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
A novel method for prediction of the load carrying capacity of a corroded reinforced concrete beam (CRCB) is presented in the paper. Nine reinforced concrete beams, which had been working in an aggressive environment ...A novel method for prediction of the load carrying capacity of a corroded reinforced concrete beam (CRCB) is presented in the paper. Nine reinforced concrete beams, which had been working in an aggressive environment for more than 10 years, were tested in the laboratory. Comprehensive tests, including flexural test, strength test for corroded concrete and rusty rebar, and pullout test for bond strength between concrete and rebar, were conducted. ne flexural test results of CRCBs reveal that the distribution of surface cracks on the beams shows a fractal behavior. The relationship between the fractal dimensions and mechanical properties of CRCBs is then studied. A prediction model based on artificial neural network (ANN) is established by the use of the fractal dimension as the corrosion index, together with the basic information of the beam. The validity of the prediction model is demonstrated through the experimental data, and satisfactory results are achieved.展开更多
To meet the requirement of fire endurance for concrete structures strengthened with CFRP sheets, this study develops an inorganic adhesive whose strength at 600 ℃ is not lower than that at normal room temperature. Th...To meet the requirement of fire endurance for concrete structures strengthened with CFRP sheets, this study develops an inorganic adhesive whose strength at 600 ℃ is not lower than that at normal room temperature. The inorganic adhesive is then used to bond CFRP sheets on reinforced concrete beams in order to strengthen them. The fire protection of the CFRP sheets is done using the thick-type fireproofing coatings for tunnel ( TFCT) and steel structure ( TFCSS) respectively. Four specimens are tested in the furnace together. Specimens are exposed to fire for 1. 5 h in according to the ISO834 standard fire curve,and then naturally cooled for 1 h. In the tests,the largest displacements at the mid-span positions of specimens are only from 1 /1400 to 1 /318 of actual span corresponding to the highest temperatures from 300 ℃ to 470 ℃. After the specimens are naturally cooled to the normal temperature and the fireproofing coatings are then removed,it can be seen that the CFRP sheets keep in a good state,which indicates that CFRP sheets can be tightly bonded on the concrete and work well together with the concrete beams during and after fire. Besides,the tests also verify that the fire performance of TFCT is superior to TFCSS for the strengthened beams.展开更多
In order to research the strengthening effects of aramid fiber reinforced polymer (AFRP) sheets on the flexural performance of corroded reinforced concrete (RC) beams, the static and fatigue performance of corrode...In order to research the strengthening effects of aramid fiber reinforced polymer (AFRP) sheets on the flexural performance of corroded reinforced concrete (RC) beams, the static and fatigue performance of corroded RC beams strengthened with non-prestressed AFRP sheets under different degrees of corrosion (minor: reinforcement mass loss is 2.0%, medium: reinforcement mass loss is 6.0%) have been researched experimentally in this paper, to compare with that of the control beams (un-strengthened and un-corroded) and un-strengthened corroded beams, and additionally compare with fatigue performance of those medium corroded RC beams strengthened with prestressed AFRP sheets with permanent anchors. The results show that, (1) compared with un-strengthened corroded beams under the same degrees of corrosion, the cracking, yield and ultimate monotonic loads of the minor corroded RC beam strengthened with non-prestressed AFRP sheets is respectively increased by 20%, 27% and 60%, whereas for the medium corroded RC beam strengthened with non-prestressed AFRP sheets increased by 15%, 36% and 83% respectively. The ultimate deflection of the medium corroded beam strengthened with non-prestressed AFRP sheets is 166% larger than that of the corroded un-strengthened beam under the monotonic load. (2) The fatigue life of the non-prestressed AFRP strengthened medium corroded beam is 10.4 times more than that of the un-strengthened corroded beam, but lower than that of the unstrengthened-uncorroded (virgin) beam. (3) Fatigue experiments of the beams strengthened with prestressed AFRP sheets and with those non-prestressed AFRP sheets show that the fatigue life of the retrofit RC beams increase with increasing prestress level of AFRP sheets.(4) The use of AFRP sheets for strengthening corroded RC beams is an efficient technique that can maintain the structural integrity and enhance the structural behavior of such 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
Due to creep characteristics of wood,long-term loading can cause a significant stress loss of steel bars in rein-forced glulam beams and high long-term deflection of the beam midspan.In this study,15 glulam beams were...Due to creep characteristics of wood,long-term loading can cause a significant stress loss of steel bars in rein-forced glulam beams and high long-term deflection of the beam midspan.In this study,15 glulam beams were subjected to a 90-day long-term loading test,and the effects of long-term loading value,reinforcement ratio and prestress level on the stress of steel bars,midspan long-term deflection,and other parameters were compared and analyzed.The main conclusions drawn from this study were that the long-term deflection of the reinforced glulam beams accounted for 22.5%,20.6%,and 18.2%of the total deflection respectively when the loading value was 20%,30%,and 40%of the estimated ultimate load under the long-term loading.The higher the loading level was,the smaller the proportion of the long-term deflection in the total deflection was.Compared with ordinary glulam beams,the long-term deflection of the reinforced glulam beam was even smaller.Under the condition of the constant loading level,the total stress value of the steel bars decreased by 17.5%,13.6%,and 9.1%,and the proportion of the long-term deflection of the beam midspan in the total deflection was 26.9%,24.2%,and 20.6%respectively when the reinforcement ratio was 2.05%,2.68%,and 3.39%.With the increase of the reinfor-cement ratio,the stress loss of the steel bars decreased,and the proportion of the long-term deflection decreased as well.When other conditions remained constant and the prestress level of the steel bars was 0 MPa,30 MPa,and 60 MPa,the total stress value of the steel bars decreased by 9.1%,9.4%,and 10.2%,respectively,and the propor-tion of the long-term deflection in the total deflection was 20.6%,26.1%,and 64.9%,respectively.With the increase of the prestress value,the stress loss of the steel bars increased,and the proportion of the long-term deflection increased as well.展开更多
A damage detection method for complicated beam-like structures is proposed based on the subsection strain energy method (SSEM), and its applicability condition is introduced. For a beam with the continuously varying...A damage detection method for complicated beam-like structures is proposed based on the subsection strain energy method (SSEM), and its applicability condition is introduced. For a beam with the continuously varying fiexural stiffness and an edge crack, the SSEM is used to detect the crack location effectively by numerical modal shapes. As a complicated beam, the glass fiber-reinforced composite model of a wind turbine blade is studied based on an experimental modal analysis. The SSEM is used to calculate the damage index from the measured modal parameters and locate the damage position in the blade model successfully. The results indicate that the SSEM based on the modal shapes can be used to detect the damages in complicated beams or beam-like structures for engineering applications.展开更多
Many beam structures suffer from gradual performance degradation with the increase of service life.To recover the bearing capacity of these beams,carbon fiber reinforced polymer(CFRP)plates are developed to attached o...Many beam structures suffer from gradual performance degradation with the increase of service life.To recover the bearing capacity of these beams,carbon fiber reinforced polymer(CFRP)plates are developed to attached on the beam bottom.To check the structural performance of the CFRP reinforced beams,smart CFRP plate with FBGs in series is designed and LVDTs are adopted to measure the deformations.The deflection of the reinforced beam is given based on the elastic conversion cross-section method.The experimental results validate the effectiveness of the proposed algorithm.The study shows that the CFRP reinforced zone has a larger flexural rigidity than the pure steel beam zone.The general distribution of the deflection along the span of the CFRP reinforced beam can be described by the proposed formula.It provides a scientific design guidance for the deflection control of CFRP reinforced structures.展开更多
This paper evaluates two methods of diagnosing damage, Natural frequency and Stiffness-Frequency change-Based damage detection method in reinforced concrete beams under load using vibration characteristics such as nat...This paper evaluates two methods of diagnosing damage, Natural frequency and Stiffness-Frequency change-Based damage detection method in reinforced concrete beams under load using vibration characteristics such as natural frequency and mode shape. The research uses finite element method with crack damage instead of deleting or reducing the bearing capacity of the element like in previous studies. First, a theory of the damage diagnosis method based on the change of natural frequency and mode shape is presented. Next, the simulation results of reinforced concrete beams using ANSYS will be compared with the experiment. Particularly, the investigated damage cases are cracks in reinforced concrete beams under loads. Finally, we will evaluate the accuracy of the damage diagnosis methods and suggest the location of the vibration data and specify the failure threshold of the methods.展开更多
Due to the increase of service life,the phenomenon of performance degradation of bridge structures becomes more and more common.It is important to strengthen the bridge structures so as to restore the resistance level...Due to the increase of service life,the phenomenon of performance degradation of bridge structures becomes more and more common.It is important to strengthen the bridge structures so as to restore the resistance level and extend the normal service life.Carbon fiber reinforced polymer(CFRP)materials are thus used for the assembly reinforcement of bridges for the advantages of high strength,light weight,corrosion resistance and long-term stability of physical and chemical properties,etc.In view of this,based on the previous theoretical study and the established formula of the interfacial shear stress of CFRP reinforced steel beam and the normal stress of CFRP plate,this paper discusses the sensitive parameters that affect the interfacial interaction of CFRP strengthened beam structures.Through the analysis,the priority design indicators and suggestions are accordingly given for the design of reinforced beam structures.Young’s modulus of CFRP composite and shear modulus of the adhesive have the greatest influence on the interfacial interaction,which should be carefully considered.It is suggested that CFRP material with Ec close to 300 GPa and thickness no less than 3 mm,and adhesive material with Ga less than 5 GPa and 3-mm thickness can be adopted in CFRP reinforced steel beam.The conclusions of this paper can provide guidance for the interfacial damage control of CFRP reinforced steel beam structures.展开更多
With the increased application of High Strength Concrete(HSC)in construction and lack of proper guidelines for structural design in India,behavioral study of high strength concrete is an important aspect of research.R...With the increased application of High Strength Concrete(HSC)in construction and lack of proper guidelines for structural design in India,behavioral study of high strength concrete is an important aspect of research.Research on the behavior of HSC reinforced beams with concrete strength more than 60 MPa has been carried out in the past and is still continuing to understand the structural behavior of HSC beams.Along with the many benefits of the high strength concrete,the more brittle behavior is of concern which leads to sudden failure.This paper presents the behavior of reinforced HSC beams in shear with considering the effects of various factors like shear reinforcement ratio,longitudinal reinforcement ratio,l/d ratio(length to depth ratio),etc.Ten numbers Reinforced Concrete Beams of various sizes using concrete mix with three different w/c ratios(0.46,0.26 and 0.21)were cast for shear strength assessment.The beams were tested in simply supported condition over two fixed steel pedestals with load rate of 0.2 mm/minute in displacement control.Mid-point deflection was measured using LVDT.A comparative analysis of theoretical approaches of Euro code,extension of current IS code up to M90 and the experimental data was done to understand the behavior of beams.Shear capacities of beams without any factors of safety were used to assess the actual capacities and then was compared with the experimental capacity obtained.Results of this study can be used in the design of high strength concrete and will be more reliable in Indian continent as the regional materials and exposure conditions were considered.展开更多
Theoretical approach with analytical and numerical procedure for determination initial displacement of a reinforced and prestressed concrete members, simple and cantilever beams, loaded by axial forces and bending mom...Theoretical approach with analytical and numerical procedure for determination initial displacement of a reinforced and prestressed concrete members, simple and cantilever beams, loaded by axial forces and bending moments is <span style="font-family:Verdana;">proposed. It is based on the principle of minimum potential energy with</span><span style="font-family:Verdana;"> equality of internal and external forces. The equations for strain internal energy have been derived, including compressed and tensile concrete and reinforce</span><span style="font-family:Verdana;">ment. The energy equations of the external forces with axial flexural dis</span><span style="font-family:Verdana;">placement effects have been derived from the assumed sinusoidal curve. The trapezoid rule is applied to integrate the segment strain energy. The proposed method uses a non</span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">-</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">linear stress-strain curve for the concrete and bilinear elastic-plastic relationship for reinforcement;equilibrium conditions at a sectional level to generate the strain energies along the beam. At the end of this article are shown three specific numerical examples with comparative, experimental (two tests)</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">results with the excellent agreement and one calculation result with a great disagreement, by obtaining results of virtual principle method.</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">With this method is avoiding the adoption of an unsure (EJ), as in the case of underestimating or overestimate initial flexural rigidity.</span></span></span>展开更多
As an important component,the bond behavior of carbon fiber-reinforced polymer(CFRP)-concrete interface for a reinforced concrete(RC)beam is very significant.In this study,a theoretical model was established to analyz...As an important component,the bond behavior of carbon fiber-reinforced polymer(CFRP)-concrete interface for a reinforced concrete(RC)beam is very significant.In this study,a theoretical model was established to analyze the flexural behavior of CFRP-strengthened RC beams,and the CFRP-concrete interfacial bond-slip relationship under hygrothermal environment was unified into one model.Two failure criteria corresponding to two types of failure modes,i.e.,concrete crushing and intermediate crack(IC)-induced debonding,were developed.Through the theoretical model,the flexural behavior of deflection,interfacial shear stress distribution and ultimate load of a CFRP-strengthened RC beam under hygrothermal environment were obtained and predicted.Moreover,the theoretical model was verified by test results.The results showed that the hygrothermal environment had a significant impact on the CFRP-concrete interface behavior.Compared with the control beam without hygrothermal environment pretreatment,the deflection and ultimate load of the strengthened RC beam decreased by 51.9%and 20%,respectively.展开更多
Three-point bending tests were carried out on nineteen Reinforced Concrete(RC)beams strengthened with FRP in the form of completely wrapping.The strip width to spacing ratios,FRP type,shear span to effective depth rat...Three-point bending tests were carried out on nineteen Reinforced Concrete(RC)beams strengthened with FRP in the form of completely wrapping.The strip width to spacing ratios,FRP type,shear span to effective depth ratios,the number of FRP layers in shear,and the effect of stirrups spacing were the parameters investigated in the experimental study.The FRP contribution to strength on beams having the same strip width to spacing ratios could be affected by the shear span to effective depth ratios and stirrups spacing.The FRP contributions to strength were less on beams with stirrups in comparison to the tested beams without stirrups.Strengthening RC beams using FRP could change the failure modes of the beams compared to the reference beam.In addition to the experimental study,a number of equations used to predict the FRP contribution to the shear strength of the strengthened RC beams were assessed by using a limited number of beams available in the literature.The effective FRP strain is predicted by using test results,and this prediction is used to calculate the FRP contribution to shear strength in ACI 440.2R(2017)equation.Based on the statistical values of the data,the proposed equation has the lowest coefficient of variation(COV)value than the other equations.展开更多
In determining the shear capacity of reinforced concrete beams, current codes do not provide any calculation method to evaluate the influence of web horizontal reinforcement, although they exist as structural reinforc...In determining the shear capacity of reinforced concrete beams, current codes do not provide any calculation method to evaluate the influence of web horizontal reinforcement, although they exist as structural reinforcements (or skin reinforcement). The present paper comprises results of 11 reinforced concrete beams in an effort to investigate the influence of web horizontal reinforcement on the shear behavior of reinforced concrete beams. The primary design variables are the shear-span-depth ratio, different reinforcement ratio of stirrups and web horizontal reinforcement. Influence of web horizontal reinforcement on crack patterns and failure mode was studied. It was found that web horizontal reinforcement can increase the shear capacity of the beams and restrain growth of inclined cracks effectively. Test results are very valuable, as very few references of shear tests can be found focusing on the effect of web horizontal reinforcement on the shear capacity of the beams.展开更多
A novel damage assessment method based on the decay ratio of acceleration signals(DRAS)was proposed.Two experimental tests were used to show the efficiency.Three beams were gradually damaged,and then the changes of dy...A novel damage assessment method based on the decay ratio of acceleration signals(DRAS)was proposed.Two experimental tests were used to show the efficiency.Three beams were gradually damaged,and then the changes of dynamic parameters were monitored from initial to failure state.In addition,a new method was compared with the linear modal-based damage assessment using wavelet transform(WT).The results clearly show that DRAS increases in linear elasticity state and microcrack propagation state,while DRAS decreases in macrocrack propagation state.Preliminary analysis was developed considering the beat phenomenon in the nonlinear state to explain the turn point of DRAS.With better sensibility of damage than modal parameters,probably DRAS is a promising damage indicator in damage assessment.展开更多
This paper uses the spectral stochastic finite element method(SSFEM)for analyzing reinforced concrete(RC)beam/slab problems.In doing so,it presents a new framework to study how the correlation length of a random field...This paper uses the spectral stochastic finite element method(SSFEM)for analyzing reinforced concrete(RC)beam/slab problems.In doing so,it presents a new framework to study how the correlation length of a random field(RF)with uncertain parameters will affect modeling uncertainties and reliability evaluations.It considers:1)different correlation lengths for uncertainty parameters,and 2)dead and live loads as well as the elasticity moduli of concrete and steel as a multi-dimensional RF in concrete structures.To show the SSFEM’s efficiency in the study of concrete structures and to evaluate the sensitivity of the correlation length effects in evaluating the reliability,two examples of RC beams and slabs have been investigated.According to the results,the RF correlation length is effective in modeling uncertainties and evaluating reliabilities;the longer the correlation length,the greater the dispersion range of the structure response and the higher the failure probability.展开更多
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.
文摘A novel method for prediction of the load carrying capacity of a corroded reinforced concrete beam (CRCB) is presented in the paper. Nine reinforced concrete beams, which had been working in an aggressive environment for more than 10 years, were tested in the laboratory. Comprehensive tests, including flexural test, strength test for corroded concrete and rusty rebar, and pullout test for bond strength between concrete and rebar, were conducted. ne flexural test results of CRCBs reveal that the distribution of surface cracks on the beams shows a fractal behavior. The relationship between the fractal dimensions and mechanical properties of CRCBs is then studied. A prediction model based on artificial neural network (ANN) is established by the use of the fractal dimension as the corrosion index, together with the basic information of the beam. The validity of the prediction model is demonstrated through the experimental data, and satisfactory results are achieved.
基金Sponsored by Changjiang Scholars Program of China( Grant No 2009-37)the National Natural Science Foundation of China( Grant No 50678050)Innovative Science Foundation of HIT ( Grant No HIT2005C-3)
文摘To meet the requirement of fire endurance for concrete structures strengthened with CFRP sheets, this study develops an inorganic adhesive whose strength at 600 ℃ is not lower than that at normal room temperature. The inorganic adhesive is then used to bond CFRP sheets on reinforced concrete beams in order to strengthen them. The fire protection of the CFRP sheets is done using the thick-type fireproofing coatings for tunnel ( TFCT) and steel structure ( TFCSS) respectively. Four specimens are tested in the furnace together. Specimens are exposed to fire for 1. 5 h in according to the ISO834 standard fire curve,and then naturally cooled for 1 h. In the tests,the largest displacements at the mid-span positions of specimens are only from 1 /1400 to 1 /318 of actual span corresponding to the highest temperatures from 300 ℃ to 470 ℃. After the specimens are naturally cooled to the normal temperature and the fireproofing coatings are then removed,it can be seen that the CFRP sheets keep in a good state,which indicates that CFRP sheets can be tightly bonded on the concrete and work well together with the concrete beams during and after fire. Besides,the tests also verify that the fire performance of TFCT is superior to TFCSS for the strengthened beams.
基金supported bythe National Natural Science Foundation of China (Grant No.50978006)
文摘In order to research the strengthening effects of aramid fiber reinforced polymer (AFRP) sheets on the flexural performance of corroded reinforced concrete (RC) beams, the static and fatigue performance of corroded RC beams strengthened with non-prestressed AFRP sheets under different degrees of corrosion (minor: reinforcement mass loss is 2.0%, medium: reinforcement mass loss is 6.0%) have been researched experimentally in this paper, to compare with that of the control beams (un-strengthened and un-corroded) and un-strengthened corroded beams, and additionally compare with fatigue performance of those medium corroded RC beams strengthened with prestressed AFRP sheets with permanent anchors. The results show that, (1) compared with un-strengthened corroded beams under the same degrees of corrosion, the cracking, yield and ultimate monotonic loads of the minor corroded RC beam strengthened with non-prestressed AFRP sheets is respectively increased by 20%, 27% and 60%, whereas for the medium corroded RC beam strengthened with non-prestressed AFRP sheets increased by 15%, 36% and 83% respectively. The ultimate deflection of the medium corroded beam strengthened with non-prestressed AFRP sheets is 166% larger than that of the corroded un-strengthened beam under the monotonic load. (2) The fatigue life of the non-prestressed AFRP strengthened medium corroded beam is 10.4 times more than that of the un-strengthened corroded beam, but lower than that of the unstrengthened-uncorroded (virgin) beam. (3) Fatigue experiments of the beams strengthened with prestressed AFRP sheets and with those non-prestressed AFRP sheets show that the fatigue life of the retrofit RC beams increase with increasing prestress level of AFRP sheets.(4) The use of AFRP sheets for strengthening corroded RC beams is an efficient technique that can maintain the structural integrity and enhance the structural behavior of such 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This research work was supported by the Fundamental Research Funds for the Central Universities(2572017DB02)the natural science foundation of Heilongjiang Province(LH2019E005)the natural science of Heilongjiang Province(LH2020E009).
文摘Due to creep characteristics of wood,long-term loading can cause a significant stress loss of steel bars in rein-forced glulam beams and high long-term deflection of the beam midspan.In this study,15 glulam beams were subjected to a 90-day long-term loading test,and the effects of long-term loading value,reinforcement ratio and prestress level on the stress of steel bars,midspan long-term deflection,and other parameters were compared and analyzed.The main conclusions drawn from this study were that the long-term deflection of the reinforced glulam beams accounted for 22.5%,20.6%,and 18.2%of the total deflection respectively when the loading value was 20%,30%,and 40%of the estimated ultimate load under the long-term loading.The higher the loading level was,the smaller the proportion of the long-term deflection in the total deflection was.Compared with ordinary glulam beams,the long-term deflection of the reinforced glulam beam was even smaller.Under the condition of the constant loading level,the total stress value of the steel bars decreased by 17.5%,13.6%,and 9.1%,and the proportion of the long-term deflection of the beam midspan in the total deflection was 26.9%,24.2%,and 20.6%respectively when the reinforcement ratio was 2.05%,2.68%,and 3.39%.With the increase of the reinfor-cement ratio,the stress loss of the steel bars decreased,and the proportion of the long-term deflection decreased as well.When other conditions remained constant and the prestress level of the steel bars was 0 MPa,30 MPa,and 60 MPa,the total stress value of the steel bars decreased by 9.1%,9.4%,and 10.2%,respectively,and the propor-tion of the long-term deflection in the total deflection was 20.6%,26.1%,and 64.9%,respectively.With the increase of the prestress value,the stress loss of the steel bars increased,and the proportion of the long-term deflection increased as well.
基金supported by the National Basic Research Program of China (973 Program)(No. 2007CB714603)
文摘A damage detection method for complicated beam-like structures is proposed based on the subsection strain energy method (SSEM), and its applicability condition is introduced. For a beam with the continuously varying fiexural stiffness and an edge crack, the SSEM is used to detect the crack location effectively by numerical modal shapes. As a complicated beam, the glass fiber-reinforced composite model of a wind turbine blade is studied based on an experimental modal analysis. The SSEM is used to calculate the damage index from the measured modal parameters and locate the damage position in the blade model successfully. The results indicate that the SSEM based on the modal shapes can be used to detect the damages in complicated beams or beam-like structures for engineering applications.
基金The work described in this paper was supported by the National Natural Science Foundation of China(Grant No.51908263)Double First-Class(First-Class University&First-Class Disciplines)Funds of Lanzhou University(Grant No.561119201)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.lzujbky-2020-56)Key Laboratory of Structures Dynamic Behavior and Control(Ministry of Education)in Harbin Institute of Technology(Grant No.HITCE201901).
文摘Many beam structures suffer from gradual performance degradation with the increase of service life.To recover the bearing capacity of these beams,carbon fiber reinforced polymer(CFRP)plates are developed to attached on the beam bottom.To check the structural performance of the CFRP reinforced beams,smart CFRP plate with FBGs in series is designed and LVDTs are adopted to measure the deformations.The deflection of the reinforced beam is given based on the elastic conversion cross-section method.The experimental results validate the effectiveness of the proposed algorithm.The study shows that the CFRP reinforced zone has a larger flexural rigidity than the pure steel beam zone.The general distribution of the deflection along the span of the CFRP reinforced beam can be described by the proposed formula.It provides a scientific design guidance for the deflection control of CFRP reinforced structures.
文摘This paper evaluates two methods of diagnosing damage, Natural frequency and Stiffness-Frequency change-Based damage detection method in reinforced concrete beams under load using vibration characteristics such as natural frequency and mode shape. The research uses finite element method with crack damage instead of deleting or reducing the bearing capacity of the element like in previous studies. First, a theory of the damage diagnosis method based on the change of natural frequency and mode shape is presented. Next, the simulation results of reinforced concrete beams using ANSYS will be compared with the experiment. Particularly, the investigated damage cases are cracks in reinforced concrete beams under loads. Finally, we will evaluate the accuracy of the damage diagnosis methods and suggest the location of the vibration data and specify the failure threshold of the methods.
基金The work described in this paper was supported by the National Natural Science Foundation of China(Grant No.51908263)Double First-Class(First-Class University&First-Class Disciplines)Funds of Lanzhou University(Grant No.561119201)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.lzujbky-2020-56)Key Laboratory of Structures Dynamic Behavior and Control(Ministry of Education)in Harbin Institute of Technology(Grant No.HITCE201901).
文摘Due to the increase of service life,the phenomenon of performance degradation of bridge structures becomes more and more common.It is important to strengthen the bridge structures so as to restore the resistance level and extend the normal service life.Carbon fiber reinforced polymer(CFRP)materials are thus used for the assembly reinforcement of bridges for the advantages of high strength,light weight,corrosion resistance and long-term stability of physical and chemical properties,etc.In view of this,based on the previous theoretical study and the established formula of the interfacial shear stress of CFRP reinforced steel beam and the normal stress of CFRP plate,this paper discusses the sensitive parameters that affect the interfacial interaction of CFRP strengthened beam structures.Through the analysis,the priority design indicators and suggestions are accordingly given for the design of reinforced beam structures.Young’s modulus of CFRP composite and shear modulus of the adhesive have the greatest influence on the interfacial interaction,which should be carefully considered.It is suggested that CFRP material with Ec close to 300 GPa and thickness no less than 3 mm,and adhesive material with Ga less than 5 GPa and 3-mm thickness can be adopted in CFRP reinforced steel beam.The conclusions of this paper can provide guidance for the interfacial damage control of CFRP reinforced steel beam structures.
文摘With the increased application of High Strength Concrete(HSC)in construction and lack of proper guidelines for structural design in India,behavioral study of high strength concrete is an important aspect of research.Research on the behavior of HSC reinforced beams with concrete strength more than 60 MPa has been carried out in the past and is still continuing to understand the structural behavior of HSC beams.Along with the many benefits of the high strength concrete,the more brittle behavior is of concern which leads to sudden failure.This paper presents the behavior of reinforced HSC beams in shear with considering the effects of various factors like shear reinforcement ratio,longitudinal reinforcement ratio,l/d ratio(length to depth ratio),etc.Ten numbers Reinforced Concrete Beams of various sizes using concrete mix with three different w/c ratios(0.46,0.26 and 0.21)were cast for shear strength assessment.The beams were tested in simply supported condition over two fixed steel pedestals with load rate of 0.2 mm/minute in displacement control.Mid-point deflection was measured using LVDT.A comparative analysis of theoretical approaches of Euro code,extension of current IS code up to M90 and the experimental data was done to understand the behavior of beams.Shear capacities of beams without any factors of safety were used to assess the actual capacities and then was compared with the experimental capacity obtained.Results of this study can be used in the design of high strength concrete and will be more reliable in Indian continent as the regional materials and exposure conditions were considered.
文摘Theoretical approach with analytical and numerical procedure for determination initial displacement of a reinforced and prestressed concrete members, simple and cantilever beams, loaded by axial forces and bending moments is <span style="font-family:Verdana;">proposed. It is based on the principle of minimum potential energy with</span><span style="font-family:Verdana;"> equality of internal and external forces. The equations for strain internal energy have been derived, including compressed and tensile concrete and reinforce</span><span style="font-family:Verdana;">ment. The energy equations of the external forces with axial flexural dis</span><span style="font-family:Verdana;">placement effects have been derived from the assumed sinusoidal curve. The trapezoid rule is applied to integrate the segment strain energy. The proposed method uses a non</span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">-</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">linear stress-strain curve for the concrete and bilinear elastic-plastic relationship for reinforcement;equilibrium conditions at a sectional level to generate the strain energies along the beam. At the end of this article are shown three specific numerical examples with comparative, experimental (two tests)</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">results with the excellent agreement and one calculation result with a great disagreement, by obtaining results of virtual principle method.</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">With this method is avoiding the adoption of an unsure (EJ), as in the case of underestimating or overestimate initial flexural rigidity.</span></span></span>
基金The authors would like to acknowledge the financial support from the National Natural Science Foundation of China(Nos.11872185,11627802,51678249,11132004)the Natural Science Foundation of Guangdong Province(No.2019A1515012222).
文摘As an important component,the bond behavior of carbon fiber-reinforced polymer(CFRP)-concrete interface for a reinforced concrete(RC)beam is very significant.In this study,a theoretical model was established to analyze the flexural behavior of CFRP-strengthened RC beams,and the CFRP-concrete interfacial bond-slip relationship under hygrothermal environment was unified into one model.Two failure criteria corresponding to two types of failure modes,i.e.,concrete crushing and intermediate crack(IC)-induced debonding,were developed.Through the theoretical model,the flexural behavior of deflection,interfacial shear stress distribution and ultimate load of a CFRP-strengthened RC beam under hygrothermal environment were obtained and predicted.Moreover,the theoretical model was verified by test results.The results showed that the hygrothermal environment had a significant impact on the CFRP-concrete interface behavior.Compared with the control beam without hygrothermal environment pretreatment,the deflection and ultimate load of the strengthened RC beam decreased by 51.9%and 20%,respectively.
文摘Three-point bending tests were carried out on nineteen Reinforced Concrete(RC)beams strengthened with FRP in the form of completely wrapping.The strip width to spacing ratios,FRP type,shear span to effective depth ratios,the number of FRP layers in shear,and the effect of stirrups spacing were the parameters investigated in the experimental study.The FRP contribution to strength on beams having the same strip width to spacing ratios could be affected by the shear span to effective depth ratios and stirrups spacing.The FRP contributions to strength were less on beams with stirrups in comparison to the tested beams without stirrups.Strengthening RC beams using FRP could change the failure modes of the beams compared to the reference beam.In addition to the experimental study,a number of equations used to predict the FRP contribution to the shear strength of the strengthened RC beams were assessed by using a limited number of beams available in the literature.The effective FRP strain is predicted by using test results,and this prediction is used to calculate the FRP contribution to shear strength in ACI 440.2R(2017)equation.Based on the statistical values of the data,the proposed equation has the lowest coefficient of variation(COV)value than the other equations.
文摘In determining the shear capacity of reinforced concrete beams, current codes do not provide any calculation method to evaluate the influence of web horizontal reinforcement, although they exist as structural reinforcements (or skin reinforcement). The present paper comprises results of 11 reinforced concrete beams in an effort to investigate the influence of web horizontal reinforcement on the shear behavior of reinforced concrete beams. The primary design variables are the shear-span-depth ratio, different reinforcement ratio of stirrups and web horizontal reinforcement. Influence of web horizontal reinforcement on crack patterns and failure mode was studied. It was found that web horizontal reinforcement can increase the shear capacity of the beams and restrain growth of inclined cracks effectively. Test results are very valuable, as very few references of shear tests can be found focusing on the effect of web horizontal reinforcement on the shear capacity of the beams.
基金supported by the National Natural Science Foundation of China(Grant No.50579081)the Graduate Innovation Fund of Zhejiang(No.YK2008025).
文摘A novel damage assessment method based on the decay ratio of acceleration signals(DRAS)was proposed.Two experimental tests were used to show the efficiency.Three beams were gradually damaged,and then the changes of dynamic parameters were monitored from initial to failure state.In addition,a new method was compared with the linear modal-based damage assessment using wavelet transform(WT).The results clearly show that DRAS increases in linear elasticity state and microcrack propagation state,while DRAS decreases in macrocrack propagation state.Preliminary analysis was developed considering the beat phenomenon in the nonlinear state to explain the turn point of DRAS.With better sensibility of damage than modal parameters,probably DRAS is a promising damage indicator in damage assessment.
文摘This paper uses the spectral stochastic finite element method(SSFEM)for analyzing reinforced concrete(RC)beam/slab problems.In doing so,it presents a new framework to study how the correlation length of a random field(RF)with uncertain parameters will affect modeling uncertainties and reliability evaluations.It considers:1)different correlation lengths for uncertainty parameters,and 2)dead and live loads as well as the elasticity moduli of concrete and steel as a multi-dimensional RF in concrete structures.To show the SSFEM’s efficiency in the study of concrete structures and to evaluate the sensitivity of the correlation length effects in evaluating the reliability,two examples of RC beams and slabs have been investigated.According to the results,the RF correlation length is effective in modeling uncertainties and evaluating reliabilities;the longer the correlation length,the greater the dispersion range of the structure response and the higher the failure probability.