The fire proofing put on buildings in NYC is meant to last for two hours. Both building lasted just under that notably the South Tower which collapsed first because it was struck at and angle.
What do you mean by ‘’hollow beams’’?
[What do you mean by ‘’hollow beams’’? ]
Mea culpa. I meant hollow tube design. There are people, including a Berkeley structural engineering professor, who contend a more conventional structure would have prevented their collapse:
https://www.chron.com/news/nation-world/article/Engineers-society-accused-of-disaster-probe-1775659.php
[Astaneh-Asl, who received money from the National Science Foundation to investigate the collapse, insisted most New York skyscrapers built with traditional designs would survive such an impact and prevent the kind of fires that brought down the twin towers.
He also questioned the makeup of the society’s investigation team. On the team were the wife of the trade center’s structural engineer and a representative of the buildings’ original design team.
Gene Corley, a forensics expert and team leader on the society’s report, said employing people with ties to the original builders was necessary because they had access to information that was difficult to get any other way.
Corley said the society’s study was peer-reviewed and its credibility was upheld by follow-up studies, including one by the National Institute of Standards and Technology.]
Re the lack of asbestos cladding:
https://www.nytimes.com/2001/09/18/science/nation-challenged-haunting-question-did-ban-asbestos-lead-loss-life.html
[As the World Trade Center was being built in the late 1960’s and early 1970’s, scientists were learning that asbestos fibers in materials commonly used to fireproof steel beams could cause cancer in workers and bystanders who were intensively exposed to the fibers, especially around mines and manufacturing plants dealing with asbestos.
Anticipating a ban, the builders stopped using the materials by the time they reached the 40th floor of the north tower, the first one to go up.
Now some engineers and scientists — including at least one whose research supported an asbestos ban in New York City — are haunted by a troubling question: were the substitute materials as effective in protecting against fire as the asbestos-containing materials they replaced?]