Investigation On The Global Buckling Behaviour Of GFRP-high Strength Steel Welded Box Section Members Under Axial Compression

In order to enlarge the use of GFRP in steel structure,GFRP is directly pasted on the outer surface of the high-strength steel welded box columns under axial compression to delay global buckling.In this paper,an experimental study was conducted on 12 GFRPhigh strength steel welded box columns under axial compression with different steel grades and different number of GFRP layers.Based on the finite element simulation verified through the load-mid span deflection curve of the axial compression members,the effects of steel yield strength,GFRP confinement rate,GFRP length ratio,member width-to-thickness ratio,slenderness and compressive strength of GFRP in fiber direction on the overall stability performance of GFRP-high strength steel welded box columns under axial compression were analyzed with reference to the experimental results.Research shows that The effect of adhesive damage on the rate of load-bearing capacity improvement is more obvious,and GFRP should be applied in the outer ring of longitudinal GFRP to improve its interaction with the steel members.The finite element model established in this paper can better simulate the experiment result;the change of elastic modulus of GFRP along the fiber direction has less than 0.2% effect on the overall buckling capacity of the member,so the definition of GFRP restraint rate is revised;when the length to slenderness ratio of the member is less than 130,the member is basically in the compressed state before reaching the peak load,so the compressive performance of GFRP fiber direction has a greater effect on the the overall buckling capacity improvement rate of the member has a greater impact;when the member length to slenderness ratio continues to increase,the convex surface of the member may appear tensile strain when reaching the peak load,indicating that the slenderness has a greater impact on the mechanism of the member;when the yield strength of steel rises to 690 MPa,the corner residual tensile stress value becomes larger,and the residual compressive stress range of the cross-section becomes wider,which decreases the overall stability coefficient of the member.The increase of steel yield strength,the increase of plate thickness of steel section,and the decrease of compressive strength of GFRP in fiber direction will lead to the decrease of member load capacity improvement rate,and the increase of GFRP restraint rate can improve the overall buckling capacity of the member;the influence of width-to thickness ratio on the overall buckling performance of the member is small;the load capacity improvement rate is basically unchanged after the GFRP length ratio exceeds 70%,which means that the contribution of GFRP at the end of the member to the load capacity is small The rate of increase of the bearing capacity is basically unchanged after the GFRP length ratio exceeds 70%;the modified formula considering the regularized slenderness ratio and the GFRP restraint rate can be biased to safely predict the overall buckling capacity of such members under axial compression.