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Introduction
Sitting on Benelong Point in Sydney Harbour, the Sydney
Opera House is one of the icons of twentieth century
architecture. After winning an international competition for
the design of the building, Danish architect Jørn
Utzon supervised the completion of the first two stages of
the project; the podium and the concrete shells. After years
of experimentation, much of it in conjunction with the
innovative Sydney plywood manufacturer, Ralph Symmonds Ltd,
Utzon was finalising the design for the interiors of the
building when, after considerable controversy, he resigned
in 1966. The assembled partnership of Hall, Todd and
Littlemore was commissioned to finish the interiors. A
change in brief and a more conservative structural approach
resulted in a different design. The rich and extensive
timber interiors, contrasting with the heavy concrete
masonry of the exterior, remain however an exemplary example
of the use of plywood and laminated hardwood in a public
building.
Utzon's Scheme
From the beginning Utzon envisaged timber as the primary
material for the interiors, with the warmth, colour and
tactility of timber providing a contrast with the heavy,
monochrome, load bearing concrete of the podium and sails.
The ceiling was to consist of a series of
plywood box beams radiating out from the stage and suspended
at points from the concrete arches of the shells. Each beam
was to be made up of two plywood box beams bolted together,
with acoustic insulation in the cavity inside each beam.
Spanning horizontally between the box beams was to be panels
of plywood reinforced with hot bonded aluminium. These
horizontal elements were attached to the top of one beam and
the bottom of the next creating a stepped form to the
ceiling. On the top of these panels was to be bonded 2mm of
lead for low frequency sound insulation.
Utzon saw the ceiling of the performance
halls being like a floating cloud. This was to be expressed
from the harbour side foyers where the waiting audience
would be able to see over the banks of seating, into the gap
between the top of the suspended plywood ceiling and the
underside of the sails' concrete ribs.
The ceiling was designed to be divisible
into large, separate elements that could be constructed with
services installed and finishes applied off site then
erected into position and bolted together. It was
anticipated that this would add flexibility to the
installation process.
Built Scheme
For many of the same reasons as Utzon, Hall, Todd and
Littlemore chose timber as the dominant material for the
interiors. For the timber finishes to the floors and walls,
the new architects faithfully followed the direction set out
by Utzon. However for the ceiling of the concert halls,
while still using plywood, the design took a significantly
different direction.
Throughout the interiors, prefabricated
panels of laminated Brush Box were used for flooring, stair
treads and risers and wall panels. An extremely hard and
dense timber, Brush Box was chosen for its warm, rich colour
and grain, acoustic performance and high durability.
Made up of 38mm wide kiln dried strips of
timber glue laminated together, each panel used in the Opera
House was around 1200mm wide and varied in length depending
on application. The flooring and tread panels were 51mm
thick and fastened to timber joists. The wall panels were
19mm thick and fastened to steel channels. Smaller panels of
laminated Brush Box were also used for balustrades,
parapets, and handrails.
The ceilings in the Concert Hall and
Opera Theatre, while differing from Utzon's intentions, are
still a spectacular use of plywood. Both ceilings are
constructed of White Birch plywood panels backed with
acoustic plasterboard and suspended from steel purlins. The
purlins in turn are suspended from arched steel trusses in
between the shells and the ceiling. With the trusses picking
up all the loads of the ceiling and distributing them to the
side of the shells, the ceiling itself no longer has any
structural elements like the plywood beams in Utzon's
scheme. A crown of plywood dominates the ceiling of the
Concert Hall over the stage. Radiating out from this is a
series of ribs that cascade down to their junction with the
walls.
The complex geometry of the ceiling
created several problems in its prefabrication. The crown
alone consists of eighty separate sections of plywood all of
which had to be assembled to an accuracy of 0.8mm. To cut
arcs with such precision long swinging arms were developed
to carry the plywood accurately through bandsaws. At various
points, curved cuts had to be made into already curved
pieces of plywood. A computer was used to generate the
dimensions for such cuts, an early example of this
technology's use in Architecture.
A Strategy for Design with
Timber
Timber and Acoustics
Timber has historically been used for acoustic applications
for a number of reasons. A timber surface does not just
reflect sound, but resonates slightly, giving it a
particular quality and colour. A hard surface such as
concrete reflects sound with a hard and sharp quality. In
the Sydney Opera House, the musicians were happy to have
timber used as it was a material they understood, many of
their instruments being made from timber. They were
accustomed to the quality of sound timber spaces created.
Timber is well suited to the control of
excessive echo or reverberation off surfaces in performance
and public spaces. As in Brand, Denkin & Hay's John
XXIII College chapel [07] a common practice is to clad walls
or ceilings in lecture halls and performance spaces with
spaced timber battens. This surface treatment breaks up the
sound, reducing echoes. As a contrast to many of the hard
concrete surfaces, sections of the walls in the foyers, the
two theatres and other public spaces are lined with panels
made up of spaced Brush Box battens over a sound absorbing
mat.
Quality Control
Quality control has always been an important issue in timber
design and construction, especially for interiors. Timber is
a natural and therefore variable material. This is what
gives its surface life, compared with manufactured products.
Too much variation however, especially over large surfaces,
can be undesirable. Pale colours also present a particular
problem in achieving consistency. With darker colours,
variation in tones is not as noticeable.
The architects for the final stage of the
Sydney Opera House set up a rigid quality control system
right from where the timber was milled. The White Birch used
for the Concert Hall ceiling was graded against control
samples three times: when it was cut at the mill, as it was
received at the plywood plant and when the laid up sheets
were received in Sydney for fabrication. Any veneers
differing in tone from the control samples were rejected. To
ensure matching grain in adjacent panels, each veneer was
tagged as it was cut so that it could be laid out in
sequence on the finished ceiling. Similarly, the Brush Box
used was colour graded after milling to eliminate overly
dark or light coloured strips.
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