The end bearing capacity of a rectangular hollow section (RHS) steel tube can be substantially increased through local strengthening using bonded carbon fiber reinforced polymer (CFRP) plates. This paper presents a combined experimental and numerical study into the behavior of such CFRP-strengthened RHS steel tubes with particular attention to debonding failure in such tubes. The results of an experimental study are first presented, which showed that debonding failure occurred in all the CFRP-strengthened steel tubes and the effectiveness of strengthening depended significantly on the slenderness of the webs. A finite element approach for modeling the behavior of such CFRP-strengthened steel tubes is next presented, in which a coupled cohesive zone model is employed to depict the response of FRP-to-steel bonded interfaces with a linear or a nonlinear adhesive. The finite element approach, which is shown to provide close predictions for CFRP-strengthened RHS steel tubes under an end bearing load, offers a valuable tool for understanding the behavior of these CFRP-strengthened steel tubes.