Research On Axial Compression And Low-velocity Impact Performance For The Circular Constructional Steel Tube Wrapped By GFRP

With the development of social economy and engineering technology,building structures will become higher and larger.For the large span space structure,such as the stadium and airport,the bearing capacity greatly depend on the self-weight of structure.Thus it highlights the study on the component with lightweight and high strength.Because the various countries in the world continually improve the requirement of structure security,the research works on structural components can not just focus on the static performance,especially after the 9.11 attack the accidental loading,such as impact and blast,have drawn wide attention.In recently years,the fortuitous accidents such as structures striked by aircrafts or automobiles happened frequently,which make the researchers in civil engineering field realize that the low-velocity impact is a possible load during the service period of structure and should be paid more attention.Combined the fiber reinforced polymer(FRP)with circular constructional steel tube can harness the advantages of each material.Compared to the traditional steel component the composite component is more lightweight and have better bearing capacity and energy-dissipating capacity,which is conductive to the lightweight of engineering structure and improve its performance under low velocity impact load.Besides,the FRP can protect the circular constructional steel tube,so that the composite component have good resistance to corrosion and have good application prospect in corrosion environment.For the above background,this paper using experiment,simulation and theoretical prediction studies the performances of circular constructional steel tube wrapped by glass fiber reinforced polymer(GFRP)under load,such as static axial compression,axial impact and lateral impact.The specific study contents and achievements as follows:(1)The constitutive model and finite element application method for GFRP have been studied.The quasi-static material properties of steel tube and GFRP,as well as the interfacial properties were obtained through material tests and debonding tests.Based on the composite material mechanics and fracture mechanics,the existing FRP failure criteria were improved.A FRP constitutive model considered 6initial failure modes(fiber tension and compression failure,matrix tension and compression failure,as well as in-layer tension and compression delamination failure)and damage evolution was built,on this basis two material subroutines applicable to the ABAQUS implicit analysis and explicit analysis respectively were introduced.The comparison with Hashin criterion,Puck criterion and Chang-Changcriterion had proved that the FRP constitutive model proposed was better when analyzing the dynamic problems.(2)The response regularity and failure mechanism for composite component under axial compression have been studiedAxial compression tests were conducted on 27 GFRP winding circular constructional steel tubes,9 circular constructional steel tubes and 2 circular GFRP tubes;and based on the ABAQUS and material subroutine the simulations of axial compression processes were developed.The effects of fiber winding angle(the angle between the axis of the tube and the tangential direction of winding fiber),radius-thickness ratio,slenderness ratio and GFRP volume ratio were discussed,and then the failure mechanisms and failure discipline of components under axial compression load were obtained.Additionally,the FRP equivalent coefficients for both strength failure and overall instability were proposed,and then based on the strength theory and Perry-Robertson equation the predicted formulas for both ultimate strength and buckling strength were obtained.(3)The response regularity and failure mechanism for composite component under axial low-velocity impact have been studiedAxial low-velocity impact tests for 13 working conditions were conducted on18 GFRP winding circular constructional steel tubes and 3 circular constructional steel tubes;and based on the ABAQUS and material subroutine the simulations of axial impact processes were developed.The effects of cross section geometric dimension,GFRP ply mode,impact energy and slenderness ratio were discussed,and then the failure mechanisms and failure discipline of components under axial low-velocity impact load were obtained.Additionally,the predicted formula for the peak load of component under axial impact were proposed by importing strain effect to the static ultimate strength predicted formula,and based on the plastic theory and energy theory the predicted formula for the mean load of component under axial impact were proposed.(4)The response regularity and failure mechanism for composite component under lateral low-velocity impact have been studiedLateral low-velocity impact tests for 45 working conditions were conducted on37 GFRP winding circular constructional steel tubes and 14 circular constructional steel tubes;and based on the ABAQUS and material subroutine the simulations of lateral impact processes were developed.The effects of drop hammer shape,cross section geometric dimension,GFRP ply mode and impact energy were discussed,and then the failure mechanisms and failure discipline of components under lateral low-velocity impact load were obtained.Research finding that GFRP can significantly improve both the bearing capacity and energy-dissipating capacity of circular constructional steel tube under lateral impact load,moreover theenhancement effectiveness depend on the GFRP equivalent axial strength.Comprehensive considered the bearing capacity and energy-dissipating capacity,the recommended GFRP ply modes are [0/0/?/-?]_n.