Prestressed GFRP

[shanmur]

Hi All,

I am looking into the use of prestressed GFRP reinforcement for the design of bridge girders (box, NU or AASHTO type). Is anyone familiar with this? I am still determining the layout of the structure but most likely, it will be a single 100' span on 25 deg skew. Any example calculations for the GFRP reinforcement would be great but will also gladly take any suggestions/advice. Thank you.

 

[Shz713]

Mufti has very extensive background on using rehabilitation of bridge decks, you may check out his other publications for use of GFRP. With regard to calculation, I am not very familiar as I mostly deal with bridge assessment. Yet, if you want to model it numerically, I suggest use CSiBridge to crosscheck your manual calculation.

Memon, A.H. (2003). "Crack control with GFRP bars in steel-free concrete deck slab". Proceedings, Annual Conference - Canadian Society for Civil Engineering , 2003 , p. 906.

Precast concrete decks for slab-on-girder systems: a new approach
Author: Mufti, AA

Cheers,

Shoot for the Moon, even if U miss, U still land among Stars!

 

[EQguys]

Shanmur,

May I ask why the unique choice of using GFRP rebars for girders ? Are there material availability constraints to this project ? Please elaborate.

 

[shanmur]

EQGuys,

It is the preference of the client based on past experience. Material availability is not an issue but the client has not had success with cast-in-place concrete so they prefer everything precast. I believe their biggest reasoning for going in the direction of GFRP instead of steel for reinforcing is due to location and environment (Northern Ontario). The temperature drops to -40 Celsius with lots of snow therefore they use lots of salts for anti-icing. So it is likely durability and maintenance issues that led to this thinking. I have seen a few bridge designs using prestressed GFRP but I have not come across any design guidelines from CSA or ACI.

Shz713, thanks for sharing!

 

[EQguys]

Shanmur,

Thanks for the info. I have come across GFRP rebars being used in bridge decks, but not in girders. I am aware of some studies conducted by NY State DOT on using GFRP. You can find them on their website.

 

[TehMightyEngineer]

We've used GFRP in some prestressed bridge deck panels but used traditional steel prestressing tendons. One thing we discovered is GFRP does not contain the bursting stresses from the prestressing forces as well as steel (due to the lower modulus of elasticity). Some adjustments to the prescriptive provisions in your design code for the GFRP properties will be required.

The only other major lesson learned was that as the GFRP has to be bent when manufactured, and if they are ordered the wrong size or shape it can have a long delay in redelivery of the new bars which can cause issues. Use as many straight lengths as possible, field cutting is possible but field bending is not.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com