Civil Engineering Reference
In-Depth Information
Reinforced concrete mega core
(circular cross-section with
internal diameter of 10.6m and
varying wall thickness of 2m to 40cm
from bottom to top)
External
.steel spine
a
r-
10.6m
5.9-7.5m
11.4-14.6m
-13.6-15.2m
-34m
Figure 3.28
HSB Turning Torso, Malmö, Sweden, 2005
(photo courtesy of Santiago Calatrava/Samark Architecture & Design)
Outriggered frame systems have been developed by adding outriggers to shear-frame
systems with core (core-frame systems) so as to couple the core with the perimeter
(exterior) columns. The outriggers are structural elements connecting the core to the
perimeter columns at one or more levels throughout the height of the building so as
to stiffen the structure (
Figure 3.29
).
An outrigger consists of a horizontal shear truss
or shear wall (or deep beam). This structural element is a horizontal extension of the
core shear truss/wall to the perimeter columns in the form of a knee. To make them
sufficiently effective, outriggers are at least one storey deep, and have a high flexural
and shear rigidity (adequately stiff in flexure and shear). Because the outriggers affect
the interior space, they are generally located at the mechanical equipment floors in
order not to hinder the use of normal floors.
The outriggers, which are connected rigidly to the core and by hinges to the
perimeter columns, increase the effective flexural depth and so the flexural stiffness
of the system in the direction of bending under lateral loads by enabling the core to
receive support from the perimeter columns. The outrigger supports the core shear
truss/wall against bending, creating axial tension and compression on the perimeter
columns. In this way, the cantilever tube behaviour of the system is ensured, and the
stiffness of the shear-frame system is increased, while reducing the lateral drift of the
building to a significant degree.
At the levels of the outriggers, connecting the perimeter columns to each other
with belts, improves the efficiency of the system by equalising the axial column loads
along the perimeter. In this manner, the column, which is connected to the core by the
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