A new quantitative method of assessing fire damage to concrete structures

This paper describes a laboratory investigation into the adoption of the stiffness damage test to assess fire-damaged concrete structures. Laboratory-prepared concrete cores (75 mm diameter, 175 mm long) were fired under different heating regimes and their uniaxial compression stress-strain response at low stress level was determined. The area of hysteresis of the load-unload loops and other characteristics of the response such as the degree of concavity, the loading chord modulus, the unloading modulus and the residual plastic strain provide a quantitative measure of the extent of structural damage caused by thermal exposure. Fire-damaged specimens were also monitored by measuring the ultrasonic pulse velocity. The microstructure of the damaged specimens was studied using scanning electron microscopy (SEM) and X-ray diffraction. 320°C marked the onset of significant modification in the characteristics of the stress-strain response loops, with a sudden increase in the damage index (area of hysteresis loop...