Effect of High Temperature (Fire Flame) on the Behavior of Post-tensioned Concrete Beams

Abstract

Experimental research was carried out to investigate the effect of fire flame (high temperature) on the load capacity of post-tensioned concrete beams to determine the residual strength after burning. To simulate the real practical fire disaster, six specimens were exposed to high temperature, (fire flame; 300, 500 and 700 ᴏC), for one hour using special furnace manufactured for this purpose. Next, cooling was performed gradually by leaving the beams in air or suddenly by splashing them with water. After that, the beams loaded till failure to determine the effect of different cooling rate on the residual strength of specimens. The results were compared with the behavior of post-tensioned beam without burning (reference beam). The average percentage of residual cubic concrete compressive strength after exposure to 300, 500, and 700 °C were found to be 80, 55, and 45 % for the beams cooled gradually and 73, 50, and 40 % for the beams cooled suddenly (high rate of cooling), respectively. The residual value of the modulus of rupture was 91, 79, and 43 % for the beams cooled gradually and 89, 74, and 35 % for the suddenly cooled beams, respectively. The ultimate load capacity of the beams decreased with increasing fire flame temperature, at a burning temperature of 300, 500, and 700°C; the average residual ultimate load capacity for gradually cooled beams were 84, 72, and 60 %, respectively. For the beams cooled suddenly, the average residual ultimate load capacity was 80, 64, and 52 %, respectively, for the same burning temperatures.