4 Common FRP Myths and Misconceptions: The Stuff Not Everyone Talks About

The primary benefit of fiber-reinforced polymer (FRP) systems as compared with traditional retrofit methods is that significant flexural, axial or shear strength gains can be realized using an easy-to-apply composite that does not add significant weight or section to the structure. Many times it is the most economical choice given the reduced preparation and labor costs and may be installed without taking the structure out of service. However, it is important to make sure the composite is properly designed following industry standards in order to ensure that it is the right product for the application.

To provide you with a better understanding of the topic, it’s important to dispel some common myths and misconceptions that you might hear about FRP:

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FRP Concrete Strengthening – Five Case Studies

Fiber-reinforced polymer (FRP) composite systems can be used to strengthen walls, slabs and other concrete or masonry members in buildings and other structures. The case studies below show ways in which Composite Strengthening Systems™ (CSS) provide valuable solutions for strengthening buildings and other structures for our customers.

Residential Project in San Francisco

The homeowner for this project wanted to repair some spalling concrete on his concrete piers and also wrap the piers with FRP. We worked with the contractor and homeowner to design a cost-effective solution. This was a successful project for all involved, since the alternative was to jacket the piers with costly and unsightly steel jackets.

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Materials: CSS-CUCF Carbon Fabric, CSS-ES Epoxy Saturant & Primer

School Project in Argentina

The goal of the project was to analyze a standard design of approximately 400 schools in Argentina that were built in the 1980s and to make recommendations to retrofit the structures to meet current seismic code requirements.  On analysis, it was found that columns were in need of shear reinforcement for the schools to meet the new seismic requirements.

Materials: CSS-UCF Carbon Fabric, CSS-CA Carbon FRP Anchors, CSS-ES Epoxy Saturant & Primer
Materials: CSS-UCF Carbon Fabric, CSS-CA Carbon FRP Anchors, CSS-ES Epoxy Saturant & Primer

Hospital Project in Butler, PA

The Engineer of Record on this project wanted to provide continuity across the slab construction joints, something which the existing rebar did not provide. We provided a design of Near-Surface-Mounted (NSM) laminates, which are installed in saw-cut grooves in the top of the concrete slab. This installation allows a flush finished surface, important for allowing the floor finishes to be installed on the slab.

Materials:CSS-CUCL Carbon Precured Laminate, CSS-EP Epoxy Paste & Filler
Materials: CSS-CUCL Carbon Precured Laminate, CSS-EP Epoxy Paste & Filler

Silo Project in Garden City, IA

The concrete silos on this project had spalling at the top portion, which caused a hazard at this site. After repairing the concrete, we provided a ring of carbon fabric to assist in keeping the top concrete of the silos solid for years to come.

Materials:CSS-CUCF Carbon Fabric, CSS-ES Epoxy Saturant & Primer
Materials: CSS-CUCF Carbon Fabric, CSS-ES Epoxy Saturant & Primer

Bridge Project in MN

MNDOT wanted to gain experience working with our CSS products on one of their bridges. We worked with their staff to design several types of strengthening solutions for bridge pier caps and columns. We then provided onsite installation training for the MNDOT maintenance staff to install the FRP products on the bridge.

Materials:CSS-CUCF Carbon Fabric CSS-CUGF E-glass Fabric CSS-ES Epoxy Saturant & Primer CSS-EP Epoxy Paste & Primer frp concrete strengthening
Materials: CSS-CUCF Carbon Fabric, CSS-CUGF E-glass Fabric, CSS-ES Epoxy Saturant & Primer, CSS-EP Epoxy Paste & Primer

We recognize that specifying Simpson Strong-Tie® Composite Strengthening Systems™ is unlike choosing any other product we offer. Leverage our expertise to help with your FRP strengthening designs. Our experienced technical representatives and licensed professional engineers provide complimentary design services and support – serving as your partner throughout the entire project cycle. Since no two buildings are alike, each project is optimally designed to the Designer’s individual specifications. Our pledge is to address your specific condition with a complete strengthening plan tailored to your needs, while minimizing downtime or loss of use, at the lowest possible installed cost.

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Your Partner During the Project Design Phase 

During the Designer’s initial evaluation or preparation of the construction documents, Simpson Strong-Tie can be contacted to help create the most cost-effective customized solution. These plans include detailed design calculations for each strengthening requirement and design drawings with all the necessary details to install the CSS system. Simpson Strong-Tie Engineering Services will work closely with the Design Engineer to provide all the necessary information required to design the system.

Why Use Our Design Services?

  • Assess feasibility studies to ensure suitable solutions to your application
  • Receive customized FRP strengthening solutions
  • Work with our trained contractor partners to provide rough-order-of-magnitude (ROM) budget estimates
  • Collaborate during the project design phase
  • Receive a full set of drawings and calculations to add to your submittal
  • Maintain the flexibility to provide the most cost-effective solution for your project
  • Gain trusted technical expertise in critical FRP design considerations

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Learn more: Webinar – Introducing Fabric-Reinforced Cementitious Matrix (FRCM)

In this free webinar we dive into some very important considerations including the latest industry standards, material properties and key governing limits when designing with FRCM.

Continuing education credits will be offered for this webinar.
Participants can earn one professional development hour (PDH) or 0.1 continuing education unit (CEU).


For complete information regarding specific products suitable to your unique situation or condition, please visit strongtie.com/css or call your local Simpson Strong-Tie RPS specialist at (800) 999-5099.

 

Fiber Reinforced Polymer (FRP) Design Example

The following FRP Design example walks the reader through the typical process for designing an FRP strengthening solution for a concrete T-beam per ACI 440.2R Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures.

One of the most important initial checks for an Engineer of Record is to confirm that the unstrengthened structure can support the load combination shown in Equation 5.5.1 in ACI 562 Code Requirements for Evaluation, Repair, and Rehabilitation of Concrete Buildings:

Eq. 5.5.1: (φRn)existing ≥ (1.2SDL + 0.5SLL)new

This check is to prevent a structural failure in case that the strengthening is damaged in an extraordinary event. If the structural element cannot pass this check, then external reinforcement is not recommended.

We have a Design Questionnaire where we ask Engineers of Record for more specific information related to the element to be strengthened:

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For this particular example, the following information was provided for the concrete T-beam.

1.  Structure Type (e.g., building, bridge, pier, garage):

  • 5-story commercial concrete building

2. Element(s) to be Strengthened/Repaired (e.g., beam, column, slab, wall):

  • Reinforced concrete beams

3. Type of Deficiency (e.g., shear, flexural, axial):

  • Flexural

4. Existing Factored Capacity of Section (e.g., kips, kip-ft):

  • 265 kip-ft

5. Ultimate Demand to be Supported (e.g., kips, kip-ft):

  • 320 kip-ft

6. Existing Concrete Compressive Strength:

  • 4,000 psi

7. Existing Rebar Yield Strength:

  • 60 ksi

8. Existing Reinforcement Layout:

  • 3 #7s 2.6875 inches from bottom of web to centroid of steel

9. Existing Dimensions:

  • 36 inches total beam height, 8 inches slab, 24 inches web width, 120 inches effective slab width

10. Relevant Existing Drawing Sheets and/or Pictures:

  • See attached

11. Finish Coating Requirements/Preferences:

  • None

12. For Flexural Strengthening:

  1. Dead Load Moment Applied at Time of Installation
    1. 60 kip-ft
  2. Service Dead Load Moment After Installation
    1. 80 kip-ft
  3. Service Live Load Moment After Installation
    1. 140 kip-ft

We then plug this information into our design program to come up with an FRP solution that meets the needs of the member:

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For a beam that was at 83% of the capacity required for the new loading, we specified a simple, low-impact FRP solution to maintain clearances under the beams. If a traditional fix of adding cross-section to the beam had been specified instead, then additional concrete and rebar would need to be added to the beam, which would impact clearances under the beam and also increase the seismic weight of the building. The additional weight could also translate all the way through the building and even impact footing designs.

FRP can be used to increase the flexural strength up to 40% per ACI 440.

For your next retrofit project, please contact Simpson Strong-Tie to see if FRP would be an economical choice for strengthening your concrete or masonry element.

Add Simpson Strong-Tie to Your Design Team

Simpson Strong-Tie Composite Strengthening Systems™ is unlike choosing any other product we offer.

For your next retrofit project, please contact Simpson Strong-Tie to see if FRP would be an economical choice for strengthening your concrete or masonry element.


Unreinforced Masonry (URM) Buildings: Seismic Retrofit

Unreinforced Masonry buildings in moderate to high seismic areas can be a disaster in waiting. These types of structures have little or no ductility capacity (reference the recent “Building Drift – Do You Check It?” blog post for a discussion on ductility) required for structures to prevent loss of life in a seismic event. Many of these buildings are in densely populated areas, have historical meaning, and can be costly to retrofit. Fortunately, there are tools available for engineers to assess and design the needed retrofits to mitigate the potential loss of life and increase the seismic resiliency of these buildings.

Image credit: International Code Council (ICC).
Image credit: International Code Council (ICC).

ASCE 31-03, Seismic Evaluation of Existing Buildings, and ASCE 41-06, Seismic Rehabilitation of Existing Buildings, are two reference standards that are referenced in the 2012 International Existing Building Code (IEBC). (It should be noted that both of these reference standards are currently being combined into one document – ASCE 41-13.) Although ASCE 31 and 41 provide assistance to engineers in determining minimum seismic retrofits for these brittle structures, it is recommended that design of the retrofits be performed by a qualified engineer with experience in working with these types of brittle structures.

Currently the 2012 IEBC has been adopted in 39 states in the U.S. and several other areas (see reference map below).

2012 IEBC Adoption Map. Image credit: International Code Council (ICC).
2012 IEBC Adoption Map. Image credit: International Code Council (ICC).

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