there have only been 4 building that have collasped due to fire ever. they were WTC1, 2, 7, and I think it was 5. There have been other steel frame building that have caught fire and completely burnt out the floors above them and have had fire buring in them for or 20 hrs and still didn't collapse.
when it comes to 9/11 there are not many unanswered questions and a ton of shit that does not add up. NOt bad we will never know in full detail. If our goverment had a hand it it that really sad but we will really never know.