CRFP concrete column jacketing

[asixth]

Hi guys

I have the task of bringing the design of a column which is not reinforced with closed ties up to standard. I am thinking of jacketing the column with CFRP. Does anyone know of any codes, manufacturers data, technical papers that would be useful in the design of this element. I am only starting out with this branch of structural engineering and it is likely that I will need to develop a design procedure and specification that satisfies my local building regulation.

All help on this topic will be greatly appreciated. I have found the quakewrap website that is listed on this site but found it to be full of technical publication that relate to PhD research projects. Is there a code out there that is a leading example in this field.

 

[youngstructural]

Canada has a published Fibre design code: CAN/CSA-S806

I find it very useful, and it is quite important that you really study this material before you begin. The fundamental design philosophy is quite different from normal reinforced concrete.

Further, the lack of stirrups in your column probably is something that you can address, but you need to remember that FRP is not a panecea: You MUST have sufficient capacity to carry the factored dead loads WITHOUT the fibre... The wrap is only permitted to bring the capacity up to the full factored dead + live.

Cheers,

YS

B.Eng (Carleton), P.Eng (Ontario), MIPENZ (Structural-New Zealand)
Working in Canada, and missing my adoptive New Zealand family... at least I brought the little Kiwi with me!

 

[InDepth]

asixth, are you retrofitting the column for axial or shear? Depending on the loading, you will need to specify a wrap orientation and type. Usually I specify a performance spec (load spec) for the column or beam retrofit and let the manufacturer calculate it out....but you do need to make sure that the number of layers is reasonable for the load. I believe the rule off thumb is D/C = 1.2 or less...beyond that you will need concrete/steel encasement or new load path.


A few good companies to talk to are listed below. They usually will provide a free design of the retrofit if you give them loads, fire rating, color, etc...because they want the work. They usually perform the calculations based on ACI 440 documents.

1)Fyfe

http://www.fyfeco.com/

Reports:

http://www.fyfeco.com/resources/tests.aspx

If you call fyfe up they can send you a design guide

2) SIKA Wrap

http://www.sikaconstruction.com/con/con-prod-app-sss.htm

3) Structural Group

http://www.structural.net/Structura...ralPreservationSystems/tabid/413/Default.aspx

 

[HamishMcTavish]

asixth, not sure if it will be of any use to you but you could try looking at the Concrete Society website, they have various guides related to use of composites but the most appropriate given your post seemed to be the following:

Design Guidance for Strengthening Concrete Structures using Fibre Composite Materials. 2nd Edition
Catalogue ID: TR55

http://www.concrete.org.uk/bookshop/detail.aspx?ID=650

Alternatively you could search for terms involving seismic retrofit of structures to see if that turns anything up.

Kind regards, HM


No more things should be presumed to exist than are absolutely necessary - William of Occam

 

[LittleWheels]

The Highways Agency in Britain has some worthwhile technical documents available on this topic.

 

[asixth]

thanks for all the responses. I have obtained a copy of the document prepared by the concrete society. I have also obtained a copy of the following handbook that is issued by my code administrator:

Design handbook for strengthening with FRP

Although it is not a standard it is a helpful document.

What I want to achieve when complete is a standard design procedure for strengthening an existing concrete column by FRP jacketing complete with specifications. Although I think it would be best if the specification was left to the manufacturer of the CRFP.

 

[youngstructural]

Just make sure you specify your minimum requirements... Most manufacturers have more than one product, often with widely differing material properties. And your design is completely dependant upon the material properties (of course).

I don't know the documents you'll be working with, however there are normally ranges of values and requirements you need to meet with FRP; Not more than this amount, not less than that amount. And the use of GFPR (Glass Fiber) is less expensive, but if you need to carry permanent loads it has been known to loose 80% of stiffness and strength with time (ie: really bad creep problems).

For your stirrups, it might just be the thing; IF your columns are otherwise good to go and have shown good in-service preformance and the loads are not being increased. I've justified not upgrading existing stirrup spacing with similar arguments in the past, as long as they are not seismic columns and would never be expected to be subjected to a load that might form a plastic hinge effect.

Cheers,

YS

B.Eng (Carleton), P.Eng (Ontario), MIPENZ (Structural-New Zealand)
Working in Canada, and missing my adoptive New Zealand family... at least I brought the little Kiwi with me!

 

[asixth]

I have been able to obtain two documents, the technical report mentioned above from the UK concrete society and another document published by the FIP-CEB titled "Externally Bonded FRP Reinforcement for Concrete Structures" with both documents quite comprehensive on how to calculate the increase in column capacity when confining FRP is provided, but it does not link to the structural requirements of concrete codes which is really what I am after.

Has anyone had experience with the document ACI440.2 "Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures"? And if they have, do they recommend this code as a best practice and would they recommend buying it.

Concrete codes specify that longitudinal reinforcement shall be provided in each corner and sufficient lateral restraint provided. In the absence of closed ties, I have not got sufficient lateral restraint which is the reason why I want to wrap the column using FRP.

When designing a concrete column element, it is assumed that a compressive stress is developed over the cross-section that is equal to 0.85*fc (may vary depending on what code is being used). When going through the calculations using externally bonded FRP, the compressive stress which is developed is much higher than this value (say 1.2*fc) because it is confined. Why aren't the same provisions made for closed ties, I haven't read through my concrete textbooks that relate to this but I am sure that providing closed ties would confine the concrete to some degree. What are others opinions on this?

Also, what is the general bond strength that is typically specified between the FRP and concrete and what measures are used to test this bond strength. I need to speak with representative from the FRP manufacturer on this one but it is recommended that a bond strength of 1.5MPa (220psi) minimum be specified and tested, is this common across the industry seeing that the bond strength between the two materials is critical in application of this construction.