NSC 31
June 19
grouted up only after all umbrella steelwork
is complete and the final tensioning has been
carried out. The anchor blocks will then be
completely encased in concrete.
With the core completed and the anchor blocks
in position, erection of the steelwork, generally
of high yield stress quality, could begin.
The main elements from which the floors are
suspended are 15ft 1in deep lattice girders
at the periphery of the building. These are
supported at plant room floor level by a series
of cantilever struts, consisting of four 17in × 4in
channels built into a concrete ring beam on the
outside of the core, which are in turn supported
by ties from the anchorage blocks. Each tie
comprises three 18in wide plates in parallel, the
outer ones being ¾in thick, and the central one,
1½in thick. The top booms of the lattice girders
are tied back to the core through plant room and
roof steelwork.
The hangers, suspended outside the lattice
girders, are at 8ft 1¼in centres around the
building. At the four corners, 8in × 8in × 1in
angles are used for the full length of 166ft 9in.
All other hangers consist of two 9 × 5/8 in plates
from the top down to 7th floor level and then
they are single plates of the same section.
At the top of the building the hangers extend to a
height of 3ft above the highest roof level to form
a parapet. They are tied together on their inner
edges by a parapet rail of rectangular hollow
section. There is a similar extension below the
3rd floor (the bottom suspended floor). With
the rectangular hollow section mullions placed
centrally between them, the hangers form a
uniform vertical feature.
In the design and fabrication of the hangers,
account had to be taken of extensions due to
loading and movements due to temperature
changes. The components of each hanger were
therefore laid out in the shops against a full
length template, the splices are made with
high strength turned barrel bolts., and the floor
beams are connected to the hangers by a single
1¼in diameter pin of high yield stress steel to
permit articulation.
The floors consist of simple steel framing with 2in
Half floor being raised on the lifting rig
thick prestressed concrete planks surmounted
by 2in of structural topping. Although erection
proceeded from the top down, the floors were
in fact prefabricated (except for the topping)
in two halves on lifting rigs mounted on top of
the podium and winched up. Erectors travelled
on the completed half floors and fixing was a
reasonably simple matter.
The steel floor beams trim into a fascia channel,
which also serves to support cladding, at the
outside and into another channel fixed to
brackets set in the concrete core. The inner
ends of the beams rest on rocker bearings so
that, with the pinned connections to the hangers,
articulation is possible at both ends.
The floor steelwork, protected against fire
by sprayed asbestos, will be concealed by a
suspended ceiling above which air conditioning
ducts and other services will be housed.
Cladding
The Hearts of Oak development is unique in that
the hangers are external to the cladding. This
has been done to obtain the maximum usable
floor area and they achieve a prominent external
architectural feature. All the hangers will be
clad in stainless steel which will be shaped to
form vertical tracks for the maintenance cradles.
The intermediate mullions, likewise external
to the enclosing envelope and clad in stainless
steel, will also serve a dual purpose. In addition
to supporting the glass and block granite infill
panels, they will be used as air conditioning
ducts and will thus help to conserve space inside
the building. The glass itself is unusual; the type
to be used has been specially chosen because of
its anti glare and insulating properties so that
occupants will be able to work in comfort and the
air conditioning plant will be smaller because of
the reduced refrigeration required.
Podium
This consists of a basement for parking cars and
two floors for additional offices. The basement
and the exterior beams above ground level are of
reinforced concrete construction but all interior
framing for the offices is of steelwork, high yield
stress steel again being used to minimise weight
and conserve space. Large circular holes in the
webs of the floor beams throughout their length
serve for the passage of services within a limited
floor depth.
A roof garden is planned for the open area
above the first floor, whilst the part under the
suspended building will provide a covered
concourse.
Architects for the development are Sidney
Kaye, Eric Firmin & Partners, the Consulting
Engineers are H L Waterman & Partners and
Basil A Cohen & Partners are the Quantity
Surveyors.
Construction of the core and podium commenced
in June 1967 and it was topped out complete
with core cap and anchorages in October 1968.
The steel work erection took 24 weeks and the
project is due for completion in late 1969.
Completed core with anchorage and cantilever
struts and ties in position
View at the halfway stage
50 Years Ago