Is Sutro Tower Seismically Safe?

Cover story, The Independent, January 31, 1998
(quoted with permission)

By Emily Soares

Heated disagreement over addition of new antenna to structure

Residents living in the shadow of Sutro Tower- many of whom are worried about the tower's structural integrity if the city approves plans for the installation of a digital-television antenna - were dealt a blow last week when the Building Inspection Commission decided not to require more stress testing of the tower than is asked for in the city building code.

The commission issued the decision at its January 21 meeting, after hearing testimony on behalf of community members who have safety concerns about the antenna. Residents fear that if the 10-ton antenna is approved and installed without additional l tests, the tower will be at risk of collapse during an earthquake - a fear that has been echoed by some seismic-safety experts.

An appeal filed by the Twin Peaks Improvement Association charged that the Department of Building Inspection should have mandated additional seismic testing of the tower when the DBI determined it to be an "essential facility" on December 3.

Under state law, essential facilities, or those structures capable of providing public services after a disaster, require higher seismic standards than other structures, a condition that the antenna-project sponsors and the DBI say the tower already meets.

Project sponsors claim that retrofit work currently under way on the tower will make the structure even more sound than is required by essential facility standards.

But a member of the California Seismic Safety Commission, Lloyd Cluff, speaking as a Twin Peaks resident, holds that the approval of the 10-ton antenna without testing based on new seismic data would be "foolhardy."

Cluff, who has studied similar towers internationally, contends that recent findings on the behavior of steel structures gathered in the wake of the Northridge and Kobe, Japan, earthquakes show that more rigorous seismic testing and higher seismic standards should be applied to towers like Sutro.

"We have empirical data that shows that some of these structures have collapsed," Cluff told the Independent. "I'm worried about the safety of the community."

Cluff and some other seismic safety experts argue there is no way to accurately determine the seismic soundness of the 977-foot tower, the tallest structure in the Bay Area, without applying the new data to a dynamic analysis, a procedure that tests the strength of a structure when in motion, such as that produced during an earthquake.

The DBI has maintained that it will not require any tests that aren't specified in the building code, but residents argue that the city has jurisdiction to require testing beyond the code if public health and safety warrant it.

Permit approval pending

Neighbors fear that if the DBI does not take action to require more tests, the antenna permit may be approved at a scheduled February 19 Planning Commission hearing without the tower having been sufficiently reinforced.

Project lobbyist Robert McCarthy argued at the commission meeting that the digital television, or DTV, antenna would account for only a minor percentage increase in the structure's overall weight of 1,800 tons.

The vice-president and general manager of the tower, Eugene Zastrow, also says community fears are misplaced. "My sense is that the tower would be the last thing to go in an earthquake," Zastrow told the Independent, explaining that it had been built to withstand an 8.3-Richter earthquake.

But Cluff charges that the data used in tests to determine how much shaking the tower could withstand are now obsolete. "The thing I want them to do is to look at performance under earthquake conditions that we now know are likely to occur," said Cluff. "The analysis they did was 20 years ago, and they got everything right but the answer."

FCC-mandated change

The move to DTV is mandated by Federal Communication Commission law and must be implemented by area broadcasters by May 1999. Several of the tower's owners, a consortium that includes KRON, KPIX, KGO and KTVU, have voluntarily opted for a November 1998 deadline.

At the commission meeting, McCarthy charged that community-safety concerns were intended to make meeting that schedule impossible. "This is just another effort on the part of a small group of neighbors to make us miss that deadline," he said.

Neighbors say they are not surprised by the DBI's decision. "Our intention is to keep on working and letting the public's voice be heard through the environmental-review process," said Doris Linnenbach of the Twin Peaks Improvement Association. "We had to exhaust our administrative remedies," she explained.

To confirm the date of the Planning Commission hearing on Sutro Tower, call 558-6422.

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