Non-linear finite element investigation on the behavior of CFRP strengthened steel square HSS columns under compression

This paper presents a numerical finite element investigation on the behavior of steel square hollow structural section (HSS) columns strengthened with CFRP. Three dimensional finite element (FE) models of square HSS sections were developed using shell elements considering both material and geometric nonlinearities whereas CFRP strengthening was incorporated with additional layers of shell elements. The developed FE models were used to simulate experimental studies done by past researchers. Good agreement has been found between numerical analysis and past experimental results, which has validated the acceptability of the FE model to carry out further investigation. Study is then focused on some selected non-compact AISC square HSS columns and the effects of number of CFRP layers, slenderness ratio and cross-sectional geometry on the strength gain of those columns has been observed. It is observed that CFRP strengthening is comparatively effective for higher slenderness ratios. For smaller sections strengthening tends to be effective at smaller slenderness ratios as well. For relatively large AISC square HSS columns, with increasing number of CFRP layers (from 1 to 5 layers) the axial strength gain is only approximately by about 1 to 20%. For medium and small square HSS sections, effectiveness of CFRP strengthening increases approximately by about 10 to 90%. The findings of the present study provide us a better understanding of the behavior of HSS sections strengthened with CFRP and shall be useful to engineers in applying CFRP retrofitting techniques to strengthen steel columns.