| The typical nodes of steel truss web concrete composite box girder are steel lid box node,double casing node and PBL node.Among them,PBL node is a new type of node that mainly relies on PBL shear key to resist horizontal shear force.Under the action of the load,the axial force on the concrete chords changes suddenly,resulting in a difference in axial force in the PBL node area.At the same time,pressure and tension are generated on the steel tube web members respectively,resulting in complex deformations such as translational and rotational deformation of the nodes.In order to study the ability of this type of node to resist deformation,based on an engineering example,combined with the finite element model,this article has carried out research on the following aspects:(1)Based on the component method,the components of the PBL node of the steel truss web concrete composite box girder are simplified into different spring models based on the assumptions.Through mechanical analysis,the calculation model is established,and the chord is derived using the second theorem of the card type.The deformation of the web member,considering the shear force of the interface between the steel plate and the concrete,the influence of the shear resistance of the concrete falcon and the bolt on the initial translational stiffness,and then obtain the calculation expression of the initial translational stiffness of the PBL node,and use The finite element model was validated,and the results showed that the Cassette Second Theorem can easily calculate the deformation of chords and webs;consider the shear force of the interface between the steel plate and the concrete,the shear resistance of the concrete falcon and the bolt against the initial flatness.Due to the influence of dynamic stiffness,the calculated translational stiffness of the PBL node is closer to the actual state;the deduced formula can easily calculate the initial translational stiffness of the PBL node.Compared with the finite element result,the error is within 8%,and The greater the load in the elastic range,the higher the accuracy.(2)The finite element model is used to study the influence of load on the initial translational stiffness of PBL joints,and the parameters that affect the initial translational stiffness of PBL joints are analyzed in the elastic stage.The results show that the translational stiffness of the PBL node gradually decreases with the increase of the axial force difference.In the elastic phase,with the increase of the load,the change of the translational stiffness of the PBL node is smaller.When the node enters the elastic-plastic In the stage,the translational stiffness value changes more than the elastic stage,indicating that the ability of the PBL node to resist translation is stronger in the elastic stage than in the plastic stage.In the elastic phase,the translational stiffness of the PBL node increases with the increase of the strength of the concrete,the diameter and wall thickness of the web member,the hole diameter and thickness of the open steel plate,and the diameter of the shear bolt.The increase of the rod diameter increases the most,and the stiffness of the web member accounts for the largest proportion of the initial translational stiffness of the PBL node,about 76.33%,and its significance index is also the largest.Therefore,the translational displacement of the PBL node is mainly generated.The deformation from the web rod also shows that the weakest part against the translational movement of the node is the web rod.The contribution of other components to the overall initial translational stiffness is in the order of perforated steel plate>shear bolt>PBL shear key>concrete chord.(3)Using the component method,each member in the node domain is simplified into different spring models based on assumptions.Through mechanical analysis,the calculation formula for the initial rotational stiffness of the PBL node is deduced,and the effect of tensile bolts and compression bolts on the initial rotational stiffness is considered.In the elastic phase,the parameters that affect the initial rotational stiffness of the PBL node are analyzed.The results show that the contribution of tensile bolts and compression bolts to the initial rotational stiffness cannot be ignored,and the contribution of tensile bolts to the initial rotational stiffness is even greater.Big.The deduced formula can easily calculate the initial rotational stiffness of the PBL node.Compared with the finite element results,the error is within 6%.In the elastic phase,the rotational stiffness of the PBL node increases with the increase of the concrete strength,the hole diameter of the holed steel plate,the thickness of the holed steel plate,and the diameter of the tensile and compressive bolts.The increase is the largest,and the perforated steel plate accounts for the largest proportion of the overall initial rotational stiffness of the joint,which is about 63.4%.Therefore,the rotation displacement of the joint mainly comes from the deformation of the perforated steel plate.The contribution of the remaining components to the overall initial rotational stiffness is in the order of(2)type tensile bolt>concrete chord>(1)type shear bolt>PBL shear key.(2)The significant index of the tensile bolts is the largest,indicating that it has the greatest impact on the overall initial rotation stiffness of the joint,and the weakest resistance to the initial rotation of the joint.It is recommended to increase the diameter of this type of bolt or change its arrangement to improve the initial rotational stiffness of the node.(4)Using the multi-factor orthogonal analysis method,the optimal parameter combination under the multi-objective is optimized.The results show that the orthogonal analysis method can optimize the design parameters reasonably and effectively.The range can be used to quickly determine the priority order of the design parameters,and the variance can be used to separate the influencing factors and the error of the factor level itself from the deviation caused by the calculation error.Using the F distribution in mathematics and probability statistics to test,the degree of influence of influencing factors on the calculation results can be judged.On the basis of the original design,the orthogonal analysis method can increase the initial translational stiffness of the PBL node by about 25.02%,and the initial rotational stiffness by 24.98%. |
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