Tall Building case studies - Tall Buildings: Structural Systems and Aerodynamic Form - page 131

“H” cross-sections. The core columns, varying in number between 44 and 47, were
supported by steel braces at the mechanical equipment floors and the atrium at the
ground floor.
Outriggers were used at the roof to contribute to the framed-tube system's stiffness
against wind induced lateral loads ( Figure 4.29 ). The outriggers connected the core
and the perimeter columns in both directions.
The composite floor slab system of WTC I-II ( Figure 4.30 ) outside the core
consisted of a row of main double trusses spaced 203 cm apart with a depth of 74 cm
spanning spaces of 18.3 m and 10.7 m, and, perpendicular to these, a 10 cm thick
reinforced concrete layer on 3.8 cm thick trapezoidal metal deck resting on transverse
(secondary) trusses spaced 406 cm apart. The floor slabs were 13.8 cm thick outside
the core and 16.5 cm in the core.

Steel
outrigger

Figure 4.29 WTC I-II outrigger location at the upper storeys

(a)

centerline

Core

Transverse
truss
(with a
spacing o f
406cm .)

M ain
double
truss
(w ith a
spacing o f
203cm .)

4>
_C
0 >
c O) o