GFRP Rebar in Coastal Structures

[pootypeters]

I've been designing a lot of structures lately that are right along the coastline. Retaining walls, soil nail walls, box culverts, etc... Since they are getting constantly battered with waves, we have been using stainless steel and GFRP rebar. The stainless steel is used mainly for the flexural reinforcement and the GFRP more for temperature and shrinkage. I do, however, use some GFRP bars in the less critical flexural zones such as in the shear key or the toe of the footing. Since the glass bars do not behave the same as a typical isotropic alloy, what "yield strength" would you use in the design of the bars? I keep reading that the ultimate strength is much higher than standard steel ~ 110ksi. But I'm not sure if the glass bar experiences a transition from the elastic to inelastic range at a much lower value. I have been using 60ksi as this is what has been recommended to me. Thanks.

 

[abusementpark]

Have you reviewed ACI 440 yet? I've done a couple MRI machine foundations using GFRP bars and found that to be a pretty reference.

You are correct in that the failure is more much brittle than regular rebars and this should considered accordingly in design.

 

[TXStructural]

Glass bar does not transition to inelastic. Once you reach proportional/elastic limits, and the bar begins to break, there is no residual inelastic strength. You will design to stay elastic and fail by concrete crushing. For this reason, using non-ductile reinforcement to resist unpredictable loads (seismic in particular) is not desirable. The use of these materials requires that the designer accept brittle failure and design accordingly.

 

[pootypeters]

Thanks for the advice. I am reviewing the ACI 440 right now.