Each year, Simpson Strong-Tie teams up with the West Coast’s top earthquake scientists and preparedness experts to take questions from Redditors about earthquakes and tsunamis. The Reddit AMA is part of the Great ShakeOut, the world’s largest earthquake drill, where 55 million people drop, cover and hold on. The next Great ShakeOut is scheduled to take place at 10:17 a.m. on October 15, 2020.
This year’s AMA guests were:
- Emory Montague — Simpson Strong-Tie R&D engineering manager (expert on structural engineering during earthquakes)
- Jon Siu — City of Seattle, principal engineer and building official
- Marc Eberhard — University of Washington, professor of civil and environmental engineering
- Bill Steele — Pacific Northwest Seismic Network, director of communications
- Corina Forson, Daniel Eungard, Alex Dolcimascolo — geologists and tsunami experts with the Washington Geological Survey
- Elyssa Tappero, Maximilian Dixon, and Brian Terbush — earthquake, tsunami, and volcano preparedness experts with Washington Emergency Management Division
- Amanda Siok — FEMA Region 10 earthquake program manager
Returning for his sixth year to share structural engineering knowledge on behalf of Simpson Strong-Tie was our R&D engineering manager, Emory Montague.
Below we’ve pulled some of the highlights tackled by Emory.
Question by ablue312:
How much should we be willing to invest in earthquake retrofits to our home? For example, is $20k enough to install a reasonable level of retrofits on an average home? I understand it is variable based on the home and local environment, but I’m just looking for a ballpark estimate.
Is “the big one” likely to trigger an eruption from Rainier or any other volcanoes?
This was a two-part question. Emory tackled part one while Brian tackled part two.
Answer by Emory:
For the first part, if you hire a qualified professional retrofit contractor to perform a retrofit, the costs do vary as you point out based upon the complexity of the work required. For example, retrofit costs can range from approximately $5,000 up to $30,000 or more. If the home has a finished basement, and drywall has to be removed to access the wood framing, then the cost could be toward that higher end.
Follow-up by Brian:
For the second part of the question: It didn’t happen in 1700 (last time we had a “Big One,” and it didn’t happen in Japan in 2011, or Sumatra in 2004 — two other extremely volcanically active areas. So it’s not considered a likelihood.
It’s best to think of those as two separate hazards, and to know how you would get information about each: When an earthquake strikes, drop, cover, and hold on; if there is a lahar coming towards you (Mt. Rainier’s most significant hazard), get to higher ground as quickly as possible.
Question by skis4hire:
I have a 1974–built split–level in the Portland, OR area, I’ve gotten 3 quotes on earthquake retrofit and they said 3 different things:
- Your house has some bolts, so no additional bolting is required
- Recommend adding additional bolting of the sill to foundation
- Additional bolting is needed in addition to shear panels on the lower level of the two-story side of the house
I’d appreciate a general feedback on what the different levels of retrofit buy you. In the case of (3) above — with shear panels and lots of bolting — could I expect little structural damage apart from drywall repair in a 9.0 Cascadia quake?
Is the existing bolting to 1974 Oregon code sufficient to at least survive and escape immediately following a quake?
Answer by Emory:
It is recommended that homes located in earthquake–prone areas and built prior to about 1985 be evaluated for a potential retrofit. You’ve done that already, so that is a great first step! While I can’t say what is appropriate for your home, a local qualified structural engineer can help you with that. The three different solutions you mentioned can all be appropriate and come at different price points. My house was built in 1970 and does have some bolts at roughly 6 feet on center at the perimeter of the foundation; however, it would perform better (especially in a 9.0 quake) if there was additional anchorage. The most vulnerable part to older homes is the attachment to the foundation and the cripple walls (short walls between the first floor and the foundation). In general, you get the most bang for your buck by strengthening those areas in the crawl space or basement area. The improved anchorage and cripple wall bracing are in order to get your home through more moderate earthquakes without sliding off the foundation. It’s usually a total loss if the house comes off the foundation. Additional bracing in the first floor can be recommended if your home has lots of large window and door openings or possibly at the garage front if there is a second story above.
Here is some information for homeowners and a link to a Seismic Retrofit Guide:
Wood–frame single–family homes do perform pretty well in earthquakes and rarely collapse, so if you follow the drop (under something sturdy), cover (your head and neck), and hold on (to keep the sturdy object from moving) advice mentioned in this thread, you give yourself a great chance of avoiding injury. A 9.0 earthquake is a big one and the building codes are focused on life safety, not damage prevention so even with retrofit scenario 3 you could still have significant damage.
Here is a testimonial from a building owner who retrofitted her building before the 6.0 earthquake in Napa, CA in 2014.
Some other things to consider for protecting your family are to make sure that your water heater is strapped to the wall; that heavy furniture is anchored to the wall; that, if you have a brick fireplace, it’s anchored and braced. Look up at what you have on shelves that has the potential to come down on you during an earthquake. I used museum wax to anchor some heavier display items to shelves (for example, sports trophies on shelves in your kid’s room).
Question by SneakyPete_six:
Hello. Thanks for having this AMA session. I’ve been curious about the structural integrity of my three-story apartment building built in the late 80s and located in the San Fernando Valley. It is a three-story building with parking underneath the building and an elevator located roughly in the center of the building. You can see inside the parking space that there are some concrete pillars supporting the building. How screwed am I in the event of a major earthquake? Of course, I’m located on the first floor of apartments. Thanks in advance.
Answer by Emory:
Some buildings like that with lots of wall openings in the bottom story might be classified as a soft–story building and can be vulnerable in an earthquake if they don’t have enough lateral resistance in the bottom story. The good news is that they are fairly easy to retrofit if that is needed. There is some good information related to what is involved with a softstory retrofit here. What you’ve described doesn’t necessarily mean your building is at risk, but you might want to ask the owner to see whether it’s been evaluated.
Question by quick_Ag:
What should I expect in general (obviously every structure is unique) living in a hundred-year-old timber–frame house with cosmetic brick on the outside when the big rip occurs? Should I expect to be pancaked?
Answer by Emory:
As you say, every structure is unique, but building practices were very different 100 years ago. I’ve seen some really well-crafted wood–frame historic structures. Generally light–frame residential structures perform well. There will likely be damage and some homes can slide off their foundation, but generally we don’t see them collapse. So you shouldn’t be too worried about being pancaked (although that does make me think about the book/movie Cloudy with a Chance of Meatballs….)
There are two main concerns for a building of that age with brick veneer.
- Something like the Heli-Tie can help stitch the brick veneer to the wood framing behind if it is not currently well anchored.
- The second most vulnerable area for an older wood–frame building is the connection to the foundation. If you have a crawl space or basement, that can be an area where some strengthening may be beneficial. Check out our Seismic Retrofit guide for some common solutions.
Question by mrs_cutes:
Hello, we have a newly built (2019) house on Bainbridge Island that’s on expansive clay soils located almost directly on top of the fault line on the south end of the island. What problems can we expect during an earthquake?
Answer by Emory:
Newly built homes are designed to modern building codes and typically take into account the structure’s proximity to an earthquake hazard. Residential wood, light–frame structures generally perform pretty well in earthquakes. For a well-designed house, you still might expect some damage depending on the size of the earthquake. Common areas of damage to look for would be cracking around window and door openings. Also depending on the shape of the house, there may be some damage at reentrant corners (if it is an L shape or something like that) or at other what we call “structural irregularities.“ A boring square box with no windows would perform the best, but no one wants to live in that.
Question by wizang:
How do you feel about the science behind earthquake retrofits and how effective they will be in a real earthquake? How do you go about choosing a quality contractor for the job?
Answer by Emory:
I feel earthquake retrofits can be very effective in a real earthquake if designed and constructed well. Being in California, I’ve seen retrofitted structures fare much better than unretrofitted similar buildings next door. Here’s a testimonial from someone who strengthened their structure prior to the Napa, California, earthquake several years ago. Depending on the type of structure you are looking to retrofit, there will be areas of vulnerability that you’ll want to focus your retrofit dollars on so as to get the greatest benefit. For a home, we’ve got a seismic solutions page with lots of good resources for homeowners, and there’s also a seismic retrofit guide with good info.
For choosing a quality contractor, Seattle has a list of contractors that have passed a seismic retrofit class. Check with your local building department to see whether they have something similar. You can also search for structural engineers who specialize in seismic retrofits, and they may be able to recommend experienced contractors. Interview the contractors and ask about their experience with seismic retrofits.
Question by Olga973:
Question from a suburban home. I’ve been looking at the “sticks” my house balances on and wondering about investing in attaching the frame to the foundation. My great fear is that my 1970 split-level will just slide off the foundation in an earthquake. My other half thinks that’s an unlikely scenario, but I’m the safety beaver in the house. Our bedrooms are over the garage, which is not secured to the foundation.
So my question is: Would you hire someone to bolt the frame to the foundation, and then possibly also add cross bracing?
Answer by Emory:
Hi Olga973. We have seen older homes slide off the foundation in an earthquake. It really depends on the age of your home and how close you are to a fault line. Simpson Strong-Tie has a seismic solutions page which has lots of information and resources for homeowners. There’s a good testimonial there from an owner that had retrofitted their building prior to the Napa, California, earthquake several years ago. The Seismic Retrofit Guide gives you some good info on how to get the most bang for your buck when doing a retrofit.
- Protecting Homes Against Earthquakes — a New Blog Series