Concrete Design and Construction Issues for the MCGRedevelopment

Mark Sheldon Senior Associate, Connell Mott MacDonald

60 Albert Road, South Melbourne, Vic, Australia, 3205

Erik Guldager-NielsenArup

Level 17, 1 Nicholson Street, Melbourne, Vic, Australia, 3000

Steven RichardsonProject Manager, Grocon Constructors

MCG Site, Yarra Park, Vic, Australia, 3002

AbstractThe design and construction of the MCG Redevelopment, scheduled for completion for the 2006Commonwealth Games, has presented numerous challenges for the design and construction team.

The $400 million project is being constructed by Grocon Constructors, working closely with thenovated consultant team lead by MCG-5 Sports Architects, a joint venture between Daryl JacksonArchitects, HOK Sport+Venue+Event, Cox Architects, Tompkins Shaw + Evans and HassellArchitects. The engineering consultancy is a joint venture between Connell Mott MacDonald and Arup(CMMA).

Immediately upon novation of MCG-5 and CMMA to the successful tenderer, Grocon, the design teamset about incorporating the preferred concrete solutions. High on Grocon’s priority list was the need toexpedite the construction. This led to the adoption of a variety of structural systems on site, eachchosen for their ability to overcome particular constraints at each location. The typical systemincorporates a concrete superstructure with hollowcore planks utilising a purpose built beam formworksystem. High strength precast columns were used extensively throughout the superstructure, as wellas bored pier retention systems.

Other interesting aspects of the design of the MCG include the concrete counterweight to the roofstructure and the construction staging methodology developed for the site.

The ProjectThe Melbourne Cricket Ground (MCG) is one of Australia's most famous sporting icons, and has beenundergoing a major redevelopment in the last 3 years. The three original stands on the northern sideof the ground (the Ponsford and Olympic Stands and the Member’s Pavilion) have being demolishedto make way for a new single stand. The only portion of the stadium left standing after the progressivedemolition was the Great Southern Stand, which was designed by Connell Mott MacDonald in theearly 1990's, although even this has had some modifications to accommodate enhanced lighting andsound equipment.

Whilst the 150+ year old ground has hosted AFL matches in the past with 120,000+ spectators, theintroduction of seats to replace standing areas had whittled the capacity down to just over 96,000,with many seats in the older stands having restricted viewing and uncomfortable timber slatted seats.To maintain its reputation as Australia’s premier sporting venue, the Melbourne Cricket Club (MCC)realised that a major redevelopment was essential.

Following an extensive feasibility study completed in December 2000, the MCC and the MCG Trustconfirmed it would proceed with a redevelopment of the aging stadium based on the followingcriteria:-

• There should be no loss of public seating or overall capacity• Sightlines should be of world standard• Individual seating spacings should be at least equal to that in the Great Southern Stand• The number of under-cover seats should be optimised

Through careful planning by the design team, the original capacity criteria has been exceeded, as thecapacity of the new stadium when complete will again exceed the magic 100,000 number.

Another key component of the architectural design was the concept of opening the stadium out to theparklands north of the ground. This is a different philosophy to the Great Southern Stand which had arelatively unattractive vista overlooking the busy Brunton Avenue and the rail yards. With its proximityto Yarra Park, it was decided to make more a transparent wall in the new stand to engageapproaching patrons as they arrive at one of the three major entry points. Each entry features a grandatrium behind large glass facades, serviced by escalators taking patrons to the upper levels.

Whilst the “front-of-house” areas essential for a stadium are critical for the MCG, there are otherfeatures of the redevelopment that will not become obvious until the facility is fully opened to thepublic. Whilst there is no net increase in corporate seats (considered an important criteria by the MCCto maintain the MCG’s mantle as “The People’s Ground”), dining room capacity will almost double.Large, deep rooms will enable tenant sports and clubs to accommodate up to 500 guests and theMCC Members Dining Room has a similar capacity. Large new changerooms, press facilities andcoaches boxes will service the needs of both football and cricket. The stadium will have extensivecatering facilities, and will have nine passenger lifts and 13 escalators to supplement stairs.

A major feature of the redevelopment is the relocation of the Australian Gallery of Sport as part of aseven day attraction, featuring interactive devices and a museum precinct. This will be linked to theMCC’s library, which boasts the world’s finest repository of sporting literature. And, of course, thefamous Long Room in the Members Area will be recreated, complete with the memorabilia that madeit much loved by generations of Victorians.

StagingIn the latter part of 2001, the consultant team working for the MCC, issued tender documents for a“Novation” style contract. These were not full “for construction” documents, but rather a preliminarydesign issued to identify to the tenderers the client’s expectation for the project and a way in whichthe stadium could be completed. Grocon Constructors commenced on the project in mid-2002, andimmediately set about directing the consultant team to modify elements of this partially completeddesign to suit their preferred construction techniques. The final documentation was then completed byCMMA and MCG5 based on Grocon’s preferred methods of construction.

All construction techniques, when evaluated, had to address the requirement that the stadium had toremain operational throughout the AFL and cricket seasons, with a minimum number of seats to beavailable for major events.

The old Ponsford Stand was the first to be demolished, immediately after the 2002 AFL Finals. Thiswestern end of the new stand was then the first portion to be constructed, with patrons occupying thisfor the 2003 AFL Grand Final. Following the 2003 Finals, the Members Pavilion was taken down. Halfof the Olympic stand went next, with further new seats made available for the 2004 AFL Grand Final.Following this event, the remainder of the Olympic Stand was demolished and the final portion of thestand could commence.

Much of the engineering design by Connell Mott MacDonald Arup was completed at a site officeworking along side the MCG-5 Sports Architects and Grocon Constructors. Speed of construction hasbeen high on the design team’s agenda, driven by Grocon’s tight construction program.

The new Northern Stand itself is expected to be completed by the end of 2005 in time for the 2006Commonwealth Games. Between the 2005 AFL Grand Final (in late September) and Boxing Day, theentire playing surface will be stripped off and essential track and field base works will be completed,prior to the turf pitch being reinstated for the traditional Test match. Then between January and April2006, the turf will be removed again and the track must be set up, as well as data, communicationsand electrical conduits installed for the events and ceremonies. Once the games are finished, thewhole stadium must then be turned back into an AFL ground for the balance of the 2006 AFL season.

Ecologically Sustainable Development (ESD)A key criteria for the entire MCG redevelopment project was to introduce world-class sustainabilitycriteria in the building and managing of the stadium. The onus for the engineering design team was toreduce the demand for energy, use building systems that provided optimum operational and resourceefficiency, and incorporate innovative and environmentally sustainable initiatives into theredevelopment where feasible.

The architects coined a phrase on the outset – MCG Green – which has been part of the drivingphilosophy behind a lot of the work. For example, trying to minimise the impact on the MCG'ssurrounding parkland has taken into account the whole precinct concourse redevelopment andinteraction. As part of this aim, the main entry points for the new Northern Stand will be three atria thatwill take advantage of passive ventilation for cooling. The engineering team used daylight studies andthermal modelling to achieve this. The shading design has been optimised to provide sufficient solarheat gain control, but at the same time letting in sufficient daylight and controlling glare in the space.

Through sophisticated computer simulation, CMMA have also predicted the air flow, air temperature,surface temperatures, radiant heat, daylight levels and contrast glare in the space. As a result, thethree atria have a series of louvres, each differently arranged to give the best control of light within thespace. Apart from the thermal modelling, the simulations also addressed openings and access topassive air flow. As a result, mechanical cooling is only needed in heavy use and high heat areas likethe food court.

As another part of the new sustainability measures, CMMA looked at storm water quality improvementinitiatives from the site and reuse of water. Previously all the water that came off the site wasdischarged to the stormwater system, which went to the Yarra River. The new Northern Stand has a1.5ML tank to collect water that falls on the 1hectare roof. This harvested water will be treated andused for seating plat wash down.

The Structural FrameThe completed new Northern Stand will effectively be a 400m long seven-storey high building, withtwo basement levels. The team looked at many alternative structural schemes before adopting asolution of what is effectively five buildings, separated by movement joints. Within each of thesebuildings, shear walls have been incorporated in the radial direction to provide stability and maximiseceiling zones for reticulation of services around the stand. In the circumferential direction, however,shear walls would hamper viewing areas, so beams have been provided, working with the columns asa sway frame. This assisted with support of the floors, as Grocon's solution was for hollowcore planksspanning radially for typical suspended floors of the stadium – a win-win situation.

Another aspect of the project where concrete has been used extensively is in the retention system tothe double basement. Bored piers by Wagstaff Piling were drilled from the surface level and shotcretepanels sprayed between the bored piers progressively during excavation. Interestingly, whereverpossible large diameter bored piers are designed to cantilever out of the base in the temporarycondition, rather than smaller diameter piers restrained by temporary ground anchors.

The Floor SystemWith over 10hectares of floors to construct, Grocon elected to use a number of different flooringsystems throughout the project. Examples of the types used, and the reasons for selecting thesesystems are summarised below: -

STRUCTURAL SYSTEM LOCATIONS USED

CONVENTIONAL CONCRETECONSTRUCTION (FORMWORK,REINFORCEMENT & INSITUCONCRETE)

� Areas with large penetrations or where floor platewas curved in plan.

� Cantilevered slab edges or slabs requiring cast inplates.

� Main circumferential beams which support theHollowcore precast floor planks on Levels 1-4.

� Inclined columns in the 3 main entry Atria� Level 1 seating plats using Grocon Lubeca jigs to

form up the seating plats incorporating BAMTECreinforcement system.

PRECAST FLOOR PLANKS (Hollowcore) � Typical level 1-4 suspended slab areas withminimal penetrations in the floor plate.

POST-TENSIONED PRECASTCONCRETE SEATING PLATS

� All seating areas on Levels 2, 3 and 5.

BONDEK SLABS � Areas with very high soffits, such as bar overMembers Atrium.

� Areas with tight floor-to-floor height, such as LongRoom Mezzanine.

� Areas with sloping soffits not suitable forHollowcore

� Non-typical areas where the architectural finish tothe soffit was not a driving issue

PRECAST WALLS � All Goods and Passenger Lifts shaft wallsthroughout the project, integrated with surroundingconcrete structure.

� All Vomitory walls leading to Level 1 & Level 5seating.

PRECAST COLUMNS � All areas from LB2 to Level 3.� Level 1 tapered columns fully integrated with steel

rakers and tensioned concrete back-spanssupporting Level 2 precast concrete seating plats.

The typical grandstand circumferential beams are post-tensioned and span approximately 16m. Tomaximise services zones, the design incorporated haunches in these beams, with depths of 900mmat columns stepping down to 600mm at mid-span. Beam depths were set to maximise the use ofstandard forms, recognising that to speed up construction the hollowcore planks were to be supportedby the formwork prior to the beams being poured. Considerable coordination was undertaken by theproject team, particularly at the many floor set-down areas, to achieve this goal. This enabled thehollowcore planks to be used as a working platform for installation of reinforcement andpost-tensioning tendons in the circumferential beams. The structural topping to the hollowcore ispoured simultaneously with the beams, to minimise construction time on site. In a co-operativeapproach, the floor system was designed in conjunction with Hollowcore Pty Ltd to be continuousconstruction. Hollowcore were responsible for the design of the planks, with CMMA responsible forthe top flexural reinforcement over supports. Particular attention was paid to the shear characteristicsof the planks in zones of negative bending.

The Seating TiersA feature of the stadium evident to all spectators is the large cantilevering rakers that support theupper seating tiers. The largest of these cantilever approximately 11metres and are spacedapproximately 12metres apart.

Carrying folded precast concrete seating plats with crowd loading, it is easy to see that a significantsteel beam is required. What is not so evident is the fact that we needed to design these elements formore stringent dynamic performance criteria than what was appropriate when the Great SouthernStand was designed.

Our team developed an analysis methodology that modelled the interaction of the steel beams, theconcrete supporting frame and the precast seating plats. Tweaking the relative stiffnesses of therespective elements and researching to develop a rational design criteria meant we were able to savethe client over a million dollars compared to other stadia designed using a less sophisticated ‘deemedto comply’ approach. Even with this reduction, steel beams up to 2.7metres deep with 80mm thickflanges were still required.

The upper level seating tier consists of 36metre long boxed steel girders supported on slopingtapered columns, and carries considerable forces from the roof down to the superstructure. Becauseof the large horizontal thrust forces, up to 18No x 15.2mm dia post-tensioned strands are coupled tothe steel’s baseplates and traverse the top floor at each grid to counterbalance the opposing forces.

A similar challenge was how to connect the 2.7metre deep steel cantilever beams at level 2 back tothe concrete frame. Typically 36No x 15.2mm post-tensioned strands are anchored though a 3metredeep concrete backspan beam into the superstructure. These required careful detailing to avoidsignificant congestion of reinforcement at the junction with the columns.

Precast ColumnsIn keeping with Grocon’s philosophy for the project of prefabrication for speed of erection, many of thecolumns are precast concrete. Strengths of up to 80MPa are being used to enable the sizes ofcolumns to be standardised, reducing the number of moulds. The use of precast columns expeditedsite construction times, but required additional input from the design team coordinating levels prior tofabrication.

FoundationsOne of the areas of risk Grocon identified early in the design phase was potential delays associatedwith excavation for footings on a site with a history of previous buildings. It was also known that adyke of weaker material traversed the site, the extent of which was not fully known. As a result,Grocon instructed the team to reduce the number of columns through the structure in the final post-novation design. This increased the spans of the circumferential beams and the stability moments inthe columns, but reduced the number of footings. Allowable bearing pressures were increased on thebasis that significant additional inspections by the geotechnical engineer were undertaken, allowingthe footing sizes to be reduced.

In the vicinity of light tower 1, unusually soft ground conditions due to the dyke were encountered,requiring pile foundations instead of the usual pad footings.

The External ConcourseThe concrete paved concourse to the west and north of the new stand provides a link to thesurrounding parkland and access to the ticket booths and entrances.

The choice of a structural system was dictated by the need to maintain existing underground servicesin the area, noticeably a 66 kV power cable, which transverses the site in close proximity to the newstructure. It was necessary that a 6 metre wide corridor around this cable be kept free of allconstruction work, including excavation. It was further agreed that engineered filling should be kept to

a maximum depth of about 1 metre, to avoid time-consuming operations of placing and compacting inthin layers.

Thus the structural system evolved as parallel walls on each side of the power cable, with the outerwall designed as a free-standing retaining wall. The deck over the cable is a hollow-core slab, with aheavy in-situ topping, designed as simply supported, to allow removal in parts for repair of the cableshould that be necessary. Inside the cable corridor the slab is conventional in-situ concrete, generallyslab and band-beams. This structure is supported on the shoring piles around the basement underthe stand, but separated from the main structure by a movement joint. Outside the corridor a concreteslab is constructed on compacted fill.

A major complication arose in the area where two columns, supporting one of the external servicespods, landed within the cable corridor. Here it was necessary to construct a temporary hollow-coreslab with minimum clearance over the ground, acting as support for an 1100mm deep transfer slab,which carried the column load to piles placed outside the restricted zone.

A Novel Use of ConcreteThe brief for the main roof over the new Northern Stand was for an elegant, light and transparent roofstructure, which maintained the MCG’s iconic status and complemented the Great Southern Stand(GSS) without replicating it.

The Engineering team developed several options for the roof structure, and tested each againstarchitectural, cost and staged construction requirements. Some of these options included a large,single mast within Yarra Park, a roof structure suspended from 2 different arch trusses or asuspended roof utilising individual masts.

The adopted solution involves an innovative tension structure with rafters suspended from cable staysrunning over individual masts. Utilising counterweight to resist uplift wind forces, the structure alsomakes use of a cablenet to distribute peak wind loads determined from wind tunnel modelling. CMMAwere then able to engage a large portion of roof weight to resist uplift winds - which occur in peakzones - resulting in a very efficient and light structure. The cablenet also serves the purpose ofrestraining the top of the individual masts, eliminating the need for a bulkier bracing system.

The primary roof structure is comprised of fabricated steel box section rafters ranging in length from37m to 42m. The rafters are concrete filled to provide counterweight against uplift wind and to furtherassist this, a front hoop beam, consisting of a 600 square fabricated steel box section, was placedtowards the front of the roof and also concrete filled. The fabricated steel masts are tapered to givetheir appearance a further element of slenderness and vary in height from 13m to 28m.

Grocon initiated prototyping to determine how the members providing counterweight for the roof canbe filled with concrete. This showed that the specially engineered concrete can be poured in throughholes in the top of the steel beams without vibration.

Another benefit of this scheme over other options, is its suitability to staged construction, as it couldbe built bay by bay with minimal temporary support required.

Great Southern Stand ExtensionOne aspect of the project already “forgotten” by the public is the fact that, to maintain symmetry of thestadium, the redevelopment also included the extension of the Great Southern Stand (GSS) by onebay and the two main stands will be separated by large scoreboard structures at each end. This wasessential due to limited space on the site due to the proximity of Brunton Avenue and the rail yard.

The techniques for the construction of this extra bay were a hybrid of those used in the original standand those proposed to be used for the new stand.

Top Down ConstructionThe normal construction activities continuing around from west to east meant that the last portion tobe commenced would be the difficult interface with the Great Southern Stand, including workingaround the existing Light Tower No 2 and Tower Crane No 9. This also included the non-typical lasttwo bays which feature the large electronic scoreboard. The significant retention systems supportingthese structures presented a challenge from both a construction and programming point of view.

To expedite the construction on site, Grocon initiated a ”jump start” construction methodology to theeastern end of the project. The easternmost two bays were redesigned to enable construction afterthe 2004 Finals to commence at concourse level. Columns through the basements previouslydesigned as precast concrete were replaced by bored piers installed from ground level. Constructionbegan at the eastern end at concourse level and continued upwards as the excavation for thebasements continued to work its way eastwards. The excavation then continued under the completedconcourse and the basement structure formed and attached to the newly rendered piers. Rampaccess into the two-basement hole for excavation vehicles required considerable coordination withconcourse construction activities particularly in the vicinity of the retention system to the light tower.This “top and tail” technique saved considerable time in Grocon’s construction program by removingthe retention/ excavation off the critical path of the works.

SummaryThe MCG redevelopment features many different examples of the uses for concrete in theconstruction of major buildings. Due to the enormity of the task, Grocon Constructors, Connell MottMacDonald Arup, and MCG5 developed a series of different structural systems, each chosen to bethe right solution for that particular set of circumstances.

The primary system used for the main superstructure was post-tensioned concrete circumferentialbeams poured in purpose built steel forms able to support hollowcore planks and the structuraltopping. Other areas featured conventional reinforced concrete, some using the OneSteel “Bamtec”reinforcing mats. Areas of slabs were also formed using Bondek, whilst significant program benefitswere gained by maximising the use of precast elements, such as the precast, pretensioned seatingplats that span up to 16metres. A significant number of bored piers were installed to provide theperimeter retention system, and as footings in areas of weaker bearing material. A novel use ofconcrete is in the main roof rafters, which are concrete filled steel boxes. The concrete providesdeadweight to resist the dominant uplift loads as well as adding rigidity to the steel wall plates.