Below is an image of what it looks like under a house without a cripple wall. The red arrows represent earthquake forces trying to slide the floor 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
The way this sliding is corrected 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 that many houses were built without a building code, the varieties of floor framing are legion.
Below are the names of some of the Shear Transfer Ties available. These are also known as framing anchors.
L70, L90, LS70, LS90, A23, A35,
LTP4, H10R, H10, H2.5, lag bolts,
12d toenails, 8d toenails, 15 gage staples
Often they must be fabricated out of wood on site.
Each Shear Transfer Tie can resist a certain amount of force.
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. (The bottom nailing to the mudsill is not visible in this photo.) The Shear Transfer Ties transfer earthquake force into the mudsill.
- The image below shows how Shear Transfer Ties are part of a system. The yellow arrow represents earthquake forces pushing against the floor you walk on.
- The white arrow is force going into the Shear Transfer Tie which tries to make the mudsill slide.
- Finally the red arrow shows that force entering into the Foundation Anchor and into the Foundation.
- Again, this is only one kind of Shear Transfer Tie. There are many others.
Shear Transfer Ties Systems where a new Mudsill is Bolted to the Side of the Foundation
Below you can see how Shear Transfer Ties are used when new mudsills are placed on the side of the foundation.When the Floor Joist moves in the direction of the red arrow, it pushes against the Shear Transfer Tie, which pushes against the mudsill bolted to the side of the foundation and is stopped by the bolts.
In this illustration, the plywood (also called a diaphragm or Shear Transfer Diaphragm) is nailed to the top of the new mudsill on one side, and to the floor joist where you see the red arrow on the other. When the floor joist moves, that movement is transferred into the Side Bolt Mudsill and into the bolts, thereby preventing movement of the floor and saving the house.
The houses below were bolted, but the floor was not attached to the mudsill with nails or Shear Transfer Ties.
Types of Metal Shear Transfer Ties
Some Shear Transfer Tie types by Simpson Strong-Tie