EarthquakesSeismic retrofitting of older buildings helps, but it has its limits
Even before last Sunday’s magnitude-6 earthquake struck Napa, officials anticipated that such an event would damage many of Napa’s historic brick buildings. So years ago, brick structures were required to get seismic retrofitting — bolting brick walls to ceilings and floors to make them stronger. “We can’t keep every single brick in place in many of these older buildings without extraordinarily costly retrofits,” says a structural engineer. “We can reduce the damage in losses, but not eliminate them entirely in older buildings.”
Even before last Sunday’s magnitude-6 earthquake struck Napa, city officials anticipated that such an event would damage many of Napa’s historic brick buildings. So years ago, brick structures were required to get seismic retrofitting — bolting brick walls to ceilings and floors to make them stronger. Napa’s landmark Alexandria Square building was retrofitted years ago, but the recent earthquake caused the walls on the top floors of the 104-year-old property to crumble.
“We can’t keep every single brick in place in many of these older buildings without extraordinarily costly retrofits,” said Fred Turner, structural engineer with the California Seismic Safety Commission. “We can reduce the damage in losses, but not eliminate them entirely in older buildings.”
Governing reports that many cities in California require building owners to seismically retrofit old buildings. Los Angeles passed a law in the 1980s requiring brick buildings to be retrofitted, so when the 1994 Northridge quake struck, only a few buildings crumbled and no one died inside them. “It’s not a guarantee,” said Napa City Manager Mike Parness of retrofitting brick buildings. “A strong enough earthquake is going to cause damage.”
By 2009, twelve of eighteen identified historic brick buildings in Napa had been retrofitted, while three buildings were in the process of retrofit planning. Brian Silver, the owner of the buildings could not afford the $500,000 retrofitting cost, but after last Sunday’s earthquake, he plans to bring his buildings up to code. He warns, however, that retrofitting a building does not guarantee that the buildings will emerge unscathed.
“There’s a limit to that level of retrofit,” said David Cocke, a member of the Structural Engineers Association of Southern California. “Everything has got to work right, and if the shaking is strong enough, it could still result in a dangerous situation. And no owner is going to spend the money to come in and make that particular building as strong as a hospital. It’s just not going to happen; it’s not economically feasible.”
