Visualisation of the
completed structure
NSC 15
Annual Review
Having an offset core coupled with an
inclined north elevation means that the
loads on the building are eccentric from the
main stability-giving core. To counteract
this, the north elevation, as well as the east
and west façades, have been designed as
large perimeter moment frames to add
stiffness to the building.
The core houses three banks of lifts,
one for the lower levels (1 to 12), one for
the mid-levels (13 to 24), and one for the
upper levels (25 to 35). This means the core
decreases in size towards the top as only one
bank of lifts is accommodated at the upper
levels. Again, this has helped the project
further maximise the available floor space.
Because of the building’s inclined
northern elevation, floor areas decrease from
1,466m2 on the second floor to 614m2 on
level 35, the uppermost office floor. Up to
level 21 the building has one row of internal
columns, but as the floorplates decrease
these are no longer needed and by level 24
there are none.
Commercial
Wind protection
Because of the building’s triangular-like shape and
the prevailing south-westerly winds that will hit
the structure’s narrowest point, a total of seven
viscous dampers have been installed within the north
elevation steelwork.
Viscous dampers are hydraulic devices that dissipate
the kinetic energy of the building and stop the build-up of
uncomfortable side to side accelerations in a wind storm.
Because they are built into the stability system of the
building they provide damping at a fraction of the cost
and take up less space than the more traditional ‘Tuned
Mass Damper’ or TMD.
No time to take in the
view as steel erectors
complete a bolted
connection
Topping the building is a 10-storey
triangular attic that will house plant
and maintenance walkways.
A high piece count would have
ordinarily been expected for this
structure so, in order to make the
erection process as easy as possible and
iron-out any snags, William Hare trial
erected this portion of the building at
its fabrication yard.
“Once it had been trial erected the
attic structure was dismantled and then
brought to site in the largest pieces that
could be transported and was erected
by the on-site tower cranes,” explains
Mr Perry.
The attic is a complex steel structure
designed to be erected floor level by
floor level, with each level immediately
stable upon erection. Designing the
attic in this way was vital as there is
no core this high up the building to
give stability and no internal floors to
provide any diaphragm action.
A confined site has
provided many
construction
challenges