Effects of Liquefaction on Existing Building
Effects of Liquefaction on Existing Building
(OP)
I am preparing to perform an ASCE31 Tier 1 Evaluation of an existing building. The building is a small single story structure housing bathrooms and lockers for workers at a warehouse in Oakland, CA. The walls are CMU block and the roof is wood trusses with a plywood diaphragm. The geologic hazards checklist requires that liquefaction be evaluated so I looked at the USGS maps and found that the site falls within the liquefaction hazard zones. My question is, what effect can liquefaction have on the structural performance? The site is flat as can be, so it seems to me that the worst that could happen is that we'll end up with signifant differential settlement and damage to the building that may be beyond repair, not really a Life Safety issue. Any thoughts on this would be appreciated.





RE: Effects of Liquefaction on Existing Building
So you need to look more carefully at what the liquefaction at the exact location will be. The CGS published the liquefaction hazard maps for a reason, but the exact effects from liquefaction at a site can't be determined from the CGS maps. You need a site specific subsurface investigation to determine that. Do you have any old geotechnical reports for the building on file with the city or county? Start there.
Also CGS put out a new version of SP117 just very recently I haven't even had a chance to read it yet. You need to look at this as well.
RE: Effects of Liquefaction on Existing Building
Note that we still plan to recommend to the owner that they hire a geotechnical engineer to assess the liquefaction hazard at the site, but I'm just trying to anticipate what this is something that could become a huge issue given the building type as I have described it.
RE: Effects of Liquefaction on Existing Building
RE: Effects of Liquefaction on Existing Building
After receiving the soils report, as the structural engineer, you may then compute rotation, support settlement for column footings.
Take liquefaction very serious and do not assume structural performance is similar to past behavior. Oakland, CA is in zone 4 and is susceptible to strong ground motions. If you were 60 miles east, like Merced county, I would not be as concerned, unless your GWT is shallow. The difference between the two sites being PGA of 0.6g(Oakland) vs. 0.2g(Merced county).
By the way are the CMU walls reinforced?
RE: Effects of Liquefaction on Existing Building
htt
RE: Effects of Liquefaction on Existing Building