Three-dimensional finite element modelling of the fire response of passive and prestressed near-surface mounted (NSM)-CFRP-strengthened reinforced concrete slab strips

This paper presents a numerical study about the fire behaviour of reinforced concrete (RC) slab strips strengthened with passive and prestressed carbon fibre reinforced polymer (CFRP) laminates installed according to the Near-Surface Mounted (NSM) technique. 3D finite element models were developed to simulate fire resistance tests in which the NSM-CFRP-strengthened-RC slab strips were simultaneously subjected to a service load and the ISO 834 fire. The CFRP-concrete interface was modelled through temperature-dependent bi-linear bond-slip laws. In addition to the prestress levels applied to the CFRP (0%, 25% and 50% of their tensile strength), the presence/geometry of fire protection (calcium silicate boards) was also assessed. The comparison between numerical and previous experimental results showed the models accuracy in predicting the thermomechanical response of fire exposed passive and prestressed NSM-CFRP-strengthened-RC slab strips, presenting a fire resistance decrease when the prestress increased from 0% to 50%, from 13 to 6 min when no fire protection was used, and from 152 to 127 min with fire protection. The numerical results allowed predicting the decrease of critical temperature in the CFRP anchorages with the prestress increase: 3.4-3.6Tg, 3.0Tg, and 2.1-2.4Tg respectively for prestress levels of 0%, 25% and 50% (Tg - adhesive's glass transition temperature).