Sydney Architecture Images- Central Business District

Governor Phillip Tower and Governor Macquarie Tower 

architect

Denton Corker Marshall

location

Corner Phillip and Bridge Streets

date

1993

style

Late 20th-Century Late Modern

construction

reinforced concrete 227 m  745 ft 54 floors
The building is clad with 13,000 panels of granite with grey and pink tones. 
Sits on top of the Museum of Sydney, on the first Government House site.

type

Office Building

notes

Sydney's "belle of the ball" for the nineties. Incorporates an ingenious structural system to cantilever over landmarked terrace houses.
 
 
 
 
 
 
 
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Project 
Name Governor Phillip Tower 
Project Team 
- Architect Denton Cocker Marshall

- Structural engineer Ove Arup & Partners 
- Builder Grocon Pty. Ltd. 
Function Commercial office building 
Year 1993 
Location Phillip Street, Sydney, NSW 
Cost $300 million 

Building 
Type office building with parking 
Form 
- Plan shape rectangular with central core 
- Number of stories 64 levels with 10 basement levels 
- Typical floor area 1872 sq m (52m x 36m) 
- Net rentable floor area 1400 sq m 
- Number of zones 4 - offices, plant rooms, foyer area and car parks. 
Relationship to ground ground level pedestrian entrance, 10 basement floors for parking and 
plant facilities 

Primary Structure 
floor system 
- material reinforced concrete 
- type reinforced concrete beams and slab 

- pattern one-way floor slab on parrallel (E-W) beams 

- beam clear span 12 m 

- floor slab span 4 m 
core structure 
- material reinforced concrete 
- type shear walls 
- shape rectangular 
- position in plan central 
support structures 
- material reinforced concrete and composite structural steel/concrete 
- types external columns, transfer structure and outrigger trusses 
footings 
- material reinforced concrete 
- type pads for columns and raft slab for core 


Design requirements 
Governor Phillip Tower is located within the first Government House site which is in the heart of 
Sydney's CBD and is bounded by Bridge, Phillip, Bent and Young streets. The site contains 
heritage listed terrace housing along both Young and Phillip streets as well as the important 
remnants of the footings of both the original, and many extensions to, the first Government 
House. 

The brief called for a state of the art quality high-rise office building, in terms of both the 
design and construction, with maximum site development. The total rentable office space of 55,000 
square meters is to be provided with each office floor having a minimum net rentable area of 1400 
square meters of flexible floor space. In addition, the design should maximise floor efficiency, 
allow for optimum flexibility in tenancy planning and provide parking for 650 cars, while 
retaining the terrace housing and the remnants of the footings undisturbed. 

The building designed to meet the above requirements was 250 meters tall with 64 levels above 
ground and ten levels of basements. The lettable office space occurs from level 21 onwards, which 
is 40 meters above Young street. The typical office floor is rectangular in plan with dimensions 
36 m by 52 m, has an overhang of 8 m on the eastern facade over the Phillip street terraces and 
includes a central 12 m wide core with clear 12 m space around it. The plant rooms are double 
floor heights and occur at levels 31,51 and 62. 

The structural design requirements arising from these decisions are a span of 12 m for the office 
floor system, a floor to floor height of 4.05 m and an overhang for the floor system of 8 m above 
level 21. A system to provide lateral stability to the building by stiffening the slender core in 
the East-West direction, supports that avoid the remnants of the existing footings and a smaller 
functional module of 8.5 m x 8.5 m for the car park floors. 

In addition, office floor slabs are required to carry 4 kPa ( 3 kPa for general area and 1 kPa 
for partitions) for general areas and 10 kPa for compactus zones. The foyer structural elements 
are required to carry a design live load of 5 kPa with 1.5 kPa for finishes, while the car 
parking and loading dock areas are required to carry 3 kPa and 10 kPa respectively. Plant room 
slabs are required to carry a general live loading of 7.5 kPa along with 2 kPa for partitions. 

Structural Systems Alternative 
In response to the brief, two options of the built form were considered:- 

(a) a building form with its three central facade columns striking through the terraces, 

(b) a rectangular tower overhanging the terrace housing. 

Option (a) is not appropriate as the terrace houses have to be preserved. Thus, option (b) is 
used. 

Transfer Structure 

The following are the three alternatives considered for the transfer structure: 

(i) 12m deep cantilever trusses connected to the east side of core only. 

(ii) 12m deep truss spanning the full width in N-S direction under the eastern facade columns 
supported by the end columns located outside the terraces. 

(iii) 12m deep trusses transversing the tower from the east to west facades. 

Option (iii) was chosen because it is the most suitable system tested against economy, 
buildability and architectural requirements. 

Lateral Stability System 

The core is slender in the east-west direction as the aspect ratio of 14 is not achieved, for the 
core alone is insufficient to resist wind forces. There were three options to solve the problem: 

(i) increase the width of the core 

(ii) provide tube in tube system by modifying the facade with additional columns. 

(iii) strengthen the central core with outrigger trusses system connecting core and facade 
columns. 

Option (iii) was used since the first two did not satisfy the brief and architectural 
requirements. 

Final Structural Solution 

The project proposed to meet two, sometimes conflicting, aspects of the brief which resulted in a 
64 storey rectangular building which had to overhang the Phillip street terrace housing. This 
250cm tall building with a typical floor of 36m by 52m had an ideal service core of only 12m 
wide. 

The major structural challenges were to: 


develop a lateral stability system in the east-west direction to replace or augment the very 
slender service core 

provide a structural system, integrated within the architectural form, to support the overhanging 
eastern facade above the terrace houses 

provide within the design, structural systems and techniques which would assist the builder with 
the shortest possible construction time While considering possibilities in structural design 
solutions, Arup attempted to reduce the risk factor to the client by adopting tried and tested 
construction methods where possible. They also tried to minimize the cost and quantity of 
construction by using new technologies and active methods of control where appropriate. 

The usual construction of an Australian high rise building is in reinforced concrete. In fact the 
local industry has perfected this technique to a degree which few other countries can challenge. 
The building normally has a slip or stage formed concrete service core which also provides the 
lateral stability system. Unfortunately, as the building get taller, this system starts to 
seriously compromise the planning as the core must get wider to fulfil its stability function. 

The American solution to this problem is to use the "tube-in-tube" concept where the facades 
activated in bending as a giant tube in conjunction with the inner service core. As a result the 
facade tend to become a solid wall punctured by small window openings. This proved to be an 
undesirable solution since the view of Sydney Harbour is one of the most breathtaking in the 
world, and as a result would act as an important parameter in the pricing of rental property. 
Furthermore, this option would have been considerably more expensive and taken longer to build 
than the normal construction. 

The final solution was to introduce steel outrigger trusses to link the core to the facade 
columns and increase the stiffness of the building only where necessary. A similar effect could 
have been created using concrete shear walls, but they would have severely affected planning. 

The outrigger system had the potential problem of unwanted vertical interaction with the core. 
Instead of using more material to make the trusses stronger, the structural engineers develop a 
sequence of disconnecting the trusses periodically throughout the construction period to avoid 
any potentially damaging stresses. 

The cantilever of the eastern facade was dealt with by using steel transfer trusses which spanned 
right across the building. Any deflection of the tip would have a major impact on both the 
construction and performance of the upper floors and the building cladding. the effect was 
minimized by controlling the deflection in an active manner by both precambering and 
post-tensioning the trusses. 

The consulting engineers also devised a construction sequence which turned the transfer trusses 
from a difficult item which could severely impede the programme into a huge time saving. They 
were prefabricated and erected in such a way that the typical floor construction cycle could 
commence whilst the basement construction was barely under way. A similar technique was to remove 
the outrigger truss assembly from the critical construction path. 

having adopted the structural solution above, Arup over came the challenges to the structure 
whilst giving as much freedom as possible to both the planning and construction. Thus, minimizing 
cost and materials used in the building as well as ensuring that it could be build in the 
shortest time possible, without compromising the quality of the final product. 

The structural elements that contribute to the different functional systems are: Structural 
types: concrete floor,composite steel deck, core, facade columns, transfer truss 
material- composite steel/concrete/steel 

Structural type: core, outrigger truss
material - reinforced concrete, steel 
Structural types: raft slab , column, footings.
materials - reinforced concrete 

Design Decisions 
The brief was very difficult to satisfy, demanding a highly efficient, large floor plan, 64 
storey tower of the highest quality on a site where heritage listed terrace housing and the 
remains of Governor Phillip's House left little space at ground level. To make the development 
more commercially successful the construction also had to occur in the shortest possible time. 

The best way to satisfy the brief from a planning point of view, was to cantilever the east face 
of the tower some eight metres out of the historic terrace houses, 40 metres below. A very narrow 
service core of only twelve metres wide in the east-west direction, was required to obtain the 
ideal planning efficiency. To compensate for the slenderness of the core, steel outriggers were 
introduced at two levels of plantrooms. This combination of steel and concrete is not without 
problems and it's believed to be the first time such a hybrid system has been used. 

From the beginning, structural design of the building had to satisfy the difficult constraints 
applied to the structure whilst giving as much freedom as possible to all other parties involved 
in the design and construction process. The structural system selected did not impinge on the 
ideal planning; it utilised the best of Australian construction practice for the majority of the 
building; and it introduced new technology to augment this construction, not only in terms of 
structural performance, but also in minimum use of materials. 

Steel outrigger and belttrusses were inserted at plant room levels to mobilise the openly spaced 
concrete facade columns while leaving the lateral shear force in the concrete core walls. This 
composite structure had the desired performance under wind loads. The outrigger structure was 
specifically designed to allow the typical floor construction to proceed upwards ahead of the 
truss installation, thus removing it from the critical construction path. 

Another major addition include massive steel trusses inserted below level 21, the first office 
floor, to cantilever the east facade out over the terrace houses in Phillip street. To emphasise 
their presence, they were mounted on huge steel box columns which sprang from the foundation 70m 
below. 

The box columns were installed early in the program, in parallel with the jump-formed core. the 
trusses were simultaneously pre-assembled at ground level prior to being winched up to level 21 
as soon as the columns and core were ready. A steel supported slab was then constructed at level 
21 to allow the typical floor construction cycle to commence whilst the basement was yet to be 
fully excavated and constructed. A more conventional programme would have taken 15 weeks longer 
to reach this stage. 

Both the above structural items could have caused difficult interaction problems with 
deflections. Instead of just adding material to control these, it was decided that a more 
sophisticated analysis and active method was employed to control them. 

References 
Governor Phillip Tower, Specifier Vol.3 1994 pp. 114-116 Commercial Award. 
Governor Phillip Tower, AB July 1994, Architectural Awards: Sir John Sulman Award Commercial 
Governor Phillip Tower, Australian Architecture Vol. 83 No.6,pp.52-53 
Governor Phillip Tower, National Architectural Awards 1994 

Thanks to http://www.arch.usyd.edu.au/kcdc/caut/html/GPT/front.htm 
  www.sydneyarchitecture.com 

links