CMU Building Strengthened with Fiber Reinforced Polymer (FRP)

This is the first reported application of fiber composites to strengthen an existing building and was completed in spring 1994.

This one-story building had been previously retrofit for seismic performance by addition of steel columns and tying the roof joists to the top of the walls with anchors. Nevertheless, the 12-in. wide CMU wall on the southern side of the wall cracked severely during the Northridge earthquake that occurred on January 17, 1994.

Conventional approach of shotcreting the wall could not be utilized because the wall was located just on the edge of the property line; due to the presence of a conveyor belt hanging from the ceiling, there was limited access to shotcrete the wall from the inside.

Because this was the first such field application, the city engineers were reluctant at first. But after presentation of extensive R&D data, including assurances for non-toxicity of the resins to the Fire Marshall, a construction permit was issued.

The wall was first sandblasted and cleaned with high pressure air. At the time, we had not designed and constructed an impregnator machine, so the 3-ft wide glass fabrics were saturated by hand. The fabrics were placed in vertical strips. Where steel anchor plates were present from the earlier seismic retrofit, the washers were removed and the bolts penetrated the wet fabric; the washer and nuts were immediately placed over the fabric.

To ensure proper anchorage, the fabrics were secured through blockings on the inside, at roof line. As the photos demonstrate, the finished wall was painted. The total thickness of the wall was increased by less than ¼ in. and none of the conveyor belt equipment had to be removed from the ceiling for this retrofit.

Details of this project has been discussed in an article published in The Masonry Society Journal.

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