Main contractor ISG helped to deliver £1 million in savings to the ODA after it rejected concerns over the design of the Olympic Velodrome.
Speaking at a UK Green Building Council learning legacy event on the stadium, former ODA head of sustainable development and regeneration Dan Epstein said ISG rejected concerns raised by cost consultants that the cable net roof system design would lead to spiralling costs.
He said: “We had a situation where the cost consultant said we cannot do the cable net system cost effectively and [ISG] said actually we can do it more cost effectively. If the right contractor had not come in and said we can do this in another way then none of this would have happened. Putting liability and indemnity on the line through the right contractor was a critical part of the success.
“It is very hard to find truly integrated project teams but that was not the case here. Yes, there were disputes and details that had to be resolved but there was an understanding in a much more subtle way of the need to reduce costs and work so that the design team could rely on each other.”
ISG health, safety, quality and environmental director Vincent Busk said: “I can’t stress enough how important it is to get contractors involved early in schemes.
“The whole risk of the cable net concept was that it had not been done on this magnitude in the UK before so we had to look at where it had been used around the world and what lessons had been learned. We then had to procure the cable very early on so that they could be strung out and splayed to the correct lengths.
“By moving to the cable net system we saved about £1m on the purchase of steel. When the rope access guys came to work [installing the cables] there were calls to the ODA about unsafe working but we had the most highly skilled guys you could get to make sure the structures were safe.”
History of the cable net design:
The design team’s vision for the Velodrome called for a minimal structure, ‘shrink-wrapped’ around the track and spectators.
The resulting roof geometry could be constructed with a cable-net structure spanning the 130-metre track area. However the cable-net scheme was abandoned in favour of a conventional steel arch system due to concerns on risk and what was described as an ‘overly cautious cost estimate’.
However, ISG persuaded the client to commission a study into four alternative roof systems, including: a tensioned cable-net, compressive steel arches, glulam timber arches and a cable and timber hybrid system as they could see significant cost and programme savings in resurrecting the cable-net scheme.
The option was then reselected and resulted in a 15 per cent saving in embodied carbon over the original competition scheme, and a 27 per cent saving over the steel arch option.
Source: Olympic learning legacy document: Reducing embodied carbon through efficient design.
Speaking about what could be done differently with hindsight on the Velodrome or what particular lessons needed to be learned, ODA project sponsor Richard Arnold said: “My key message is that the client has to show real leadership. It is sometimes too easy for clients to hide behind cost and programme times.”
Hopkins Architects partner Chris Bannister said: “We were under cost and time pressure but had to deliver a world class venue. We had a requirement to provide 6,000 seats during the games and also the legacy so we weren’t required to make changes to the building envelope which was lucky.
“We were keen to get contractors involved early so they could talk to their subcontractors and make sure we could prefabricate as much as possible and do everything we wanted to.”
Contractors involved in the design and construction of the Olympic Velodrome
BDSP Partnership: design services; Bespoke Precast: concrete substructure and superstructure; Ecotricity Group; Expedition Engineering: design services; Foundation Developments: concrete substructure and superstructure; Goodmarriott & Hursthouse: mechanical and electrical; Hopkins Architects: design services; ISG: main contractor; Lee Warren Fabrication & Design: architectural metalwork; Pfeifer Holding GmbH & Co. KG: roofing infill fabric and cable structure; Prater: roof finish and roof lights; R I Building Services: blockwork; Rock & Alluvium: piling; Ron Webb: track design; Schindler: lifts; Watson Steel Structures: structural steelwork; Wood Newton: roof finish and roof lights; Wood Newton: curtain walling/cladding
Structural and civil engineer Expedition’s director Andrew Weir said: “I have worked on projects where they say they have an integrated design team but they actually only get together every Thursday. That was not the case [on the Velodrome] and it has to be throughout the process.
“The diversion to steel arches wouldn’t have happened if ISG had been involved earlier and we were lucky that they did get in at [design] stage B and I would plead with clients to get contractors involved earlier on schemes - they are the experts.”
“It is very difficult to choose sustainable materials because when you go to the market some people say it is too expensive. We need to move, as an industry, towards clients specifying low carbon materials for projects.”
However Mr Epstein said for future Olympics he would set standards even higher as the Velodrome proved energy efficiency targets could easily be increased and he would also increase the measurement of embodied carbon.
An example of the project team working together was in proving that the Velodrome stand structure was fit-for-purpose. The natural frequency of the stand is approximately 2.3 Hertz which falls well below the 3.5Hx recommended by building codes.
However the team provided analysis to justify the lower frequency through detailed computer modelling and post-construction vibration tests to confirm that the level would not cause a problem with crowds in the finished building.