Tuesday, November 20, 2007

WTC Floor Construction

The following two quotes are from the FEMA report into the collapse of the World Trade Center towers.

Floor construction typically consisted of 4 inches of lightweight concrete on 1-1/2-inch, 22-gauge non-composite steel deck. In the core area, slab thickness was 5 inches. Outside the central core, the floor deck was supported by a series of composite floor trusses that spanned between the central core and exterior wall. Composite behavior with the floor slab was achieved by extending the truss diagonals above the top chord so that they would act much like shear studs, as shown in Figure 2-6.

The above photo clearly shows the truss diagonals extending above the top chord. They extend a few inches above the present floor/deck level, and will be set in the concrete floor slab, once it is poured. They are the wire-like projections from the floor/deck (at the bottom of the picture). Each 60 foot span of double truss had about 15 pairs of "shear studs" with each pair of studs separated by 40 inches. Each 35 foot span of double truss had about 8 pairs of "shear studs".

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