EFFECT OF ELEVATED TEMPRATURE ON STRUCTURAL PERFORNACE OF R.C. COLUMNS CONFINED BY CFRP Ahmed Khalifa 1 , Adel El-Kurdi 1 , Aly Eldarwish 2 , and Alaa Morsy 3 1 Structural Engineering Department, Faculty of Engineering, Alexandria University Email:khalifa20@yahoo.com 2 Head of Construction & Building Engineering Department, College of Engineering & Technology, AASTMT Email: aeldarwish@aast.edu 3 Construction & Building Engineering Department, College of Engineering & Technology, AASTMT Email: alaamorsy@aast.edu ABSTRACT This paper addresses the structural effectiveness and thermal endurance of R.C. 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 "100 o c, 200 o c, 250 o c, and at 300 o 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 the 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, subsequently, tested under a monotonic axial compression load. Based on experimental evidence, the use of thermal insulating material improves the thermal endurance effectiveness for the insulated columns but to different extents. 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 at constant temperature 100 o c until 24 hours. While at 200 o 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 o c for 4 hours and 8hours, as it lose 42 % of its load capacity while it loss all of the confinement effectiveness at 8 hours. All columns tested at 350 o 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. KEYWORDS Thermal endurance, CFRP, insulating material, strength, heat transfer INTROUDUCTION The repair and strengthening of concrete structures is a challenging and growing segment of the concrete repair industry for both engineers and contractors. Several studies have been conducted to investigate the axial behavior of concrete columns confined with CFRP jackets 1-5 . These studies have all indicated that CFRP jackets enhance the compressive strength and axial strain of confined concrete by providing adequate lateral confining pressure to the column. On the other hand, the most commonly asked question about the use of FRP for strengthening is, quite rightly, "How does it perform at elevated temperature and fire?" However, when FRPs are used for column wrapping in interior exposures, such as in building, parking, garages, and many industrial structures, there is a real concern that FRP material will perform poorly when exposed to elevated temperature or fire. FRP materials are sensitive to elevated temperature and experience severe deterioration of strength, stiffness, and bond properties at elevated temperature. ACI 440 R-06 states that no information is currently available on the specific behavior of the bond between unprotected externally FRP materials and concrete at high temperatures 6 . This gap of knowledge is primary factor preventing the widespread application of FRP. 463