Fire protection systems for reinforced concrete slabs strengthened with CFRP laminates

This paper presents experimental and numerical investigations on the fire behaviour of reinforced concrete (RC) slabs flexurally strengthened with CFRP laminates, aiming at developing a methodology for the design of fire protection systems. The first part of this paper summarises the main experimental results obtained from fire resistance tests on loaded RC slab strips strengthened with CFRP laminates according to the externally bonded reinforcement (EBR) technique. Fire protection systems, comprising calcium silicate (CS) boards or vermiculite/perlite (VP) cement based mortar, were applied along the bottom soffit of the specimens; in addition, the anchorage zones of the CFRP laminates were highly thermally insulated. Such protection strategy provided remarkable extensions of the fire endurance, as it was able to provide considerable reduction of the temperature of the strengthening system, (i) maintaining it below a certain limit in the current zone and (ii) keeping it beneath the glass transition temperature (Tg) of the epoxy resin along the anchorage zone. The numerical study described in the second part of this paper included the development of (i) 2D finite element (FE) thermal models of the tested slab strips, which were validated based on the agreement between calculated and measured temperatures, and (ii) 3D FE thermal models of CFRP-strengthened RC slabs. The numerical thermal models were used to design different fire protection systems based on the above mentioned strategy. In particular, the numerical study investigated the effect of the following parameters on temperature distributions along the CFRP strengthening system: (i) geometry of the fire protection system, namely at the anchorage zone; (ii) strengthening technique, namely EBR or near surface mounted (NSM); and (iii) Tg of the epoxy resin.