Glass Fiber Reinforced Polymer bars in residential foundations GFRP

[YoungGunner]

One of our clients is saying they may have a rebar supply crisis near the end of the month and are putting pressure on us to use GFRP bars for residential basement foundation walls, footings, and the lintels over openings. A neighboring engineering firm is declaring the use of GFRP in place of standard steel bars with a 1:1 replacement. After diving into the ACI design guide, ACI 440-1R-15, that discusses the calculations for FRP bars, I'm coming to the conclusion that a 1:1 replacement is highly unconservative, especially for lintels over openings with shear, and vertical spacing of foundation bars. Does anyone have any experience on this material's use for basement foundation walls and footing and gut feel of the replacement ratio? To clarify, we live in a region of higher seismic activity, usually in Seismic Design Category D, so we don't work with plain concrete basement walls.

 

[rapt]

GFRP bars are not a one 1:1 replacement for reinforcing bars where ductility is important.

GFRP has no plastic region in the stress/strain curve, it is elastic to failure.

And modulus is very different.

You would have to redesign using lower stress limits as there is no defined "yield" point for GFRP, only a breaking point.

A nominal yield would normally be set at 30-60% of the breaking depending on the application. External applied is lower due to bond failure. Internal bars probably closer to 60%, but depends on the design code/guide. Canada has a design code, not just a guide!