Study On Local Stability Of Axial Compression Members Of GFRP-High Strength Steel Welded Round Section

Since the beginning of this century,high strength steel has been gradually applied in practical engineering by virtue of its super high strength,good plasticity and toughness.Among them,high-strength steel round pipe has been successfully applied in transmission tower structure,long-span structure and offshore platform structure,but its local stability has been an important factor hindering its application.Generally speaking,the reasonable use of the postbuckling strength of the member can obtain economic benefits,but the Chinese Steel Structure Design Standard(GB50017-2017)tends to conservatively not use the post-buckling strength of the tubular axial compression member.In recent years,it has been found that pasting Fiber Reinforced Polymer(FRP)outside steel components can improve the mechanical properties of the components.However,these researches mainly focus on high-modulus and high-strength carbon fiber reinforced composites(CFRP)and ordinary steels.There are few glass fiber reinforced composites(GFRP)and high strength steels with good deformation ability.Therefore,in this paper,the finite element method is used to systematically study the local stability of welded circular tube axial compression members with GFRP-high strength steel.The main research contents and results are as follows:(1)The GFRP in the 0° and 90° directions were studied in detail,including elastic modulus,ultimate strength and failure mode,and the test results were used for finite element analysis.(2)ABAQUS finite element analysis software is used to establish a model that can accurately simulate the axial compression short column members of GFRP-high strength steel welded round pipe section,and the influence of material nonlinearity,geometric nonlinearity and residual stress is considered in the modeling,and the interface bonding performance between GFRP and steel pipe is considered.Based on the existing experimental research data,the correctness of the finite element model is verified from three aspects: load-axial displacement curve,failure mode and ultimate bearing capacity.(3)Based on the verified finite element modeling method,the finite element models of480 GFRP high-strength steel welded tubular short column axial compression members were established,and their local stability properties were analyzed.The influence of the number of GFRP layers,the Angle and the bonding mode,the diameter to thickness ratio of high strength steel round tube,the yield strength of steel,and the thickness of steel plate on the local stability of the axial compression member of GFRP high strength steel welded round tube is studied.The results show that the lateral GFRP can inhibit the local buckling deformation of the pipe,and the longitudinal GFRP can improve the stiffness of the member.When the sticking Angle of GFRP is 0°～±60°,the ultimate bearing capacity of the specimen decreases greatly with the increase of the Angle.When the sticking Angle of GFRP is ±60°～90°,the ultimate bearing capacity of the specimen increases slightly with the increase of the Angle.With the increase of steel yield strength and the increase of steel pipe diameter to thickness ratio,the increase of GFRP on ultimate bearing capacity increases,but the increase rate decreases slightly.With the increase of steel pipe thickness,the lifting rate of GFRP on the ultimate bearing capacity of the member decreases significantly.When the wall thickness exceeds 6mm,the decreasing range gradually tends to a fixed value.(4)Based on the finite element calculation results of high strength steel round pipes,the accuracy of these formulas is compared and analyzed.The results show that the calculation results of American specification(ANSI/AISC 360-16)are in good agreement with the finite element calculation results and are safe.(5)Based on the American standard(ANSI/AISC 360-16),the calculation formula of local stable bearing capacity of GFRP-high-strength steel welded round pipe section axial compression member was proposed.Based on the direct strength method,a calculation formula for the locally stable bearing capacity of GFRP-high-strength steel welded circular tube section axial compression members with GFRP longitudinal arrangement and GFRP cross-sectional staggered arrangement is proposed,and the accuracy of the formula is verified according to the finite element calculation results.