A major feature of the new building is a spectacular spiral walkway that winds its way up from the lower ground level, around the assembly room, and then up to the public gallery on the top floor.
The walkway, a 1,500mm wide by 400mm deep composite steel and concrete box, will be hung with minimal supports, making it a prime candidate for a Millennium bridge style wobble. The walkway will connect to each storey at floor level, but between floors will be supported from the 'diagrid' in a maximum of two locations.
The design team immediately recognised the potential for a 'Millennium Bridge effect', and has specified that lateral damping be provided in the form of an energy-absorbing bituminous plastic layer installed between the steel frame and concrete body.
The diagrid - a tubular steel lattice-like grid structure - supports the walkway as it spirals above the assembly room, transferring the load to the main body of the structure via connection with the primary columns at every second storey.
The grid sweeps down from roof level to the ground, carrying the glazing that forms the roof and enclosing the assembly room and lower ground floor atrium.
To stop downdrafts in such a large open space, water at 65degreesC will be pumped through the lateral hollow steel sections of the diagrid to provide trace heating.