Zinc melts @~420 F. You can melt zinc in a frying pan on your stove, all you'll need besides a hunk of zinc is a hunk of steel.

That paper describes a very limited set of circumstances and alloys LME affects, not ordinary steel but austenitic stainless steel. Not one girder in the Twin Towers was made of stainless, so LME didn't contribute at all to the 9/11 demolition.

I can appreciate how the specific details of LME are a bit esoteric, and note you're a welder, not a metallurgist. However, the hypothesis regarding 9/11 isn't supported by the paper you link, and you seem to write well, indicating good intelligence, so I think you should be competent to understand the paper.

"...the heat of welding can readily induce liquid metal embrittlement cracking in 300 series stainless steel when it is welded to galvanized carbon steel..."

That's the only conditions in which LME is produced according to the paper.

I hope your understanding now includes that LME only affects austenitic stainless steel, which does not include the support structure of the Twin Towers.

BTW, don't melt any zinc without a full respirator. The fumes from boiling zinc are extremely toxic. Never, ever weld galvanized steel without a respirator. An ordinary mask won't stop the vapor.