The behavior of members during fire, as part of a structure, is different from that exhibited by
small unrestrained samples. Full scale fire tests are costly and, because fire cannot be controlled,
data is sometimes lost during testing. In this investigation 1/5 scale model frames were prepared
from normal strength, high strength, fiber reinforced, latex modified and lightweight aggregate
concrete. After heating to 800 °C, with either a superimposed load or without any loading, the
frames were assessed using Schmidt hammer and ultrasonic pulse velocity. The effect of fire on
compressive strength was studied on companion cubes made from the same concrete types. It
was found that the deterioration suffered by a member depends not only on the type of concrete,
from which the frame was made of, but also on the type of member and stress state. The Schmidt
hammer test is not suitable for assessing concrete after a fire, mainly because fire reduces the
rebound number greatly and this in turn makes readings obtained using the conventional hammer
invalid. Pulse velocity measurements reflected the internal damage suffered by members, but the
results need to be interpreted in light of materials properties, restraint, visual examination and
stress states of members within structures. Pulse velocity-compressive strength relationship was
profoundly affected by fire. For example, a UPV reading of 3 km/sec would indicate a
compressive strength of either 382 or 82 kg/cm2, depending on whether the concrete has been or
has not been subject to elevated temperature, respectively. This needs to be taken into account in
recommended procedures for assessing structures after fire. |
