Wednesday, September 08, 2010

EARTHQUAKE ENGINEERING OF THE DAY: Base isolation

billindxIt's surely occurred to everyone at some stage during an earthquake that when the ground is moving underneath you, the best place to be would be well away from the ground.

That thought also occurred to a very smart New Zealand engineer back in the 1970s, Dr Bill Robinson (right), and in 1976 he developed a system to do it that is now implemented in around 3,000 buildings and bridges worldwide—including, unfortunately, Wellington’s parliament buildings (simultaneously protecting its inhabitants, and making the idea of a Wellington earthquake far less attractive).

lead_rubber Robinson’s basic system is essentially a lead-rubber bearing (left) placed between the ground and a buildings foundations either during original construction (as with Te Papa) or afterwards (as with the parliament buildings) to reduce the force exerted on the building by the ground’s movement.  The outer rubber “sandwich” gives the bearing flexibility, while the lead damps down the movement and absorbs the earthquake’s kinetic energy, turning it into heat. 

 isolation1figure3Working together in the same way a car’s springs and dampers do, they reduced the earthquake force in buildings and bridges in both the Northridge and Kobe quakes to about one-fifth the seismic force that un un-isolated building or bridge would suffer—allowing bridges, hospitals and buildings necessary after a major shake to to ride out the earthquake undamaged, even while all around them is a sea of destruction.

You can see how effective it is in these videos of building models on a “shake table” set up to compare buildings that have been base-isolated and those which haven’t.  It’s a pretty persuasive demonstration.

Since Robinson’s invention of the lead-rubber bearing, many other systems have been developed following the same principle—including base-isolated tables designed to protect fragile objects during a quake. And there’s even one Canterbury economist who’s protecting his child right now with what he calls “a Gerry-rigged earthquake base isolation unit” for his 4 month old, which has successfully kept Eric Crampton’s youngster safe through two aftershocks.

There’s a neat video here at the Science Learning site where Robinson explains the life-saving concept of his lead-rubber bearing and how he came up with it—and there’s plenty more links there to take you further…

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11 Comments:

Blogger Owen McShane said...

One good idea leads to another.
You may remember that Chris Parkin owned the hotel that they moved across the road in Wellington.
He was in the DFC office in San Francisco at the time the Base Isolation system was licensed to a Californian company and was naturally familiar with the "base isolation" idea.
It always seemed to me that it was that experience that made him realise that you could pick up a whole hotel and move it across the road.
Different technology but the concept has to come first.

9/08/2010 02:47:00 pm  
Anonymous James said...

Good thing that state regulation can magic these things up eh?

;-)

9/08/2010 02:53:00 pm  
Blogger Dave Mann said...

Honestly Peter, this blog is absolutely fantastic.

Thank you for a great and informative article. Where do you find the time to write this amazing stuff?

9/08/2010 03:51:00 pm  
Blogger Oswald Bastable said...

When I lived in the Village of the Damned, I wondered how the quake-proofing that was going on at the time would hold up when put to the test.

Looks like it did!

Thanks to ENGINEERS (not the frickin' council) those magnificent old structures preserved are still there.

9/08/2010 05:48:00 pm  
Blogger Oswald Bastable said...

A strong smell of sulphur spreading across Christchurch's eastern suburbs is unlikely to be gas and there was no cause for concern, Civil Defence says..."

I can answer this one.

I worked doing drain laying in the Village of the Damned some years ago.
The gas lines from the old coal gas plant leaked and the smell of this gas permeated the soil throughout the city. When you dig, you release the smell.

I'm picking that the subterranean disturbances have released this rater foul but harmless odor.

9/08/2010 07:32:00 pm  
Anonymous Falafulu Fisi said...

Here is one research paper from Department of Architectural Engineering, The Pennsylvania State University, that I came across which may be of interest to engineers/architects:

Abstract:

Architectural precast concrete cladding systems are considered non-load bearing wall systems and are designed primarily to transfer their self-weight and out-of-plane lateral loads to the supporting building structure. They are typically not designed for significant structural in-plane forces resulting from
cladding-structure interaction. In fact, modern earthquake-resistant design requires that these cladding panels
be isolated from the lateral force-resisting system. Finite element technique was employed to study precast concrete panels and special modeling strategies were developed for panel connections to the structural frame. The precast concrete panel was designed to participate in the building lateral force-resisting. Finite element modeling techniques were adopted to better understand the strength and stiffness characteristics of these concrete cladding panels subjected to significant in-plane loading. Good correlation was obtained between
finite element modeling results and existing experimental results. The analytical results were used to develop a simplified mathematical model that can be incorporated into suitable building models to evaluate its
performance as a lateral force-resisting system to withstand earthquake-induced lateral loads.


Finite Element Modeling of Reinforced Concrete Cladding Panels

9/08/2010 08:44:00 pm  
Blogger Eric Crampton said...

Here's my base isolation apparatus for the 4 month old. Works well.

9/08/2010 09:24:00 pm  
Blogger Gary.Dierking said...

The Kaiser Center in Oakland California, a 28 story building completed in 1960, was also built on rubber mounts. That seems to predate the "Kiwi invention".
http://en.wikipedia.org/wiki/Kaiser_Center

9/09/2010 07:36:00 am  
Blogger Gary.Dierking said...

The Kaiser Center in Oakland California, a 28 story building completed in 1960, was also built on rubber mounts. That seems to predate the "Kiwi invention".
http://en.wikipedia.org/wiki/Kaiser_Center

9/09/2010 07:36:00 am  
Anonymous Sean Fitzpatrick said...

For those outside Welly if you visit Te Papa you can see the buildings base isolators - just walk into a small display near the front door and there is a whole section about them with a light shining under the building to reveal them.

9/09/2010 08:03:00 am  
Blogger Owen McShane said...

Gary Dierking
The 1960 system of rubber mounts does not pre-date the Kiwi invention.
If it had we would not have been granted the US patent.
The Kiwi base isolation system is a total system which includes a lead rubber bearing in which the lead absorbs the kinetic energy – indeed in a serious quake the lead may melt and need to be replaced if it escapes.

9/09/2010 09:11:00 am  

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