A Review of Off-site Manufacture At Skilled Stadium
04-09-2010 - Construct - June 2008
Robina Stadium in Queensland Australia was built during 2007, and successfully utilised a high degree of off-site manufactured products. The main structural steel and concrete plats were manufactured off-site. The main benefits of using OSM on the Robina Stadium project were vast improvements in construction time, reduced onsite labour, improved OHS, better quality, improved interface coordination and better environmental performance. However barriers in the process essentially surrounded the coordination and design aspects, which differ in the context of OSM-intense projects. The main lesson arising from the project was the importance of ensuring that coordination and cooperation between all parties is commenced very early in the project process so that design of the products and processes maximise the benefits of OSM.
Introduction
The use of off-site manufacture products (OSM) in stadium construction is not uncommon. Watpac successfully utilised OSM throughout the construction of Robina stadium in Queensland during 2006 and 2007. This case study provides a context of the project, before describing the main elements that were manufactured off¬site. The study closes with a brief discussion of the benefits and barriers of OSM use on the stadium project, before reflecting on lessons learnt from the use of OSM on the project.
Historical context
Watpac has a history of constructing stadiums in Queensland (Ballymore Stadium extension, Queensland Sport and Athletics Centre extension, Brisbane Cricket Ground and Suncorp Stadium) and therefore has a good knowledge base for this type of construction. Watpac were originally approached to submit a guaranteed construction sum (GCS) based on the initial design documents that had been submitted by a consortium to a government design competition. Initially the organisation aided the consortium until it produced the final documents to which Watpac could submit a guaranteed price. The consortium novated the project to Watpac, which then managed the project to the guaranteed sum.
The design of Robina differed from other stadiums that Watpac had constructed. HHK Architect's, although experienced in stadium design, had not worked with Watpac before. Nevertheless, by being involved early in the project they were able to consider buildability and tailor the design to accommodate OSM. The system of construction was selected based on experience gained during the Brisbane Cricket Ground project. OSM is particularly suited to stadium construction as they tend to have large elements, with large volumes, spaces and heights, all of which introduce particular construction and OHS risk.
At Robina the main driving forces for OSM were the limited time available for construction and the restricted labour market, which encouraged the minimisation of onsite work. The client required the regional stadium to be completed in time for seasonal sports requirements in order to generate income as soon as possible.
Construction was started onsite in August 2006 and was completed in late 2007.
The products
Structural steel was selected for the main structural frame as it could be constructed quickly and easily offsite in many sections. The company then considered incorporating further off site manufactured items into the development, eventually deciding to undertake the whole production process off-site. The structure consisted of the following components:
- Structural steel for the main structure of the stadium;
- Seating plats, being the main concrete beams that support the stadium seating;
- Precast planks forming the load-bearing floor structure that is placed on the structural steel before a topping is poured in-situ to tie them into the structure;
- All verticals - the stair shafts, lift shafts and vomitories (Spectator exit points); and
- Roof structure, consisting of a fabric roof manufactured by a German company in Poland.
Steel
The main Steel fabricator Beenleigh Steel Fabrication (BSF) worked early on in the design process. Once material quantities were established, they were able to start ordering metal from suppliers while simultaneously working-up the detailed drawings for manufacture. This reduced the possibility of being delayed at a later stage. BSF tend to use shop detailing companies who work exclusively for them to ensure good levels of communication. BSF had two main roles on the Robina project: fabrication and erection.
Fabrication
The steel was constructed in a controlled environment to eliminate any adverse weather effects. BSF have two factory locations that, among other things, enable them to have a stable workforce of boiler workers. All sections were made-up on the bench and then broken-down into transportable sections. The overhead cranes in the factory make it possible to easily move larger items around when required. These were then stored until they were dispatched for protective finishing and painting. From there the items went directly to site. All items were labelled for identification and could be referenced back to the shop drawings if required.
Erection
BSF erected its steelwork together with the precast concrete elements. The company owns its own cranes and supplies crane drivers and riggers onto site. Erection began once the in-situ foundations had been placed. The erection process had very low tolerances - typically a couple of millimetres, requiring precision in the onsite and off-site elements. BSF also installed the precast concrete elements as these required installation concurrently with the steel frame, and it was deemed more efficient to have one contractor complete both aspects. This further aided the project programming.
Concrete plats
Precast concrete plats (long beams to which the seating is attached) have for a long time been used as a standard item for stadium design, as these are both cost and time efficient. Casting these in-situ would take considerable time and also expose a large number of people to high levels of risk during the construction process.
Precast Elements manufactured the seating plats. Previously seating plats were cast where a large surface area had to be steel dowelled. The Plats were T shaped and moulded at 90 degrees to the final orientation to reduce the amount of dowelling required. This gave the maximum amount of off-mould surface, which result in a high quality surface finish - typically a class 1 or 2 surface.
The T shape (on its side section) was designed to overcome a perceived problem that was considered by the architects and engineers (normal plats are L-shaped). It was feared that a crowd jumping on the plats simultaneously would induce a natural frequency in the elements, hence the introduction of the T-shape to stiffen the plats.
Precast Elements have four, 60m moulds and can make different length plats by using adjustable end plates. Using these moulds they have the capacity to make up to 24 plats a day. Steel reinforcements were laid and tensioned in the moulds before pouring the concrete. Magnets are used to hold the fully-adjustable mould sides in place.
To speed up the production process quick-curing high strength concrete was used in conjunction with steam curing. The steam increases the temperature of the moulds to around 55-60C and reduces the cure time. The process took around 18 hours from start to finish, with pours commencing at 2pm and finishing by 8pm. By 6am the following morning, the plats could be removed from the moulds and stacked. Generally the plats required no patching or repair. The pre-stressing of the plats necessitated a half inch cut in the steel to tension the concrete on removal from the moulds. Once cut and trimmed the ends of the steel were then painted with an epoxy paint to seal them and prevent corrosion.
The connection systems and fasteners, together with stencils for product identification, were cast into the product allowing easy installation and product identification.
Online - The Australian Institute of Building