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Abstract
One of the main problems that inhibit the widespread of using FRP in constructions fields is the problem concerning the elevated temperature and fire resistance for FRP strengthening system, ifFRP strengthening system isn’t properly protected it will be totally lost when exposed to temperature above the glass transient temperature of the epoxy resin (Tg) which for most commercially available epoxy resins varies fw.m 60°c to 100°c. Accordingly special thermal and fire protection consideration must be included as an essential and integral part of the design of FRP strengthening works.
This research addresses the structural effectiveness and thermal endurance of R.e. columns confined by CFRP and subjected to elevated temperature; nine different insulating materials have been tested to protect CFRP sheets and its epoxy resin. An experimental program has been conducted to investigate the effect of different temperature levels ”below100oc, 100°c, 200°c, 250°c, 300°c, and at 350°c” and durations ”4, 8, 12, and 24 hours” on the structural performance of R.C. square columns. Subsequently, evaluate the effectiveness of different thermal protection materials in increasing their thermal endurance and decrease the heat transfer rate to reach CFRP surface. A total of 19 R.C. square columns were tested thermally using an electric furnace which constructed to serve this experimental program, it has special specifications for this specific purpose, and it is designed to have ultimate temperature equal 1000oc, subsequently, tested after being cold under a monotonic axial compression load to measure its residual capacity.
Based on experimental evidence, the use of thermal insulating material improves the thermal endurance effectiveness for the insulated columns but to different extents depend on the used insulating material thermal properties and their moisture content. This beneficial effect was tremendous with respect to granular insulating material rather than fibrous insulating materials. According to the structural effectiveness, no significance deterioration in the CFRP confinement effectiveness occurs for exposure to constant temperature 100°c until 24 hours. While at 200°c the CFRP confinement effectiveness depended mainly on the exposure duration, it lost only 13 % for exposure for 4 hours, and 20 %, 24.6 %, and 33.3 % for 8, 12, and 24 hours respectively. On the other hand, no significant loss of column ductility has been measured at this temperature level. Results also indicate that, there is a large difference between the loss in CFRP effectiveness when exposed to 300°c for 4 hours and 8 hours, as it lose 42 % of its load capacity while it loss all of the confinement effectivene at 8 hours. All columns tested at 350°c lose all of the CFRP confinement effectives and their failure mode govern by de-bonding between the CFRP sheets and concrete surface. This finding may seriously be considered for columns confined by CFRP and subjected to fire temperature.
The research used commercially finite element software (ANSYS) to conduct thermal model conducted on insulated square R.e. columns confined by CFRP sheets and subjected to elevated temperature. The model simulates the transient heat transfer through different insulating material in accordance to the furnace heating rate. The ultimate goal of the research is to provide thermal insulation guidelines that can be suggested for protecting R.C. confined by CFRP using different insulating materials according to the standard fire. Moreover, model predicts the temperature distribution through different interfaces of the insulating material and concrete specimen accurately. The thermal endurance for each insulating material has been validated with the experimental program. On the other hand, the model has been developed to simulate the rate of heat transfer through insulating material in accordance with the standard fire curve, this leads us to compute the fire
endurance and the critical time that the insulated CFRP confining system can be by fire exposures. For further validation of the model, it was compared to results in other research studies. Comparing with all available published test results to . correlation between the predicted and measured temperature is fairly accurate for time-temperature history. Finally, employing the validated FEM approach, a p study is carried out to predict the effect of insulation thickness on their fire endu