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

Basic to understanding what and how much seismic retrofitting your house needs, you should understand the earthquake engineering that applies to the seismic strengthening of your home and to bolting your house to the foundation.

The crawl space photograph below is to help you visualize what it looks like under the floor you walk on and how the floor joists, shear transfer ties, and foundation anchors that suffice as foundation bolt substitutes, all work together to protect a house from earthquake damage .  When a house does not have a cripple wall the floor is to close to the foundation so that the floor can be connected to the foundation  directly with steel.  This direct floor-to-foundation steel connection makes these retrofits 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.   Any type of shear transfer tie that is rated to resist the earthquake force the building code tells us to expect will be effective.  The specific type we use is determined by what we find under your house.

A Sound Load Path in Every Effective Seismic Improvement

The colored arrows below correspond to the sliding motion of the floor caused by an earthquake.  The load path transfers the earthquake force from the floor, through the shear transfer tie, into the foundation anchor,  into the foundation, and finally into the ground where the earthquake force dissipates.  This process is known as the load path.   The colored letters below correspond to the way earthquake forces are transferred into the ground.

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.

Company License Info

Works' Comp #3900008328-011
Contractors Lic #558462
Bond #511-67-26
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