement ratio, Mcr/Mu could be increased to delay the cracking of CARCB. As the load increased, crack width(w) would also increase. At the beginning of the loading, w increased slowly. And then it increased rapidly when the load reached to the ultimate load, which then led to beam failure. Meanwhile, with a comprehensive consideration of the effects of steel corrosion on the loss of steel section and the decrease of steel yield strength, a more reasonable calculation model for the flexural capacity of CARCB was proposed.展开更多
By ring test and bend test, the improvement of waste tire rubber particles on the crack- resistance and flexural behaviors of cement-based materials were investigated. Test results show that the cracking time of the r...By ring test and bend test, the improvement of waste tire rubber particles on the crack- resistance and flexural behaviors of cement-based materials were investigated. Test results show that the cracking time of the ring specimens can be retarded by the incorporation of rubber particles in the cement paste and mortar. The improvement in the crack-resistance depended on the rubber fraction. When the rubber fraction was 20% in volume, the cracking time was retarded about 15 h for the paste and 24 d for the mortar respectively. Flexural properties were evaluated based on the bend test results for both mortar and concrete containing different amount of rubber particles. Test results show that rubberized mortar and concrete specimens exhibit ductile failure and significant deformation before fracture. The ultimate deformations of both mortar and concrete specimen increase more than 2-4 times than control specimens.展开更多
Bamboo is a renewable and environmentally friendly material often used for construction.This study investigates the flexural behavior of bamboo beams through theoretical and finite element(FE)analyses.Considering the ...Bamboo is a renewable and environmentally friendly material often used for construction.This study investigates the flexural behavior of bamboo beams through theoretical and finite element(FE)analyses.Considering the material’s nonlinearity,a method of calculating load-deflection curves is proposed and validated via FE analysis.The interfacial slippage dominated by the shear stiffness of the interface between two bamboo poles significantly influences the flexural behavior of double-pole bamboo beams.Thus,the load-deflection curves for different shear stiffnesses can be obtained via theoretical and FE analyses.Subsequently,a novel configuration using diagonal steel bands to avoid slippage is presented.An inclination angle of 45°is suggested to adequately develop the stiffness and bearing capacity of the steel band.展开更多
In order to study the mechanical behavior of corroded channel steel beam,experiment on five corroded channel steel beams is carried out. Test results show that the bending failures may occur under the ultimate load ca...In order to study the mechanical behavior of corroded channel steel beam,experiment on five corroded channel steel beams is carried out. Test results show that the bending failures may occur under the ultimate load carrying capacity of members,compared with the calculating results of non-corrosion channel steel beam,and the bearing capacity of corroded channel steel beam is reduced,while the deflection is increased. With the increase of shear-span ratio,the bearing capacity of corroded channel steel beam reduces and the deflection increases gradually; with the increment of heightspan ratio, the bearing capacity increases and the deflection decreases gradually; with the enhancement of width-height ratio,the bearing capacity reduces and the deflection-span ratio increases gradually. The measured results indicate that the load-deflection relationship curves of corroded channel steel beam may be divided into four sections: the exfoliated rust layer stage,the elastic stage,the yielding stage and the descending stage. The load-strain relationship curves include two sections: the elastic stage and the yielding stage. The strain measurement of web proves that the average strains agree well with the assumption of plane section. This paper could provide some scientific bases for the maintenance and reinforcement of the corroded steel structure.展开更多
Engineered Cementitious Composites(ECC)is a class of high-performance fiber reinforced composites with ultra-ductility designed based on micromechanics,and it has been developed for increasing application in the const...Engineered Cementitious Composites(ECC)is a class of high-performance fiber reinforced composites with ultra-ductility designed based on micromechanics,and it has been developed for increasing application in the construction industry during recent decades.The properties of ECC at room temperature have been tested and studied in depth,however,few studies focus on its performance after high temperature that is one of the worst conditions to ECC.To investigate the change tendency and mechanism for the high temperature flexural properties of hybrid fiber reinforced ECC and the feasibility of calcium carbonate whisker to reduce the cost of ECC materials,polyvinyl alcohol fiber(PVA)reinforced strain hardening cementitious composites(PVA-ECC),steel fiber+PVA fiber reinforced ECC(defined as HyFRECC-A)and steel fiber+PVA fiber+CaCO3 whisker reinforced ECC(defined as HyFRECC-B)subject to room temperature and 200℃,400℃,600℃,800℃elevated temperature exposure were experimentally compared.The results indicate that equally replacing PVA fibers by steel fibers degraded the flexural hardening ability of PVA-ECC at room temperature,while the addition of appropriate amount of CaCO3 whisker improved the flexural strength,toughness and flexural hardening behavior.The elevated temperature posed a significant effect on the flexural strength and toughness of the three types of ECCs.Flexural deflection hardening behavior of the three types of ECCs was eliminated after high temperature exposure.Flexural strength and toughness of PVA-ECC presented an exponential decay along with the increase of temperature.The addition of steel fiber slowed down the decay rate.Although the use of CaCO3 whisker increased the post-temperature flexural strength and toughness of HyFRECC-B,the decay rate was not further decreased.展开更多
The influence of polypropylene fiber on the flexural fatigue performance of high-strength concrete (HSC), which could be used as cover of reinforcement of segment, was investigate by three-point load bending tests. Al...The influence of polypropylene fiber on the flexural fatigue performance of high-strength concrete (HSC), which could be used as cover of reinforcement of segment, was investigate by three-point load bending tests. Also, the flexural fatigue equations of high-strength concrete with and without polypropylene fiber were established through test analysis. The experimental results indicate that the addition of polypropylene fiber can improve the static bending strength of segment concrete, and the important is that it can markedly increase the flexural fatigue performance of the HSC subjected to cyclic bending load. Especially when with 1.37 kg/m3 addition of the fiber was corporate with silica fume and slag powder, the fatigue life of the HSC can be increased by 43.4% compared to that of the segment concrete without fiber, silica fume and slag.展开更多
This paper presents the results of four partially prestressed ultra-high strength concrete beams in flexure. The test results are used to evaluate the effects of prestressing tendon depth and area on flexure behavior ...This paper presents the results of four partially prestressed ultra-high strength concrete beams in flexure. The test results are used to evaluate the effects of prestressing tendon depth and area on flexure behavior of specimen beams. The test results indicate that: the cracking load,yielding load,peak load and stiffness postcracking of specimen beams are enhanced by reducing prestressing tendon depth or increasing prestressing tendon area, and the flexural ductility is improved by increasing prestressing tendon depth or reducing prestressing tendon area. The effect of complex reinforcement index considering the strength of the equivalence principle and the reinforcement position on loading levels under serviceability limit state,flexural strength and displacement ductility factor are studied. The influence coefficient of prestressing tendon kpis introduced in the complex reinforcement index. As the complex reinforcement index increases, the loading levels under serviceability limit state and flexural strength increases linearly,and the displacement ductility factor decreases linearly. The test results also verify the conventional beam flexural theory based on the plane cross-section assumption for predicting ultimate flexural strength of partially prestressed ultra-high strength concrete beams is valid. After the introduction of the coefficient kp,the calculation method of cracks in code for design of concrete structure in china are appropriated for the specimen beams.展开更多
Reinforcement corrosion has a serious impact on the durability and safety of reinforced concrete structures.Six reinforced concrete(RC)beam specimens are constructed.After beam specimens are subjected to accelerated c...Reinforcement corrosion has a serious impact on the durability and safety of reinforced concrete structures.Six reinforced concrete(RC)beam specimens are constructed.After beam specimens are subjected to accelerated corrosion with the constant current,beam specimens are repaired with epoxy mortar and the flexural test of beams is investigated.Then the behaviors of repaired corroded reinforced concrete beams are evaluated.The experimental results show that cracking and ultimate loads of corroded RC beams are enhanced after being repaired.And the strain distributions measured across sections of beam specimens still obey the assumption of plane section.After being repaired,the number of cracks decreases and the crack spacing increases.展开更多
Fiber-reinforced polymer(FRP)bars have been increasingly recognized in the field of civil engineering due to their advantages of light weight,high strength and excellent durability.FRP bars can replace steel bars in c...Fiber-reinforced polymer(FRP)bars have been increasingly recognized in the field of civil engineering due to their advantages of light weight,high strength and excellent durability.FRP bars can replace steel bars in concrete beams and effectively improve the durability of beams.In this paper,the literature relevant to the short-term mechanical properties of FRP bars and FRP-reinforced concrete beams was reviewed based on previous studies and practical engineering application.Firstly,the mechanical properties of FRP bars were reviewed.Different types of fibers or steel and fibers can be combined to obtain hybrid fiber-reinforced polymer(HFRP)or steel-fiber composite bars(SFCB)with excellent mechanical performance,respectively.The bond performance and bond-slip model between FRP bars and concrete were discussed.Several common bond-slip models were usually used to study the bond performance between carbon fiber-reinforced polymer(CFRP)bars or glass fiber-reinforced polymer(GFRP)bars and concrete,but changing the type of FRP bars will lead to larger dispersion.Then,the experimental studies,theoretical calculation methods and finite element simulation methods of flexural/shear behavior of FRP-reinforced concrete beams were presented.Finally,their applications in practical engineering were discussed and the prospects of further research were proposed.It is pointed out that FRP-reinforced ultra-high performance concrete(UHPC)beams,FRP-reinforced geopolymer concrete(GPC)beams,engineered cementitious composites(ECC)-FRP-reinforced concrete beams,prestressed FRP-reinforced concrete beams and steel/FRP hybrid-reinforced concrete beams can effectively improve the deformation resistance and poor ductility of pure FRP-reinforced concrete beams.展开更多
In recent years, an emerging technology termed high-strength concrete (HSC) has become popular in construction industry. Present study describes an experimental research on the behavior of high-strength concrete bea...In recent years, an emerging technology termed high-strength concrete (HSC) has become popular in construction industry. Present study describes an experimental research on the behavior of high-strength concrete beams in ultimate and service state. Six simply supported beams were tested, by applying comprising two symmetric concentrated loads. Tests are reported in this study on the flexural behavior of high-strength reinforced concrete (HSRC) beams made with coarse and fine aggregate together with Microsilica. Test parameter considered includes effect of being compressive reinforcement. Based on the obtained results, the behavior of such members is more deeply reviewed. Also a comparison between theoretical and experimental results is reported here. The beams were made from concrete having compressive strength of 66.81-77.72 N/mm2 and percentage reinforcement ratio (P/Pb) in the range of 0.56% - 1.20%. The ultimate moment for the tested beams was found to be in a good agreement with that of the predicted ultimate moment based on ACI 318-11, ACI 363 and C SA-04 provisions. The predicted deflection based classical formulation based on code provisions for serviceability requirements is found to underestimate the maximum deflection of HSC reinforced beams at service load.展开更多
To study the flexural behavior of prestressed concrete beams with high-strength steel reinforcement and high-strength concrete and improve the crack width calculation method for flexural components with such reinforce...To study the flexural behavior of prestressed concrete beams with high-strength steel reinforcement and high-strength concrete and improve the crack width calculation method for flexural components with such reinforcement and concrete,12 specimens were tested under static loading.The failure modes,flexural strength,ductility,and crack width of the specimens were analyzed.The results show that the failure mode of the test beams was similar to that of the beams with normal reinforced concrete.A brittle failure did not occur in the specimens.To further understand the working mechanism,the results of other experimental studies were collected and discussed.The results show that the normalized reinforcement ratio has a greater effect on the ductility than the concrete strength.The cracking-and peak-moment formulas in the code for the design of concrete(GB 50010-2010)applied to the beams were both found to be acceptable.However,the calculation results of the maximum crack width following GB 50010-2010 and EN 1992-1-1:2004 were considerably conservative.In the context of GB 50010-2010,a revised formula for the crack width is proposed with modifications to two major factors:the average crack spacing and an amplification coefficient of the maximum crack width to the average spacing.The mean value of the ratio of the maximum crack width among the 12 test results and the relative calculation results from the revised formula is 1.017,which is better than the calculation result from GB 50010-2010.Therefore,the new formula calculates the crack width more accurately in high-strength concrete and high-strength steel reinforcement members.Finally,finite element models were established using ADINA software and validated based on the test results.This study provides an important reference for the development of high-strength concrete and highstrength steel reinforcement structures.展开更多
This study presents experimental and numerical investigations on the mechanical properties of ultrahigh-performance concrete(UHPC)reinforced with single and hybrid micro-and macro-steel and polypropylene fibers.For th...This study presents experimental and numerical investigations on the mechanical properties of ultrahigh-performance concrete(UHPC)reinforced with single and hybrid micro-and macro-steel and polypropylene fibers.For this purpose,a series of cubic,cylindrical,dog-bone,and prismatic beam specimens(total fiber by volume=1%,and 2%)were tested under compressive,tensile,and flexural loadings.A method,namely multi-target digital image correlation(MT-DIC)was used to monitor the displacement and deflection values.The obtained experimental data were subsequently used to discuss influential parameters,i.e.,flexural strength,tensile strength,size effect,etc.Numerical analyses were also carried out using finite element software to account for the sensitivity of different parameters.Furthermore,nonlinear regression analyses were conducted to obtain the flexural load-deflection curves.The results showed that the MT-DIC method was capable of estimating the tensile and flexural responses as well as the location of the crack with high accuracy.In addition,the regression analyses showed excellent consistency with the experimental results,with correlation coefficients close to unity.Furthermore,size-effect modeling revealed that modified Bazant theory yielded the best estimation of the size-effect phenomenon compared to other models.展开更多
基金financially supported by the National Key R&D Program of China(No.2021YFB3701203)the National Natural Science Foundation of China(Nos.U22A20113,52201116,52071116,and 52261135543)+1 种基金Heilongjiang Touyan Team ProgramChina Postdoctoral Science Foundation(No.2022M710939).
文摘To enhance the Young’s modulus(E)and strength of titanium alloys,we designed titanium matrix composites with intercon-nected microstructure based on the Hashin-Shtrikman theory.According to the results,the in-situ reaction yielded an interconnected microstructure composed of Ti_(2)C particles when the Ti_(2)C content reached 50vol%.With widths of 10 and 230 nm,the intraparticle Ti lamellae in the prepared composite exhibited a bimodal size distribution due to precipitation and the unreacted Ti phase within the grown Ti_(2)C particles.The composites with interconnected microstructure attained superior properties,including E of 174.3 GPa and ultimate flexural strength of 1014 GPa.Compared with that of pure Ti,the E of the composite was increased by 55% due to the high Ti_(2)C content and interconnected microstructure.The outstanding strength resulted from the strong interfacial bonding,load-bearing capacity of interconnected Ti_(2)C particles,and bimodal intraparticle Ti lamellae,which minimized the average crack driving force.Interrupted flexural tests revealed preferential crack initiation along the{001}cleavage plane and grain boundary of Ti_(2)C in the region with the highest tensile stress.In addition,the propagation can be efficiently inhibited by interparticle Ti grains,which prevented the brittle fracture of the composites.
基金Project(51551801)supported by the National Natural Science Foundation of ChinaProject(14JJ4062)supported by Natural Science Foundation of Hunan Province,China
文摘Long-term load and flexural failure experiments are carried out on two prestressed concrete(PC) simply supported box girders. In the long-term load experiment, girder-1(G1) is in an elastic state, while girder-2(G2) is in a cracking state. To investigate the influence of cracking on the flexural behaviors of PC simply supported box beams, the experiment results are analyzed from many aspects, such as load–deflection, load–strain, and failure mode. Experiment results show the following: 1) the shrinkage and creep of concrete have considerable influences on the long-term deflection and strain of the two girders; 2) in the flexural failure experiment, the cracks and ultimate loads of the two girders are close. The rigidity degeneration of G2 is significantly faster than that of G1, and thus G2 shows nonlinear characteristics earlier; 3) to prove the validity and rationality of the current code, the cracking load and ultimate load of the two girders are calculated according to the current code.
基金the Science and Technology Research Project of Chongqing Education Commission(Nos.KJZD-K201901201,KJZD-202101201)the Top-notch Young Talents in Chongqing(No.CQYC201905086)the Technology Innovation and Application Development Project in Wanzhou District,Chongqing(No.wzstc-2019031)。
文摘To improve the brittleness characteristics of magnesium phosphate cement-based materials(MPC)and to promote its promotion and application in the field of structural reinforcement and repair,this study aimed to increase the toughness of MPC by adding jute fiber,explore the effects of different amounts of jute fiber on the working and mechanical properties of MPC,and prepare jute fiber reinforced magnesium phosphate cement-based materials(JFRMPC)to reinforce damaged beams.The improvement effect of beam performance before and after reinforcement was compared,and the strengthening and toughening mechanisms of jute fiber on MPC were explored through microscopic analysis.The experimental results show that,as the content of jute fiber(JF)increases,the fluidity and setting time of MPC decrease continuously;When the content of jute fiber is 0.8%,the compressive strength,flexural strength,and bonding strength of MPC at 28 days reach their maximum values,which are increased by 18.0%,20.5%,and 22.6%compared to those of M0,respectively.The beam strengthened with JFRMPC can withstand greater deformation,with a deflection of 2.3 times that of the unreinforced beam at failure.The strain of the steel bar is greatly reduced,and the initial crack and failure loads of the reinforced beam are increased by 192.1%and 16.1%,respectively,compared to those of the unreinforced beam.The JF added to the MPC matrix dissipates energy through tensile fracture and debonding pull-out,slowing down stress concentration and inhibiting the free development of cracks in the matrix,enabling JFRMPC to exhibit higher strength and better toughness.The JF does not cause the hydration of MPC to generate new compounds but reduces the amount of hydration products generated.
基金financially supported by the National Key Basic Research Development Plan of China(973 Program,Grant No.2015CB655102)the National Natural Science Foundation of China(Grant Nos.51508272 and 51678304)+2 种基金the Natural Science Foundation of Jiangsu Province(Grant No.BK20180433)the Project funded by China Postdoctoral Science Foundation(Grant No.2018M630558)the Open Research Funds for State Key Laboratory of High Performance Civil Engineering Materials(Grant No.2015CEM001)
文摘Through the flexural behavior test of coral aggregate reinforced concrete beams(CARCB) and ordinary Portland reinforced concrete beams(OPRCB), and based on the parameters of concrete types, concrete strength grades and reinforcement ratios, the crack development, failure mode, midspan deflection and flexural capacity were studied, the relationships of bending moment-midspan deflection, load-longitudinal tensile reinforcement strain, load-maximum crack width were established, and a calculation model for the flexural capacity of CARCB was suggested. The results showed that with the increase in the reinforcement ratio and concrete strength grade, the crack bending moment(Mcr)and ultimate bending moment(Mu) of CARCB gradually increased. The characteristics of CARCB and OPRCB are basically the same. Furthermore, through increasing the concrete strength grade and reinforcement ratio, Mcr/Mu could be increased to delay the cracking of CARCB. As the load increased, crack width(w) would also increase. At the beginning of the loading, w increased slowly. And then it increased rapidly when the load reached to the ultimate load, which then led to beam failure. Meanwhile, with a comprehensive consideration of the effects of steel corrosion on the loss of steel section and the decrease of steel yield strength, a more reasonable calculation model for the flexural capacity of CARCB was proposed.
基金the National Natural Science Foundation of China(No.50679054)
文摘By ring test and bend test, the improvement of waste tire rubber particles on the crack- resistance and flexural behaviors of cement-based materials were investigated. Test results show that the cracking time of the ring specimens can be retarded by the incorporation of rubber particles in the cement paste and mortar. The improvement in the crack-resistance depended on the rubber fraction. When the rubber fraction was 20% in volume, the cracking time was retarded about 15 h for the paste and 24 d for the mortar respectively. Flexural properties were evaluated based on the bend test results for both mortar and concrete containing different amount of rubber particles. Test results show that rubberized mortar and concrete specimens exhibit ductile failure and significant deformation before fracture. The ultimate deformations of both mortar and concrete specimen increase more than 2-4 times than control specimens.
基金This research was supported by the National Key Research and Development Program of China(Grant No.2017YFC0703502)the National Natural Science Foundation of China(Grant No.51608433)+2 种基金the Key Lab of Plateau Building and Eco-Community in Qinghai(KLKF-2020-001)the Shaanxi Province Youth Science and Technology New Star Program(Grant No.2019KJXX-040)These financial supports are greatly acknowledged.
文摘Bamboo is a renewable and environmentally friendly material often used for construction.This study investigates the flexural behavior of bamboo beams through theoretical and finite element(FE)analyses.Considering the material’s nonlinearity,a method of calculating load-deflection curves is proposed and validated via FE analysis.The interfacial slippage dominated by the shear stiffness of the interface between two bamboo poles significantly influences the flexural behavior of double-pole bamboo beams.Thus,the load-deflection curves for different shear stiffnesses can be obtained via theoretical and FE analyses.Subsequently,a novel configuration using diagonal steel bands to avoid slippage is presented.An inclination angle of 45°is suggested to adequately develop the stiffness and bearing capacity of the steel band.
基金National Natural Science Foundation of China(No.51578001)Natural Science Foundations of Anhui Province,China(Nos.KJ2010A046,KJ2015ZD10)the Science and Technology Item Foundation of Ma'anshan,China(Nos.2012(6),2013(79))
文摘In order to study the mechanical behavior of corroded channel steel beam,experiment on five corroded channel steel beams is carried out. Test results show that the bending failures may occur under the ultimate load carrying capacity of members,compared with the calculating results of non-corrosion channel steel beam,and the bearing capacity of corroded channel steel beam is reduced,while the deflection is increased. With the increase of shear-span ratio,the bearing capacity of corroded channel steel beam reduces and the deflection increases gradually; with the increment of heightspan ratio, the bearing capacity increases and the deflection decreases gradually; with the enhancement of width-height ratio,the bearing capacity reduces and the deflection-span ratio increases gradually. The measured results indicate that the load-deflection relationship curves of corroded channel steel beam may be divided into four sections: the exfoliated rust layer stage,the elastic stage,the yielding stage and the descending stage. The load-strain relationship curves include two sections: the elastic stage and the yielding stage. The strain measurement of web proves that the average strains agree well with the assumption of plane section. This paper could provide some scientific bases for the maintenance and reinforcement of the corroded steel structure.
基金This study was supported by the National Natural Science Foundation of China(51908247)Jiangsu Natural Science Foundation Project(BK20170192)Open Fund Project of State Key Laboratory of Green Building Materials(YA-616).
文摘Engineered Cementitious Composites(ECC)is a class of high-performance fiber reinforced composites with ultra-ductility designed based on micromechanics,and it has been developed for increasing application in the construction industry during recent decades.The properties of ECC at room temperature have been tested and studied in depth,however,few studies focus on its performance after high temperature that is one of the worst conditions to ECC.To investigate the change tendency and mechanism for the high temperature flexural properties of hybrid fiber reinforced ECC and the feasibility of calcium carbonate whisker to reduce the cost of ECC materials,polyvinyl alcohol fiber(PVA)reinforced strain hardening cementitious composites(PVA-ECC),steel fiber+PVA fiber reinforced ECC(defined as HyFRECC-A)and steel fiber+PVA fiber+CaCO3 whisker reinforced ECC(defined as HyFRECC-B)subject to room temperature and 200℃,400℃,600℃,800℃elevated temperature exposure were experimentally compared.The results indicate that equally replacing PVA fibers by steel fibers degraded the flexural hardening ability of PVA-ECC at room temperature,while the addition of appropriate amount of CaCO3 whisker improved the flexural strength,toughness and flexural hardening behavior.The elevated temperature posed a significant effect on the flexural strength and toughness of the three types of ECCs.Flexural deflection hardening behavior of the three types of ECCs was eliminated after high temperature exposure.Flexural strength and toughness of PVA-ECC presented an exponential decay along with the increase of temperature.The addition of steel fiber slowed down the decay rate.Although the use of CaCO3 whisker increased the post-temperature flexural strength and toughness of HyFRECC-B,the decay rate was not further decreased.
基金Funded by the National "863" Program (No.2005AA332010)
文摘The influence of polypropylene fiber on the flexural fatigue performance of high-strength concrete (HSC), which could be used as cover of reinforcement of segment, was investigate by three-point load bending tests. Also, the flexural fatigue equations of high-strength concrete with and without polypropylene fiber were established through test analysis. The experimental results indicate that the addition of polypropylene fiber can improve the static bending strength of segment concrete, and the important is that it can markedly increase the flexural fatigue performance of the HSC subjected to cyclic bending load. Especially when with 1.37 kg/m3 addition of the fiber was corporate with silica fume and slag powder, the fatigue life of the HSC can be increased by 43.4% compared to that of the segment concrete without fiber, silica fume and slag.
基金Sponsored by the National Natural Science Foundation of China(Grant No.50878037,51078059,51178078)
文摘This paper presents the results of four partially prestressed ultra-high strength concrete beams in flexure. The test results are used to evaluate the effects of prestressing tendon depth and area on flexure behavior of specimen beams. The test results indicate that: the cracking load,yielding load,peak load and stiffness postcracking of specimen beams are enhanced by reducing prestressing tendon depth or increasing prestressing tendon area, and the flexural ductility is improved by increasing prestressing tendon depth or reducing prestressing tendon area. The effect of complex reinforcement index considering the strength of the equivalence principle and the reinforcement position on loading levels under serviceability limit state,flexural strength and displacement ductility factor are studied. The influence coefficient of prestressing tendon kpis introduced in the complex reinforcement index. As the complex reinforcement index increases, the loading levels under serviceability limit state and flexural strength increases linearly,and the displacement ductility factor decreases linearly. The test results also verify the conventional beam flexural theory based on the plane cross-section assumption for predicting ultimate flexural strength of partially prestressed ultra-high strength concrete beams is valid. After the introduction of the coefficient kp,the calculation method of cracks in code for design of concrete structure in china are appropriated for the specimen beams.
基金supported by the Program for the Transport Science & Technology Project of Jiangsu Province
文摘Reinforcement corrosion has a serious impact on the durability and safety of reinforced concrete structures.Six reinforced concrete(RC)beam specimens are constructed.After beam specimens are subjected to accelerated corrosion with the constant current,beam specimens are repaired with epoxy mortar and the flexural test of beams is investigated.Then the behaviors of repaired corroded reinforced concrete beams are evaluated.The experimental results show that cracking and ultimate loads of corroded RC beams are enhanced after being repaired.And the strain distributions measured across sections of beam specimens still obey the assumption of plane section.After being repaired,the number of cracks decreases and the crack spacing increases.
基金financial support provided by National Key Research and Development Program of China(No.2021YFB2601000)Scientific Research Project of Zhejiang Provincial Department of Transportation(2018007).
文摘Fiber-reinforced polymer(FRP)bars have been increasingly recognized in the field of civil engineering due to their advantages of light weight,high strength and excellent durability.FRP bars can replace steel bars in concrete beams and effectively improve the durability of beams.In this paper,the literature relevant to the short-term mechanical properties of FRP bars and FRP-reinforced concrete beams was reviewed based on previous studies and practical engineering application.Firstly,the mechanical properties of FRP bars were reviewed.Different types of fibers or steel and fibers can be combined to obtain hybrid fiber-reinforced polymer(HFRP)or steel-fiber composite bars(SFCB)with excellent mechanical performance,respectively.The bond performance and bond-slip model between FRP bars and concrete were discussed.Several common bond-slip models were usually used to study the bond performance between carbon fiber-reinforced polymer(CFRP)bars or glass fiber-reinforced polymer(GFRP)bars and concrete,but changing the type of FRP bars will lead to larger dispersion.Then,the experimental studies,theoretical calculation methods and finite element simulation methods of flexural/shear behavior of FRP-reinforced concrete beams were presented.Finally,their applications in practical engineering were discussed and the prospects of further research were proposed.It is pointed out that FRP-reinforced ultra-high performance concrete(UHPC)beams,FRP-reinforced geopolymer concrete(GPC)beams,engineered cementitious composites(ECC)-FRP-reinforced concrete beams,prestressed FRP-reinforced concrete beams and steel/FRP hybrid-reinforced concrete beams can effectively improve the deformation resistance and poor ductility of pure FRP-reinforced concrete beams.
文摘In recent years, an emerging technology termed high-strength concrete (HSC) has become popular in construction industry. Present study describes an experimental research on the behavior of high-strength concrete beams in ultimate and service state. Six simply supported beams were tested, by applying comprising two symmetric concentrated loads. Tests are reported in this study on the flexural behavior of high-strength reinforced concrete (HSRC) beams made with coarse and fine aggregate together with Microsilica. Test parameter considered includes effect of being compressive reinforcement. Based on the obtained results, the behavior of such members is more deeply reviewed. Also a comparison between theoretical and experimental results is reported here. The beams were made from concrete having compressive strength of 66.81-77.72 N/mm2 and percentage reinforcement ratio (P/Pb) in the range of 0.56% - 1.20%. The ultimate moment for the tested beams was found to be in a good agreement with that of the predicted ultimate moment based on ACI 318-11, ACI 363 and C SA-04 provisions. The predicted deflection based classical formulation based on code provisions for serviceability requirements is found to underestimate the maximum deflection of HSC reinforced beams at service load.
基金The research in this paper was financially supported by the National Natural Science Foundation of China(Grant Nos.51878233 and 51778201)the Anhui Key Laboratory of Civil Engineering and Materials(No.PA2019GDPK0034).
文摘To study the flexural behavior of prestressed concrete beams with high-strength steel reinforcement and high-strength concrete and improve the crack width calculation method for flexural components with such reinforcement and concrete,12 specimens were tested under static loading.The failure modes,flexural strength,ductility,and crack width of the specimens were analyzed.The results show that the failure mode of the test beams was similar to that of the beams with normal reinforced concrete.A brittle failure did not occur in the specimens.To further understand the working mechanism,the results of other experimental studies were collected and discussed.The results show that the normalized reinforcement ratio has a greater effect on the ductility than the concrete strength.The cracking-and peak-moment formulas in the code for the design of concrete(GB 50010-2010)applied to the beams were both found to be acceptable.However,the calculation results of the maximum crack width following GB 50010-2010 and EN 1992-1-1:2004 were considerably conservative.In the context of GB 50010-2010,a revised formula for the crack width is proposed with modifications to two major factors:the average crack spacing and an amplification coefficient of the maximum crack width to the average spacing.The mean value of the ratio of the maximum crack width among the 12 test results and the relative calculation results from the revised formula is 1.017,which is better than the calculation result from GB 50010-2010.Therefore,the new formula calculates the crack width more accurately in high-strength concrete and high-strength steel reinforcement members.Finally,finite element models were established using ADINA software and validated based on the test results.This study provides an important reference for the development of high-strength concrete and highstrength steel reinforcement structures.
文摘This study presents experimental and numerical investigations on the mechanical properties of ultrahigh-performance concrete(UHPC)reinforced with single and hybrid micro-and macro-steel and polypropylene fibers.For this purpose,a series of cubic,cylindrical,dog-bone,and prismatic beam specimens(total fiber by volume=1%,and 2%)were tested under compressive,tensile,and flexural loadings.A method,namely multi-target digital image correlation(MT-DIC)was used to monitor the displacement and deflection values.The obtained experimental data were subsequently used to discuss influential parameters,i.e.,flexural strength,tensile strength,size effect,etc.Numerical analyses were also carried out using finite element software to account for the sensitivity of different parameters.Furthermore,nonlinear regression analyses were conducted to obtain the flexural load-deflection curves.The results showed that the MT-DIC method was capable of estimating the tensile and flexural responses as well as the location of the crack with high accuracy.In addition,the regression analyses showed excellent consistency with the experimental results,with correlation coefficients close to unity.Furthermore,size-effect modeling revealed that modified Bazant theory yielded the best estimation of the size-effect phenomenon compared to other models.