PSI - Issue 42

Maha Assad et al. / Procedia Structural Integrity 42 (2022) 1668–1675 Assad et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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common are externally bonded reinforcement (EBR), where FRP is attached to the concrete surface by a bonding adhesive or via near-surface mounting (NSM) technique, which involves bonding FRP strips or rods inside grooves in the concrete cover (Rasheed, (2015)). Both strengthening systems offer significant enhancement to the strength of RC structural members. Nevertheless, RC beams and slabs strengthened using the NSM method show better bond performance between the FRP and concrete interfaces (Firmo et al., (2015)). The behavior of FRP strengthening systems under elevated temperatures has been extensively studied in the literature since FRP composites possess poor performance under fire conditions. Specifically, the bond between the FRP material and concrete is highly degraded at increasing temperatures (Firmo et al., (2018)). It was found that the mechanical properties of both the FRP and the bonding matrix are decreased due to the softening of these adhesive materials at their glass transition temperature T g , which is typically between 45 and 120 ℃ (Azevedo et al., (2022)). Also, if the matrix is organic, which is the used matrix in almost all cases, then the matrix will decompose at temperatures of 300 – 500 ℃ (Carlos et al., (2018)). This means that FRP strengthening system will be subjected to failure in incidents of fire. Thus, studying the performance of FRP-strengthened structural members under elevated temperatures is crucial to propose safety guidelines and develop effective fire protection systems. Several investigations have been conducted to study the behavior of CFRP-strengthened RC structural members under fire (Ahmed et al., (2011); Bhatt et al., (2021); J. P. Firmo & Correia, (2015); M. Naser et al., (2012)). (Ahmed et al., (2011)) tested RC beams externally bonded with CFRP sheets exposed to fire and service load. The authors inspected several variables including type of fire exposure, anchorage zone, and insulation type. Their test results indicated that anchorage and insulation can significantly improve the fire resistance of RC beams. Carlos et al., (2018) assessed the influence of different insulation materials on the fire resistance of externally bonded RC beams through an innovative testing apparatus, where the beam and its supports were completely in the furnace. The behavior of EB RC beams was assessed in other research studies as well (Firmo et al., (2015); Firmo and Correia, (2015); João P. Firmo et al., (2012)). Papers studying the performance of NSM-RC members are much less available in the literature. Firmo & Correia, (2015) tested RC beams strengthened with NSM-CFRP strips. The authors analyzed the efficacy of different fire protection schemes along with other influential variables as well. Similarly, CFRP-strengthened slab’s behavior under fire exposure was rarely examined in the previous experimental tests. (Azevedo et al., (2022)) tested the fire resistance of RC slabs strengthened using different techniques: EBR, NSM, and continuous reinforcement embedded at the end (CREaTE). The authors studied the effect of the fire protection layer thickness on the improvement of the slab fire resistance and concluded that the CREaTE technique provided the best performance with fire protection, while EBR offered the least fire resistance whether with or without fire protection. (Bhatt et al., 2021) also tested several protection schemes’ effects on the performance of EB-RC slabs and concluded that fire-protected slabs can withstand three hours of standard fire exposure. Finite element modeling (FEM) has been a powerful tool for predicting the response of structures and thus avoiding the hassle of expensive, time-consuming experimental tests. In particular, testing structural members under fire requires considerable endurance, from having suitable temperature-controlling facilities and maintaining the standard temperature for 2 to 8 hours (ASTM E119 (2000)). Moreover, the development of FE models allows researchers to inspect a limitless number of variable s that affect the structure’s performance. Therefore, many attempts were directed toward the simulation of the behavior of RC members under fire (Abdalla et al., (2020); Hawileh, (2012), Assad et al., (2022); Hawileh et al., (2011), (2018); (2017); Naser et al., (2012); Naser et al., (2021) ) . Most of the studies mentioned above have also contained the development of a FE model that can predict the obtained experimental results. Other FE papers investigated the fire behavior of CFRP-strengthened RC beams using EBR and NSM techniques. However, few of the papers simulated the fire performance of strengthened RC slabs. In fact, the only numerical investigation of the fire resistance of slabs was conducted by (Ahmed et al., (2011)), and the slabs were strengthened by EBR only. Therefore, the literature still lacks information about the comprehensive understanding of the parameters that affect the fire resistance of strengthened RC slabs and the influence of FRP configuration and application technique on the bond performance and overall performance of the slabs. Therefore, this study aims to develop a 3D FE model that can predict the thermal and mechanical response of strengthened RC slabs under standard fire exposure. Two different strengthening techniques were studied: EBR and NSM. In addition, Temperature-dependent material properties were incorporated into the FE model. The results of the numerical model were compared and verified with previously published data (Azevedo et al., (2022)).