Retrofit Engineering for Homes without Cripple Walls.

        Retrofit Designs and Foundation Bolts

Understanding retrofit design is by far the most important tool you can have in evaluating contractors’ bids and determining exactly what your home needs.  A bad design means an expensive ineffective retrofit.  A good design means an affordable effective retrofit.  If you install too much hardware, or the wrong type of hardware, or not enough, or in the wrong places, or in the wrong way, you can end up with an expensive retrofit that will not withstand a strong earthquake.

It is Simpler than you can Imagine

Engineering a retrofit for a houses without cripple walls works like this:

  1. Geologic research tells us our anticipated ground movement acceleration, measured in Gs, will be 0.186 Gs. This G force is from Standard Plan A and is slightly higher that that used for new construction.
  2. Multiply this by the weight of the house as determined by these exhaustive engineering calculations 
  3. The result is the pounds of force your retrofit must resist.

All hardware is designed to resist a certain force measured in pounds.  Install enough hardware to resist this force and our retrofit is  complete.

For example, if a houses weighs 80,000 lbs and we multiply that by 0.186gs (our anticipated ground acceleration) we get 14,480 lbs.  We therefore need to install enough hardware to resist 14,480# of force. We look through the hardware catalog and see that a bolting hardware can resist 1,480 pounds of force.  This means we need ten piece of this bolting hardware to resist.  We also discover shear transfer tie hardware that can resist 740 pounds of force so we install 20 of those.  Our retrofit is now complete.  That’s all there is too it!!

In this example we need to resist 16,000# of force.  In order to retrofit the house we need bolting hardware than can resist 8,000 pounds of force on each side.  We also need shear transfer ties that can resist 8,000# of force.  Add that hardware and our retrofit is complete.

This webpage shows how to install this hardware and what it looks like.

 THIS IS THE FOUNDATION VIEW FROM THE AIR. THE HARDWARE FOR THIS HOUSE MUST RESIT 16,000# OF EARTHQUAKE FORCE. OR 8,000# OF FORCE ON EACH SIDE.

THIS IS THE FOUNDATION VIEWED FROM THE ABOVE. THE HARDWARE FOR THIS HOUSE MUST RESIT 16,000# OF EARTHQUAKE FORCE. OR 8,000# OF FORCE ON EACH SIDE.

 

 

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And Surrounding Areas
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