A house may be at risk of damage if it has an old pier foundation. The foundation is the plane the house sits upon, and, ideally, that foundation secures the house in position. In any event, so that the house is stable and safe, the foundation needs to perfect. Regardless of the strength of the house, if the foundation is frail, a strong earthquake could raise the house from its piers, and side torsion could even cause it to collapse.
The usual drawback with posts and pier foundations when there is an earthquake is that the posts tend to move off piers and beams to move off posts. Failure at any of these points could set off the foundation, and at times can cause the whole house to fall down. But there are things that can be done to strengthen an existing pier foundation. Securing posts to piers and beams is one standard practice. Lateral bracing could be attained by installing a 2x4 as a diagonal bracket from one post to the other.
A bracing system must give the least resistance to lateral forces for the house. The support must be set up around the border of the structure and, at a minimum, each second line of interior posts, in every direction. Be careful in planning the spaces to be braced so that the braces from each direction do not run into the same post. This kind of support must be regarded as sufficient for temporary stabilization until a stable, adjoining, poured-in-position foundation system is ready to be put in place. This bracing system could be used for terraces and other outdoor features as well.
Set the Forms
Remove the lattice from the spot to be strengthened, and set the forms between the existing piers. Notice that the earth has been taken down one foot deep, although it won't be as much if the solid bedrock is hit. Put in reinforcing bar before pouring and then place the fastener bolts into the concrete and allow it to set.
When the cement is set, bolt a sill into place, then toe-nail the cripple studs into the post under the existing support above. At this time, since the house is attached to a strong load of concrete, it should not jump up above the piers during an earthquake.
Pin a piece of half-inch plywood over the sills and cripple beams. At this point, it would obstruct the house from cutting off or racking in the event of an earthquake, as the support of a bookshelf stops it from moving sideways.
To avoid damage to the framework of the house, a series of shear walls can be built to strengthen the foundation. Shear walls do not have to be constructed throughout the whole border of the house. It is suggested to construct six walls all in all with a wall on every end of the house that's eight feet long, and then two walls at every side of the house that are six feet long.