BridgesResilience of California’s transportation infrastructure questioned
A significant number of bridges and elevated roadways lie above or close to active fault lines, and Californians often wonder how the state’s towering interchanges and freeway network would perform during a major earthquake.The California Department of Transportation (Caltrans) has spent over $13 billion in the last forty years to reinforce vulnerable bridges and interchanges. Caltrans officials note that during a major earthquake, freeways are likely to sustain significant damage, but engineers feel confident that freeways will not collapse.
Californians often wonder how the state’s towering interchanges and freeway network would perform during a major earthquake. A significant number of bridges and elevated roadways lie above or close to active fault lines. “You see it looming, and as you get closer, it just gets taller and taller,” said Noel Vasquez of Whittier, as he eyes the Harbor Freeway before connecting with the 105 freeway. “You drive by and you think, ‘Man, I’d hate for that thing to break.’”
During the 1989 Loma Prieta earthquake, a double-decked portion of interstate 880 crumbled in Oakland, killing forty-two people. The 1971 magnitude 6.7 San Fernando temblor destroyed ramps linking the 5 and 14 freeways in the Newhall Pass interchange. After reopening two years later, the interchange collapse during the 1994 Northridge quake.
The California Department of Transportation (Caltrans) has spent over $13 billion in the last forty years to reinforce vulnerable bridges and interchanges. The Los Angeles Times reports that recently the department concluded a campaign to strengthen tall, flexible bridges and make short, strong spans more elastic. “We used to think that bridges just needed to be very strong, but it’s pretty hard to compete with the magnitude that we face here,” said Tom Ostrom, the head of Caltrans’ earthquake engineering office. “We’ve changed our philosophy to make bridges that are very flexible. They’ll move quite a bit.”
Caltrans has reinforced 555 state owned bridges in Los Angeles County alone, with local agencies having retrofitted about 280 more. Drivers tend to be less concerned about shorter bridges, but they may be more brittle than expected. Caltran engineers have added deeper underground support columns to make the shorter bridges “act taller.” Engineers assure drivers that taller interchanges are safer in an earthquake. “Tall bridges are more flexible,” said Ostrom. “They have the potential to move around more during an earthquake, but they can also absorb more movement.” Seismic pulling and twisting can cause concrete to break apart, so for major interchanges, engineers have encased support columns in steel jackets to prevent concrete from cracking and falling off.
Caltrans officials note that during a major earthquake, freeways are likely to sustain significant damage, but engineers feel confident that freeways will not collapse. “The goal is to keep things from coming down immediately,” Ostrom said. “Some older bridges that are near an epicenter may have to be torn down afterward, but they won’t collapse.”
