Integrated Buildings & Structures

Hi Everyone,

I have been recently conducting an academic study to check which solution is more feasible in retrofitting of structural elements:

1- Using Carbon Fiber sheets CFRP

or 

2- Increasing the section of the structural element using reinforced concrete.

I have searched a lot of articles but still couldn't find a clear answer.
I would like to request your opinion regarding this subject.

Thanks,

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Hassan Dankar S.M.ASCE
Principle engineer
Maarabani and Partners
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​Retrofitting existing structures for me is more of an art than a science.  So I can not provide a straight forward answer.  Here are the things I consider when facing this type of problem.

1. What is best solution to match the deflection capability of the existing structural system, for example CFR can be used with reinforced concrete provided concrete strength does not govern, however using CFR for flexural reinforcing of post tension concrete members is not great since the member needs to deflect too much for the CFR to activate.
2. What solution suits the contractors doing the work best, Contractors prefer doing what they know best.
3. What room do you have for the reinforcement of the member
4. What environment do you have to deal with. 

Unfortunately no one approach fits all and often item 2 dictates the final and least cost solution.

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David Thompson P.E., M.ASCE
Principal
KTA Structural Engineers Ltd.
Calgary AB
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------Original Message------

Hi Everyone,

I have been recently conducting an academic study to check which solution is more feasible in retrofitting of structural elements:

1- Using Carbon Fiber sheets CFRP

or 

2- Increasing the section of the structural element using reinforced concrete.

I have searched a lot of articles but still couldn't find a clear answer.
I would like to request your opinion regarding this subject.

Thanks,

------------------------------
Hassan Dankar S.M.ASCE
Principle engineer
Maarabani and Partners
------------------------------

In terms of effectiveness, externally bonded CFRP laminate is better for flexural strengthening / retrofitting of beam or slab subjected to eliminate debonding failure rather than section enlargement

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Md Ashraful Alam A.M.ASCE
Universiti Tenaga Nasional
Kajang
------------------------------

Hello Mr. Hassan Dankar,

In my opinion, there are four things that should be considered to select the appropriate retrofitting method. These are:
1- space available for retrofitting and its effect on the appearance of the structural element.
2- cost of retrofitting materials
3- cost of labor 
4- applied loads and required strengthening level 

While the rehabilitation of existing concrete structures using CFRP sheets is expensive in terms of material cost, it is not in terms of labor.
On the other hand, increasing the section of the structural element using reinforced concrete is less expensive in terms of material cost but more expensive in terms of labor cost compared to the use of CFRP sheets. In addition, increasing the section of a structural element affects the appearance and consumes more space.
It should also be noted that the type and level of loading might require to use one of the aforementioned retrofitting methods specifically.

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Alaa Al-Sammari, BSc, MSc, S.M.ASCE
Structural Engineering PhD Candidate
Civil and Environmental Engineering Department
University of Massachusetts Amherst
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This post was removed

------Original Message------

Hi Everyone,

I have been recently conducting an academic study to check which solution is more feasible in retrofitting of structural elements:

1- Using Carbon Fiber sheets CFRP

or 

2- Increasing the section of the structural element using reinforced concrete.

I have searched a lot of articles but still couldn't find a clear answer.
I would like to request your opinion regarding this subject.

Thanks,

------------------------------
Hassan Dankar S.M.ASCE
Principle engineer
Maarabani and Partners
------------------------------

In my Opinion, the system of Carbon Fiber Sheet, need high level of technique for " Application", by a well versed Contracting Agency. Another negative aspect, is about instant self-destruction in the event of a Fire, and the Retrofitted Structural Elements loosing the retrofit, almost instantly.

Another Method could be using same " Matrix" of Cement as of Original Construction, in Two Options

(i) by using addition of adequately supplementing of Reinforcement, with proper Shear Connection and deploying Cement:Sand Shotcreting or also known as pneumatic Gunite.
OR
(ii) according to need-base, whether simply retrofitting OR incremental Load carrying Capacity, similar to (i) above and deploying " Micro-Concrete, as available from leading Polymer Products Manufacturers, of High Early Strength gain, even upto equivalent of M-35, within 24 hours of placing, within temporary Form-work.

This all depends upon the priorities of the " Structural Consultant" associated with such retrofitting Projects.

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SATISH DHUPELIA , PROPRIETOR
Consulting Structural ENGINEER
STRUCT-ARCH
MUMBAI, INDIA
+919820028705
SatishSatishSatish
------------------------------

​I've used flat procured carbon fiber reinforcing strips several times and I think they are a good solution for reinforcing existing sections that need a moderate increase in capacity.  Because there is no way for the fiber to be protected against the effects of fire (once the epoxy loses bond with the concrete you are back to the basic concrete section), ACI 440 requires a check of the concrete section with original steel reinforcing against a less severe load combination.  So, it is not as though you can increase the capacity of your concrete section without limits.  If you need another 20% flexural capacity, I think carbon fiber reinforcing is a good option in most cases.  If you need a lot more additional strength, I've usually come to the conclusion that I need to add depth and reinforcing to my section.

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Jeffrey Davis P.E., M.ASCE
VICE PRESIDENT
Dunbar Milby Williams Pittman & Vaughan
Richmond VA
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Andrew Holmes P.E., L.S., M.ASCE
Consulting Engineer
Melbourne FL
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Thank you all for sharing your experiences and knowledge,

As a conclusion I realized that there is no general formula that can be applied.
It is more of a case study in which many variables should be considered.

I will share with you my paper work once it is done.

Kind regards,

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Hassan Dankar S.M.ASCE
Principle engineer
Maarabani and Partners
------------------------------

Original Message:
Sent: 08-16-2017 09:56
From: Andrew Holmes
Subject: Retrofitting of Structural Elements

This is a question that will have an answer that depends upon the facts of each specific situation. Structural retrofits are, by nature, customized solutions designed for a particular situation or conditions. You will not find an answer that is the same in every case.

With that said, you may want to focus your research paper on finding and supporting examples of different solutions and why those solutions were selected vs. other possible alternatives. 

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Andrew Holmes P.E., L.S., M.ASCE
Consulting Engineer
Melbourne FL
------------------------------

Check out this professor's research: Statler College of Engineering and Mineral Resources | GangaRao, Hota V.

He has numerous repair applications from the past 20 years utilizing CFR. 
He has been working on getting CFR into the IBC.
He admits the up front costs are more expensive, but the long-term repair costs are practically zero.
So depending on the application, like bridge piers and abutments, the CFR becomes more and more practical. 

However, from a feasibility stand point, increasing the concrete's cross section is rarely reasonable unless you actually need to increase load carrying capacity. 
CFR will not increase you load carrying capacity; it will only restore the structure back to its original capacity without requiring future repairs.

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Matthew Lee P.E., M.ASCE
Pennoni Associates Inc.
Pittsburgh PA
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You haven't found a clear answer because there isn't one.  There are a number of things in play here, and there are tradeoffs with each approach.

If space is a premium, carbon fiber would be the preferred option.
If cost is the driver, expanding the section will likely be more economical.
Are there elements that would be overloaded by the increased concrete section, either for gravity or lateral loads?
Are aesthetics of the increased size an issue?
Are aesthetics of exposed concrete desirable?
Is durability of exposed concrete needed?

This is a design decision that needs to be discussed with the design team and the property owner, not just made by the engineer.

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Conrad Guymon P.E., M.ASCE
Senior Design Engineer
CKR Engineers
Orem UT
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I agree with Conrad that the solution for each retrofitting project is unique.  Some additional things that may need to be reviewed are:

1. Time restraints for the work. 
2. The economic cost of the work to the owner.
3. The temperature of the object being supported.
4. The customer's operations.

 Working in the refining industry, I have retrofitted the foundations supporting coke drums without removing the drums from the foundations.  The project team determined what procedures needed to be us to:

• Support 1 million ton coke drums during retrofitting
• Raise the coke drums about 1/8" to relieve the stress on the foundation
• Remove the deteriorated concrete from the foundation 
• Reinforce the existing and new concrete
• Form and install new anchor bolts under the existing coke drums
• Place new concrete using a specialty concrete that reached design strength in 24 hours 
• Shut down the Coker Unit for less than 2 weeks

We were able to accomplished this within the time allotted.

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Kenneth Clark P.E., M.ASCE
Civil Engineer
Oklahoma City OK
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Original Message:
Sent: 08-16-2017 10:10
From: Conrad Guymon
Subject: Retrofitting of Structural Elements

You haven't found a clear answer because there isn't one.  There are a number of things in play here, and there are tradeoffs with each approach.

If space is a premium, carbon fiber would be the preferred option.
If cost is the driver, expanding the section will likely be more economical.
Are there elements that would be overloaded by the increased concrete section, either for gravity or lateral loads?
Are aesthetics of the increased size an issue?
Are aesthetics of exposed concrete desirable?
Is durability of exposed concrete needed?

This is a design decision that needs to be discussed with the design team and the property owner, not just made by the engineer.

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Conrad Guymon P.E., M.ASCE
Senior Design Engineer
CKR Engineers
Orem UT
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Dear All, 

I am new to this group. 

When it is a retrofitting work, one should think about the effectiveness and efficiency of the retrofitting method to be employed. 

Please see the latest research work by our group published in ASCE - Journal of Performance of Constructed Facilities. 

Sivaganesh Selvaraj and Mahendrakumar Madhavan. (2018)."Retrofitting of Structural Steel Channel Sections using Cold-Formed Steel Encasing Channels, "Journal of Performance of Constructed Facilities (ASCE), (Vol 32, No. 4) DOI: 10.1061/(ASCE)CF.1943-5509.0001187. 

Article <g class="gr_ gr_305 gr-alert gr_gramm gr_inline_cards gr_run_anim Style multiReplace" id="305" data-gr-id="305">link :</g> click here to view

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Sivaganesh Selvaraj S.M.ASCE
Ph.D Research Scholar
Indian Institute of Technology Hyderabad
Telangana, INDIA
LinkedIn: https://www.linkedin.com/in/sivaganesh-selvaraj-33395448/
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Hi Hassan,

Besides to the very good answers I have read here, I'd also add some points:
1. On an academic basis, it will be difficult to include a cost study (labor, time, space,..etc) so this parameter will be omitted.
2. The mechanical properties of FRP sheets are significantly varied and should be considered as high and low bounds (for instance Ef= 50 to 300 GPa; Ftu= 500 to 3000 GPa; nf=0.15 to 3 mm). I am talking about GFRP and CFRP, ignoring the ultra high strength CFRP.
3. Concrete strength to flexural and transverse reinforcement ratios can easily change your findings so be careful with conclusions.

Based on that, understanding the work conducted by past studies should guide you towards building up your project by choosing the adequate parameters and continue the train of this work. Good luck!



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Ahmed Mohamed A.M.ASCE
Sherbrooke QC
1819 7915120
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