Reply #99: Some issues about the demise of the WTC Towers [View All]

[Carefulplease]

while the trusses were *also* bracing the walls against vertical deflections.

-- Obviously, but their loss would have no effect except maybe in a hurricane, as the perimeter walls were also braced by the structural elements I mentioned above.

(2) There were no joist girders in the truss framed floors.

--Wrong. The NIST report simply doesn't mention them. How the hell do you think the corners were supported?

The corners of the two-way floor assemblies were supported by the corner core columns. We've already been over the issues of these joist girders. You seem to be the only person on Earth to know them to have ever existed. Have you found some new evidence?

http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=125&topic_id=56836&mesg_id=99797

Some floors were beamed framed or some combination (some elevator floors were beam framed in the short span zones). The impacted and burning floors mostly were truss framed.

--You're thinking of the escalator floors, not elevator floors, and I don't think that last statement is accurate.

I am thinking of transit elevator floors such as the lobbies. The floors in the impact area of both towers all were truss framed. See the thread referenced above for references.

(3) The spandrel plates and the hat truss would not have helped much with bowing. Quite the contrary, the hat truss would have redistributed some of the load of the creeping core to the walls.

--Just the opposite. The hat trusses would have redistributed loads away from the damaged columns.

It works both ways -- whatever subsystem buckles or creeps transfers some load to the other until both are oveverloaded.

(4) Pronounced bowing would eventually leads to buckling and/or failure or splice plate connections.

--So you're admitting there was no observed buckling, but there "would" have been. Okay.

Bowing and loss of lateral support would have lead to one or the other (plastic buckling or splice failure.) I would assume that significant lateral deflection would soon lead to column failure. This is something all structural engineers who have studied the WTC demise seem to agree on.

(5) The pronounced bowing isn't an hypothesis; it is an observed datum.

--Any perimeter column bowing was a result of the top sections beginning to rotate. The certainly didn't cause it, except in the fantasy world of the 9/11 faithful.

This makes no sense. The bowing was observed half an hour before the collapse initiation. The top section began to rotate when a perimeter wall buckled past its yield point.