Base Isolation at Te Papa

A Major Contributor to Earthquake Safety

Visitors to Te Papa are able to view some of the 152 base isolators that the National Museum sits on. The isolators reduce the severity of the shaking felt inside the building in the event of a major earthquake by as much as 80 percent, protecting both the people and contents inside. Base isolators are large rubber blocks laminated with steel, and with pure lead columns inside which act as an earthquake shock absorber. During an earthquake the lead deforms and is stretched sideways as the earth shakes. It is able to move sideways to a distance equal to its height - a few hundred millimetres being ample for even the most powerful of earthquakes. The rubber and steel then pulls it back into shape ready for the next shock. A typical bearing is less than half a metre high.

Lead-rubber base isolators are the invention of a Wellington scientist, Dr Bill Robinson. Like many good inventions the concept is simple and was developed out of a morning tea conversation about energy absorption. The first structures to use the bearings were the William Clayton building in Wellington in 1981 and the Toe Toe and Waiotukupuna bridges also in 1981. Almost thirty years after that morning tea, there are now an estimated 10,000 buildings and structures around the world, including in Japan and California, that have been fitted with isolators, with more undergoing the renovation every year.

They have been installed under Wellington’s parliament buildings, including the Parliamentary Library, the Wellington Press building, several historical buildings, and other key public buildings in Wellington city. In the United States, the San Francisco City Hall and the Golden Gate Bridge approach now rest on base isolators.

Take the stairs down where it says Quake Breaker outside the museum’s main entrance to see a cross-section of a base isolator, and a ‘scratch pad’ that shows the movement between a base isolated building and its base. A video and interactive ‘shake table’ demonstrate how base isolation works, and what happens to a base-isolated building during an earthquake.