Study the behaviour of normal and lightweight R.C. columns under effect of fire

The properties of steel bars, fibre bars and concrete material are severely affected when the reinforced concrete R.C. columns are exposed to high temperatures by fire. Three types of reinforcing were used: steel bars, glass fibre reinforced polymer bars G.F.R.P, and hybrid reinforcing (steel bars and fibre bars). In comparison to unheated column specimens, the heated columns showed an increase in width and number of cracks. These columns with the three different types of reinforcement were exposed to very high temperatures, in order to know the extent of the effect of this temperature on the properties of concrete and the reinforcement used, as well as to know the weakest and best reinforcement at high temperatures. It was noted that steel reinforcement was the best, while fiber reinforcement was the weakest at high temperatures. The force required to cause a first crack is lower when the specimen is subjected to higher temperature values. All specimens’ axial and lateral displacement values increased as the eccentricity ratio or applied load values rose; the reason for this because the heating causes a drop in specimen stiffness because the elastic modulus of concrete decreases, and the depth section of the specimen also due to the thermal effect and appear the cracks due to expansion of concrete that subjected to high temperatures. The increasing or decreasing in lateral or axial displacement values for all specimens and decreasing in load value due to eccentric load value or due to increasing the heated temperature may be attributed to the low axial and lateral elastic stiffness property of these columns and also due to the low axial and lateral ductility index values, where the elastic stiffness values and the ductility in all specimens decreased due to increase the eccentric value e/h from 0 to 1, and also due to increase the heated temperature from 20 to 700 °C.