A true structural steel building is composed of steel columns, steel bar joist, steel purlins, steel roof frames, and steel siding. This is all load bearing structural steel. The vulnerable area of a steel building is the exposure of this steel to extreme temps during a fire. Steel becomes weak at high temps and begins to twist and distort like a noodle in hot water. Most all steel buildings now are specified by the architect/engineer to have fire retardant spray applied to the key components to protect against high heat during a fire. Steel framing is very flexible, the bar can be bend without breaking it. The greatest advantage of steel frames is they not collapse immediately, they will bend out of shape, which is warning to inhabitants to escape. One more benefit of steel frames is in earthquake they will not collapse like other materials.
The past two decades have seen great advances in understanding of steel in fire, and it can now justifiably be claimed that more is known about steel than any other framing material in fire. These have been adopted by specialist consultancies which are at the leading edge of capability in terms of their ability to deliver efficient engineered solutions for fire in buildings.