[Greenbuilding] Earthquakes and older houses

[Alan Abrams]

Bob--

imagining the Oklahoma version of "The Big One," I think the gravest danger
is the collapse of the brick foundation walls. in our region,bricks from
the 20's can be pretty soft, and the mortar can be powdery.

if that all describes the scenario, simply anchoring the floor system to
the top of the brick walls might be inadequate. the strength of the
foundation walls would be limited to the compressive force exerted by the
weight of the house above. in this sense, the weight of the brick veneer is
your friend--but I think the veneer is going to be the first element to
fail when things start to shake. The point being, that even if the floor is
anchored, the foundation walls could rotate in, between corners.

one could of course jack up the house and install a new reinforced cmu or
poured concrete foundation beneath it. Or form up and pour new walls
against the existing walls.

but less intrusively, one might strengthen the walls by increasing the
compressive force--perhaps by excavating and installing a set of pier
footings at intervals around the basement perimeter, each pier footing
undermining the existing footing--maybe 2' wide or so. each pier would have
a reinforced anchor bolt, to fasten some set of threaded rods and
turnbuckles--which in turn would be bolted to the floor joists. Ideally,
there would be two rods for each pier footing, run diagonally in opposite
directions, parallel to the foundation walls.

There a lot of boggling variables here--such as the moisture content and
plasticity of the soil, height of backfill, direction of seismic waves--so
sizing the footings and rods, and determining how many to install would be
speculative. Maybe a big shaker would overcome this effort. Or maybe it
would hold up long enough for you to escape before it all comes down. I
don't envy your situation.

-aa



Alan Abrams

*certified professional building designer, AIBDcertified passive house
consultant, PHIUS*
*certified passive house builder, PHIUS*
cell     202-437-8583
alan at abramsdesignbuild.com
HELICON WORKS *Architecture and Education*
<http://www.heliconworks.com/index2.html>

On Tue, Mar 29, 2016 at 11:05 PM, ErgoDesk <ergodesk at gmail.com> wrote:

> California... I would reinforce your FIRE Insurance first.
>
> Sincerely,
> George Hawirko
> *http://about.me/StyroHome <http://about.me/StyroHome>*
>
>
> On Tue, Mar 29, 2016 at 11:40 AM, Jason Holstine <jason at amicusgreen.com>
> wrote:
>
>>
>> I think you can find retrofit resources online from California. I think
>> their state emergency mgmt agency, state NAHB, etc. have docs. It could
>> become a nice side biz tightening up Okie corrals.
>>
>>
>>
>> On 3/29/16 1:41 PM, "Bob Waldrop" <bwaldrop1952 at att.net> wrote:
>>
>> > So here in central Oklahoma, we have been experiencing a growing series
>> > of earthquakes over the last few years.   The USGS just released a map
>> > showing the risk of human-induced earthquakes, and Okie City is right
>> > there. The news said we were at perhaps a 10% risk of a level 6
>> > earthquake.  Most of the thus far have been in the 2 to 4 range.
>> >
>> > Now we are not only tornado alley, but also earthquake central, more
>> > earthquakes last year even than California had.
>> >
>> > I lived in the Bay Area of California and in SLC (on top of the actual
>> > wasatch fault a geologist friend told me), and never experienced a
>> > quake, but I've felt several here.  I've also been watching the cracks
>> > in the interior plaster/lathe walls and my exterior brick veneer
>> develop
>> > and progress.
>> >
>> > I do have earthquake insurance, but it is really only good for a
>> > complete catastrophe.  It has a 10% deductible, and it doesn't cover
>> > masonry.
>> >
>> > The house has always seemed very sturdy.  It was built in 1929, the
>> > studs are on 12 to 14 inch centers and are a hard wood.  THe sheathing
>> > is 1 x 8 planks.  Then there is brick veneer over that. The foundation
>> > is brick.  The back and front porch construction seems separate from
>> the
>> > rest of the house. The concrete front porch is certainly pulling away
>> > from the rest of the house over the 16 years I've lived here.
>> >
>> > Any thoughts about retrofits that would strengthen the house in the
>> face
>> > of the growing earthquake risk here?
>> >
>> > Bob Waldrop, Okie and Shaky City
>> >
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