Old, unreinforced brick buildings — also known as unreinforced masonry, or URM — have long been the focus of concern in quake-prone areas, including San Luis Obispo County.
So far, retrofitting requirements have focused mostly on URMs, but that’s changing.
The city of Los Angeles recently passed an ordinance requiring investigation and, if necessary, upgrades of other types of buildings prone to collapse in earthquakes.
That action should trigger other areas, including San Luis Obispo County, to consider whether they need to expand seismic safety policies.
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The two types of buildings targeted by the new Los Angeles ordinance are:
▪ Pre-1976, brittle concrete buildings that lack the steel reinforcement to safely withstand a quake. Los Angeles has a preliminary list of 1,500 buildings that may fall into the category. Industrial buildings and warehouses account for most, but there are schools, shops, offices, hotels and parking structures on the list as well. And not all are big, multistory buildings. Single-story structures occupied by fewer than a dozen people are on the list, too.
▪ Older, wood-frame “soft-story” buildings. Apartments with carports on the bottom floors and housing units above are the most prevalent. However, offices and stores with lots of big windows on the ground floor can also be seismically vulnerable.
We contacted local officials in three jurisdictions — the cities of San Luis Obispo and Paso Robles and San Luis Obispo County — and all of them told us they don’t believe there are many buildings here that fall into the brittle concrete or soft-story categories. However, it would require an inventory to come up with a definitive number.
We believe it’s worth taking that step.
These are buildings known to be more prone to collapse in earthquakes. And even if there aren’t many around, the seismic failure of even a single building can have tragic consequences. We saw that in the 2003 San Simeon Earthquake, when two women were killed after the Acorn Building in Paso Robles collapsed.
Additionally, 16 people died in the 1994 Northridge Earthquake when one soft-story apartment building collapsed.
In the wake of that disaster, several cities — including San Francisco — passed ordinances targeting soft-story apartments.
Of course, we don’t have nearly as many apartments here. And most of the soft-story apartment buildings we saw have just a single story above the carports, which is not as much of a concern. (San Francisco requires retrofitting of soft-story apartments only if there are five or more units and two or more stories over a basement or underfloor area.)
Still, given the potential for disaster, we believe it makes sense to determine if there are any brittle concrete or soft-story buildings that could pose a problem.
If there aren’t, job done.
If conducting an inventory would be too costly or time consuming, here’s an idea: involve Cal Poly students. That happened in the city of Berkeley. Graduate students in UC Berkeley’s engineering program partnered with the city in a walkabout to identify soft-story buildings.
Bottom line: Following the San Simeon Earthquake, local communities did an excellent job of speeding up the timetable for retrofitting unreinforced masonry buildings.
If there are other types of buildings that pose a similar risk of failing in an earthquake — a risk that can be avoided through retrofitting — they should be the focus of similar efforts.