Study On The Behavior Of Eccentrically Compressed Steel Columns Strengthened With Grouting-infilled FRP Tube

In this study,steel members under eccentric compression load were strengthened with fiber reinforced polymer(FRP)tubes with grouting in order to enhance their buckling resistance.With both experimental investigation and finite element modeling,load-displacement behavior,ultimate strength as well as failure mode of strengthened specimens were investigated.At the same time,the calculation method of ultimate strength of members is verified and revised in this paper.The main works of the paper are listed below:(1)Experimental investigation.A total of 22 specimens were tested under eccentric compression load.Two strengthening methods,i.e.“composite tube-filling grouting materials-fiber cloth wrapped outside”(herein method a)and “composite tube-filling grouting materials”(herein method b)were conducted onto steel core.Two types of steel sections,i.e.I-and box-shape section steel members,were tested monotonically.Influence of slenderness,eccentricity was also studied.Load-displacement curve,failure mode,ultimate strength and the strains on the specimens were obtained in the test.Test results showed that failure mode of the specimens strengthened by “method a” were changed from the overall bucking to concentrated deformation failure of the unstrengthend ends,Ultimate strength was increased up to 169%.Ductility of strengthened specimens was also improved.Since “method b” reduced the lateral constraint of FRP tube comparing with “method a”,the FRP tubes were failed by end rupturin.Strengths of “method b” specimens were also improved to some extent,but the effectiveness is less than “method a”.(2)Finite element modeling.Finite element study was conducted using ABAQUS.Firstly,the test specimens were modeled with tested material properties,The FE results showed good agreement with the test results.With the validated FE model,parametric studies were conducted on(i)the length ratio of reinforcement section;(ii)bending stiffness ratio of reinforcement section;(iii)yield strength and ultimate strength of steel;(iv)geometric imperfection of steel and(v)slenderness ratio of steel.Results of parametric study showed that strengths of specimens become larger as the length ratio or bending stiffness ratio of reinforcement section,as well as the yield strength of steel;With the increase of the ultimate strength of steel,ductility of specimens were improved,but their strength were less influenced;The strengthening methods could reduce the sensitivity of specimens to the initial deflection;The ultimate strengths of specimens decreases with the increase of slenderness ratio of specimens.(3)Theoretical analysis and calculation of ultimate strength.Based on the test and finite element results,the formula for calculating ultimate strength of steel members subjected to eccentric loading in the Standard for Steel Structural Design is verified and revised in this paper,and the correction coefficient suitable for this test was put forward,meanwhile,suggested values and applicable ranges of correction coefficients for calculation formulas of steel members with different sections are given,which adopting the reinforcement method involved in the paper.Finally,the section structure and reinforcement process of practical engineering were given in this paper.