Seismic Retrofit of a Brick Foundation in an 1890 Victorian

April 2000

The house had a brick foundation that was only two bricks wide. The first step was to dig a trench on the inside of the existing foundation. It was dug down 18 inches and is 12 inched wide. Steel was set into the new footing and rods were placed up against the face of the existing brick foundation. Later these will be used to reinforce the 6 inch wide stem wall that will be placed on the inside of the bricks.

A 36 inch trench was dug across the mid point of the house. A shear wall will be built above it. Not all the steel is in yet. 5 bars were placed in this trench.

A new electrical ground rod was placed on the footing.

Temporary supports are added to prevent settling or shifting of the bricks. Later almost half of the bricks will be removed to allow for placement of 28 inch anchor bolts directly under the sill plate.

The footing has been poured and now all you can see are the rods sticking out of the new concrete footing. Here you can see how the new concrete wall that will be poured just inside the exiting brick foundation is tied into the new bolts and hold downs in the sill. Sections of the existing brick are being removed and steel is being looped into the openings. Standard J bolts are being used to provide shear strength. There are pairs of 28" SSTB hold down bolts going in where there is a solid panel in the knee wall. The large number of windows makes creating solid shear panels more difficult.

Smaller sections have been removed to allow the placement of J bolts. The goal is to get one J bolt for every two feet of sill. They need to be grouped to preserve sections of the existing brick. The brick foundation was providing good support for the building, but the mortar had weakened and would not have provided much seismic strength. Some sections of brick could be removed by hand. Notice above how the foundation is just two bricks wide. There were brick hold downs installed when the house was built. They go down between the two columns of bricks and had a flat piece that rested between two rows. One can be seen above at the rear of the new opening.

The temporary posts installed during the construction are visible below. You can see how much of the brick is removed in some places. Below there are two shear panels on each side of the window, so a SSTB hold down is required on each side. Each has a mate outside the edge of the picture.

Two of the 28" SSTB bolts were poured into the footing at the end of two short transverse walls. One of these can be seen below, lagged into the knee wall studs. The hold down has been extended with 7/8ths threaded rod to bring it above the sill level.

A good view of the SSTB hold down. It is curved to give it better grip in the concrete. The new ground rod rises out of the new footing. It is connected to 24 feet of horizontal steel set near the bottom of the footing.

Most of the North wall is visible here. The footing and reinforcement has a gap to allow for the stairway.

For the "pour" of the retaining walls shotcrete was used. It is a very thick mix of concrete that is pumped like regular concrete but at the nozzle high pressure air is used to propel the concrete into a "spray." The mix will not slump and we had sections that were 14 inches thick and three feet high that stood up without forms.

This is a good view of the hose and nozzle. Note the separate air hose. The partially applied concrete adheres to the existing brick very well.

The laundry room looks like it will never be the same again. Notice the wire that is used as a forming guide running along the wall on the right.

Here one of the workers uses a screed to remove excess concrete. He is using piano wire that was strung prior the concrete application.

Excess concrete sits along the floor after it has been removed. The rough surface of the wall is smoothed out using trowels. The excess concrete was shoveled out the window and was discarded.

Plastic helped to protect the wall and windows from over-spray. But the smoke detector still went off from the dust.

The troweled concrete starts to take on its final form.

Next the shear panels need to go up.