Experimental Study on Bonding Improvement of CFRP Strips Used for Strengthening of Steel Beams

The strengthening of aging steel structures has become a task for civil engineers in recent years. The steel girders in aging bridges are among the structures which can be effectively strengthened by epoxy bonding carbon fiber reinforced polymers (CFRP) laminates to the damaged tension face of the girders. Though this method is very simple to use, it usually suffers from the problem of debonding failure of CFRP strip used for strengthening of steel members. Therefore it is worthwhile to provide a proper and practical bonding enhancement detail. In this paper, a method of adding steel patch plates on CFRP strip is introduced. Eight steel beam specimens which are artificially damaged at their mid-span (notched) and then repaired with CFRP laminates are tested through a four-point loading setup. Also, double-lap shear tests are performed to validate the effect of using the proposed method in comparison with another anchoring method known as mechanical clamping. The effect of different bonding lengths of the CFRP laminates is investigated, too. The experimental results of the repaired steel beam specimens show that adding small pieces of steel plate (patches) over CFRP laminate and beam s flange at high stress concentration zones can increase the bonding strength about 50% in comparison with the beams repaired with no patches. The results of double-lap shear tests show that the methods of adding steel patches and mechanical clamping increase the bonding resistance up to about 59% and 35%, respectively, in comparison with the cases of without patches or clamps.