Behavior and flexural strength of fire-damaged high-strength reinforced rectangular concrete beams with tension or compression zones exposed to fire repaired with CFRP sheets

Motivated by the fact that fire is one of the most dangerous threats to buildings and structures, the main goal of this research is to determine the residual flexural capacity of high-strength simply supported reinforced concrete beams after exposing the tension and compression zones to various fire exposure intervals, as well as the effect of strengthening using carbon fiber reinforced polymer CFRP laminates. Ten simply supported high-strength reinforced concrete beams 2000 mm in length, with a cross-section width 200 mm and height of 250 mm, were tested to failure after exposure to standard fire ISO-834 or ASTM E-119 for 45, 90,120 min and strengthened with CFRP sheets. The beams were classified into three groups. A series of nine beams were exposed to standard fire for various exposure times, in addition to the control beams. Following that, carbon fiber reinforced polymer at the soffit were used to strengthen three fire damaged beams. And, the compression faces of three beams were exposed to fire. All specimens failed in a flexural mode, with minor spalling, according to the test findings. The beam subjected to fire for two hours lost 12% of its strength without exploding, although the deflection at failure was almost identical to the control beam. It has been noticed that using EB-CFRP to reinforce fire-damaged beams considerably reduces the impacts of fire exposure. It was also enough to restore the majority of the stiffness that had been lost. The reduction in ultimate flexural-bearing capacity for beams with compression faces exposed to fire was greater than the drop for beams with tensile faces exposed to fire. The beam subjected to fire for two hours had a 35% reduction in ultimate load. When exposed to fire for 90 and 120 min, the ductility of the compression zone exposed to fire beams was reduced by roughly half. The behaviour of the fire-damaged specimens was properly predicted using simple plane section analysis and the assumptions of the 500 °C isotherm method stated in EN-1992–1–2 (2004).