What happens to steel structural members when they are heated by fire?

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Multiple Choice

What happens to steel structural members when they are heated by fire?

When steel is heated, it expands along its length. That expansion, even before any melting occurs, can push connected members and the walls outward if the frame is restrained. In a fire, the rising temperature weakens steel, increasing deformation, but the observable effect described here is the lengthening that creates outward thrust on the structure. The other options describe outcomes that don’t match how steel behaves in typical fire conditions: it doesn’t shorten with heat, and melting of structural steel is unlikely in ordinary building fires; cracking is not the primary response of steel to fire.

When steel is heated, it expands along its length. That expansion, even before any melting occurs, can push connected members and the walls outward if the frame is restrained. In a fire, the rising temperature weakens steel, increasing deformation, but the observable effect described here is the lengthening that creates outward thrust on the structure. The other options describe outcomes that don’t match how steel behaves in typical fire conditions: it doesn’t shorten with heat, and melting of structural steel is unlikely in ordinary building fires; cracking is not the primary response of steel to fire.

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