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.
At the bottom of this page is a sketch taken from plans drawn by a local engineer. This drawing tells a contractor how to reinforce the column to beam connection. This procedure is not recommended by any seismic retrofit guidelines. Ill-conceive recommendations like this happen when contractors and engineers are not familiar with the building code or these guidelines. Rather many theorize about how an earthquake will impact a house rather than looking at photographs, studying both old and modern building codes, 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. At the lower left is a photo of a T strap often recommended for this connection.
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 Post to Pier Connetion
Here is a post to pier connection at the bottom of the post. A pier is a concrete block. As pointed out in the code reference only one nails is necessary at this location. We usually see 3 nails, though 3 are not required. You may want to put this work low on your retrofit priority list.
More Examples of Post to Beam Recommendations