EarthquakesCalifornia implements earthquakes’ lessons
In California, government engineers study structures that did not survive the earthquake, with plans to make improvements to building codes. The most important code changes tend to occur because earthquakes uncover weaknesses in contemporary construction standards.”Every time the earth shakes there’s something a little different about it,” says one official.
When the 5.1 magnitude La Habra earthquake struck Los Angeles on 28 March 2014, city and county officials considered the incident an opportunity to learn and prepare for the next major earthquake. “Every time the earth shakes there’s something a little different about it,” said Luke Zamperini, Los Angeles’s chief inspector for the Department of Building and Safety. Government engineers study structures that did not survive the earthquake, with plans to make improvements to building codes.
According to Tom Heaton, an engineering seismology professor at California Institute of Technology, the most important code changes tend to occur because earthquakes uncover weaknesses in contemporary construction standards. The San Gabriel Valley Tribune reports that the 1971 San Fernando earthquake (Sylmar earthquake) showed engineers that non-ductile concrete buildings, which were made of reinforced concrete and designed to resist earthquakes, could still collapse in a strong earthquake. “There’s more than 1,000 of those buildings in Southern California and they’re probably quite dangerous if they’re shaken strongly,” Heaton said.
Since the Sylmar earthquake, Caltrans, the state agency responsible for highway, bridge, and rail transportation, has retrofitted 2,200 bridges.
Even modern buildings built with steel-framed structures, which were designed to bend during strong earthquakes, have weaknesses that were only discovered after the buildings collapsed. “No one could find bent steel” after the 1994 Northridge earthquake, Heaton said. “Instead they found the connections between the beams and columns had broken before forces ever got large enough to bend the steel.” Thereafter, welding practices were changed for future steel-framed buildings.
The Tribune notes that damage from the La Habra earthquake was minor compared to previous seismic events thanks to lessons learned and the implementation of improved standards. The 1933 Long Beach Earthquake led engineers to discover that traditional brick buildings, or unreinforced masonry buildings, were not reliable during California’s earthquakes, and as a result building requirements were changed in 1934, and in the 1980s Los Angeles identified all the brick buildings built prior to 1934 and retrofitted them.
“Every time there’s an earthquake they find some building system that can be designed better for the future,” Zamperini said. Retrofitting, however, has become a political battle in Los Angeles since the cost associated with upgrading old buildings can be high.
