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The Northridge Quake 20 years later

Posted: January 17, 2014 2:00 a.m.
Updated: January 17, 2014 2:00 a.m.

In this Signal file photo, police officers investigate the scene where the Highway 14 transition to Interstate 5 crumbled and LAPD Officer Clarence W. Dean was killed when his motorcycle went over the edge on Jan. 17, 1994.

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By Luke Money
Signal Staff Writer

It’s been 20 years today since the 1994 Northridge earthquake struck Southern California, toppling buildings, collapsing freeway bridges and rattling citizens in and around the Santa Clarita Valley.

During the two decades since the last “big one” hit locally, officials have worked to update codes and retrofit buildings in an effort to ensure they are left standing should another major earthquake shake the area.

City changes
Since the destructive quake struck, building codes and regulations have been updated to better take into account the risk of seismic activity.

Some older construction techniques have been reduced or outright banned as building practices advance.
One of the major differences is the way in which steel-framed buildings to give them more flexibility in case of an earthquake.

John Caprarelli, an associate engineer with the city of Santa Clarita, used the metaphor of a toothpick versus a paper clip to describe construction changes.

A toothpick will bend to a point and then suddenly snap, he said in an interview Thursday, whereas a paperclip can be bent and twisted much more.

“The big thing we learned in the Northridge earthquake was that buildings were designed like the toothpick,” he said. “The connections were not designed for the building to yield.”

Buildings constructed since then are built in a way that allow joints to be more flexible and better withstand the power of an earthquake.

During the Northridge earthquake, many buildings saw their concrete walls detach from the wood roofs they were supporting. Today, the connections between the walls and roofs are designed to withstand much higher seismic forces than in 1994.

Additional major changes include using plywood shear walls instead of stucco or drywall to make structures more stable and incorporating more flexibility into ceiling construction, among many others.

“The buildings we’re building today, we expect them to perform better based on the new codes and the new research that has been done,” Caprarelli said.

County changes

Similar changes have been an emphasis of the county since the Northridge earthquake, according to Kerjon Lee, a spokesman for the Los Angeles County Department of Public Works.

“Some of the major changes implemented as a result of the Northridge earthquake include placing greater emphasis on residential structures being properly anchored to their foundations and retrofitting buildings made of tilt-up walls and unreinforced masonry,” Lee wrote in an email.

Changes and updates to building codes apply to development and construction moving forward.

But changes can be made to older structures on a voluntary basis. One major example is Santa Clarita City Hall.
“We are currently under way with a steel reinforcement to the City Hall building to meet codes required for housing the city’s emergency operations center in the event of a significant seismic event,” wrote city spokeswoman Gail Morgan in an email.

Work on that project is expected to start in May.

City Hall was heavily damaged during the Northridge earthquake.

“The science we have now really makes it an opportune time for a retrofit,” Caprarelli said.

Transportation

One of the memorable images from the Northridge earthquake is that of the collapsed Highway 14 and Interstate 5 interchange, which effectively isolated the Santa Clarita Valley in the immediate aftermath of the disaster.

In response, the California Department of Transportation reconstructed both spans.

In the aftermath of the 1994 quake, Caltrans identified 1,155 state-owned bridges in need of retrofitting to better prepare them to withstand earthquakes, according to information on the agency’s website.

About 1,152 of those bridges have since been successfully retrofitted, according to Caltrans.

While older bridges were typically built with vertical steel rods that could be stressed or collapse during the lateral movement accompanying an earthquake, the standard now is to incorporate spiraled steel around the rods, providing additional support should the earth start to rumble.

Footings for bridge columns are also typically bigger and drivendeeper into the ground to provide additional support for columns built into softer soil.

Future goals
Despite all the work that has been done over the last 20 years, it’s virtually impossible to prepare for every different disaster scenario.

But one thing is virtually certain; another earthquake will strike the Santa Clarita Valley at some point in the future.

“We’ll do everything we can to make sure our community is safe,” Morgan said.

Lmoney@signalscv.com
661-287-5525
On Twitter
@LukeMMoney

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