What is Earthquake Bracing and bolting?

earthquake bracing and bolting:

We brace and bolt raised foundation homes to their concrete foundations to prevent them from sliding off during earthquakes. This includes bolting the wood floor framing to the concrete foundation and connecting the weak links between wood floor framing members using structural steel hardware.

It may also include bracing the short wood walls, commonly called cripple walls, with plywood to increase their ability to withstand sideways motion and the resulting stress caused by an earthquake.

Why brace the cripple walls?

When an earthquake occurs, the shaking ground moves buildings in a side-to-side manner, making the cripple walls the most vulnerable parts of the house.

You see back in the early 1900’s the crawlspace walls found along the perimeter of the house were not braced nor bolted from the wood framing to their concrete foundations.  All these walls are under the most stress when an earthquake happens, and it is these walls that will first collapse from the stress of a seismic tremor as we saw in the Northridge Earthquake in 1994.

All retrofit work is completed in accordance with the California Existing Building Code Appendix Chapter A3 (LA Standard Plan Set 1) which applies to raised-foundation, wood-framed houses with concrete foundations.