The most important thing a city can do to reduce its earthquake risk is to ensure its buildings meet a strong seismic code. San Francisco is rolling out new safety laws about soft story collapse, but not everyone is complying. In response, they're harnessing public pressure to help with enforcement.
The Mandatory Soft Story Retrofit Ordinance requires retrofitting multi-unit soft-story buildings. The law applies to any multi-story wood-framed structure containing at least five residential units with a soft story built since 1978.
A soft story is a floor level that is open with few internal walls like parkades and commercial spaces. The lack of internal walls means the structure cannot resist shear force very well, so are prone to collapsing during earthquakes. When the soft story collapses, everything above it also comes crashing down.
Soft story collapse during an earthquake engineering test.
Building owners had a full year to submit screening forms for the first step of the retrofit program. San Francisco had about 90% compliance, but that last 10% is about to get a lesson in enforcement. The city is mounting placards on buildings that haven't filled out their screening paperwork along with violation notices.
Locations of buildings that did not submit seismic screening forms between September 2013 and September 2014. Image Credit: Screen shot of San Francisco Chronicle map.
Where are the troublesome buildings located? The San Francisco Chronicle has an interactive map of all non-compliant buildings. Remember that these are just buildings where no one submitted a screening form; it has nothing to do with if these buildings need to be retrofit to meet the new seismic building code. But if you do live or work in these buildings, it's probably time to start asking about that form.
The first floor of this building is composed entire of garages with few internal walls to resist shear. Consequently, the soft story collapsed during the 1989 Loma Prieta earthquake. Image credit: USGS/J.K. Nakata
Predictably, not every is happy about how public compliance is with the installation of placards. The LA Times writes:
"You're putting people in panic mode. That would be a horrible thing to put in a window. All you see is the words 'earthquake warning,' " said Huy Le, who owns a salon in the Castro District and leases space underneath a hotel. "It's almost as good as saying, 'Don't come into this building because it's going to collapse.' "
Yet, that's exactly the point. The building owners that didn't submit their forms deserve to be called out: it doesn't matter if they failed to comply due to laziness, ignorance of the law, or the economic decision that paying fines was cheaper than retrofitting. Everyone who uses, or worse, lives in, a building that refuses to adhere to the new seismic codes has the right to know what's going on in order to balance their personal risk and make an informed choice.
From here, building owners will need to either retrofit any building that needs it, or, if they choose not to retrofit, post a formal notice that their building may collapse during an earthquake.
Spray paint marking beams for retrofitting plans. Image credit: John Stamets/Seattle Department of Transportation
Retrofitting soft stories is relatively straightforward: add lateral structure to increase shear strength. The engineering solution is to strengthen existing walls, add new shear walls, or add a steel frame to critical areas. The choice of which technique is most appropriate depends on finances, safety, and building function.
And if they don't retrofit? At least you'll know when you're walking into a seismic timebomb.
Good luck, San Francisco. You deserve to have strong building codes protecting you, and to have knowledge to make smart choices.