Changes Urged in L.A. Double-Decking Plan

With a few design changes, the proposed double-deck Harbor Freeway in downtown Los Angeles “would certainly not collapse” during a major earthquake, the Governor’s Board of Inquiry into the Oct. 17 Bay Area earthquake was told this week.

During the board’s meeting Wednesday and Thursday at Caltech, two Southern California engineering professors offered insights into a report they have prepared for Caltrans examining plans for an upper level for the overburdened freeway.

Construction on the milelong upper deck had been scheduled to begin last month.

But after the Oct. 17 Northern California quake caused the collapse of the elevated double-deck section of the Nimitz Freeway in Oakland, Caltrans asked a group of academic engineering experts to review its plans for the Harbor. Design changes suggested by the Harbor Freeway contractor after the quake also were examined.

UC San Diego Prof. Nigel Priestly and Prof. Ronald L. Scott of Caltech said their committee considered an earthquake of magnitude 8 on the San Andreas Fault or--potentially more damaging to the Harbor Freeway--a magnitude 7 quake on the Newport-Inglewood Fault, which parallels the double-deck section and is only three or four miles from it.

“We concluded on the basis of the analysis . . . that it would certainly not collapse” in earthquakes of those magnitudes “or even in a bigger earthquake,” if design changes are made, Priestly told the 11-member board.

Priestly emphasized that the committee thought “some aspects could be improved” in both the original design and the suggested changes proposed by the contractor.

“This is in fairly soft soil, so there could be significant displacement,” he said. “We are confident it can ride out those (quakes) providing some fairly minor adjustments are made to the design.”

Beyond that, he did not elaborate on what changes the committee recommended.

Though Priestly described the recommended changes as minor, Scott emphasized that the changes must be made.

Asked if the committee found the design basically acceptable without the unspecified changes, Scott said pointedly: “I think there is a statement in there that it is not acceptable. Our report is quite critical in places. It says that work has to be done.”

Caltrans must decide whether to adopt the proposed changes.

The scientists said the proposed 67-foot-wide Harbor Freeway upper deck--poised on 50-foot-high single columns rooted 70 feet into the ground and designed for use by multipassenger vehicles--would withstand such quakes, even though the deck would sway four feet.

“I am trying to picture driving a bus up there,” said inquiry board member Robert Wallace, a geologist emeritus with the U.S. Geological Survey.

“That would be extremely difficult, I think, to control a vehicle,” agreed Scott, pointing out that the committee was asked to determine the effect of potential earthquakes on the freeway, not on vehicles traveling on it.

The board, which must report to the governor by June 1, also heard about the city of Los Angeles’ efforts to make its buildings earthquake safe.

Karl Deppe, chief of the city’s Earthquake Safety Division, said that as of last month 5,600 of the city’s 8,200 buildings requiring work to bring them up to code have been or are being strengthened. He said the city program, which began in 1981, will be completed in 1992.