Structural Design of High-Rise Residential Buildings in Austrlia, Budownictwo, BUDYNKI WYSOKIE, c) artykuły, ...

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Owen Martin, FIE Aust
Connell Mott MacDonald
Owen Martin is director of Connell Wagner and a board member of Connell Mott MacDonald’s global building
engineering business. His extensive experience and most recognized skills include advance structural design
and analysis of wind sensitive, long-span, cable, and architectural structures; dynamics; and structural engineering
of high-rise buildings.
Mr. Martin is one of Australia’s leading tall building designers and has been involved in all three of Australia’s
current 85-plus-story buildings, including World Tower and Eureka. He pioneered the use of outriggers in Australian
residential buildings on the Avillion Hotel and further developed and refined this system on World Tower.
He has personally led the structural design of a large number of concrete high-rise buildings in Australia ranging
from 40 to 85 stories in height.
Advances in the Structural Design of High-Rise Residential Buildings in
Connell Mott MacDonald has designed numerous tall buildings in various parts of the world and has advanced
the state of the art in recent times in Australia. This presentation is based on a paper by the presenter and
Brian Dean, principal at Connell Mott MacDonald, and will refer to experience gained from World Tower (85
stories, 853 feet/260 meters high), Eureka Tower (90 stories, 894 feet/300 meters high), Avillin Hotel (55 stories,
541 feet/165 meters high), and others. These buildings are all slender (up to h/b = 9) and residential, and
contain many innovations in the area of structural engineering.
In particular, this presentation will examine advances in analysis techniques, structural systems (including
post-tensioned outriggers), concrete strength and technology (particularly as it relates to stiffness and
shortening), and structural systems. Results of monitoring of behavior (sway and shortening) will be presented
and discussed. A specific research study was conducted in conjunction with the concrete industry to examine
and monitor the creep properties and behavior of very high strength concrete (15,000 psi/100 MPa cylinder
strength). The results of this will be summarized.
The use of special detailing (jacking and release) to avoid permanent dead-load transfer into wind elements
(outriggers and sloping columns) will be of particular interest. This deals with the difficult problem of differential
shortening between columns and core which are connected by outriggers.
In conclusion, the presentation will contribute to the state-of-the-art knowledge in our industry in tall concrete
buildings around the world.
Advances in the Structural Design of High Rise Residential Buildings in Australia
Owen Martin
, Principal
CTBUH Member
Connell Mott MacDonald
116 Military Road, Neutral Bay NSW 2089, AUSTRALIA
Tel: 612 94655599 Fax: 612 94655598
This paper examines developments in the structural design of high rise concrete residential buildings in
Australia’s two major cities, Sydney and Melbourne. Reference is made to four projects where the use of
reinforced and post tensioned outriggers in various configurations has been successfully implemented. The
90 storey Eureka Tower project, soon to be completed incorporates a liquid mass damper.
: Outrigger, high-rise, concrete, damper.
The four projects, which are used to illustrate the developments in tall/slender concrete buildings are
summarised below:
Table 1. Four Tall Building Projects
Wind Structure
To we r s
concrete outrigger &
shear wall
The Aston
Offset outriggers
To we r
90 MPa
Post tensioned
concrete outriggers
Concrete shear
Damper at
roof level
The 55 level Hordern Towers project is 165m high with a slender basic width of 29m. At the base of the
building the core is only 9m wide and for the upper 30 levels is only 5m wide. The 400mm thick, 9m deep
reinforced concrete outriggers rigidly link the core to columns at the Level 23 plant room levels.
CTBUH 2005 - Advances in the Structural Design of Tall Concrete Buildings in Australia
Fig. 1 Typical Tower Floor
Fig. 3 - Section
Fig. 2 - Plan at Outrigger Level
The outriggers significantly reduce the bending actions in the core such that wall thickness and
reinforcement are not unduly penalised. In fact the core takes only 50% of the overturning moment in
bending. Wall thicknesses of the core at the base of the building are 500mm for perimeter walls and 200mm
for all other walls.
In the upper levels the core is further assisted by a single shear wall constructed between units to connect
the core to the facade.
A relatively simple solution to deal with differential shortening was developed which sees the outriggers
connected to the columns by flat-jacks which are inflated with hydraulic fluid. Thus they remain effective in
resisting lateral load whilst allowing any residual stress carried by differential movement to be released
periodically. Monitoring of creep movements was carried out and the final connection of the outriggers to
the columns was carried out when movements were minimal some 3 years after commencement. This has
been a most successful solution.
CTBUH 2005 - Advances in the Structural Design of Tall Concrete Buildings in Australia
An interesting building, the Aston, has also recently been constructed in Sydney and whilst only 90m high,
has a similar slenderness ratio of 7:1.
Here, an innovative wind resisting system using “offset outriggers” has been developed to reduce building
deflections and core bending stresses. This system mitigates some of the disadvantages of conventional
outrigger system, such as the outrigger arms obstructing occupiable and valuable floorspace. The offset
systems enables the outrigger arms to be placed across the full building width at locations away from the
plane of the lift cores.
These outriggers then rely on the floor diaphragms to transfer shear to mobilise the perimeter columns of
the building.
Fig. 4 – Frame Perspective
Fig. 5 – Typical High Rise Plan
The offset outriggers, consisting of two storey high shear walls 200mm thick, are located on the side
elevations at mid-height on levels 12 to 14 and at the top of the building as shown in Figure 4.
The offset outriggers limit the drift of the building and reduce the bending actions in the core, minimising
wall thicknesses and core reinforcement (core wall thicknesses were limited to 200mm even in the lower
levels of the building, resulting in a very simple and quick to construct core with no variation of thickness
over the entire thirty storeys.
A significant advantage is that the outrigger walls effectively link perimeter columns of similar load and no
problems are encountered with differential shortening between core and columns.
The effectiveness of the outriggers has seen the requirement for only a lightly reinforced core, which is
required to resist only 20% of the total base bending moment.
CTBUH 2005 - Advances in the Structural Design of Tall Concrete Buildings in Australia
The 260m 84-storey high World Tower building has eight below-ground parking levels, nine
commercial/retail podium levels with 80 commercial suites, and 665 apartments on 67 levels. It is 28m wide
and has a height to base ratio of 9. Construction of the structure was completed in June 2003.
The Structure
The chosen solution includes:
Central reinforced concrete core boxes coupled by header beams.
2 pairs of 8 storey high diamond shaped post-tensioned outrigger walls at mid-height and
three-quarter height of the building, which link the lift core to the perimeter columns.
2 storey high belt walls located at the tips of each outrigger at the level 37 and 60 plantroom levels,
which engage the entire east and west facades to the outrigger walls.
Outrigger trusses consisting of wind columns and inclined tower columns between levels 14 and 9.
Perimeter belt beams at the level 37 and 60 plant levels.
Fig. 7 - Floor plan showing elements of
lateral load resisting system
Fig. 6 - World Tower South Elevation
The plan dimensions of the typical floors in the tower are 55m x 28m, with large cantilevered balconies.
The typical residential level floors are post-tensioned slabs of flat plate construction spanning nine metres
between the core and perimeter columns. The vertical structure of the tower comprises a central core of
reinforced concrete, shear wall elements and 20 architecturally expressed columns.
With the lateral load resisting system adopted, approximately 70% of the total overturning moment acting
on the building under lateral loads in the critical direction is resisted by a push-pull couple generated by
compression and decompression forces in the perimeter tower columns.
Of the 70% of total overturning moment resisted by the perimeter columns, 8% is due to frame action
generated by the edge beams, 13% is due to the outrigger truss located at 1/4 height of the building, 30%
(the most significant contribution) is due to the lower outrigger walls, and 19% is due to the upper outrigger
CTBUH 2005 - Advances in the Structural Design of Tall Concrete Buildings in Australia
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