Fire Performance of Bridge Members Retrofitted With Near-Surface-Mounted Carbon Fiber Reinforced Polymer Composites

015946932015PDFTech ReportMPC 15-303Bond strength (Materials)Bridge membersCarbon fibersEpoxidesFiber reinforced polymersFire resistanceInterfacesMechanical loadsResidual strengthRetrofittingSimulationThermal analysisBridges and other structuresHighwaysMaterialsUnited StatesColoradoMountain Plains ConsortiumKim, Yail JimmyUniversity of Colorado at Denver. Department of Civil EngineeringMountain Plains ConsortiumNorth Dakota State UniversityUniversity Transportation Centers Program (U.S.)United States. Department of Transportation. University Transportation Centers (UTC) ProgramSiriwardanage, ThusharaNamrou, AbdulUS Transportation CollectionThis report presents a two-phase research program studying: (1) the interfacial response of near-surface-mounted (NSM) carbon fiber reinforced polymer (CFRP) strips embedded along a concrete substrate at elevated temperatures, and (2) the behavior of NSM CFRP strips for strengthening concrete members subjected to thermomechanical distress (thermal and mechanical loads are applied simultaneously). In the first phase, two types of bonding agents are used: ordinary and high-temperature epoxies. Residual behavior of the interface, including the characteristics of individual constitutive materials, is examined when subjected to a temperature range varying from 25\ub0C [77\ub0F] to 200\ub0C [392\ub0F]. Test results reveal that residual strength of the concrete and CFRP is not influenced by thermal exposure; however, residual strength of the adhesive is affected. The performance of the interface bonded with ordinary epoxy is better than that of the high-temperature one without thermal distress. The latter becomes superior to the former with an increase in temperature. Interaction between the adhesive and concrete controls interfacial capacity and corresponding failure mode, rather than the individual strength of the materials. Probability-based simulation that complements limitation of the experimental investigation, in terms of sample numbers, was conducted to develop design factors. In the second phase, the focus of the research lies in examining temperature-dependent interfacial responses that control the performance of such a CFRP-strengthening system. An experimental investigation was conducted to study various technical aspects associated with the thermal relaxation, heat conduction, load-carrying capacity, failure mode, and damage characterization of the NSM CFRP-concrete interface. Analytical approaches were entailed to generate practical information that can promote use of CFRP-strengthening technologies, based on the two-parameter Weibull function and probability-based capacity simulation. The thermal relaxation of a polymeric bonding agent influenced the transfer of interfacial stresses, including the stress-decrease response time of the interface with temperature. Transient heat flow was apparent across the interface until the strengthening system failed due to the thermomechanical load. The failure plane of the interface was controlled by progression of heat energy in conjunction with the phase transition of the adhesive. The slip of the interface articulated a thermal hysteresis mechanism, when loaded cyclically. The characteristic parameters proposed aided the design of NSM CFRP systems exposed to elevated temperatures.90