What it takes to weaken structural steel
 

Gasoline. Gasoline burns at the perfect temperature to weaken structural steel, 2000 degrees Fahrenheit. 8600 gallons of it also helps. Good thing jetliners aren't full of the stuff.

There are more pictures at the link but here's a couple;
http://cavimike.com/fire1.jpg
http://cavimike.com/fire2.jpg

http://sfgate.com/cgi-bin/article.cg...AGVOPHQU46.DTL

Whoa, I just read about this on Yahoo.
->here: http://news.yahoo.com/s/nm/20070429/...rash_bridge_dc

Apparently the collapse of the highway expanse was caused by a gas tanker truck that ignited shortly after it had crashed. Also said that the flames shot up more than 200 feet high during the blaze.

Whoa... we had a gas truck go up on I90 just east of Seattle a couple of years ago. It wasn't under an overpass or anything, but it still burned hot enough to destry the road underneath it.

Luckly, no one was killed... Amazing shots...

The comment about our infrastructure not being where it needs to be is sort of interesting... I don't know that you'd ever justify building your infrastructure to withstand 8600 gallons of burning fuel... that'd be way overkill.

Jason

I understood that concrete also weakens at sufficiently high temperatures.. which makes me wonder how underwater demolitions are done.....
hhmmmm.....

Demolitions rely on the concussive force of explosives placed in bored holes and the shearing force of shaped charges. If a structure is very sturdy or needs to fall in a certain direction, "kicker" charges made of concussive explosives are used to push the supports to one side after they are cut by shaped charges. For scuttling ships, charges are used to blow holes in the hull; either shaped charges cut the hole where it's intended to be or concussive charges impact the hull and displace large amounts of water, which quickly rushes back into the void made by the expanding gases, slamming into the weakened hull and puncturing it.