Figure 3:
Structural
schemes
(3a)
(3b)
The core could have been designed to be strong enough for
this torsional load, but that would have meant that the reinforced
concrete (RC) walls of the core would have had to be two
metres thick; therefore a clever structural scheme needed to
be devised to eliminate or balance this load and thus reduce the
core wall thickness.
Figure 3 shows the three schemes considered. In the first
scheme (Fig. 3a) all the structural columns slope away from or
towards the centre of the building. All lateral components of the
axial forces in the columns therefore intersect in the centre of the
building, and consequently no torsion is generated. This scheme
thus eliminates the torsional load completely. Unfortunately it
detracts from the architectural spiralling form of the tower and
was not pursued any further.
In the second scheme (Fig. 3b) the columns are arranged in
an internal spiral, countering the twist of the building. By placing
the columns at the right slope it would be possible to generate
a countering torsional load equal to the primary torsional load.
Architecturally, this scheme was acceptable. Unfortunately, it
did not perform well from a space-planning point of view. The
internal ring of columns are not identical on each floor, implying
a unique space planning strategy on each floor.
The third scheme (Fig. 3c) is similar in strategy, but instead of
placing the columns internally, they are pushed out to the faces
of the building, thus clearing the floor plates for a flexible space
planning strategy.
Calculating the slope of the columns in the scheme was
however not easy. In reality, to conform to the concave, warped
façade geometry, the columns could not have a fixed slope. This is
where parametric modelling came in. Using parametric modelling
software, we were able to construct the tower’s geometry in
such a way that certain variable input parameters determine the
eventual geometry. In other words, the slope of the columns are
not fixed in the model. Instead, the parametric model sets a rule
for the column geometry, and by varying the input parameters,
various column arrangements could be explored. In this way, the
Parametric Modelling
(3c)
structural performance of the columns could be evaluated and an
optimal and aesthetically pleasing column arrangement could be
chosen. In the final chosen geometry, the columns generate a
sufficiently large counter-torsion to reduce the core wall thickness
from 2m to 450mm, resulting in significant cost savings and
added floor space.
Parametric modelling was also used in a smart way to devise
a practical façade scheme to the warped, twisted faces of the
building. A number of factors had to be considered, including
glass utilisation, façade maintenance access and integration of
Figure 2: Gravity-induced torsional loads
17