This study aims at studying the structural behavior of slender hollow steel sections (HSS) strengthened with carbon fiber reinforced polymer (CFRP) fabrics under axial compression. An experimental investigation has been performed on twenty short square and rectangular hollow sections (SHS and RHS) steel columns. These sections cover a plate slenderness ratio range of 50 to 84. Un-strengthened five columns are used as control specimens. The remaining fifteen specimens are classified into three groups of strengthening. The first group is fully wrapped, that is strengthened using a single layer of CFRP wrapped in transverse direction. The second group is partially wrapped, that is strengthened by 100 mm CFRP transverse single layer strips spaced at 50 mm. The third group is similar to the second with using double layer strips instead of the single layer strips. Both of failure modes and ultimate capacity of each specimen are investigated. The confinement action provided by the CFRP wrapping effectively delay the local buckling of fully strengthened specimens. However, in case of partially strengthened specimens, failure occurs at the un-strengthened zones between CFRP strips. In general, the stiffness and load carrying capacity of strengthened specimens are increased. The enhancement in ultimate capacity ranges between 19.1 % and 34.5 % for SHS, and between 18% and 41.3% for RHS specimens. It has been noticed that, the improvement in the behavior for specimens strengthened with two layer strips is limited compared to specimens strengthened with one layer strips. Three dimensional non linear finite element analyses are performed for the control and strengthened specimens. The finite element results are found to be in good agreement with their experimental counterparts. The reliability index between the finite element and the experimental ultimate capacities ranges between 0.01 and 0.1. An analytical model has been developed to predict the failure load of the control specimens. The obtained results of the developed model are in a good agreement with the the finite element and test results. |
