SACRAMENTO — Caltrans' chief of structures said Thursday that the very system designed to prevent the Nimitz Freeway from collapsing during an earthquake may have contributed to the magnitude of the double-decker roadway's failure during the Oct. 17 Bay Area quake.
Responding to questions at a news conference, James E. Roberts said the Caltrans project of tying sections of bridge roadways together with steel cables to prevent them from coming apart could have contributed to the collapse of the one-mile section of freeway in Oakland. At least 39 people were killed when the top deck collapsed onto the lower. The Nimitz roadbed was lashed together in 1977.
Roberts explained that tying the roadbed sections together may have caused the entire structure to sway as a single unit, putting tremendous pressure on all the vertical columns at the same time.
"They (the columns) might have all broken at once," he said. "It just seems strange that it dropped straight down. Because I've sure never seen it (before) and you can look at earthquake pictures from all over the world." Although UC Berkeley engineers looked into that possibility during a study conducted after the quake, they announced Wednesday that results were inconclusive. The preliminary finding of the UC Berkeley analysis is that the primary cause of the Nimitz collapse was inadequately reinforced joints or "hinges" where vertical columns meet horizontal supports at the roadbed.
Roberts agreed that weaknesses in the hinges probably were a factor but said that he believes there were multiple causes for the structure's failure.
Gov. George Deukmejian took a step toward determining a definitive cause for the collapse by appointing one of the world's top experts on earthquake engineering to head a special investigation into the disaster.
George W. Housner, 78, a former Caltech professor, is described as the "father of earthquake engineering."
Housner, who taught at Caltech for 36 years and is now a professor emeritus at the university, will replace Ian G. Buckle, a New York earthquake expert who was the governor's initial choice for the job.
Deukmejian rescinded his appointment of Buckle, deputy director of the National Center on Earthquake Engineering Research in Buffalo, after Buckle wrote an article in The Times absolving Caltrans of any blame in the disaster even before his investigation had begun.
The governor announced his new appointment Thursday in a speech dedicating the Beckman Institute at Caltech in Pasadena. Housner is chairman of the National Academy of Sciences committee on earthquake engineering.
"I am confident that Prof. Housner is extremely well qualified to lead this important inquiry," Deukmejian said.
Deukmejian has said he was shocked and "sickened" by the collapse. He said no one at Caltrans ever told him that the Nimitz or any other freeway structure could collapse in an earthquake of the magnitude that leveled the Nimitz.
One of the tasks of the governor's independent examining team will be to determine if Caltrans should have known that the Nimitz was vulnerable and if there was anything the department could have done to strengthen the freeway.
In a statement released by his office, Deukmejian said he and Buckle agreed that Buckle should not lead the inquiry. "The team's review of the I-880 collapse must be fair, objective and complete," Deukmejian said. "The public will be satisfied by nothing less."
In contrast to Buckle, Housner is a world-renowned engineer with no connection to Caltrans. He also is a Californian, a trait that many in the state's engineering community consider crucial for anyone who is going to lead such an important investigation.
"George Housner is the father of earthquake engineering," said Wilfred Iwan, a colleague of Housner at Caltech and former chairman of the state Seismic Safety Commission. "His integrity and objectivity is beyond reproach, and he possesses the stature in the community to attract good people to participate in this activity."
Housner has consulted on earthquake matters for dozens of government agencies and private companies. He led inquiries into the Alaska earthquake of 1964. Earlier this year, when the Earthquake Engineering Research Institute established the George W. Housner Medal to honor outstanding contributions to earthquake engineering, Housner was the first recipient.
A final answer to what caused the Nimitz disaster is not expected for several months. Immediately after the earthquake, many engineers speculated that the freeway collapsed because of failures in the vertical columns, which might have been prevented by reinforcing the supports with steel jackets.
Even though the UC Berkeley findings and similar conclusions reached last week by UC San Diego engineers have shifted the focus to the column hinges, speculation persists as to what could have been done to prevent the disaster.