Monday, April 5, 2010
San Diego roads and buildings appear to have sustained relatively little damage from Sunday's earthquake. Seismic engineers say current building codes protect newer structures from the kind of shaking experienced here, but older structures are vulnerable.
Caltrans engineer, Dennis Wilder, says their protocols require bridge inspections within a 50 mile radius of quakes that measure more than 5.5. The shaking in San Diego did not get that strong. But Wilder says Caltrans crews were out this morning checking on the temporary supports for concrete overpasses under construction. He says they had to tighten up some supports.
A crack in Interstate 8, east of El Centro, should be patched by this afternoon.
Wilder says Caltrans is responsible for some 400 structures in San Diego. The agency changed its building codes in 1971 to make bridges more resistant to earthquakes. Structures built before then, including the Coronado Bay Bridge, were retrofitted by 2001.
Medhi Shadyab a senior structural engineer with San Diego city’s development department, says he responds to calls when people request an inspection.
He says the damage reported to the Sheraton Harbor Island was to the seismic joints connecting the three hotel towers, rather than to the towers themselves. The hotel will have to get the damage repaired by a licensed contractor.
Shadyab says city ordinances require retrofitting buildings constructed before 1939, since many of those were made of un-reinforced brick. The most recent code update for buildings in the city was in 2007.
Seismic engineer Chris Poland of Degenkolb Engineering says the energy of the shaking experienced in San Diego was actually 1/10 of the amount that houses are currently built to withstand. But, he points out, older buildings are more vulnerable.
“Most people believe that because the building department allows you to continue to use a building, it means that it meets the modern code and it’s safe,” Poland said, “but what it means is, it meets the code of the day it was built.”
Poland says houses built after the mid 1980s are more likely to be designed to withstand earthquakes. He says more than 80 percent of the buildings in California were built before the mid 1980s.