Fire behaviour of thermally insulated RC beams strengthened with EBR-CFRP strips: Experimental study

This paper presents experimental investigations on the fire behaviour of reinforced concrete (RC) beams flexurally strengthened with externally bonded carbon fibre reinforced polymer (CFRP) strips. Different fire protection schemes were studied, comprising a thinner insulation layer along the bottom soffit of the beams and a thicker one at the CFRP anchorage zones. The main goals of this investigation were (i) to understand in further depth the structural effectiveness of CFRP strengthening systems during fire and (ii) to evaluate the efficiency of the above-mentioned fire protection strategy in extending the CFRP mechanical contribution; in addition, the (potential) beneficial effects of (iii) applying mechanical anchorages at the CFRP strips, and (iv) using a bonding adhesive with high glass transition temperature (Tg) were also evaluated. The results obtained showed that the strengthening system is able to retain its structural effectiveness through a cable mechanism, even after the CFRP strip debonding in the central zone of the beams; it was possible to extend the fire endurance of the CFRP system up to 70 min and the debonding of the strengthening system occurred when the average temperature in the adhesive at the anchorage zones attained values from 1.2 × Tg to 1.5 × Tg.