Building the London Aquatics Centre was a huge feat. Here are some of its unique construction facts.
The roof is supported by a concrete wall at one end, with two columns holding up the other end 125 meters away. The roof then cantilevers an additional 40 meters, creating the illusion that it’s suspended in air. To pull off this effect, the contractor had to build temporary vertical supports, called trestles, to remain in place as the roof was painstakingly erected section by section.
Permanent horizontal trusses were also installed, and varied in size, with some so large that they had to be delivered in smaller sections and bolted together on-site. The horizontal trusses rested on the temporary vertical trestles.
“The deepest part of the roof is 12 meters,” says Robert Hearn, project director for contractor Balfour Beatty Engineering Services Ltd. in London. “So you have a vertical part of a truss 12 meters by a span that may be 30 meters. You can’t transport something that big.”
Sections of the roof had to be lifted flat. This was carried out with three cranes — two smaller ones at the ends of the truss and a larger in the middle. The two end cranes lifted each truss in a horizontal plane until they were high enough off the ground that the central crane could lift to turn the truss vertically. The truss could then be lifted into position.
Once the 10 roof trusses were complete from wall to core, the trestles needed to be removed with a technique called strand jacking. The top of the cores where the roof joined the structure acted as a pivot point, while the main section of roof was lifted off the supporting wall. The roof was elevated into the air approximately a meter, allowing the support on the top of the trestles to be removed.
The roof won the Structural Steel Design Award, from the British Constructional Steel Association and Tata Steel.
The pools, surrounding changing rooms, showers and other amenities were positioned approximately in the center of the building and required the most excavation and concrete work. With all this occurring, crews didn’t have room to build the roof and lift it in pieces. They needed an open expanse to bolt together trusses and put the roof in place.
Because of this, Balfour Beatty had to build the roof first, then construct the pools and surrounding structures underneath it.
“The roof was such a complex ergonomic structure,” Hearn says. “Just the steel structure itself weighs more than 3,000 tons. So to lift it on afterwards [would be] more of a challenge than building it with flat ground.”
With the roof in place, the various subcontractors and crews worked from the center of the building out.
“It was to allow heavy machinery in to do all the digging work and the concrete work, and slowly you sort of dug your way out of the building,” Hearn says .
Infrastructure of safety
At one point there were 39 cranes on site, with crews from several contractors in the area at once. Keeping everyone safe was one of the toughest logistical challenges. “While the cranes are in operation, you may have people within the structure building the pools, and you might have people installing within the roof space,” Hearn says. “So you have multi-leveled activities, and at the same time you’ve got a number of cranes winching materials at high levels around and near where people are working.”
To meet the safety goal, daily briefings were held every day before work began, with Balfour Beatty’s key managers, along with supervisors from each of the trades working that day, to discuss where cranes would be, which large deliveries would occur and which routes on the site were safe.
“It was a quick half-hour meeting every single morning,” Hearn says. “But all the trades working out there were aware of where the big items were, and that information was then disseminated around to all the workforce, so everyone knew which crane was moving, which crane was lifting something, etc., all day.”
Additionally, one individual was put in charge of determining the safe routes and monitoring to make sure workers didn’t stray into danger zones. Another kept track of deliveries. “Everything was pre-planned so people knew when things were going to happen and how they were going to happen,” Hearn says. “There was just continuous communication with everybody.”
The entire London Aquatics Centre sits on land that has a water table merely 2 meters below the surface.
“A lot of the piles are not just holding the building up, they’re pulling it back down as well,” Hearn says.
Waterproofing the shells also was critical. This was done by forming with waterproof concrete and using strips of hydrophilic waterstop in each joint.
“The hardest bit was to make sure the pools were watertight, not from a point of view of water leaking out, but actually water trying to get back in, as well, from outside,” Hearn explains.
On-site batch plant
The pools were built of concrete that came from one of two batch plants that were on the site itself.
Regulations by the Fédération Internationale de Nata require that both the competition and warm-up pools measure at least 50 meters (not a millimeter under), and can go over by no more than 10 millimeters. In addition, no gaps between moving elements could measure more than 7-1/2 millimeters to meet safety standards.
The training pool was built underground in an area that has no natural light. The designer recessed the equivalent of approximately 1,000 lights in the ceiling, and covered them with concrete petal cut-outs. The net effect was designed to simulate sunlight as closely as possible.