Performance Research On Short Thin-walled Square Steel Tube Strengthened With CFRP Under Axial Compression

The stability problem of steel structure is always a technical problem in engineering application.The traditional steel structure reinforcement method may cause new damage and residual stress,and the FRP reinforcement rule of steel structure has the advantage that traditional methods do not have.At present,the research on stabilizing the stability performance of thin flexible section steel structural members through external FRP is very limited.The buckling of steel structures usually occurs in the stress zone,and the advantage of FRP lies in the excellent tensile properties.How to give full play to the tensile properties of the FRP material to restrict and restrain the buckling of the pressure stress region is the key to the research of this project.First,axial compression tests were carried out on 16 specimens externally bonded to CFRP sheets.The length of 16 specimens is 700mm,and the nominal width-to-thickness ratio is 55.6.Among them,there are 2 specimens without reinforcement with CFRP sheets,and the other 14 are externally bonded with CFRP sheets.The main parameters are the layers of CFRP sheets(2 layers and 4 layers)and the direction of the CFRP sheets(transverse,longitudinal and transverse longitudinal combinations).The test results show that the local buckling capacity,the bearing capacity and stiffness can be improved by strengthening with CFRP sheets under axially loading.But the externally bonded CFRP failed to change the failure mode of specimen.The externally bonded CFRP sheets and layers have significant influence on the local buckling capacity,stiffness and ultimate bearing capacity.Among them,the stability of the load-bearing capacity of the test specimen with 1 horizontal and 1 vertical repeated alternately pasted 4 layers was the largest,up to 45.3%.;To enhance the rate of paste 4 layer CFRP cloth layer is greater than 2,CFRP and combination method is better than the longitudinal paste paste,at the same time,the pure vertical paste is better than pure transverse paste;after CFRP is attached,the stiffness of cold-formed thin-walled square steel tube has a certain degree Lifting,although 1 horizontal and 1 vertical repeated alternately pasting 4 layers of bearing capacity to enhance the maximum,but its stiffness is not the largest,the maximum stiffness increase is 2 transverse 2 vertical paste components,indicating that the increase of stiffness and bearing capacity is not proportional.Then use finite element software ANSYS to carry on the numerical analysis to the original component and the reinforced sample,introduced the finite element model to establish the concrete step,the component analysis method is the nonlinear analysis,will analyze the load-vertical curve and the ultimate bearing capacity Comparing with the test results,the validity and good applicability of the model are verified.Finally,using the reinforcement calculation method in[42],the ultimate bearing capacity of the members transversely and longitudinally pasted was calculated.Based on this method,the elastic modulus of the CFRP was modified to obtain the equivalent Eecf,and all the laterally pasted members were calculated.,And compared with the test results,verify the reliability of the calculation method within a certain range.