Keeping still in an earthquake
The new Wellington control tower has been designed to be one of New Zealand’s safest buildings.
Over the last fortnight, the construction team have been working to install 13 base isolators with the tower foundations to protect it in the event of an earthquake.
Base isolators are like shock absorbers for buildings. They're flexible bearings made of layers of rubber and steel, with a central core of lead, which separate (isolate) the tower's foundations from the ground and would absorb most of the movement during an earthquake, keeping the tower intact.
The technology was actually first invented in Wellington by seismic engineer Bill Robinson in the 1970s. It's now used extensively in seismic sensitive countries around the world, including Japan and the USA. In Wellington, base isolators have been installed below Parliament and in the foundations of Te Papa, Wellington Hospital and the Wellington Central Police station. The approach means the new control tower will meet 100 % of the building code.
Despite being a popular method of seismic protection, the use of base isolators for the tower is actually a bit unique. Typically, they're used in buildings that are wider than they are tall. To account for this, the concrete base of the tower has been designed to make the structure bottom heavy allowing the base isolators to work. Interestingly, 66% of the weight of the full tower structure will be underground.
Now that the base isolators are in place, the concrete base of the tower will be built on top and construction will move above ground.
June 2016: Base isolators installed
May 2016: Foundation concrete raft slab poured
May 2016: Steel reinforcing cage for the raft slab complete
April 2016: Excavation complete
February 2016: Piling excavation begins
5 January 2016: Construction officially begins
Base isolator close up image sourced from the Wellington City Council.