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Steel Construction Published the List of Highly Influential Articles of 2020
2022 Vol. 37, No. 5
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2022, 37(5): 1-9.
doi: 10.13206/j.gjgS21070301
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Abstract:
The research of engineered bamboo structure and the proposal of modern bamboo structure system meet the requirements of green and ecological sustainable development in our country.The modern bamboo structure is continuously popularized and applied.Joint is the focus of the structural design,it plays a vital role in the safety of the structure.
This paper summarized and analyzed the research status of connecting joints in modern bamboo structures.The current development of modern engineering bamboo and its practical application in building structures were analyzed.It was concluded that there were two main types of connection in modern bamboo structures:bolt or screw connection.The beam-column joints were mainly bolted joints,and screwed joints are more used in the field of furniture or the connection of shear walls sheathed with engineered bamboo panels.The bearing capacity and failure mode of bolted joints were summarized and analyzed by the influence of different parameters,and the calculation theory of bearing capacity of bolted joints was analyzed.According to the force direction of the screw,the research on the withdrawal capacity and the shear bearing capacity of the screw connection was summarized and analyzed.
Based on the analysis of the current research,it is concluded that the relationship between the bearing capacity of the bolted connection and different parameters is relatively abundant.However,due to the lack of modern bamboo structure specifications,there will be certain errors in the calculation theory based on the wood structure design specifications.There are relatively few studies on screw connections.It is also recommended to conduct in-depth research on screw connections and their beam-column joints,and formulate relevant specifications for engineering bamboo.
The research of engineered bamboo structure and the proposal of modern bamboo structure system meet the requirements of green and ecological sustainable development in our country.The modern bamboo structure is continuously popularized and applied.Joint is the focus of the structural design,it plays a vital role in the safety of the structure.
This paper summarized and analyzed the research status of connecting joints in modern bamboo structures.The current development of modern engineering bamboo and its practical application in building structures were analyzed.It was concluded that there were two main types of connection in modern bamboo structures:bolt or screw connection.The beam-column joints were mainly bolted joints,and screwed joints are more used in the field of furniture or the connection of shear walls sheathed with engineered bamboo panels.The bearing capacity and failure mode of bolted joints were summarized and analyzed by the influence of different parameters,and the calculation theory of bearing capacity of bolted joints was analyzed.According to the force direction of the screw,the research on the withdrawal capacity and the shear bearing capacity of the screw connection was summarized and analyzed.
Based on the analysis of the current research,it is concluded that the relationship between the bearing capacity of the bolted connection and different parameters is relatively abundant.However,due to the lack of modern bamboo structure specifications,there will be certain errors in the calculation theory based on the wood structure design specifications.There are relatively few studies on screw connections.It is also recommended to conduct in-depth research on screw connections and their beam-column joints,and formulate relevant specifications for engineering bamboo.
2022, 37(5): 10-17.
doi: 10.13206/j.gjgS21070602
Abstract:
The steel-timber composite system combines the advantages of both materials and has prospects for application in village houses,long-span structures and other building systems.Pin connections are common connection forms in steel-timber systems,and their mechanical properties significantly affect the performance of the structural system.Among them,bolts and screws are the common forms of pins connections.In order to accurately evaluate the shear resistance of thin-walled steel-timber self-tapping screw connections,connection shear tests and theoretical derivation were investigated in the paper.The mechanical properties of the potential structural material,fast-growing wood,were also calibrated.
To investigate the shear performance of the connections between timber and thin-walled section steel (2 mm) with small diameter self-tapping screws (diameter ＜ 6 mm),11 groups of single shear connections under monotonic loading were designed and tested.Timber type,dimension of connections,and connection direction are the main parameters explored.The mechanical properties such as damage mode,bearing capacity and stiffness,ductility coefficient,and cut line stiffness of the self-tapping screw connections were obtained.On the basis of Standard for Design of Timber Structure(GB 50005-2017),the bearing capacity of typical damage modes of thin-walled steel-timber self-tapping screw connections was analyzed.
The results include:the strength of fast-growing timber can meet the connection requirements,the change of timber species has a certain effect on the shear performance of self-tapping screw connections,but the change of screw size,type and embedment length significantly affects the damage mode and peak load capacity of the connections.The performance of Chinese fir,poplar and pinus radiata is lower than that of common building materials such as douglas fir and pinus sylvestris,but they still have sufficient connection strength.The self-tapping screw connections in the paper mainly occur in three damage modes:self-tapping screw rod shearing,screw pull-out and timber damage.Among them,self-tapping screw shearing is the most common damage.When the embedded length of the screw is small,the connection is prone to damage from self-tapping screw pull-out,in addition,the timber cross-grain connection specimen is prone to brittle fracture due to cross-grain tension,the actual situation should be avoided.Self-tapping screw connection has a good peak bearing capacity (about 3 kN) in steel-timber composite structures and members,but the ductility is poor due to the brittle fracture of the screw,the average ductility coefficient is 2,reducing the embedment length can increase the ductility of the connection.Through the theoretical derivation and mechanism analysis of the shear bearing capacity of self-tapping screw connections,as well as the analysis and calibration based on GB 50005-2017 and other domestic codes,it shows that the existing standards do not fully consider the rope effect,the bearing capacity are less than the actual measured value of the test.Different from the steel or wood pin-type connections,the thin-walled steel-timber composite self-tapping screw connections are dominated by bending and shear damage,and the design values derived from GB 50005-2017 account for about 30%-45% of the actual value of the bearing capacity.
The steel-timber composite system combines the advantages of both materials and has prospects for application in village houses,long-span structures and other building systems.Pin connections are common connection forms in steel-timber systems,and their mechanical properties significantly affect the performance of the structural system.Among them,bolts and screws are the common forms of pins connections.In order to accurately evaluate the shear resistance of thin-walled steel-timber self-tapping screw connections,connection shear tests and theoretical derivation were investigated in the paper.The mechanical properties of the potential structural material,fast-growing wood,were also calibrated.
To investigate the shear performance of the connections between timber and thin-walled section steel (2 mm) with small diameter self-tapping screws (diameter ＜ 6 mm),11 groups of single shear connections under monotonic loading were designed and tested.Timber type,dimension of connections,and connection direction are the main parameters explored.The mechanical properties such as damage mode,bearing capacity and stiffness,ductility coefficient,and cut line stiffness of the self-tapping screw connections were obtained.On the basis of Standard for Design of Timber Structure(GB 50005-2017),the bearing capacity of typical damage modes of thin-walled steel-timber self-tapping screw connections was analyzed.
The results include:the strength of fast-growing timber can meet the connection requirements,the change of timber species has a certain effect on the shear performance of self-tapping screw connections,but the change of screw size,type and embedment length significantly affects the damage mode and peak load capacity of the connections.The performance of Chinese fir,poplar and pinus radiata is lower than that of common building materials such as douglas fir and pinus sylvestris,but they still have sufficient connection strength.The self-tapping screw connections in the paper mainly occur in three damage modes:self-tapping screw rod shearing,screw pull-out and timber damage.Among them,self-tapping screw shearing is the most common damage.When the embedded length of the screw is small,the connection is prone to damage from self-tapping screw pull-out,in addition,the timber cross-grain connection specimen is prone to brittle fracture due to cross-grain tension,the actual situation should be avoided.Self-tapping screw connection has a good peak bearing capacity (about 3 kN) in steel-timber composite structures and members,but the ductility is poor due to the brittle fracture of the screw,the average ductility coefficient is 2,reducing the embedment length can increase the ductility of the connection.Through the theoretical derivation and mechanism analysis of the shear bearing capacity of self-tapping screw connections,as well as the analysis and calibration based on GB 50005-2017 and other domestic codes,it shows that the existing standards do not fully consider the rope effect,the bearing capacity are less than the actual measured value of the test.Different from the steel or wood pin-type connections,the thin-walled steel-timber composite self-tapping screw connections are dominated by bending and shear damage,and the design values derived from GB 50005-2017 account for about 30%-45% of the actual value of the bearing capacity.
2022, 37(5): 18-27.
doi: 10.13206/j.gjgS22031101
Abstract:
For beam-column steel joints,the moment-rotation curve is an important criterion of the ultimate bearing capacity,as well as an essential criterion for the design of joints.Generally,the moment-rotation curve of a joint has both ascending and descending range,therefore,the ultimate bearing capacity of the joint can be captured intuitively by the peak point of the curve.However,for some curve which is monotone increasing without an obvious peak point,the detemination of the ultimate bearing capacity needed to be further studied.Based on this issue,methodology of deformation limit will be discussed,in order to determine the ultimatate capacity.
Firstly,current codes as well as corresponding researches on methods of displacement limit calculation are summarized.These methods can be classified in two types,one is through the displacement of the chord,and another is through the brace.CIDECT method belongs to the type of chord,which takes the value of chord deformation in 3% of chord diameter as the ultimate deformation limit.Lu's method,as an improvement of CIDECT method,considering the relationship of load between the deformation of 1% and 3% of chord diameter,when the load of 3% is higher than 1.5 times load of 1%,and then the value of 1.5 times load of 1% is taken as the ultimate bearing capacity,otherwise,the value of 3% is taken as the ultimate point.TEC (Twice Elastic Method) is also belongs to the type of chord,which draws a straight line that the slope is half of the initial stiffness through the origin,and the intersection between the line and the curve is the ultimate point.Yura's method belongs to the type of brace,in which the brace is regarded as a simply supported beam with uniform load,when the strain in the middle of the beam span is 4 times the yield strain of the material,it is considered to reach the limit.Secondly,in view of situation that Yura's method is not adopted in codes,a series of steel circular tubular joint tests as well as finite element analysis are carried out to verify the method.Finally,the application of methods above were explored by taking the example of joints with square steel tubular column and H-shaped beam.Four groups of tests were designed and corresponding finite element simulation was carried out.After comparing the experimental and simulation results which verified the reliability of the simulation,the ultimate rotation angles of the above different methods are evaluated based on the finite element simulation results.
Results indicated that the application of Yura's method for joints of steel tubular column and H-shaped beam is feasible.The results obtained by Lu's method are relatively conservative and the operation is complicated.TEC method requires complete moment-rotation curves of joints,and is also complex to operate and prone to errors,so its applicability is limited.CIDECT and Yura's methods are relatively easy to operate,as the ultimate deformation can be estimated as long as the diameter of the chord or brace is determined,and the difference of the ultimate rotation obtained by these two methods is minor.Therefore,this research suggests to use these two methods to calculate the corresponding ultimate rotation,and take the smaller as the ultimate limit.
For beam-column steel joints,the moment-rotation curve is an important criterion of the ultimate bearing capacity,as well as an essential criterion for the design of joints.Generally,the moment-rotation curve of a joint has both ascending and descending range,therefore,the ultimate bearing capacity of the joint can be captured intuitively by the peak point of the curve.However,for some curve which is monotone increasing without an obvious peak point,the detemination of the ultimate bearing capacity needed to be further studied.Based on this issue,methodology of deformation limit will be discussed,in order to determine the ultimatate capacity.
Firstly,current codes as well as corresponding researches on methods of displacement limit calculation are summarized.These methods can be classified in two types,one is through the displacement of the chord,and another is through the brace.CIDECT method belongs to the type of chord,which takes the value of chord deformation in 3% of chord diameter as the ultimate deformation limit.Lu's method,as an improvement of CIDECT method,considering the relationship of load between the deformation of 1% and 3% of chord diameter,when the load of 3% is higher than 1.5 times load of 1%,and then the value of 1.5 times load of 1% is taken as the ultimate bearing capacity,otherwise,the value of 3% is taken as the ultimate point.TEC (Twice Elastic Method) is also belongs to the type of chord,which draws a straight line that the slope is half of the initial stiffness through the origin,and the intersection between the line and the curve is the ultimate point.Yura's method belongs to the type of brace,in which the brace is regarded as a simply supported beam with uniform load,when the strain in the middle of the beam span is 4 times the yield strain of the material,it is considered to reach the limit.Secondly,in view of situation that Yura's method is not adopted in codes,a series of steel circular tubular joint tests as well as finite element analysis are carried out to verify the method.Finally,the application of methods above were explored by taking the example of joints with square steel tubular column and H-shaped beam.Four groups of tests were designed and corresponding finite element simulation was carried out.After comparing the experimental and simulation results which verified the reliability of the simulation,the ultimate rotation angles of the above different methods are evaluated based on the finite element simulation results.
Results indicated that the application of Yura's method for joints of steel tubular column and H-shaped beam is feasible.The results obtained by Lu's method are relatively conservative and the operation is complicated.TEC method requires complete moment-rotation curves of joints,and is also complex to operate and prone to errors,so its applicability is limited.CIDECT and Yura's methods are relatively easy to operate,as the ultimate deformation can be estimated as long as the diameter of the chord or brace is determined,and the difference of the ultimate rotation obtained by these two methods is minor.Therefore,this research suggests to use these two methods to calculate the corresponding ultimate rotation,and take the smaller as the ultimate limit.
2022, 37(5): 28-35.
doi: 10.13206/j.gjgS22011402
Abstract:
U-shaped steel-encased concrete composite beam is developed on the basis of traditional composite beam,which has the characteristics of high bearing capacity,large stiffness and good stability.This kind of composite structure is relatively complicated in the joint position of primary beam and secondary beam,so it is of great significance to study the reasonable joint structure form and give full play to the mechanical properties of steel and concrete.Reference to steel structure connection mode,and it gave out the primary and secondary beam joint with the short end plate was connection beam connection signal hint:steel-encased secondary beam through the end plate was connected to the primary beam,or short beam was welded in advance on the web of primary beam,the secondary beam overlapped on the short beam was connected to the primary beam by bolts to reduce the field welding,facilitate construction hoisting,simplify the construction process.The finite element model of the primary and secondary beam joints was established by using ANSYS finite element software,and the stress mechanism and failure mode of the joints were analyzed.The influence of different structural measures such as stiffening rib,connecting cover plate and I-steel secondary beam on bearing capacity,connection stiffness,stability and deformation capacity of the joint was studied.The influence of structural parameters such as reinforcement ratio,concrete strength grade and stiffener thickness on the mechanical properties of the primary and secondary beam joints was studied by parametric analysis.
The results show that the bending stiffness of the section in the core area of joints is obviously lower than that in other areas,and the concrete in the core area is crushed first.The steel web of the primary beam is subjected to transverse deformation due to the large lateral force transferred from the direction of the secondary beam.After adding stiffeners at the joints,the deformation is significantly reduced,and the bearing capacity of the joints is increased by 7%,the rotational capacity is controlled at a lower level,and the ductility is also improved to a certain extent.The cover plate is set to enhance the tension capacity of the upper side of the joint.After analysis,the effect of the cover plate on the tension area is lower than that of the reinforcement.When the secondary beam adopts I-steel form,the bearing capacity of the joint is relatively low,and the construction operation is simple.When the span of the secondary beam is small,this form can be used to design and reduce the use of materials.Through the parametric analysis of the joint,it is found that the joint is greatly affected by the negative bending moment,and the upper reinforcement configuration has a significant impact on the bearing capacity,rotation capacity and deformation capacity of the joints.Excessive cross section angle is easy to cause the flange cracking,so it is necessary to control the rotation capacity of the joints.In addition,the reinforcement in the concrete flange plate also plays an important role in the mechanical properties of the joint.The reinforcement in the 2 metres range is relatively high,so it is recommended to consider the reinforcement in the effective flange width when calculating the ultimate bearing capacity of the joint.The strength grade of concrete and the thickness of stiffened ribs also have a certain influence on the mechanical properties of the joint.When the primary and secondary beam joints are designed as rigid connections,short beams or end plates with stiffening ribs should be used.
U-shaped steel-encased concrete composite beam is developed on the basis of traditional composite beam,which has the characteristics of high bearing capacity,large stiffness and good stability.This kind of composite structure is relatively complicated in the joint position of primary beam and secondary beam,so it is of great significance to study the reasonable joint structure form and give full play to the mechanical properties of steel and concrete.Reference to steel structure connection mode,and it gave out the primary and secondary beam joint with the short end plate was connection beam connection signal hint:steel-encased secondary beam through the end plate was connected to the primary beam,or short beam was welded in advance on the web of primary beam,the secondary beam overlapped on the short beam was connected to the primary beam by bolts to reduce the field welding,facilitate construction hoisting,simplify the construction process.The finite element model of the primary and secondary beam joints was established by using ANSYS finite element software,and the stress mechanism and failure mode of the joints were analyzed.The influence of different structural measures such as stiffening rib,connecting cover plate and I-steel secondary beam on bearing capacity,connection stiffness,stability and deformation capacity of the joint was studied.The influence of structural parameters such as reinforcement ratio,concrete strength grade and stiffener thickness on the mechanical properties of the primary and secondary beam joints was studied by parametric analysis.
The results show that the bending stiffness of the section in the core area of joints is obviously lower than that in other areas,and the concrete in the core area is crushed first.The steel web of the primary beam is subjected to transverse deformation due to the large lateral force transferred from the direction of the secondary beam.After adding stiffeners at the joints,the deformation is significantly reduced,and the bearing capacity of the joints is increased by 7%,the rotational capacity is controlled at a lower level,and the ductility is also improved to a certain extent.The cover plate is set to enhance the tension capacity of the upper side of the joint.After analysis,the effect of the cover plate on the tension area is lower than that of the reinforcement.When the secondary beam adopts I-steel form,the bearing capacity of the joint is relatively low,and the construction operation is simple.When the span of the secondary beam is small,this form can be used to design and reduce the use of materials.Through the parametric analysis of the joint,it is found that the joint is greatly affected by the negative bending moment,and the upper reinforcement configuration has a significant impact on the bearing capacity,rotation capacity and deformation capacity of the joints.Excessive cross section angle is easy to cause the flange cracking,so it is necessary to control the rotation capacity of the joints.In addition,the reinforcement in the concrete flange plate also plays an important role in the mechanical properties of the joint.The reinforcement in the 2 metres range is relatively high,so it is recommended to consider the reinforcement in the effective flange width when calculating the ultimate bearing capacity of the joint.The strength grade of concrete and the thickness of stiffened ribs also have a certain influence on the mechanical properties of the joint.When the primary and secondary beam joints are designed as rigid connections,short beams or end plates with stiffening ribs should be used.
2022, 37(5): 36-43.
doi: 10.13206/j.gjgS2112301
Abstract:
The connection form of the steel tubular members in transmission towers should be the semi-rigid connection which falls in between rigid and pinned connections.Therefore,studying the bearing capacity of steel tubular members of semi-rigid connection is more suitable for the actual loading case.Accordingly,semi-rigid characteristics of K-joints in transmission tubular towers were studied and the finite element (FE) analysis on the stability bearing capacity of steel tubular members under axial compression load considering semi-rigid joints in transmission towers was carried out.First,based on the original model of the transmission tower in actual engineering,the FE model of the K-joint was established.Additionally,the influence,including the dimension of main chord,the axial compression ratio of main chord,the angle between the main chord and the bracing member,the thickness of the gusset plate,the number of the bolts,the thickness and width of the inserted plate,the length and dimension of the bracing member,and the strength of steel,on semi-rigid characteristics of K-joint was analyzed.Moreover,the approximate range of the initial rotational stiffness of K-joints was summarized.Then,based on the study of semi-rigid characteristics of K-joints,the FE analysis on the stability bearing capacity of steel tubular members under axial compression load considering semi-rigid joints was conducted.In addition,the effect of the rotational stiffness,the form of end connection,and the steel grade on steel tubular members with the varied slenderness ratio under axial compression load was investigated.Besides,the stability-coefficient-slenderness-ratio curve between design codes and analysis results was compared.
Results show that the failure of K-joints is exhibited at the compressional area of gusset plate and the inserted plate of compression bracing member.The moment-rotation relationship of the compression steel tubular member of K-joints is nonlinear.The thickness of gusset plate,the number of bolts,the thickness and width of inserted plate,the length and dimension of the bracing member,and strength of steel have a much influence on its semi-rigid characteristics,while the dimension of main chord,the axial compression ratio of main chord,the angle between the main chord and the bracing member have a little influence on that.The range of the initial rotational stiffness of K-joints was about 247.89-983.67 kN·m/rad.In addition,the stability bearing capacity of steel tubular members considering semi-rigid joints is higher than that with hinged connection,and the difference between them is increased with the increasing of the slenderness ratio.When the slenderness ratio is larger than 80,the difference is higher than 10%.When he slenderness ratio is larger than 140,the difference is higher than 20%.It indicates that the larger slenderness ratio is and the stronger end restraint effects are.The mid-span displacement of steel tubular members considering semi-rigid joints is less than that with pinned connections,which means that semi-rigid restraints can decrease the deformation of steel tubular members.The rotational stiffness,the form of connection,and the strength of steel can have an influence in different degree on the stability bearing capacity of steel tubular members considering semi-rigid joints.
The connection form of the steel tubular members in transmission towers should be the semi-rigid connection which falls in between rigid and pinned connections.Therefore,studying the bearing capacity of steel tubular members of semi-rigid connection is more suitable for the actual loading case.Accordingly,semi-rigid characteristics of K-joints in transmission tubular towers were studied and the finite element (FE) analysis on the stability bearing capacity of steel tubular members under axial compression load considering semi-rigid joints in transmission towers was carried out.First,based on the original model of the transmission tower in actual engineering,the FE model of the K-joint was established.Additionally,the influence,including the dimension of main chord,the axial compression ratio of main chord,the angle between the main chord and the bracing member,the thickness of the gusset plate,the number of the bolts,the thickness and width of the inserted plate,the length and dimension of the bracing member,and the strength of steel,on semi-rigid characteristics of K-joint was analyzed.Moreover,the approximate range of the initial rotational stiffness of K-joints was summarized.Then,based on the study of semi-rigid characteristics of K-joints,the FE analysis on the stability bearing capacity of steel tubular members under axial compression load considering semi-rigid joints was conducted.In addition,the effect of the rotational stiffness,the form of end connection,and the steel grade on steel tubular members with the varied slenderness ratio under axial compression load was investigated.Besides,the stability-coefficient-slenderness-ratio curve between design codes and analysis results was compared.
Results show that the failure of K-joints is exhibited at the compressional area of gusset plate and the inserted plate of compression bracing member.The moment-rotation relationship of the compression steel tubular member of K-joints is nonlinear.The thickness of gusset plate,the number of bolts,the thickness and width of inserted plate,the length and dimension of the bracing member,and strength of steel have a much influence on its semi-rigid characteristics,while the dimension of main chord,the axial compression ratio of main chord,the angle between the main chord and the bracing member have a little influence on that.The range of the initial rotational stiffness of K-joints was about 247.89-983.67 kN·m/rad.In addition,the stability bearing capacity of steel tubular members considering semi-rigid joints is higher than that with hinged connection,and the difference between them is increased with the increasing of the slenderness ratio.When the slenderness ratio is larger than 80,the difference is higher than 10%.When he slenderness ratio is larger than 140,the difference is higher than 20%.It indicates that the larger slenderness ratio is and the stronger end restraint effects are.The mid-span displacement of steel tubular members considering semi-rigid joints is less than that with pinned connections,which means that semi-rigid restraints can decrease the deformation of steel tubular members.The rotational stiffness,the form of connection,and the strength of steel can have an influence in different degree on the stability bearing capacity of steel tubular members considering semi-rigid joints.
2022, 37(5): 44-50.
doi: 10.13206/j.gjgS21011201
Abstract:
In the end plate connection with high-strength bolts subjected to bending moment,the end plate occurs bending deformation and produces prying force.In the design of connection joints with weak relative stiffness,the prying force can not be ignored.The end plate connection joints designed according to domestic specifications generally have the problems of large number of bolts and large thickness of end plate.It is necessary to analyze the relationship between prying force Q,joint bearing capacity Nt,bolt tension Nb and bolt tensile bearing capacity Ntb,and find out the reasons for the conservatism of China's standards through the comparative study of the current specifications formulas and their parameters.The tensile T-stub joint model can be used to simulate the high-strength bolted end-plate connection joint.The tensile T-stub joint test and theoretical analysis at home and abroad show that the first plastic hinge of the tensile T-stub joint with obvious prying force effect first appears near the root of the wing plate of the T-stub.With the gradual increase of the external tension Nt,the wing plate of T-stub gradually enters the elastic-plastic state from the elastic state,and the prying force also gradually increases from nothing until the bolt is broken or the wing plate of T-stub is completely damaged (a second plastic hinge appears near the bolt hole).The external tension Nt is divided into two parts Nt1 and Nt2,where Nt1 corresponds to the external tension when plastic hinge occurs at the wing plate root of T-stub,Nt2 forms a moment balance with the prying force Q near the bolt.The force arm of the external tension Nt is the distance from the root of T-stub to the bolt hole,and the force arm of prying force Q is the distance from the bolt hole to the edge of T-stub.According to the joint failure mode and the bending moment balance condition at the bolt hole in the failure state,the calculation formulas of joint tensile bearing capacity Nt,prying capacity Q,bolt tension Nb and the critical plate thickness of the failure mode are obtained.According to the joint tensile bearing capacity formula,the joint bearing capacity curve can be drawn,and the control conditions of the three failure modes and the relationship between the three failure modes can be obtained.
There are differences in the design methods of high-strength bolted connections considering prying force effect at home and abroad.The comparison results with foreign specifications show that:1) both Chinese and American specifications know the external force Nt and calculate the plate thickness;the European specification is to calculate the tensile bearing capacity Nt of the joint when the plate thickness is known.Although the three have different forms,the calculation formula has the same principle and can be converted to each other.2) The tensile bearing capacity of high-strength bolts in the Code for Design of Steel Structure (GB 50017-2017) has been included in the prying force effect;Ntb is still used as the upper limit of tensile bearing capacity of high-strength bolts in the calculation formula of relevant joint bearing capacity in other relevant steel structure specifications,which will cause repeated calculation of prying force effect.3) Under the same conditions,the calculation results of European and American specifications are close to the test results,while the calculation results of Chinese specifications are conservative.The failure to correct the position of plastic hinge is an important factor that leads to the conservatism of the current specification in China.4) The latest American specification further limits the calculated width of the flange of tension T-stub.In the European specification,the effective calculated length lef of the flange of equivalent T-stub is the minimum yield line length in various possible failure forms as the calculation basis of the joint bearing capacity.The provisions on calculating the wing width of T-stub in Chinese specifications are relatively general,and it is suggested to make them clear.
In the end plate connection with high-strength bolts subjected to bending moment,the end plate occurs bending deformation and produces prying force.In the design of connection joints with weak relative stiffness,the prying force can not be ignored.The end plate connection joints designed according to domestic specifications generally have the problems of large number of bolts and large thickness of end plate.It is necessary to analyze the relationship between prying force Q,joint bearing capacity Nt,bolt tension Nb and bolt tensile bearing capacity Ntb,and find out the reasons for the conservatism of China's standards through the comparative study of the current specifications formulas and their parameters.The tensile T-stub joint model can be used to simulate the high-strength bolted end-plate connection joint.The tensile T-stub joint test and theoretical analysis at home and abroad show that the first plastic hinge of the tensile T-stub joint with obvious prying force effect first appears near the root of the wing plate of the T-stub.With the gradual increase of the external tension Nt,the wing plate of T-stub gradually enters the elastic-plastic state from the elastic state,and the prying force also gradually increases from nothing until the bolt is broken or the wing plate of T-stub is completely damaged (a second plastic hinge appears near the bolt hole).The external tension Nt is divided into two parts Nt1 and Nt2,where Nt1 corresponds to the external tension when plastic hinge occurs at the wing plate root of T-stub,Nt2 forms a moment balance with the prying force Q near the bolt.The force arm of the external tension Nt is the distance from the root of T-stub to the bolt hole,and the force arm of prying force Q is the distance from the bolt hole to the edge of T-stub.According to the joint failure mode and the bending moment balance condition at the bolt hole in the failure state,the calculation formulas of joint tensile bearing capacity Nt,prying capacity Q,bolt tension Nb and the critical plate thickness of the failure mode are obtained.According to the joint tensile bearing capacity formula,the joint bearing capacity curve can be drawn,and the control conditions of the three failure modes and the relationship between the three failure modes can be obtained.
There are differences in the design methods of high-strength bolted connections considering prying force effect at home and abroad.The comparison results with foreign specifications show that:1) both Chinese and American specifications know the external force Nt and calculate the plate thickness;the European specification is to calculate the tensile bearing capacity Nt of the joint when the plate thickness is known.Although the three have different forms,the calculation formula has the same principle and can be converted to each other.2) The tensile bearing capacity of high-strength bolts in the Code for Design of Steel Structure (GB 50017-2017) has been included in the prying force effect;Ntb is still used as the upper limit of tensile bearing capacity of high-strength bolts in the calculation formula of relevant joint bearing capacity in other relevant steel structure specifications,which will cause repeated calculation of prying force effect.3) Under the same conditions,the calculation results of European and American specifications are close to the test results,while the calculation results of Chinese specifications are conservative.The failure to correct the position of plastic hinge is an important factor that leads to the conservatism of the current specification in China.4) The latest American specification further limits the calculated width of the flange of tension T-stub.In the European specification,the effective calculated length lef of the flange of equivalent T-stub is the minimum yield line length in various possible failure forms as the calculation basis of the joint bearing capacity.The provisions on calculating the wing width of T-stub in Chinese specifications are relatively general,and it is suggested to make them clear.
