What does that have to do with the price of tea in China? It neither address HTG's point, nor did refute anything. If your steel support structure is starting to sag because it's been heated to the point where it's lost more than 60-70% of its strength, it isn't going to hold the load it was designed to.
There's also the fact that once a structure begins to collapse, it doesn't gently float down to rest at the top of the non-damaged areas. Gravity accelerates the falling portion, causing the force imparted onto the structure to spike extremely fast. It's similar to the difference between resting a sledge hammer on your foot, and having one dropped on it from six feet above the ground. The former might not even cause increased discomfort; the latter will likely break bones. This is because your foot doesn't just have to contend with the increased weight of the hammer, it also has to contend with the force imparted by acceleration due to gravity.