Precast's Winning Tactics For Sports Venues | A Star Player In Sporting Venue Construction
Work will start soon on the 2022 Commonwealth Games venues, and precast concrete will be central to their construction. But what makes it so well-suited for building sporting infrastructure and what are the challenges involved?
Precast concrete has been a star player in the construction of sporting venues around the UK. Almost every football and rugby ground, athletics stadium and indoor arena features some form of precast component, as does much of the associated infrastructure.
In recent years, these range from the 2012 London Olympics venues, where precast components were used on the main stadium, the iconic aquatics centre and in the athletes’ village, to the ultra-modern Tottenham Hotspur stadium, the biggest club ground in the capital, completed earlier this year.
In three years, the 2022 Commonwealth Games takes place, and construction work on the venues is due to start shortly, with precast again sure to feature prominently. But what makes it so popular with designers and builders of sporting venues – and what are the installation challenges for precast suppliers?
One, perhaps obvious appeal, is precast concrete’s robustness and durability.
“Of particular concern in stadium design is the effect of resonant frequency, when a structure moves due to the dynamics of crowd movement,” explains Elaine Toogood, senior architect with The Concrete Centre. “The use of concrete is widely understood to limit this.”
This was why precast sections were a safe choice for the upper terraces on the London Olympic Stadium project, she adds.
Precast concrete is also a familiar and flexible product, which was another consideration on the Olympic Stadium, where a procurement requirement was the ability to transform the 80,000-seat venue into a 25,000-seater after the Games. (In the event, the venue was reconfigured into a 55,000-capacity stadium for West Ham United Football Club.)
“The choice of concrete for demountable upper tiers might not have seemed an obvious one,” notes Toogood. “But the short design programme drove the design team to choose concrete as a low-risk, well-understood option, which ultimately provided a high-quality result.”
In all, 9,250m³ of reinforced precast concrete was used within the Olympic Stadium bowl and more than 12,000 precast elements were required for the seating steps alone.
Besides terrace units, other precast components typically used on stadia include raking beams, staircases and step blocks, vomitory walls, hollowcore slabs, flooring and cladding panels.
Mixes and finishes depend on the visual appearance the architect requires, though in areas of high spectator traffic, they tend towards the functional. “In our experience, they have been mostly a neutral colour and an acid etched finish,” says Coxwell Mupandanyama, senior structural engineer at Techrete, which has worked on the new Tottenham Hotspur stadium, Wembley Stadium and the Aviva Stadium in Dublin.
The relief possibilities of architectural precast have led some architects to introduce decorative design features. At Tottenham, Techrete created the club’s crest and motto from precast units (see page 5), while just down the road in north London, at Arsenal, the club had a more unusual requirement.
“Techrete created cantilevering letters outside the Arsenal stadium, that were free standing, fixed to the ground at the bottom only,” explains Mupandanyama. “The letters were designed to resist vehicular impact and this was achieved through reinforcement in the moulds and through setting the letter panels deep into the ground.”
Perhaps, most famously of all, Techrete recreated the Elgin Marbles from the Parthenon frieze for block 15 of the athletes’ village, using specially created precast moulds.
The high repeatability of some precast components in stadia, such as the terraces, means these units can be huge sizes.
“Terracing units are normally up to 8m long, otherwise limitations in size tend to be caused by crane capacities,” says a spokesperson for Creagh, which has worked at Tottenham Hotpsur, Lord’s Cricket Ground, and Wimbledon Court No.1.
Meanwhile, Techrete has designed special low load ‘Tech’ trailers which are adapted to transport the largest of panels to any site. “These avoid height restrictions of bridges and other restricted areas,” says Mupandanyama.
Installation of precast sections, compared to conventional buildings, can pose challenges due to the geometry of stadia, which Mupandanyama describes as “unique”
“Over-hanging terraces, pedestrian access routes, public exits and ramps all contribute to the irregularity of the projects,” he notes. “This is overcome with BIM modelling, specialised lifting equipment, adapted transportation vehicles and over-night installation in order to meet all requirements of the programme.”
On Techrete’s Wembley and Aviva Stadium projects, over-hanging terraces were constructed first. “This posed a challenge as Techrete needed to find a way to erect the precast panels underneath the over-hang,” explains Mupandanyama.
“In both cases, our specially designed Merlo telehandler, with Airvac attachment and suction pads, lifted the panels into place in these tricky areas.” “This innovative lifting equipment can lift any panels up to five tonnes in weight. The Merlo is operated by a small hand-held remote which is used to increase and release suction and to manoeuvre the panels into place.”
Creagh says installation is usually completed using main tower cranes, though at times, “smaller mobile cranes, forklift cranes and specialist lifting equipment are necessary to reach certain areas,”
their spokesperson adds.
Increasingly, BIM is used to design and construct sporting venues, which has meant close collaboration for precast firms with designers and main contractors.
“In many cases, Techrete is consulted by the architect from the stage of inception to ensure that the design intent can be achieved and maintains a close relationship with the main contractor and various sub-contractors throughout the pre-construction, construction and erection processes,” says Mupandanyama.
Installation work also means working closely with steelwork contractors. “The steel worker would have an input as well to ensure we are all on the same page, communication is key here,” says the spokesperson for Creagh. “Site work will all be done in conjunction with the steelwork contractor.
“At Tottenham we were working for the steelwork contractor so they were the liaison between us and the designers.”
The experience from the London Olympics and other sports venues completed since should put precast companies in a strong position as tendering begins for the 2022 Commonwealth Games.