AZ31B magnesium alloy is widely used in transportation and aerospace fields due to its light weight and high strength,but it often causes structural failure due to fatigue fracture during service.Fatigue fracture is u...AZ31B magnesium alloy is widely used in transportation and aerospace fields due to its light weight and high strength,but it often causes structural failure due to fatigue fracture during service.Fatigue fracture is usually caused by the initiation of cracks on the surface of structural parts and the propagation of cracks to the interior of the specimen in the form of intergranular fracture.In order to improve the fatigue performance,this study proposes a method of pre-tension deformation and surface mechanical rolling treatment of AZ31B magnesium alloy,thereby changing the crack initiation area and increasing the crack propagation resistance.The experimental results show that:As the pre-tension deformation increases,the fatigue limit shows a trend of first rising and then decreasing.The 5PT specimen exhibits the optimal strengthening effect,with a fatigue limit of 115 MPa,which is a 27.78% improvement.Under surface mechanical rolling treatment,the fatigue limit reaches 140 MPa,which is a 55.56% improvement.When pre-tension deformation and surface mechanical rolling treatment are combined,the fatigue limit is further improved compared to individual strengthening methods.Among these,the 2PT+SMRT specimen shows the most significant strengthening effect,with a fatigue limit of 150 MPa,which is a 66.67% improvement.This study proposes a new strategy for improving the fatigue performance of AZ31B magnesium alloy,and reveals the synergistic strengthening mechanism of pre-tension deformation and surface mechanical rolling treatment of AZ31B magnesium alloy,which is of great significance for improving the fatigue performance of metal materials.展开更多
In this paper, ballistic impact tests on wrapped multi-layer Kevlar 49 woven fabric systems were carried out with a flat blade projectile to investigate the impact response during a fan blade out event. The influences...In this paper, ballistic impact tests on wrapped multi-layer Kevlar 49 woven fabric systems were carried out with a flat blade projectile to investigate the impact response during a fan blade out event. The influences of the number of Kevlar layers and pre-tension were discussed particularly. Test results were used to analyze failure modes and energy absorption characteristics of multi-ply Kevlar fabrics. Results show that there are two kinds of impact damage for fabrics： global deformation mainly involving stretching of yarns in the impact region and fabric wrinkle from both sides to the impact zone, and local damage characterized by yarn fracture, yarn pull-out, and yarn unraveling. The energy absorption capability of Kevlar 49 woven fabrics improves with the number of fabric layers. The energy absorbed by multi-layer fabrics increases slightly at the beginning and then decreases substantially with pre-tension. The work in this paper can provide guidance for designing light-weight multi-layer fabrics containment systems.展开更多
The importance of the pre-tensioned force of rock bolts has been recognized by more and more researchers. To investi- gate the effect of pre-tensioned rock bolts on stress redistribution around roadways, a numerical a...The importance of the pre-tensioned force of rock bolts has been recognized by more and more researchers. To investi- gate the effect of pre-tensioned rock bolts on stress redistribution around roadways, a numerical analysis was carried out using FLAC3D and a special post-process methodology, using surfer, is proposed to process the numerical simulation results. The results indicate that pre-tensioned rock bolts have a significant effect on stress redistribution around a roadway. In the roof, pre-tensioned rock bolts greatly increase vertical stress; as a result, the strength of the rock mass increased significantly which results in a greater capacity of bearing a large horizontal stress. The horizontal stress decreases in the upper section of the roof, indicating that pre-tensioned rock bolts significantly reduce the coefficient and the size of the region concentration of horizontal stress. At the lat- eral side, pre-tensioned rock bolts greatly increase the horizontal stress; therefore, the rock mass strength significantly increases which results also in a greater capacity of bearing a large vertical stress. The greater the size of pre-tensioned force, the larger the region of stress redistribution around a roadway is affected and the higher the size of the stress on the roadway surface the more the rock mass strength increases.展开更多
Despite appropriate design of girder under bending and shear,the deflection of long steel girders usually exceeds the allowable range,and therefore the structural designers encounter challenges in this regard.Consider...Despite appropriate design of girder under bending and shear,the deflection of long steel girders usually exceeds the allowable range,and therefore the structural designers encounter challenges in this regard.Considering significant features of the cables,namely,low weight,small cross section,and high tensile strength,they are used in this research so as to control the deflection of long girder bridges,rather than increasing their heights.In this study,theoretical relations are developed to calculate the increase in pre-tensioning force of V-shaped steel cables under external loading as well as the deflection of steel girder bridges with V-shaped cables and different support conditions.To verify the theoretical relations,the steel girder bridge is modeled in the finite element ABAQUS software with different support conditions without cable and with V-shaped cables.The obtained results show that the theoretical relations can appropriately predict the deflection of girder bridge with V-shaped cables and different support conditions.In this study,the effects of the distance from support on the deflection of mid span are studied in both simply supported and fixed supported girder bridge so as to obtain the appropriate distance from support causing the minimum deflection.展开更多
The pre-tension was induced to suppress the abnormal grain growth(AGG)of ZK60 Mg profile during solution treatment.The effects of pre-tension on the microstructure evolution and mechanical properties were studied,and ...The pre-tension was induced to suppress the abnormal grain growth(AGG)of ZK60 Mg profile during solution treatment.The effects of pre-tension on the microstructure evolution and mechanical properties were studied,and the suppressing mechanism was discussed.If the pre-tension strain was larger than 10%,AGG during solution could be effectively inhibited,resulting in a sharp decrease in the grain size.The suppression effects were realized by restricting the orientation dependent of AGG and promoting static recrystallization.The pre-tension reset the distributions of stored energy and sizes of the grains with〈11–20〉and〈10–10〉orientations,and thus retarded the orientation dependent of AGG.Moreover,the pre-tension introduced a mass of dislocations,twins,and stacking faults,all of which promoted the occurrence of static recrystallization,and the grain structure was further refined.The pre-tension accelerated the precipitation kinetics during aging,resulting in fine and dense precipitates.With the increase of pre-tension strain,the strength of ZK60 Mg profile monotonically increased.展开更多
Conventional wrought Mg alloys,such as AZ31 and ZK60 rolled plates,usually exhibit significantly low tensile yield strength in the thickness direction.This can be attributed to the high activity of{10-12}tension twinn...Conventional wrought Mg alloys,such as AZ31 and ZK60 rolled plates,usually exhibit significantly low tensile yield strength in the thickness direction.This can be attributed to the high activity of{10-12}tension twinning due to the strong basal texture(<0001>//ND,normal direction).In this work,the tensile yield strength in the ND of the as-rolled(AR)AZ31 plate increased from 50 to 150 MPa(increased by 200%)via simple processing,i.e.,pre-tension and rolling-annealing(PTRA)treatment.The strong basal texture(<0001>//ND)of the AR plate was changed into a weakened fiber texture(<0001>⊥ND).The evolution of microstructures during PTRA treatment and the activated deformation modes during uniaxial tension were studied quantitatively and statistically by the means of intergranular misorientation(IM)and in-grain misorientation axes(IGMA)analysis.The results indicate that various twin variants,as well as{10-12}-{10-12}secondary twins,were activated during pre-tension and rolling,and most residual matrix was consumed by twins after annealing.The dominated deformation modes in tension changed from{10-12}tension twinning(the AR sample)to prismatic slip(the PTRA sample)in the early tensile deformation.The underlying formation mechanism of the fiber texture and corresponding strengthening mechanism were discussed.展开更多
The transverse free vibration of nanobeams subjected to an initial axial tension based on nonlocal stress theory is presented. It considers the effects of nonlocal stress field on the natural frequencies and vibration...The transverse free vibration of nanobeams subjected to an initial axial tension based on nonlocal stress theory is presented. It considers the effects of nonlocal stress field on the natural frequencies and vibration modes. The effects of a small scale parameter at molecular level unavailable in classical macro-beams are investigated for three different types of boundary conditions:simple supports,clamped supports and elastically-constrained supports. Analytical solutions for transverse deforma-tion and vibration modes are derived. Through numerical examples,effects of the dimensionless nanoscale parameter and pre-tension on natural frequencies are presented and discussed.展开更多
The deformation and fracture failure of aerospace structural components are primarily affected by complex loading conditions.This study aims to investigate how various pre-tension strains(0%,4%and 6%)influence the tor...The deformation and fracture failure of aerospace structural components are primarily affected by complex loading conditions.This study aims to investigate how various pre-tension strains(0%,4%and 6%)influence the torsional properties,deformation and fracture mechanism of the Ti-5Al-5Mo-5V-3Cr-1Zr(Ti-55531)alloy with the bimodal microstructure.The results indicate that increasing the pre-tension strain gradually decreases the torsional strength of specimens.However,their torsional ductility initially increases(from 0 to 4%pre-tension strain)and then decreases(from 4 to 6%pre-tension strain).This can be attributed to the significant influence of different pre-tension strains on the deformation mechanism of each phase in the alloy.Under pure torsion loading,the primary α(α_(p))phase mainly undergoes the{0002}basal slip for deformation.However,at a pre-tension strain of4%,the torsional deformation mechanism of α_(p)transforms into crossing reaction between the{1010}prismatic slips.As the pre-tension strain further increases to 6%,{1011}pyramidal slips were further activated.Moreover,with an increase in pre-tension strain,there is a significant rise multiple slips probability within the α_(p) during torsional deformation.On contrary,for the secondaryα(α_(s))phase,the probability of{1011}_(α)twins formation during torsional deformation firstly rises and then reduces.These findings indicate thatαphase,particularly α_(p),plays a crucial role in accommodating deformation.This discovery offers valuable insights for further adjustments and optimizations of material microstructure and properties.Additionally,modifying external load can alter the stress state of components and enhance their fracture resistance during service,thereby broadening their range of applications and improving material reliability.展开更多
The mechanism of filament pre-tension is put forward. The effect of filament pre-tension on Sirofil composite yam properties, such as hairiness and structural stability, are theoretically and experimentally studied. T...The mechanism of filament pre-tension is put forward. The effect of filament pre-tension on Sirofil composite yam properties, such as hairiness and structural stability, are theoretically and experimentally studied. The theoretical analysis agrees well with the experimental results. The present theory shows that suitable choice of filament pre-tension can enormously reduce hairiness and improve structural stability of Sirofil composite yarn.展开更多
The stiffness required for the normal operation of membrane roof comes from the application of pre-tension. When the pre-tension is too small, it is easy to cause instability under the action of wind load, which leads...The stiffness required for the normal operation of membrane roof comes from the application of pre-tension. When the pre-tension is too small, it is easy to cause instability under the action of wind load, which leads to excessive deformation of the roof and local or overall damage. In order to ensure that the membrane roof is always in normal use state in the airflow field, this paper takes the membrane pretension as the control parameter to study the value of safety pretension of closed membrane roof. According to the theory of large deflection of membrane and Galerkin method, the nonlinear vibration differential equation of membrane roof under static wind is established, and the critical state of safe working of membrane roof is determined by judging the stability of the solution of the equation, and the expression of critical wind speed is obtained. By establishing the inequality relationship between local design wind speed and critical wind speed, the safety pretension limit of membrane roof under specific site can be obtained. The research shows that the safety pretension limits of closed membrane roofs are different in different areas under different design return periods. In addition, the value of safety pretension is related to the film geometry.展开更多
In the construction of cast-in-place bridge deck of prefabricated I-beam by pretension folding line method, I-beam is used as the main stress support, well-shaped support is used on the inner side, triangular stable s...In the construction of cast-in-place bridge deck of prefabricated I-beam by pretension folding line method, I-beam is used as the main stress support, well-shaped support is used on the inner side, triangular stable support is used on the outer side, temporary support and installation formwork are erected through walking operation platform, steel bar binding and cast-in-place concrete deck construction are carried out on the upper part of I-beam and formwork, the deck thickness is only 20cm, which meets the vehicle load requirements of city -A grade bridge BZZ-100 and reduces the dead weight of the structure. Compared with the common full framing, the framing used in the construction is convenient in construction, material-saving, simple in process and short in construction time. I-beam construction adopts factory processing and production. Formwork is uniformly made of shaped steel formwork. The prefabricated members have a beautiful appearance. Prestressing is installed and tensioned in advance to ensure the straightness of the prestressing and the accuracy of the position. The overall structure of the I-beam is light in weight, and the total amount of concrete used is small. Under the condition of reducing the dead weight of each span and ensuring the stress stability, the amount of concrete used is reduced, which is beneficial to environmental protection and material conservation. In terms of formwork support system, the support form of this process is easy to build, less material is used and the construction speed is fast. And the binding of the steel bars can be completed in a short time. In the concrete pouring project, the pouring speed is fast and the construction is simple.展开更多
Pre-tensioned high strength trusses using alloy steel bar are widely used as glass wall supporting systems because of the high degree of transparency.The breakage of glass panes in this type of system occurs occasiona...Pre-tensioned high strength trusses using alloy steel bar are widely used as glass wall supporting systems because of the high degree of transparency.The breakage of glass panes in this type of system occurs occasionally,likely to be due to error in design and analysis in addition to other factors like glass impurity and stress concentration around opening in a spider system.Most design does not consider the flexibility of supports from finite stiffness of supporting steel or reinforced concrete beams.The resistance of lateral wind pressure of the system makes use of high tension force coupled with the large deflection effect,both of which are affected by many parameters not generally considered in conventional structures.In the design,one must therefore give a careful consideration on various effects,such as support settlement due to live loads and material creep,temperature change,pre-tension force,and wind pressure.It is not uncommon to see many similar glass wall systems fail in the wind load test chambers under a design wind speed.This paper presents a rigorous analysis and design of this type of structural systems used in a project in Hong Kong,China.The stability function with initial curvature is used in place of the cubic function,which is only accurate for linear analysis.The considerations and analysis techniques are believed to be of value to engineers involved in the design of the structural systems behaving nonlinearly.展开更多
基金the generous support from natural Science Foundation of Shanxi Province(No.202203021221040 and No.201901D111106).
文摘AZ31B magnesium alloy is widely used in transportation and aerospace fields due to its light weight and high strength,but it often causes structural failure due to fatigue fracture during service.Fatigue fracture is usually caused by the initiation of cracks on the surface of structural parts and the propagation of cracks to the interior of the specimen in the form of intergranular fracture.In order to improve the fatigue performance,this study proposes a method of pre-tension deformation and surface mechanical rolling treatment of AZ31B magnesium alloy,thereby changing the crack initiation area and increasing the crack propagation resistance.The experimental results show that:As the pre-tension deformation increases,the fatigue limit shows a trend of first rising and then decreasing.The 5PT specimen exhibits the optimal strengthening effect,with a fatigue limit of 115 MPa,which is a 27.78% improvement.Under surface mechanical rolling treatment,the fatigue limit reaches 140 MPa,which is a 55.56% improvement.When pre-tension deformation and surface mechanical rolling treatment are combined,the fatigue limit is further improved compared to individual strengthening methods.Among these,the 2PT+SMRT specimen shows the most significant strengthening effect,with a fatigue limit of 150 MPa,which is a 66.67% improvement.This study proposes a new strategy for improving the fatigue performance of AZ31B magnesium alloy,and reveals the synergistic strengthening mechanism of pre-tension deformation and surface mechanical rolling treatment of AZ31B magnesium alloy,which is of great significance for improving the fatigue performance of metal materials.
基金co-supported by the National Natural Science Foundation of China (No.51575262)the China Postdoctoral Science Foundation (No.2015M571754)the Aeronautical Science Foundation of China (No.2015ZB52008)
文摘In this paper, ballistic impact tests on wrapped multi-layer Kevlar 49 woven fabric systems were carried out with a flat blade projectile to investigate the impact response during a fan blade out event. The influences of the number of Kevlar layers and pre-tension were discussed particularly. Test results were used to analyze failure modes and energy absorption characteristics of multi-ply Kevlar fabrics. Results show that there are two kinds of impact damage for fabrics： global deformation mainly involving stretching of yarns in the impact region and fabric wrinkle from both sides to the impact zone, and local damage characterized by yarn fracture, yarn pull-out, and yarn unraveling. The energy absorption capability of Kevlar 49 woven fabrics improves with the number of fabric layers. The energy absorbed by multi-layer fabrics increases slightly at the beginning and then decreases substantially with pre-tension. The work in this paper can provide guidance for designing light-weight multi-layer fabrics containment systems.
基金Projects 2006BAB16B02 and 2006BAK03B06 supported by the National Scientific & Technological Foundation of China
文摘The importance of the pre-tensioned force of rock bolts has been recognized by more and more researchers. To investi- gate the effect of pre-tensioned rock bolts on stress redistribution around roadways, a numerical analysis was carried out using FLAC3D and a special post-process methodology, using surfer, is proposed to process the numerical simulation results. The results indicate that pre-tensioned rock bolts have a significant effect on stress redistribution around a roadway. In the roof, pre-tensioned rock bolts greatly increase vertical stress; as a result, the strength of the rock mass increased significantly which results in a greater capacity of bearing a large horizontal stress. The horizontal stress decreases in the upper section of the roof, indicating that pre-tensioned rock bolts significantly reduce the coefficient and the size of the region concentration of horizontal stress. At the lat- eral side, pre-tensioned rock bolts greatly increase the horizontal stress; therefore, the rock mass strength significantly increases which results also in a greater capacity of bearing a large vertical stress. The greater the size of pre-tensioned force, the larger the region of stress redistribution around a roadway is affected and the higher the size of the stress on the roadway surface the more the rock mass strength increases.
文摘Despite appropriate design of girder under bending and shear,the deflection of long steel girders usually exceeds the allowable range,and therefore the structural designers encounter challenges in this regard.Considering significant features of the cables,namely,low weight,small cross section,and high tensile strength,they are used in this research so as to control the deflection of long girder bridges,rather than increasing their heights.In this study,theoretical relations are developed to calculate the increase in pre-tensioning force of V-shaped steel cables under external loading as well as the deflection of steel girder bridges with V-shaped cables and different support conditions.To verify the theoretical relations,the steel girder bridge is modeled in the finite element ABAQUS software with different support conditions without cable and with V-shaped cables.The obtained results show that the theoretical relations can appropriately predict the deflection of girder bridge with V-shaped cables and different support conditions.In this study,the effects of the distance from support on the deflection of mid span are studied in both simply supported and fixed supported girder bridge so as to obtain the appropriate distance from support causing the minimum deflection.
基金financially supported by the National Natural Science Foundation of China(Nos.51875317 and 52222510)the Key Research and Development Program of Shandong Province(No.2021ZLGX01).
文摘The pre-tension was induced to suppress the abnormal grain growth(AGG)of ZK60 Mg profile during solution treatment.The effects of pre-tension on the microstructure evolution and mechanical properties were studied,and the suppressing mechanism was discussed.If the pre-tension strain was larger than 10%,AGG during solution could be effectively inhibited,resulting in a sharp decrease in the grain size.The suppression effects were realized by restricting the orientation dependent of AGG and promoting static recrystallization.The pre-tension reset the distributions of stored energy and sizes of the grains with〈11–20〉and〈10–10〉orientations,and thus retarded the orientation dependent of AGG.Moreover,the pre-tension introduced a mass of dislocations,twins,and stacking faults,all of which promoted the occurrence of static recrystallization,and the grain structure was further refined.The pre-tension accelerated the precipitation kinetics during aging,resulting in fine and dense precipitates.With the increase of pre-tension strain,the strength of ZK60 Mg profile monotonically increased.
基金supported by the National Natural Science Foundation of China(Nos.51575068 and 51501023)the State Key Research and Development Program of MOST,China(No.2016627 YFB0701204)+2 种基金the Fundamental Research Funds for the Central Universities(No.2020CDJDPT001)the Chongqing Natural Science Foundation(Nos.cstc2018jcyjAX0364 and cstc2021jcyj-msxmX0699)the“111”Project of the Ministry of Education(No.B16007).
文摘Conventional wrought Mg alloys,such as AZ31 and ZK60 rolled plates,usually exhibit significantly low tensile yield strength in the thickness direction.This can be attributed to the high activity of{10-12}tension twinning due to the strong basal texture(<0001>//ND,normal direction).In this work,the tensile yield strength in the ND of the as-rolled(AR)AZ31 plate increased from 50 to 150 MPa(increased by 200%)via simple processing,i.e.,pre-tension and rolling-annealing(PTRA)treatment.The strong basal texture(<0001>//ND)of the AR plate was changed into a weakened fiber texture(<0001>⊥ND).The evolution of microstructures during PTRA treatment and the activated deformation modes during uniaxial tension were studied quantitatively and statistically by the means of intergranular misorientation(IM)and in-grain misorientation axes(IGMA)analysis.The results indicate that various twin variants,as well as{10-12}-{10-12}secondary twins,were activated during pre-tension and rolling,and most residual matrix was consumed by twins after annealing.The dominated deformation modes in tension changed from{10-12}tension twinning(the AR sample)to prismatic slip(the PTRA sample)in the early tensile deformation.The underlying formation mechanism of the fiber texture and corresponding strengthening mechanism were discussed.
基金supported by the Collaboration Scheme from University of Science and Technology of China and City University of Hong Kong Joint Advanced Research Institute, and City University of Hong Kong (No. 7002357 (BC))
文摘The transverse free vibration of nanobeams subjected to an initial axial tension based on nonlocal stress theory is presented. It considers the effects of nonlocal stress field on the natural frequencies and vibration modes. The effects of a small scale parameter at molecular level unavailable in classical macro-beams are investigated for three different types of boundary conditions:simple supports,clamped supports and elastically-constrained supports. Analytical solutions for transverse deforma-tion and vibration modes are derived. Through numerical examples,effects of the dimensionless nanoscale parameter and pre-tension on natural frequencies are presented and discussed.
基金financially supported by the National Natural Science Foundation of China (Nos.52061005 and 52261025)the Science and Technology Program of Guizhou Province (Nos.YQK[2023]009 and [2023]278)。
文摘The deformation and fracture failure of aerospace structural components are primarily affected by complex loading conditions.This study aims to investigate how various pre-tension strains(0%,4%and 6%)influence the torsional properties,deformation and fracture mechanism of the Ti-5Al-5Mo-5V-3Cr-1Zr(Ti-55531)alloy with the bimodal microstructure.The results indicate that increasing the pre-tension strain gradually decreases the torsional strength of specimens.However,their torsional ductility initially increases(from 0 to 4%pre-tension strain)and then decreases(from 4 to 6%pre-tension strain).This can be attributed to the significant influence of different pre-tension strains on the deformation mechanism of each phase in the alloy.Under pure torsion loading,the primary α(α_(p))phase mainly undergoes the{0002}basal slip for deformation.However,at a pre-tension strain of4%,the torsional deformation mechanism of α_(p)transforms into crossing reaction between the{1010}prismatic slips.As the pre-tension strain further increases to 6%,{1011}pyramidal slips were further activated.Moreover,with an increase in pre-tension strain,there is a significant rise multiple slips probability within the α_(p) during torsional deformation.On contrary,for the secondaryα(α_(s))phase,the probability of{1011}_(α)twins formation during torsional deformation firstly rises and then reduces.These findings indicate thatαphase,particularly α_(p),plays a crucial role in accommodating deformation.This discovery offers valuable insights for further adjustments and optimizations of material microstructure and properties.Additionally,modifying external load can alter the stress state of components and enhance their fracture resistance during service,thereby broadening their range of applications and improving material reliability.
基金National Natural Science Foundation of China (No.10572038)the Program for New Century Excellent Talents in University .
文摘The mechanism of filament pre-tension is put forward. The effect of filament pre-tension on Sirofil composite yam properties, such as hairiness and structural stability, are theoretically and experimentally studied. The theoretical analysis agrees well with the experimental results. The present theory shows that suitable choice of filament pre-tension can enormously reduce hairiness and improve structural stability of Sirofil composite yarn.
文摘The stiffness required for the normal operation of membrane roof comes from the application of pre-tension. When the pre-tension is too small, it is easy to cause instability under the action of wind load, which leads to excessive deformation of the roof and local or overall damage. In order to ensure that the membrane roof is always in normal use state in the airflow field, this paper takes the membrane pretension as the control parameter to study the value of safety pretension of closed membrane roof. According to the theory of large deflection of membrane and Galerkin method, the nonlinear vibration differential equation of membrane roof under static wind is established, and the critical state of safe working of membrane roof is determined by judging the stability of the solution of the equation, and the expression of critical wind speed is obtained. By establishing the inequality relationship between local design wind speed and critical wind speed, the safety pretension limit of membrane roof under specific site can be obtained. The research shows that the safety pretension limits of closed membrane roofs are different in different areas under different design return periods. In addition, the value of safety pretension is related to the film geometry.
文摘In the construction of cast-in-place bridge deck of prefabricated I-beam by pretension folding line method, I-beam is used as the main stress support, well-shaped support is used on the inner side, triangular stable support is used on the outer side, temporary support and installation formwork are erected through walking operation platform, steel bar binding and cast-in-place concrete deck construction are carried out on the upper part of I-beam and formwork, the deck thickness is only 20cm, which meets the vehicle load requirements of city -A grade bridge BZZ-100 and reduces the dead weight of the structure. Compared with the common full framing, the framing used in the construction is convenient in construction, material-saving, simple in process and short in construction time. I-beam construction adopts factory processing and production. Formwork is uniformly made of shaped steel formwork. The prefabricated members have a beautiful appearance. Prestressing is installed and tensioned in advance to ensure the straightness of the prestressing and the accuracy of the position. The overall structure of the I-beam is light in weight, and the total amount of concrete used is small. Under the condition of reducing the dead weight of each span and ensuring the stress stability, the amount of concrete used is reduced, which is beneficial to environmental protection and material conservation. In terms of formwork support system, the support form of this process is easy to build, less material is used and the construction speed is fast. And the binding of the steel bars can be completed in a short time. In the concrete pouring project, the pouring speed is fast and the construction is simple.
基金the support of the Research Grant Council of the Hong Kong Government on the project“Advanced Analysis Allowing for Load and Construction Sequences”funded jointly by Construction Industry Institute-Hong Kong(CII-HK)the Hong Kong Polytechnic University and“Advanced Analysis for Progressive Collapse and Robustness Design of Steel Structures”(PolyU 5115/07E).
文摘Pre-tensioned high strength trusses using alloy steel bar are widely used as glass wall supporting systems because of the high degree of transparency.The breakage of glass panes in this type of system occurs occasionally,likely to be due to error in design and analysis in addition to other factors like glass impurity and stress concentration around opening in a spider system.Most design does not consider the flexibility of supports from finite stiffness of supporting steel or reinforced concrete beams.The resistance of lateral wind pressure of the system makes use of high tension force coupled with the large deflection effect,both of which are affected by many parameters not generally considered in conventional structures.In the design,one must therefore give a careful consideration on various effects,such as support settlement due to live loads and material creep,temperature change,pre-tension force,and wind pressure.It is not uncommon to see many similar glass wall systems fail in the wind load test chambers under a design wind speed.This paper presents a rigorous analysis and design of this type of structural systems used in a project in Hong Kong,China.The stability function with initial curvature is used in place of the cubic function,which is only accurate for linear analysis.The considerations and analysis techniques are believed to be of value to engineers involved in the design of the structural systems behaving nonlinearly.
