brian uy, professor of structural engineering & director ... · professor of structural...

Recent Innovations for Steel and Composite Steel-Concrete Structures in Australia

Brian Uy, Professor of Structural Engineering & Director, Centre for Infrastructure Engineering & Safety

Abstract Structural steel and its use in Australia can be traced back well over a century with its use in iconic bridge projects and prolific widespread use in general. Its prolific use in building projects has a much shorter history of half a century in multi-storey buildings of the 1960’s in Sydney when building height restrictions were lifted. This paper will trace the advancements and achievements in structural steel in bridges and building projects, stadia and transport infrastructure in Australia over the last century. The development of Australian Standards for the use of structural steel and composite steel-concrete structures in buildings and bridges will also be provided. This will include a review of the current project on the Australian Bridge Design Code AS5100: Part 6 for Steel and composite structures and Part 8 which also includes new aspects to deal with retrofitting and strengthening to deal with the current challenges facing the management of ageing infrastructure. The paper will also review aspects of the new Australia/New Zealand Standard AS/NZS2327 on Composite steel-concrete structures for buildings which incorporates the design of slabs, beams, columns and systems as well as the mooted development of a Australia/New Zealand Standard on Steel structures AS/NZS 4100. The paper will conclude with an analysis of the future, including a review of existing and future building and infrastructure projects and the use of structural steel. Future research into structural steel in Australia will also be provided at the conclusion of this paper.

Structure • Introduction • Bridges • Buildings • Stadia and special structures • Transport infrastructure • Australian standards • Further research • Conclusions • Acknowledgements

Introduction Major civil engineering projects involving structural steel include the 124 year old rail crossing of the Hawkesbury River north of Sydney and the 81 year old Sydney Harbour Bridge. The Hawkesbury River rail bridge was designed and built by the Union Bridge Company from New York, USA and officially opened in 1889. The Sydney Harbour Bridge completed in 1932 was based on a general design by the NSW Department of Public Works but heavily based on New York’s Hell Gate Bridge and with detailed design by Dorman Long and Co, Middlesborough, UK through Sir Ralph Freeman and Sir Douglas Fox.

Australian buildings using innovative steel construction developed significantly after the lifting of height restrictions in the Sydney Central Business District. This period saw the design and building of the AMP building in Alfred Street fronting Circular Quay. This was 45 stories in height and was Australia’s tallest building when completed in 1976. Furthermore, Australia’s tallest structure was the Centrepoint Tower now known as Westfield Tower, completed in 1981 which used AUSTEN 50 high strength weathering steel of nominal yield stress of 350 MPa in its construction.

The advantage of the use of composite construction has been less well detailed and probably would date back to post second world war developments. It is assumed that the use of composite construction techniques in Australia may have also been used for well over a century, however significant iconic structures that can be reported on appear to only be approximately 50 years old, with significant bridges and buildings in New South Wales, possibly the first to have utilised these techniques. The Hawkesbury River Road Bridge completed in 1977 was designed and constructed as a steel box girder bridge with shear connection making the concrete deck composite through the top flange.

The NSW Government Offices completed in 1965 and demolished in 1997 was Australia’s tallest skyscraper on completion in 1965 reaching 38 levels. This building relied on innovative methods of construction to achieve speed of construction and employed many composite construction methods, namely composite beams spanning 10 metres, composite slabs utilising metal decking. Furthermore, this building involved the first major use of composite construction in columns, namely encased sections.

NSW Government Offices, 1965 Demolished in 1997 was Australia’s tallest skyscraper on completion in 1965 reaching 38 levels. This building relied on innovative methods of construction to achieve speed of construction and employed many composite construction methods, namely composite beams spanning 10 metres, composite slabs utilising metal decking. Furthermore, this building involved the first major use of composite construction in columns, namely encased sections.

Tall building construction in Australia is significantly influenced by the material and labour costs involved. Since Australia has a highly skilled labour force in reinforced concrete construction and more importantly steel framed construction, labour costs are becoming more significant and thus are a primary consideration in the type of system chosen for construction. In Australia in the past it has been shown that about 50 % of tall buildings have been constructed in reinforced concrete with steel structures representing a 30 % share of the tall building market with mixed systems representing the remaining 20 % (Uy, 1997). These statistics have been contrast with a list of the tallest 100 buildings in the world, (Council of Tall Buildings and Urban Habitat, 1996). It is also anticipated that this figure has been further skewed toward concrete structures over the last fifteen years as a result of the development of high strength concrete being taken to advantage in multi-storey building systems.

Type of Framing Material

100 Tallest Buildings in the World (%)

Australian Tall Buildings(%)

Steel 53 30

Concrete 20 50

Mixed 27 20

Total 100 100

One of the driving forces for innovation in the design and construction of tall steel buildings has included the use of composite construction techniques. Some of the more innovative composite construction applications have been confined to a few iconic buildings of typically multi-storey and tall building structures. Some of these typical innovations have included the use of high strength cold formed steel for composite slabs. Conventional steel-concrete composite beams have also benefited from some innovations in the use of semi-rigid joint action and pre-cambering of steel beams in frames. The use of concrete filled steel columns has seen tremendous innovations, particularly in the use of very thin-walled steel tubes and box columns for the fabrication of concrete filled columns. Other more specialised innovations in composite construction have also included the use of post-tensioned composite trusses. More recent projects have shown that for specialty structures such as stadia, exhibition centres and transport infrastructure, the use of structural steel has promoted the ability for reuse. This is seen to be a very important initiative for the future and salient examples will be provided herein to illustrate some of the technical challenges that need addressing in order to ensure that these are made feasible.

Bridges

Structural steel standards have been important in Australia and date back to the late 19th and early 20th century when Australia typically imported much of its steel. The Sydney Harbour Bridge conceived in the late 1800’s, constructed during the 1920’s and completed in the 1930’s used steel sections imported from Dorman Long in the United Kingdom, (Lalor, 2006). This bridge is constantly being maintained and repaired and currently has a structural health monitoring system to assist in assessing damage to certain critical sections.

Bridges One of the most significant bridges in Australia is the Westgate Bridge over the Yarra River in Melbourne, which l inks the Western Suburbs of Melbourne and the southern parts of Victoria to its capital Melbourne. This bridge is a steel box girder cable stayed bridge which has a main river span of 336 m and has a total length of more than 2500 metres. This bridge collapsed during construction in October 1970, which resulted in a Royal Commission. This and a number of other notable collapses of box girder bridges in the UK and Germany also resulted in many important rules being developed by the Merrison Committee in the United Kingdom. In 2006, the Victorian government approved plans to refurbish the bridge. Some of the significant factors included strengthening the box girders whilst maintaining traffic flow over the entire works period. These works were completed in June 2011 and included significant work on the box girder. Much of the work involved the use of blind bolting techniques to increase plate stiffener thicknesses, thereby reducing the stress range operating in the boxes and subsequently the fatigue life of the structure.

A major composite bridge was built over the George’s River in Sydney in 1987. This was a parallel bridge to the 1923 Pratt Truss steel bridge which was completed in 1923. The new bridge consisted of eight 70 m spans involving three steel box girders utilising composite action with the concrete deck. A major composite-steel concrete bridge was built in Sydney in 2000 at Roberts Road crossing the Hume Highway and linking northern and southern arterial roads of Sydney. The superstructure of this bridge comprised four steel trough girders supporting a concrete deck across six continuous spans ranging from 25-40 metres. The sections adopted 350 MPa (N/mm2) steel plates with 1400 mm depth and 2250 width sections. In addition to some of the more obvious challenges, some other engineering challenges in the bridge design realm, will be in the area of urban design. Architects are finding increasing involvement in the urban design of bridges. Architectural involvement then poses unique challenges for structural engineers which need solutions to be available. A recent bridge designed in Clifton Hill, Melbourne involved significant architectural involvement and penetrations were required to achieve the architectural objective.

Roberts Road, 2000 A major composite-steel concrete bridge was built in Sydney in 2000 at Roberts Road crossing the Hume Highway and linking northern and southern arterial roads of Sydney. The superstructure of this bridge comprised four steel trough girders supporting a concrete deck across six continuous spans ranging from 25-40 metres. The sections adopted 350 MPa (N/mm2) steel plate with 1400 mm depth and 2250 width sections.

Clifton Hill, 2009 Clifton Hill, Melbourne involved significant architectural involvement and penetrations were required to achieve the architectural objective. This structure required significant finite element analysis carried out to justify the designs and this will be a continuing trend in future bridge designs.

Grosvenor Place, 1988 The innovative use of structural steel in this building included quite a few firsts in Australia. The building involved the use of high strength cold formed profiled steel sheets for the decking with a yield stress of 550 MPa (N/mm2). The beams which span approximately 16 metres from the reinforced concrete core to perimeter frame were designed for serviceability as semi-continuous, with a semi-rigid joint assumed between the beam and core. The columns in the lower levels of the buildings are quite unique and involve three perimeter columns being grouped at the ground level in a single column, with the key objective being the savings in space made for car parking in the basement. This involved the use of high strength quenched and tempered structural steel of yield stress of 690 MPa (N/mm2) being used for encased sections in this zone.

Grosvenor Place, Sydney (Cont’d) Piloti Column Encased

• Heavy steel fabricated section prior to and following encasement

• (shear studs provided for composite action)

Forrest Plaza The Forrest Plaza building is in the central business district of Perth and the building was completed in 1988. The building was designed by structural engineers Ove Arup and Partners and construction was completed by builders Multiplex, (Gillett and Watson, 1987). The building has a total height of 110 metres over 28 storeys. This building is unique in that it was the first steel building built in Perth in a decade. Some of the novel features which were used in the design and construction of this building included the use of concrete filled steel box columns. Furthermore, profiled steel sheeting fixed over two floors was used in the construction phase. Composite action for the slabs and beams were used throughout the height of the building.

Casselden Place, Melbourne The Casselden Place building is in the central business district of Melbourne and the building was completed in 1992. The building was designed by structural engineers Connell Wagner and construction was completed by builders Baulderstone Hornibrook. The building has a total height of 166 metres over 43 storeys. This building is unique in that it was the first building in Melbourne to utilize concrete filled steel tubes. Concrete filled steel tubes of twin cross-sections of 950 mm diameter have been used in the upper levels and these transition to a single 1350 mm diameter thin-walled steel tubular column at the lower levels. These columns were then filled with high strength concrete of 80 MPa compressive strength, Webb and Peyton (1990).

Central Park, Perth

The Central Park building is the tallest building in the central business district of Perth (Figure 8) and the building was completed in 1992. The building was designed by structural engineers Bruechle, Gilchrist and Evans and construction was completed by builders Multiplex. The building has a total height of 249 metres over 52 storeys. This building incorporates some unique features for steel construction, which include the use of precast concrete floor panels on steel composite beams. The columns used in the design and construction are also unique in that they include fabricated cruciform high strength steel sections utilizing 32-60 mm high strength steel plate (fy=690 MPa) at the base of the building, with mild steel (fy=250 MPa) at the upper section of the building, (Structural Steel Development Group, 1989).

Star City, 1995 The building comprised a number of innovative composite construction and high strength steel applications. Firstly, in the main gaming areas of the casino, large span composite beams of approximately 16 metres were designed and constructed. In the basement levels of the building, high strength steel fabricated sections were used to miminise the cross-sections of the columns. Due to constraints with site access for craneage, the trusses for the roofs had to be constructed with minimal weight. This required the design of 36 metre spanning trusses made composite with a topping slab and utilising high strength structural steel for the sections. Post-tensioning of the trusses was also used to help alleviate long-term serviceability concerns.

Latitude, 2005 The beams in the floor system span a total of 14 metres from core to perimeter frame and in order to achieve this the beam’s were pre-cambered by 40 mm to overcome estimated long term deflections of 60 mm. The building also uses twin composite columns on the perimeter frame, using 508 mm diameter steel tubes filled with 80 MPa concrete. The building has required the design of 7 metre deep transfer trusses using large diameter steel tubes filled with concrete and large high strength steel boxes filled with concrete.

Latitude, Sydney

One Shelley Street, 2010 The building is best known for utilising an extremely efficient steel diagrid perimeter structure to eliminate the need for internal columns and to minimise the use of internal structural cores. The diagrid members were formed from 310 UC sections and welded steel sections with 70 mm plate thicknesses of nominal yield stress, 450 MPa (N/mm2). The beams typically spanned up to 14 m at 3.2 m centres and used a 610 UB made composite with a 120 mm deep composite slab.

Column Free Floor Plate

Exoskeleton

Floor and external frame integration

Perth Tower, 2012 Whilst technical challenges will continue to be important in the design of composite steel-concrete buildings, issues relating to project management, procurement and quantity surveying may be of increasing importance. The builders of the recently completed Perth Tower, the tallest tower in Perth chose to adopt a concrete filled steel column solution. In order to secure this type of solution the builder pre-ordered and stored all steel tubes in the columns to ensure steel cost fluctuations were minimized and construction costs able to be controlled.

Perth Tower, 2012

Stadia Probably the best example of a structure which has been made demountable in Australia is the Olympic Stadium built for the Sydney Olympics in 2000. The structure was designed to seat 110,000 people during the Olympics with two large end stands. These end stands were then removed after the Olympics and thereby reducing the capacity to 80,000. These end stands were then transported to Wollongong, 80 km south of Sydney and used in the reconstruction of the WIN stadium. To facilitate the concept of deconstruction a special blind bolting technique was utilised.

Blind bolting

Post Olympics Mode

Exhibition and Convention Centre, Sydney

The original Sydney Exhibition and Convention Centre was completed in 1988 for the Australian Bicentennial celebrations in the Darling Harbour precinct, Sydney. The New South Wales Government has chosen Lend Lease to complete a $2.5 billion project which includes world class hotel facilities. The $1 billion redevelopment of the Sydney Exhibition and Convention Centre will include over 40,000 square metres of exhibition space, making it the largest in Australia. The project will be completed by December 2016. One of the significant aspects of this project involves the reuse of the concrete plinth for the foundations and carpark. The use of structural steel in the redevelopment has allowed this sustainable approach to be used for the redevelopment of this world class facility.

Exhibition and Convention Centre, Sydney

Royal Randwick Racecourse

Royal Randwick Racecourse in Sydney has recently been refurbished. The original Queen Elizabeth II stand was completed in 1969 and was constructed in reinforced concrete, with the roof being designed and constructed in post-tensioned concrete. In 2011, safety concerns regarding the roof beams closed the stadium and this forced many races away from one of Australia’s finest horse racing venues. The stadium was redesigned and rebuilt, using the lower part of the concrete stadium, with the new roof involving the use of structural steel in a $150 million redevelopment. The stadium was completed and opened for use in the Autumn racing carnival in 2013.

Royal Randwick Racecourse

Transport infrastructure A significant application of transport infrastructure which is being mooted for reuse in Australia is the Sydney monorail. The monorail which links the Darling Harbour area with the Sydney Central Business District. The plans are to dismantle this and to relocate to Hobart, which is the Capitol of the Australian island state of Tasmania, (Sydney Morning Herald, 2012).

AS4100-1998 Steel Structures

This Australian Standard was produced by committee BD1, (Standards Australia, 1998). This Australian Standard is a primary reference standard for the Building Code of Australia and deals with the design of bare steel structures. The standard was firstly released in 1990 in limit states format, (Standards Australia, 1990). One of the major innovations in this standard is the ability to allow the use of advanced analysis. The standard limits the yield stress of the material to 450 MPa (N/mm2); however a new amendment was released in 2012 to increase the yield stress to 690 MPa (N/mm2), (Standards Australia, 2012).

AS2327.1-2003 Composite structures: simply supported beams

The development of an Australian Standard in limits states form resulted in the standard AS2327.1 which was first released in 1996 and further amendments were produced for a further revision in 2003, Standards Australia, (1996 and 2003). The Australian Standard deals with the design of simply supported composite-steel concrete beams. The major innovations in this standard are the ability to allow the use of partial shear connection. The standard also requires designers to pay close attention to the various stages of loading, namely construction, service and ultimate loading stages. The document does not cover continuous or semi-continuous beam behaviour and currently does not allow for the use of precast or hollowcore slabs to be made composite with steel beams. Designers wanting to take advantage of continuity have often availed themselves of European Standards, (British Standards Institution, (1994)). Further progress over the next few years should see progress on this new standard which is ongoing in the AS/NZS 2327 project, (Standards Australia, 2014a).

AS5100.6-2004 Bridge design, Part 6 Steel and composite construction

It has been suggested that the design of composite columns may be satisfactory using the existing steel and concrete standards, Standards Australia (1998) and Standards Australia (2001), however this has some serious drawbacks. The benefits of this type of column are through savings made during the construction phase and thus these need to be considered. The Australian steel standard allows one to use a rational local buckling method to determine the local buckling coefficient however and this is useful. However the concrete standard will not allow for confinement if it is required to be taken into account for large plate thicknesses. The deficiencies of these codes have been resolved in the AS5100 Bridge design series which was produced by committee BD90 which was a partnership between Standards Australia, the Australasian Railway Association and AUSTROADS. The Standard deals with the design of members in steel and composite construction (Standards Australia, 2004). The standard draws heavily on the Australian Standards, AS4100-1998 and AS2327.1-2003 (Standards Australia, 1998 and Standards Australia, 2003) for beam and column design. The standard is also however also able to deal with composite construction members which may prove to be a forerunner to the development of a standard for composite columns produced by BD32 for buildings. This standard is currently being revised and in particular will take into account the changes in steel and concrete strengths that AS4100 and AS3600 have respectively proposed, (Standards Australia 2014b).

Reduction factor β for the use of high strength steel

Manufacturing tolerances used for capacity reduction factor calibration

Capacity factor versus reliability index for compact sections using products complying with

manufacturing tolerances given in (a) EN 10034/KS D 3502 (b) JIS G 3192/JIS A 5526

Capacity factor versus reliability index for compact

sections using products complying with manufacturing tolerances given in (c) ASTM A

6/A6M (d) AS 5100.6

AS5100 Part 8: Rehabilitation and strengthening of

bridges In addition to revisions of the

existing steel and composite bridges standard a new standard dealing with rehabilitation and strengthening of existing bridges is also being prepared. Some of the salient features for the steel and composite parts include the use of post-tensioning and the use of post-installed anchors, (Standards Australia, 2014c).

Deconstructability

Following on from recent practical examples, such as the deconstruction of the end stands of the Sydney Olympic Stadium, recent research has been carried out on deconstruction of steel and steel-concrete composite beam systems. Initial research has illustrated that for both stiffness and strength purposes, bolted shear connectors can provide the same or improved performance for composite beam behaviour when compared with headed shear studs. The following figures show the type of bolted shear connectors and how they have been shown to allow demountability in composite beams, (Mirza et al, 2010and Pathirana et al, 2012).

Deconstructability

New materials Recent trends in Australian Building Construction have been calling for the use of higher strength steel and concrete with reduced amounts of Ordinary Portland Cement (OPC), (Green Building Council, 2009, 2010a and 2010b). Recent research into column systems which use both high strength steel and reduced amounts of OPC have been recently carried out, (Khan et al. 2013).

Schematic of Kowari Strain Scanner at ANSTO, Sydney

Through thickness longitudinal residual stress distribution

-300

-200

-100

0

100

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300

400

500

600

0 5 10 15 20 25 30

Long

itudi

onal

resi

dual

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Pa]

Distance from the weld centre line [mm]

4 mm

1 mm

2.5 mm

Representative stress-strain diagrams for concrete and steel

Ratio of column/cylinder concrete strength

0.00

0.20

0.40

0.60

0.80

1.00

1.20

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10 15 20 25 30 35

Rat

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olum

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engt

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b/t

Conclusions

This paper has introduced the history of steel and composite steel-concrete construction from the perspective of applications in Australia over more than a century. Much of the innovation in these bridges, buildings, stadia and other structures has driven the research efforts in these areas in Australia. However, more recently, the research has become more pro-active and solutions for industry have had some of their fundamentals founded in the research that has been conducted in Australia. A summary of design approaches by way of Australian Standards from an Australian design perspective has been given. Much of the research conducted in Australia has been underpinning the applications and it is pertinent that Australian Standards need to be properly developed to support the applications more pro-actively. Finally this paper has identified some of the new areas of research that have eventuated due to sustainability principles. This is a new and novel method for research in structural engineering and will continue to grow in scope in the coming years.

Acknowledgements

The author would like to thank all the students, staff and collaborators at the University of Western Sydney and the University of New South Wales for their work in some of the elements presented in this paper. Furthermore, a special mention to Drs Hicks and Kang from Heavy Engineering Research Australia, New Zealand and University of Western Sydney respectively for the work that has been carried out to develop new calibration factors for steel beams in Australia.

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