Which material begins to distort and lose strength when unprotected at around 1000°F and will expand and twist at higher temperatures, with water able to stop elongation or buckling?

• A. Steel Construction
• B. Metal Deck Roof Fire
• C. Steel
• D. Concrete

Answer: (C)

When exposed to fire without protection, steel shows a clear, temperature-driven degradation pattern. Around 1000°F the steel’s strength falls off quickly, so it begins to distort even under existing loads. As temperatures climb higher, steel expands more, which can cause it to twist or buckle because its stiffness has diminished. Water helps by cooling the steel, lowering its temperature, and thereby stopping further elongation or buckling as the material regains strength and stiffness at the lower temperature. Concrete and other materials don’t exhibit this same combination of early distortion under load and controllable cooling-induced stabilization, so the description points to steel.