The vibration-based assessment of the influence of elevated temperature on the condition of concrete beams with pultruded GFRP reinforcement

Abstract

Concrete beams reinforced with glass fiber reinforced polymer (GFRP) bars subjected to elevated temperature have been experimentally studied. The influence of high temperatures on GFRP-reinforced concrete beams condition has been check both, destructively and nondestructively. The nondestructive tests foresaw vibration-based tests to obtain the natural frequency values after exposure to varying temperatures. The vibration-based tests allowed for the indirect observation of beams stiffness reduction after exposure to elevated temperature. The approach based on frequency response function (FRF) turned out to be efficient even in the case of relatively low temperatures (120 °C). The investigation involved also destructive tests which were conducted in various conditions: once the bending load and elevated temperature were applied at the same time and in the next case, the destructive tests were conducted after heating and cooling down the experimental objects. The study proved that the increase of the temperature causes the reduction of characteristic mechanical parameters, regardless the beams were cooled down or not. However, the simultaneous action of bending load and elevated temperature resulted in a greater reduction of the ultimate strength of tested objects.