This what it looks like under your house. The bottom of the posts are sitting on concrete piers and the tops of the posts hold up beams also known as girders. The building code makes no distinction between posts that are 2 feet tall or 10 feet tall.
These beams (girders) support “floor joists” that support the floor you walk on.
Sometimes the posts support a beam that the floor is nailed to and there are no joists.
The Post to Beam and Post to Pier Connections
In the building code posts are referred to as columns.
On the bottom left is a sketch taken from plans drawn by a local engineer. This is drawing that tells a contractor how to do how the column to beam connection should be reinforced even though this procedure is not recommended by any seismic retrofit guidelines. Ill-conceive recommendations like this happen when contractors and engineers are not familiar with these guidelines and theorize how an earthquake will impact a house rather than looking at photographs, referring to the building code, or reading reports about actual damage
What does the Building Code Say?
Posts in the crawl space of brand new houses built right on top of a fault only require that the bottom of the post be “restrained”. This is universally done with one or more nails in new construction. A single nail at the bottom of the post is all the code requires. At the top of the post and NOTHING is required, certainly not a steel strap. This is a photo of the same T=Strap seen in the drawing above.
Section R407.3 of the California Building Code
If your contractor or engineer is recommending this hardware he is probably unfamiliar with the fundamental retrofit engineering and practice.
The reason posts and beam connections are unimportant is that the posts can only tilt and perhaps tip over if the entire building has shifted off its foundation, at which point you are out of luck anyway. Best to put your money into retrofit components that assure this won’t happen.
The STT292 Post to Pier (the pier is the concrete block under post)
Here is a post to pier connection at the bottom of the post. As pointed out in the code referenced above only one nails is necessary at this location. We usually see 3 though 3 are not required. In light of this doing anything here is complete waste of money.
More Examples of Post to Beam Recommendations