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ICC-ES Report Update for Composite Strengthening Systems™

We’re pleased to announce that our Composite Strengthening Systems (CSS) code report, ESR-3403, has been revised to recognize Simpson Strong-Tie fiber-reinforced polymers (FRP) for concrete diaphragm applications. These FRP fabrics can be used to strengthen diaphragms for in-plane shear, flexure (chords), and axial tension (collectors) to resist seismic or wind loading.

To accomplish this, we tested dozens of full-scale specimens cyclically in accordance with ICC-ES AC125 at the ISO 17025–accredited Tyrell Gilb Research Laboratory in Stockton, CA. This criterion is used to assess FRP system performance when externally applied to concrete (and masonry) base materials. The evaluation report may be downloaded from the ICC-ES website at

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“FRP strengthening of concrete diaphragms, chords and collectors provides a distinct advantage over other traditional retrofit methods for concrete diaphragms in most cases,” said Development Manager Aniket Borwankar. “The updates to our ESR for FRP strengthening systems reflect our commitment to innovate and develop design solutions for the engineering community, a commitment that includes full-scale testing at our ISO 17025–accredited Tyrell Gilb Research Laboratory in Stockton, CA.”

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We hope that the engineering community finds value in this newly revised report, especially for applications involving nonductile concrete buildings in need of a seismic retrofit.

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