Carbon Fiber Repair?

[LCruiser]

We have a proposal in to repair a design mistake which allows too much deflection in a slab bridge, using carbon fiber layers underneath. Has anyone ever heard of that?

 

[oldrunner]

Check out Fyfe, Quakewrap and Sika. I recently specified Fyfe FRP for a under-reinforced retaining wall. Unfortunately the client decided to tear down the structure. Lots of problems besides the wall.

All of the above companies have good technical support.

 

[eric1037]

Nabil Grace, PhD, PE at Lawrence Tech in Michigan is a great resource for info regarding carbon fiber reinforcement.

A caution about the use of carbon fiber - it doesn't behave the same as steel for reinforcing concrete. When there is a failure, it is sudden because the stuff doesn't yield like steel.

 

[Qshake]

A lot of universities are in on research for repair of concrete members with FRP systems.

I suggest that general web search choosing those sites from universities as a start. Also check ACI for concrete repair committees.

Antonnio Nanni from UMR is noted in this field.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[Blackhorse007]

Probably you might want to try glass or carbon plates, they are stiffer and might help slove the prob a bit, for more as old runner suggest get fyfe or the rest to work out the FRP reinforcement for u.

I know fyfe would be glad to do the initial assessment for free

 

[tjhubo]

Actually, the stiffness of normal carbon fiber/epoxy composite is lower than that of structural steel. If the weight of the retrofitting material is not that a big deal, I don't see the necessity of using it, since it is much more expensive that steel plate.

The features of carbon or glass composites include high strength/weight ratio, high stiffness/weight ratio, good corrosion resistance, good fatigue properties and so on, but not the absolute stiffness value.

 

[LCruiser]

So it sounds like carbon fiber/epoxy might be better under a slab bridge then to get rid of some negative camber?

 

[MichSt]

External post tensioning is another option to strengthen an existing bridge and also correct the negative camber. If vertical clearance is an issue though, this option may not be viable since you will need to install some cables on the underside of the slab.

I believe California DOT uses this as method to strengthen bridges. You could do a search on their webpage to hunt down some specifics on this method (or just do a general google search).

 

[Blackhorse007]

well the speed for doing FRP is definately an advantage, and on top of that if we are talking about repairing the bridge, by drilling holes in the concrete, it might induce cracks and thus a higher stress value for the concrete, would it not do more harm to the bridge?

 

[Qshake]

Also, just from ACSCE is the latest BRidge Engineering journal for which this edition's focus is FRP bridge components and related articles.



Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[asdf]

As one of the contractors who use this site, I suggest you complete a cost analysis to determine the cost benefit of retrofitting vs. replacement prior to making the design effort. The contractor’s cost for waiting for a repair often is more than the cost for rework. But just as likely, it may turn out that a few well-spent hours may save days and dollars, but it is something to look at...

As a side note, this site is by far the best site on the web to openly discuss these types of issues, and I for one am glad it is available. My hat is off to whoever makes it possible, and to those who share their thoughts and experiences.

 

[Blackhorse007]

I did a cost comparison for my material before and this is the time cost we are looking at, not so convinent to give the actual cost hope u guys understand;

productivity for my FRP system (2 layers of wrap)
Productivity = 15/5.4 = 2.78 man hour/m2

productivity for one piece of steel plate (eqv to my wrap)
Productivity = 37/5.4= 6.85 man hour/m2

 

[Qshake]

Yes, the cost for the labor to install a FRP system isn't the most expensive component. The material is far more costly.

I think also that viewing the end benefit of how much load increase per dollar spent is also important. If you can't increase the capacity to remove a load rating, sometimes it's worth it to remove and replace. Especially in an area where it was once rural but is seeing more and more development.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.