1,364 Additional Bridges Are Put on Retrofit List : Earthquakes: Caltrans report says 302 highway structures needing seismic strengthening are in L.A. County. Plans call for an accelerated schedule that would be completed by 1997.
Revealing that far more highway overpasses are vulnerable to earthquake damage than once thought, state transportation officials announced Thursday that an additional 1,364 bridges will need strengthening to withstand a major temblor.
The largest number of highway structures newly discovered to be in need of retrofitting--302--are in Los Angeles County, where six bridges collapsed during the Jan. 17 Northridge earthquake, according to a priority list prepared by Caltrans.
Dozens of bridges on most of the major arteries have been added to the list of seismically vulnerable structures, including 61 on the Golden State Freeway, 31 on the Santa Monica Freeway, 20 on the Antelope Valley Freeway and 25 on the Long Beach Freeway.
Caltrans Director James van Loben Sels said the assessment released Thursday represented a new catalogue of highway structures that engineers believe could be damaged in an earthquake. But he said that did not mean any overpasses were generally unsafe or “in danger of imminent collapse.”
Even so, he said the retrofitting would be done on an accelerated schedule that he hoped would allow all the seismic strengthening to be completed by 1997.
“Retrofitting works,” he said. “We had graphic evidence in the Northridge quake that our retrofit program is performing as intended. All 114 retrofitted bridges in Los Angeles came through the temblor in fine shape.”
The new report, issued after Caltrans completed a screening of 1,655 bridges, was a significant departure from a March prediction that only 1,000 more highway structures would need retrofitting.
The repair work called for in Thursday’s Caltrans report represents the second phase of a two-stage seismic retrofitting program that was begun after the 1971 Sylmar earthquake but did not get fully under way until highway bridge collapses in the 1989 Loma Prieta earthquake killed 43 people.
A Times report after the Northridge earthquake showed that even four years after Loma Prieta, the program was moving slowly and more than 80% of the bridges included in the first phase of retrofitting had not been strengthened.
Shortly afterward, Gov. Pete Wilson ordered that the program be accelerated and that retrofitting get first priority on transportation funds.
Caltrans uses a variety of techniques for strengthening bridges, including the placement of steel casings around columns, enlargement of footings and the use of steel hinge restrainers that tie bridge decks to their supports.
Van Loben Sels acknowledged that the number of bridges slated for retrofitting in the second phase was higher than expected but he said it was because engineers had been scrupulously cautious in their examinations.
Caltrans was criticized after the Northridge earthquake because one of the bridges that collapsed during the temblor--a Simi Valley Freeway overpass--had not been included on the retrofitting list for the first phase of the program. Overruling two subordinates, engineers had decided that it could withstand earthquake forces.
Although the new retrofit list included more bridges than expected, Van Loben Sels insisted that the second phase of seismic strengthening would not deepen a financial crisis in the transportation program.
He said it would cost about $1.05 billion to complete that phase, which was almost exactly the amount that officials had been estimating. He said officials discovered after examining each bridge that in most cases the retrofitting work that was required was generally less extensive than had been anticipated.
Because of a revenue shortage in the transportation program, other road and rail projects will have to be postponed in order to pay for the second phase of the retrofitting program. A $2-billion bond issue, which would have paid most of the costs, was defeated by voters in June.
The announcement brought criticism from legislative transportation leaders who still questioned the Wilson Administration’s commitment to the retrofitting program.
Assemblyman Richard Katz (D-Sylmar), whose legislative district encompasses the area most heavily damaged in the Northridge quake, said the program ought to be completed much sooner than 1997. “If earthquake retrofit is going to be their No. 1 priority, they have to stop all other projects except that,” he said.
The Legislature is expected to pass a bill authored by Katz that would require all road projects except safety projects to be halted until the retrofitting program is completed. Wilson is expected to veto the measure. Caltrans officials have said that retrofit and road projects can be completed simultaneously without slowing down the seismic program.
Van Loben Sels said it would be impossible to complete the entire program before 1997 because Caltrans will have to obtain environmental permits before it can retrofit many of the bridges included in the new list. He said some of the bridges on the new list spanned wild and scenic rivers and others were in coastal areas.
Many of those bridges on the coast along Highway 1, he said, were also historic bridges, meaning that retrofitting had to be done in a way that would not change their architectural design.