Port Absorbers : New L.A. Wharf Area Will Be Test Site for Devices Designed to Cushion Shock of a Quake

A new kind of technology to reduce shaking in structures in a severe earthquake is getting its first U.S. test at the Port of Los Angeles.

Workers last week began installing the first of 46 “sliding-friction isolators” at Berth 136 to prevent a quake from ripping apart a huge new container wharf and wrecking the piles under it.

This type of seismic base isolation system has been used several times in Japan, but its American champion, Los Angeles engineer Marc S. Caspe, has struggled for years to find a suitable project in this country.

Caspe has made proposals to several government agencies to install the sliding-friction devices in medium high-rise buildings or to protect bridges, but authorities believed a more reasonable first use would be a dock designed to hold thousands of freight containers.

The term base isolation covers a variety of systems that seek to reduce shaking in a building by installing shock absorbers. These usually are rubber springs--as will soon be installed in the renovation of Los Angeles City Hall--or sliding bearings at the base of a building.

In the case of Berth 136, Caspe’s sliders are designed to keep the heavy concrete deck from moving in such a way during an earthquake that it would exert crushing, destructive pressure on the piles driven into the bedrock. The piles could then crumble, destroying the wharf.

Although Caspe and other friction-sliding exponents contend that their system is the best protection against such occurrences, some competitors have questioned how long the devices will last, saying they might have to be replaced in about 30 years.

Caspe contends that the devices, which will cost a total of $382,000, will last much longer, at least for the life of the structures they protect.

The berth under construction is close to the Palos Verdes Fault passing through the port area. Although this area of Los Angeles County has not been subject to large earthquakes lately, it had several sizable quakes in the early part of the century.

In a report delivered to a USC audience last week, USC civil engineering professor J.P. Bardet, reporting on an investigation he and Japanese engineers undertook of the Kobe earthquake, emphasized the “massive liquefaction” that wrecked many installations at the Kobe port and two man-made offshore islands.

“Much of Kobe’s port was built on very loose sand, and for some reason they did not compact it,” Bardet said. “They were not expecting a quake of this magnitude. They had twice what they expected. The damage we saw comes when you have a design value quite exceeded by nature.”

In comparison, Bardet said, “in the Port of Los Angeles, if a quake should exceed design values, we would have problems too. The port has many artificial fills. . . . I would expect that a few things we have seen in Kobe will happen in L.A., but to what extent is hard to say.”

Caspe said the port here “is much less vulnerable to liquefaction than in Kobe because our vertical piles extend through the liquefiable layers to hard supports deep in firm soil. On the other hand, the Port of Los Angeles is more vulnerable to strong horizontal forces than in Kobe, because piles are much weaker and more easily damaged than Kobe’s massive concrete structures.”

Before getting the port job, Caspe often discovered that would-be users of the sliding-friction devices were wary of incurring liability if they chose something new and it failed.

Caspe recently testified before California legislators on behalf of a proposal that the state formally absolve engineers, architects and building owners from liability if they use new seismic technologies for the protection of life and property. Eligible technologies would be listed by the state architect.