Abstract:
This thesis presents a numerical finite element (FE) investigation on the behavior of
steel square hollow structural section (HSS) columns (mild steel) strengthened with
CFRP materials. 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 both conventional and continuum shell elements. Damage
properties of CFRP and GFRP materials were incorporated in the FE model. The
developed FE models were used to simulate experimental studies done by past
researchers. Good agreement was found in between present analysis and past
experimental results, which validated the acceptability of the FE model to carry out
further investigation. Study was 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 increase in axial load capacity of those columns
were studied. From the parametric study it was found that the axial strength of
column specimens can be possible to increase by up to two-thirds to that of
unstrengthened specimens. For columns of short and intermediate lengths, variation
in strength is less significant. When column length increases, strength decreases
significantly as expected. The capacity generally increases with the increase in the
number of CFRP layers. In some cases, the strength gains, however, do not correlate
directly to the number of CFRP layers. Medium sized HSS sections benefit most
from CFRP strengthening compared to larger or smaller sized sections. This is
because addition of CFRP layers decreases the b/t ratio more for medium sized
sections and hence brings the section closer to compactness and delays local
buckling which contributes to significant increase in capacity.
