EARTHQUAKE: THE LONG ROAD BACK : How to Turn the Tables on Developing Better Quake Building Codes

Predicting earthquakes may be impossible; minimizing their damage is not. Apartment complexes don’t have to crumple; critical freeway overpasses needn’t collapse.

If California and the country don’t want to relive this week’s destruction every time a major temblor roils the earth, it’s time to invest in technologies that tell us how to build structures that are seismically safe and sound.

While seismographs are terrific for charting the course of a quake, they’re of little use in building quake-resistant highways and houses. A different tool is needed.

Talk to the structural engineers and they’ll tell you the most valuable data for designing and testing earthquake innovations doesn’t come from sophisticated computer models of digitized earthquakes striking simulated structures, but from an aptly named device called a shake table.

Shake tables shake; they can be programmed to physically simulate the bucking and thrashing of earthquakes, real and imagined. The bigger the shake table, the larger the scale model of the structure that can be attached and tested. Design innovations, new materials, innovative construction techniques and even soil conditions can be effectively emulated on the appropriate shake table.

What wind tunnels have meant to the design and development of airplanes, shake tables can--and should--mean for building and retrofitting quake-proof structures. Our earthquake investment policies must now reflect that.

“What this country really lacks is a large enough shaking table,� says Nicholas F. Forell of San Francisco-based Forell & Ellseser, one of the country’s leading earthquake engineering firms. “The shaking tests that we’ve done have been extremely revealing and helpful to us. Computer models are important for design, but even they need the empirical data that comes from the shaking tests.�

“We could have made significant inroads and cut by a significant margin much of the damage that happened (Monday) if the engineering community relied more rigorously on shake table testing,� says Jack Moehle, who directs the Earthquake Engineering Research Center at University of California, Berkeley and is part of the teams investigating the freeway collapses.

Astonishingly, there are fewer than five shake tables of any meaningful size in the entire country. The State University of New York at Buffalo has a 12-foot shake table; the University of Illinois in Urbana, along with the Army Corps of Engineers, has two tables; UC San Diego has a fairly crude one. The nation’s largest shake table is at UC Berkeley’s research center. It’s all of 20 feet long.

By contrast, says UC Berkeley structural engineering professor Stephen A. Mahin, Japan, which is very concerned about seismic design, has no fewer than 20 larger tables. In fact, the largest shake table in the world is on the island of Shikoku off the east coast of Japan--a 50-footer that was originally used to test the integrity of nuclear power plant designs.

“We don’t have the Japanese mentality to test everything that’s possible before we build it,� Mahin says, but he adds that recently the Berkeley center has done shake testing for a handful of private builders.

Still, why don’t insurance companies insist on shake table tests for new building designs or for proposed seismic retrofits? Why, for example, has the California Department of Transportation relied solely on static hydraulic tests for determining highway integrity, rather than pushing for shake table testing of scale models here in the United States or Japan?

Why aren’t shake tables being used to figure out low-cost ways to buttress and reinforce the higher-risk buildings in Southern California? Why aren’t the U.S. Department of Transportation and the Department of Housing and Urban Development working hand in hand with California and the construction community to sponsor more shake table testing?

The answers lie as much in the politics and economics of funding as in any technical problems.

For one thing, shake tables are still seen more as a research tool than as a vital testing medium and so are treated like discretionary academic Tinkertoys. For another, building and construction codes are written independently of the data that can be generated by shake tables--even though, ironically, some of the computer simulations that shape the codes are drawn from shake table tests.

According to Moehle, large shake tables can be built for less than $25 million, and the cost of maintaining them is not particularly high. Indeed, for less than 0.1% of the cost of a space station or a superconducting super collider, America can build devices that help assure that people’s homes and highways are significantly safer. If a shake table test could have saved but one freeway this past Monday, it would have more than paid for itself.

“The earthquake engineering community has not organized well on this,� Moehle acknowledges. “We haven’t gotten our act together; it’s nobody’s fault but our own.�

That has to change. What’s the point of being able to predict earthquakes if many of our key structures are not engineered well enough to survive them? While shake table testing--like wind tunnels--don’t guarantee the safety or integrity of structures, it does offer a cost-effective way to boost their chances for soundness.

As Los Angeles rebuilds from the rubble, it’s essential that state and federal governments recognize the critical importance of investing in testing. Without that investment, efforts to rebuild will merely be futile exercises in tempting fate.