RC beams exposed to elevated temperatures

In the first study, three-point flexural tests were carried on 15 beam specimens, having three levels of pre-existing damages (0mm, 13mm, 25mm deflection).

specimen No.6 (PC2) exposed to room temperature has tested in phase 1. (to 25mm load deflection)

specimens stored after phase 1.

Then, beam specimens were exposed to room temperature and elevated temperatures of 200 °C, 400 °C, 600 °C, and 800 °C, to determine the sensitivity of response parameters to these variables.

one of three 'type K thermocouples' located in beams to determine current temperature of core of concrete.

specimens are losing temperature in the oven after reaching 600 °C

The variation of crack pattern and concrete microstructure, crack width, load–deflection curves were examined in the studied specimens. The results showed that both the elevated temperatures and pre-existing damages had a significant effect on the crack initiation of concrete and the maximum crack width.

From up to down --> specimen exposed to room temperature - 200 °C - 400 °C - 600 °C - 800 °C

It was observed that the initial stiffness of beam specimens, with the maximum reduction of 58%, was reduced by increasing the exposed temperate with approximately the same reduction rate of compressive strength of concrete. The residual flexural capacity of beam specimens was also sensitive to elevated temperatures, showing up to 30% reduction after exposure to higher temperatures. The effect of the pre-existing cracks was more significant in the ductility ratio of beam specimens and with also a higher reduction rate of ductility with respect to temperature compared to other response parameters. The reduction in ductility of specimens with no and severe pre-existing damages exposed to 800 °C was 55% and 77%, respectively.

micro cracks due to high temprature (800 °C)

you can find more about this article on Experimental investigation of residual flexural capacity of damaged reinforced concrete beams exposed to elevated temperatures - ScienceDirect