Office fires can burn at a maximum of 1,800 - 2,000 Degrees F but only for a short time. Not anywhere near long enough to melt steel as has been demonstrated in many fires. Debris pile fires burn at much lower temperatures.
Thermate is the only known explanation for the melted beam.
What was witnessed was not "melting" in the normal sense of a mass phase change from solid to liquid. You've had this presented to you dozens of times, Christopher7, and in great depth. Why are you repeating the same worn-out claptrap?