Research On BFRP Square Pipe Connection Performance Based On Multi-axial Lamination Design

Fiber-reinforced polymer(FRP)pultrusions have the advantages of light weight,high strength,corrosion resistance,good durability,etc.,and excellent performance along the fiber direction.It is an ideal material for achieving lightweight structure,long life,and corrosion resistance.Applying it to the truss structure can give full play to the excellent one-way mechanical properties of FRP pultrusions,and can effectively solve the problems of traditional steel truss such as self-weight,poor durability and high maintenance costs.However,FRP profiles still have the problem of difficulty in component connection in the application of truss structures.Unlike steel structure,FRP is an anisotropic material,brittle,and cannot be welded.These problems complicate the connection behavior and make it difficult to create hard and strong connections.When bolting is used,the FRP truss structure often fails first at the nodes,and there is a prominent problem of low connection efficiency,which causes the high-strength characteristics of FRP materials to not be effectively used.Based on the problem of low efficiency of bolt connection in FRP pultrusions structure,this paper conducts an experimental study on the connection performance of typical square tube members in truss structures on the basis of the research on the connection performance of multiaxial laminated pultrusions plates.By changing the layer of BFRP square pipe,the BFRP square pipe with uniaxial layer design is used as the control group,and the mechanical properties and mechanical properties of BFRP square pipe designed with multi-axial layer,different layers of adjacent surfaces and hybrid carbon fiber layer are used as the control group.Research on connection performance.The specific research content and results are as follows:(1)The layup design of BFRP square pipe was systematically analyzed and the four types of pultrusion production(uniaxial layup,multi-axial layup,adjacent surface different layup and mixed carbon layup)were systematically analyzed.The tube was subjected to tensile,compression,bending and in-plane shear tests.The results show that the uniaxially laminated BFRP square tube exhibits higher tensile strength and tensile modulus,but the compressive strength and in-plane shear performance are poor.The tensile strength and modulus of the multiaxial layered BFRP square tube decreased slightly,but the in-plane shear performance improved significantly.The hybrid carbon fiber BFRP square tube has good tensile,compression and bending properties,and also shows good shear properties.(2)Axial force(tension and compression)tests were carried out on 192 BFRP square tube bolted joints,and the influence of joint lateral restraint conditions,end diameter ratio,bolt diameter,row spacing,and row spacing were studied.,The results show that the uniaxial BFRP square tube undergoes splitting failure under different connection geometric parameters,which is brittle,and the structure does not have the ability of plastic deformation.However,the joints of the multi-axial layered square tube,the adjacent side different layered square tube and the mixed carbon square tube exhibit a certain ductile extrusion failure under the condition of meeting the geometric parameters of the connection,and the bearing capacity has increased significantly.The connection performance of BFRP square tube nodes is of great significance.(3)Compression tests were carried out on the four triangular truss structures designed and manufactured,and the connection performance of the pipe nodes under multi-directional forces was explored.The results show that the triangular truss structure composed of uniaxially layered square tubes and differently layered square tubes on adjacent surfaces will be brittle failure under compression load,and the bearing capacity is low.The ultimate bearing capacity of the triangular truss structure composed of multi-axial layered square tubes and mixed carbon square tubes is 60.4% and 57.8% higher than that of uniaxially layered square tubes,respectively,and can exhibit good ductility characteristics,which is suitable for practical applications.In addition,finite element simulation of the triangular truss structure composed of multi-axial layered square tubes was carried out by using finite element analysis software.The test values and the simulation results are in good agreement,which proves the reliability of the test results.