The US$101.5-million biodome project will feature a 112-foot-tall geodesic canopy, created by a diagonal grid structure known as a “gridshell” – a framework of hollow steel sections arranged in a triangular grid pattern. The beams will support a series of lightweight, largely transparent ethylene tetrafluoroethylene (ETFE) pillows that will be stretched between the steelwork and held in tension.

“The arching effect of the gridshell is designed to convert the canopy’s vertical gravity loads and wind pressure into horizontal thrust at various support locations,” explained Anne Fuller, a director of building engineering at AECOM.

AECOM is responsible for all engineering services on the biodome project, including civil, structural, mechanical, electrical, lighting, fire, acoustics, thermal modeling, transportation studies, geotechnical and environmental studies. London-based Proctor and Matthews Architects is also working on the project as a sub-consultant to AECOM.

“The use of advanced 3D technologies within a BIM environment, combined with knowledge of our professionals, enabled the project team to design a fully considered biodome,” says Steven Ferguson, an associate director of building engineering at AECOM. “Finding the optimum form for the gridshell was a collaborative process requiring constant model sharing between the architect and the AECOM engineering team. Daylighting, structural efficiency, internal environment and aesthetics were all modeled and influenced the final form of the dome.”

The biodome is the centerpiece of the expansion of the Chester Zoo, known as “Natural Vision,” designed to establish the zoo as Europe’s largest conservation attraction. The biodome will feature a managed ecosystem that re-creates the plants and wildlife found in a particular region of the Congo rain forest, including gorillas, chimpanzees, okapi, and hippos, among other animals. Visitors will view the plants and animals — which will not be in cages — from paths, treetop walkways and an interactive boat ride through the animal spaces.

Among the technological innovations featured in the biodome is the unique temperature control system. During the day, the excess heat that rises to the peak of the dome will be captured by a heat recovery system consisting of a series of finned coils located within the exhaust air system. Pipes and pumps will distribute this heat to an underground thermal water tank so that the heat can be stored and used at night to maintain the building’s internal temperature.

AECOM also performed solar lighting studies that determined that ETFE pillows will provide a light admittance value of 77 percent and achieve a sufficient average daily level of light intensity for the plants that live in the biodome.