bioneural.net

Sitting on the edge of the Pacific plate, New Zealand experiences regular tectonic (and volcanic) activity. The 1931 Napier earthquake taught builders an important lesson: while flexible wooden buildings generally survive a moderate quake, brittle (e.g. masonry) structures will not. On October 29 2006 the NZ House of Representatives put on a parliamentary Open Day, and we took the opportunity to tour Parliament House (and eat lunch in the Beehive). The highlight was a visit to the basement to learn about the base isolation earthquake proofing—shock-absorbers—used in Parliament Buildings, a system invented in earthquake-prone New Zealand and now in use around the world.

The seat of government in New Zealand is an uncomfortable 400m from the Wellington Fault. During the course of 1992 to 1995, the masonry-built Parliament Buildings were separated from their solid foundations to create a 20mm "seismic gap" and rested upon 417 rubber and steel "base isolators". A supplementary measure to minimize the need for strengthening with concrete, these devices reduce the transfer of horizontal force through the ground into the building's structure. Essentially the malleable lead core of the base isolators, which look like stumpy pillars, allows up to 300mm of sideways "wobble" in the event of an earthquake. This lateral motion stretches the surrounding rubber shell of the isolator, which counters the movement by attempting to revert to its resting (unstretched) state. Laminated steel plates are also used in the isolators to provide additional strength. With this system in place, the maximum probable movement is considered to be 200mm, resulting from an earthquake having a Modified Mercalli Intensity of 9; this type of quake is predicted every 220 to 350 years, and is likely to cause only minor non-structural damage within the isolated Parliament Buildings.

I just love this whole concept, utilizing the natural and counter-effective properties of two common materials to balance out an "untamable" natural force. The engineering feat of sawing horizontally through the building's foundations and temporarily jacking it up to insert the isolators simply astounds me.

As access to the Parliamentary basement is exceptional, the best place to see a base isolator in situ in Wellington is Te Papa on the waterfront. Stairs just outside the entrance to the museum lead down to a "quake-breaker" viewing area. There are 152 base isolators beneath the museum, said to reduce the severity of any shaking by up to 80%. The display includes a base isolator in cross-section and an interactive demonstration of their function. The isolators used in Te Papa are of a different design from those used in Parliament Buildings, being square rather than rounded.

Base isolator in situ at Te Papa

Actions Send this article link by e-mail Print this article without other content Follow responses to this article: comments Follow tag feeds: geotag, New Zealand, wellington. Share on Delicious Digg Facebook StumbleUpon Twitter View on map (geotagged at lat -41.2900887, lng 174.7813416) Create a waypoint in RouteBuddy Find nearby images in CDFinder Find nearby people using Twitter Translate this page: DE | ES | FR