Degree of surface damage state caused by temperature
I (none)
The possibility of fire ignition is insignificant due to presence of streams or rivers.
II (low)
The structural components are obviously damaged. The maximum temperature reaches less than 300°C [17, 18]
III (moderate)
The structural components are slightly damaged. None of the reinforcing bars are exposed, and the damage depth is less than 20 mm. The bond strength between the concrete and the steel bars is slightly weakened. The maximum temperature ranges from 300°C to 600°C.
IV (high)
The structural components are obviously damaged. The steel bars are exposed in the local area, and the damage depth is greater than 20 mm. The bond strength between the concrete and the steel bars is seriously weakened. The maximum temperature ranges from 600°C to 900°C.
V (critical)
The structural components are seriously damaged. The bond strength between the concrete and the steel bars is seriously weakened, and several steel bars are burnt or distorted. The maximum temperature reaches more than 900°C.
