Posted by d on January 10, 2002 at 14:17:46:In Reply to: Re: SurePlate steel building connections WTC?? posted by Paul Malo on January 10, 2002 at 09:27:21:
I've gone back to the sources from which I (and many in the public, most likely) got my somewhat confused impressions of these structures:
From GreatBuildings.com:
"..prefabricated steel lattice with...columns...acting as wind bracing to resist all overturning forces. The central core takes only the gravity loads of the building... A light ...structure results by keeping wind bracing in the most efficient place.. thus not transfer the forces through the floor membrane to the core..."
"...floor construction is trussed steel, only 33 inches in depth, that spans full 60 ft to core..."Fr. Architectural Record, Oct 01
" ..the buildings' central core carried only the dead load of the elevator bank.."
CEO of Skilling WMB : it appears "floor lost connection to exterior columns.."
N. Stubbs, Professor of Civil Eng., Texas A&M: "..the floor provided the perimeter columns with resistance against buckling.."Fr. Tower Talk , 15 Sep 01 : " ..exterior column grid forms a square tube in plan to resist wind and earthquake loads, in tandem with inner core..."
Then a precis of Ngon Nguyen from Oct 3, this Forum:
Visco-Elastic Dampers
1." ..continuity moment at end of joist girder.."
2. ""..restrained the lower chord...it stabilized the concrete diaphragm..transfers compression load through bottom chord.."
3 "..joist-column connection is a moment connection..."
"...reduced energy to be absorbed by girders and columns under wind load.."
My apologies if any quotes have errors; I tried to be as accurate as possible.
I have also recently seen (I can't find it at the moment) a story which actually assigned percentages to the loads assumed by the exterior vs. the core structures.
From the lay perspective, and thus corrected by your comments and these researches, it does seem that the trusses were basically carried at each end by columns, either solely by upper chord ends or additionally by the "VED" connections, and are not described anywgere as "cantilevers".There is a question in my mind which persists, though ; aren't these rather long trusses to be only 33 inches deep ?
Also; in some diagrams and at least one photo, there appear to be diagonal truss elements running from the corners of the central core to the exterior corners ; wouldn't these be even longer than the 60 ft.?
What was the actual "activity" of the trusses? Were they "stretched" from core to exterior wall, "resting" on plates at either end, or
"pushing" against their end connections? Or some combination?This is perhaps why I am in graphics and not an Engineer....
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