Carbon Fibre 1

[ajk1]

Where can I find technical information (such as diameter, strength, modulus of elasticity, creep, etc.) about carbon fibre prestressing strands for concrete beams, and from where it is available?

 

[dik]

Just a caution some fibre strands do not hold up well with fire.

Dik

 

[Shotzie]

You may want to contact Simtrec to see if they can send you a table of contents for manual 5, which outlines prestressing concrete with FRP Link. I don't have it personally so I can't say for sure if it'll have the information you need.

 

[Ingenuity]

A good info source is ACI 440.4R-04 PRESTRESSING CONCRETE STRUCTURES WITH FRP TENDONS: Link

Part extract of table of properties:

​

And also this thread:

http://www.eng-tips.com/viewthread.cfm?qid=415482

Stressing FRP tendons is problematic due to anchorage grip devices, and even more so for FRP strands (multi wires of carbon FRP, spirally set around a center core wire):

Any specific reason you are considering FRP PT tendons? Corrosion issues, I assume. Keep in mind that FRP will have there own set of "issues". Fire (as dik stated), and also the fact that the material is near perfectly elastic (brittle rupture), and very expensive.

 

[ajk1]

Ingenuity and Dyk - that is exactly what I was looking for! Great to have responses like that. Yes it is due to corrosion that I am thinking of carbon fibre. Have you had any experience with them? Can the fire rating issue be overcome, or can they be used only in structures where no fire rating is required? Do you know of any structures where they have been used in North America?

 

[ajk1]

Also meant to thank Shotzie. I am trying to contact Simtrec.

 

[Ingenuity]

Can the fire rating issue be overcome, or can they be used only in structures where no fire rating is required?

If the tendons are 'internal' (or encased in concrete with sufficient "cover") then they could possibly be used in applications with fire requirements. Some FRP system manufacturers have UL-approved spray-applied systems that provide 2, 3 and 4-hr ratings that meet the UL-test requirements. Passing a UL fire test of these systems is easier than passing a 'real-world' fire. I would make sure my structure had sufficient existing mild steel reinforcement for min. ultimate strength under a fire, where I would assume the FRP is "gone".

Do you know of any structures where they have been used in North America?

Most application of post-tensioned FRP tendons in the US have been in academic settings (you know, professor-types in ivory towers, justifying his/her research ).

Some bridge repairs have used FRP tendons: ACI Structural Journal Volume 111, Issue 2:

"Repair of Prestressed Concrete Beams with Damaged Steel Tendons Using Post-Tensioned Carbon Fiber- Reinforced Polymer Rods" by Clayton A. Burningham, Chris P. Pantelides, and Lawrence D. Reaveley​

In the commercial building world, Sika have a flat laminate post-tensioned system (CarboSTRESS), developed in Europe, but the anchorage system is bulky, expensive and therefore not too commonly used:

Also in Europe; there have been a few post-tensioned FRP projects by other companies like S&P (purchased by Simpson Strong-Tie), and another Swiss-based company that I cannot recall. ==> EDIT: Company name is STRESSHEAD Link. Japan also has a lot of experience in stressed FRP too.

May be worth your time to give Simpson Strong-Tie a call and see where their stressed FRP system development is at, and may be Sika too - to check on their North American based-projects where CarboSTRESS has been used. Not too many, is my thinking.

 

[Ingenuity]

I was digging through some of my FRP papers/journals and found this paper that may have "local" interest for you, given the research/testing was done at Queen's University, and it is a unbonded PT building structure (parking garage) in downtown Toronto too.

ASCE JOURNAL OF PERFORMANCE OF CONSTRUCTED FACILITIES, MAY/JUNE 2011:

"CFRP Tendons for the Repair of Posttensioned, Unbonded Concrete Buildings"

By Colin MacDougall, Mark Green and Lucio Amato​

To the writers’knowledge, this is the first example of an unbonded, posttensioned tendon replacement using FRP tendons.

Here is an abstract:

An eight-story concrete parking garage was the focus of this study. It was constructed in 1977 and has unbonded, post-tensioned slabs with tendons running both east-west and north-south. Since 1995, more than 40 of the steel tendons have been replaced because of corrosion, including 15 replacements in 2007.

The maximum length of FRP tendons was 12m, so internal splicing was necessary to repair the 18m long existing tendons:

The fixed-end anchorage is cumbersome:

The stressing-end anchorage has a bond-length of 1.5m (via 23mm dia PE ducting and grouted):

Given that the FRP replaced the old steel strand tendons, there was probably no fire-related issues as it was an "internal" tendon replacement.


EDIT: Here is a link to a download of the ME thesis by one of the co-authors (Amato) from Queen's: Link

Here is a 2017 paper (by Green) that briefly discusses the long-term aspects of the project, near 10 years after the repair was complete: Link

The EoR for the repair was HALSALL and the contractor was VECTOR.

Here is the garage in downtown Toronto:

 

[rapt]

Coming to this late as I am on holidays, I want to reinforce Ingenuity,s comment regarding elastic properties of these materials.

They are purely linear elastic materials, there is not plastic strain response at all, so they cannot be designed using standard concrete design codes or design software. They result in basically non-ductile members.

Maximum stress available at Ultimate is usually limited to about .6fy and as un-tensioned materials are often limited further by bond problems. So maximum jacking force would be in the order of .4fy. Canada has a design code for this. Nor sure if anyone else has one.

RE Fire, normal fire deemed to control fire design rules limiting cover apply limits to reduce temperature to a level to give a resulting strength loss of 30% (Eurocode) so you end up with 70% of UTS of the member. This equates to a fire loading of 70% of the Ultimate loading so all should be ok.

If these materials must be ignored in fire design (not sure) then the full ultimate capacity needs to be provided by alternate reinforcing that has sufficient fire cover. Or a fire design needs to be done. It is not adequate to simply supply sufficient reinforcement for SW or SW + permanent load as the capacity of that reinforcement will be reduced by 30% under fire loading and will be inadequate.

It may be possible to provide sufficient cover to the CFC or GFC materials to reduce the temperature to acceptable levels but I doubt that would be economical.