The mass of the steel and concrete building is over 1000x more than the plane and would absorb the energy of momentum of the plane without such significant damage. If you want to talk about the heat of the burning fuel weakening the steel, jet fuel is volitile, spreads out quickly and burns way too fast to transfer enough heat soak into those MONSTEROUS steel beams to weaken them. Case in point: heat treating furnaces will burn billions of BTUs over many many hours to get such enormous steel components to 1500deg, which is nowhere near the temperature where it weakens. Yes, hand-held torches can cut through steel, but that is an EXTREMELY localized heat source intentionally applied. Not like throwing jet fuel on a beam and lighting it. The steel beams are also coated for fire protection and the other building materials, floor coverings and even the furniture are all fire rated to slow the propagation of a fire, not feed it. None of these things alone would matter much, but adding them all together makes the difference to slow the heat transfer to the beams, allowing the fuel to burn out before the beams could get hot enough to weaken.
The mass of the steel and concrete building is over 1000x more than the plane and would absorb the energy of momentum of the plane without such significant damage. If you want to talk about the heat of the burning fuel weakening the steel, jet fuel is volitile, spreads out quickly and burns way too fast to transfer enough heat soak into those MONSTEROUS steel beams to weaken them. Case in point: heat treating furnaces will burn billions of BTUs over many many hours to get such enormous steel components to 1500deg, which is nowhere near the temperature where it weakens. Yes, hand-held torches can cut through steel, but that is an EXTREMELY localized heat source intentionally applied. Not like throwing jet fuel on a beam and lighting it. The steel beams are also coated for fire protection and the other building materials, floor coverings and even the furniture are all fire rated to slow the propagation of a fire, not feed it. None of these things alone would matter much, but adding them all together makes the difference to slow the heat transfer to the beams, allowing the fuel to burn out before the beams could get hot enough to weaken.
Respectfully ....