Experimental investigation of two novel FRP retrofit schemes for strengthening steel columns

Fiber reinforced polymers (FRP) are increasingly being used to retrofit structural members due to their low weight-to-strength ratio and corrosion resistance. Results from an experimental program conducted to evaluate two recently proposed techniques for retrofitting I-shape steel columns are presented. The first retrofit technique involves the construction of a steel-concrete column, which is subsequently wrapped with resin impregnated FRP sheets with the fibers oriented in transverse direction to confine the concrete. The second retrofit technique utilizes a glass FRP (GFRP) composite tube that is placed around the column and filled with concrete. The GFRP tube acts as a stay-in-place form and provides uniform confinement. Slenderness ratios of the retrofitted specimens are selected such that they cover a range of stub to intermediate long columns. Experimental results show significant increase in load carrying capacity and ultimate displacement of the retrofitted columns due to composite action behaviour. The second proposed retrofit technique, using a GFRP tube, provides increased confinement uniformly which results in greater enhancement in the axial behavior of the retrofitted specimens. Confinement efficiency decreased by increasing the specimen length as failure occurred due to overall buckling of the columns.