Homes without Cripple Walls

By Howard Cook, Founder and General Manager of Bay Area Retrofit

Seismic Retrofitting Houses without Cripple Walls

Seismic Retrofits of Houses without Cripple Walls Transfer Earthquake Forces into the Ground

The crawl space photograph above is to help you visualize what it looks like under the floor you walk on.  The photograph below identifies the components of the floor that need to be attached to the foundation.  These are the floor you walk on, the floor joists, the rim joist, and the mudsill.  The hardware used to connect the floor to the foundation are shear transfer ties and foundation anchors. Foundation anchors hold the mudsill to the foundation exactly as a bolt would.  The shear transfer ties attach the rim  joist to the mudsill.  In new houses this is done with nails.   These retrofits which attach the floor to the foundation with direct steel connectors are extremely effective.

Earthquake Forces being Resisted by Bolt Substitutes through a Seismic Upgrade  Foundation anchors do the same thing as foundation bolts.  There are four types of foundation anchors and three types of Shear Transfer Ties.    The specific hardware used is determined by what one finds under a house.

A Sound Load Path Should be in Every Effective Seismic Improvement

The colored arrows below correspond to the arrows in the photo to the right. The retrofit hardware transfers the earthquake force from the floor, through the shear transfer ties, into the foundation anchors,  into the foundation, and finally into the ground where the earthquake force dissipates.  This process is known as the load path.   

Arrows Showing how Earthquake Forces Move into the Foundation

 

Different Types of Foundation Anchors

A very common type of Foundation Anchor used as a Foundation Bolt Substitute

A very common type of Foundation Anchor used as a Foundation Bolt Substitute

A Foundation Bolt Substitute for a Special Earthquake Retrofit

This Foundation Anchor is Nailed to the Mudsill

Foundation Anchor used when Mudsill is Embedded in Concrete

Example of Foundation Anchor used as Bolt Substitute

Foundation Anchor similar to the one Above.

 

Shear Transfer Ties

The houses below had a bolt every 4 feet but the end joists were not attached to the mudsill with nails or Shear Transfer Ties.

This is the first house

This is the first house

Blue House With Arrows

Blue House with Arrows

This is the third house

This is the third house

 

 

 

 

 

 

 

Below is an image of what it looks like under a house without a cripple wall.    The red arrows represent earthquake forces trying to push the floor off the mudsill.  If this happens, the house will slide off the foundation.  The joists that sit on top of the mudsill are called end joists on one side of the house and rim joists on the other side

Earthquake Forces on Joists

The way this sliding is avoided is by attaching the end joists and rim joists to the mudsill with Shear Transfer Ties, sometimes known as framing anchors.  A large variety of shear transfer ties are available and a contractor must know which one to use when confronted with every imaginable framing configuration.  Given many houses were built without a building code, the varieties of floor framing are legion.

Below are the types of Shear Transfer Ties available.

L70, L90, LS70, LS90, A23, A35,

LTP4, H10R, H10, H2.5, lag bolts

 

Shear Transfer Tie Restrained by STT

Each Shear Transfer Tie, also called a framing anchor as expressed in the drawing above,  can resist a certain amount of force.  You want this hardware, or a combination thereof, to resist the force that will be attacking your house.

Below is a photograph of a single L90 Shear Transfer Tie.  It is nailed at the back to the floor framing and at the bottom to the mudsill.   Shear Transfer Ties transfer earthquake force into the mudsill

Single L90 with Arrow

Types of Shear Transfer Ties

There are many types of Shear Transfer Tie hardware with different strengths.  Some are suitable for retrofits and some are not.

 

This is the shear transfer ties

 

f you would like an evaluation of your building or home, please fill out this form. I will take a look on Google maps and email you back information relevant to your building or house and provide approximate costs. If you are doing your own retrofit or have any questions about your house I am happy to help you free of charge.

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Headquartered at:

Bay Area Retrofit
427 San Pablo Ave
Albany, CA 94706
With field offices in San Jose and Hayward.

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Works' Comp #3900008328-011
Contractors Lic #558462
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