Structures Design Guidelines | Jan 2009
7 - Widening and Rehabilitation |

## 7.8 - Repair or Strengthening using Carbon Fiber Reinforced Polymers (07/06) July 2006: Per TDB C06-03, Added New Section.

### 7.8.1 System Selection

FRP composite systems used in repair or strengthening shall have carbon as the primary reinforcement (CFRP). Whether a precured laminate or wet layup system is used, the resin and adhesive shall be a thermoset epoxy formulation specifically designed to be compatible with the fibers or precured shapes.

### 7.8.2 Design

The design of CFRP systems is considered a Category 2 structure and the plans and specifications shall be reviewed and approved by the Structures Design Office for this repair portion of the project. Design shall conform to ACI Committee 440.2R-02 (“Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures” American Concrete Institute, ACI 440.2R-02, 2002, 45 pp.) except as noted herein. Loads shall be obtained using LRFD Bridge Design Specifications.

a) Replace “PART 3 – RECOMMENDED CONSTRUCTION REQUIREMENTS” with the following:

Section II of National Cooperative Highway Research Program Report (NCHRP) 514 (Mirmiran, A., Shahawy, M., Nanni, A., Karbhari, V., (2004) “Bonded Repair and Retrofit of Concrete Structures Using FRP Composites, Recommended Construction Specifications,” Transportation Research Board, 102 pp.)

b) Modify Section 8.2 as follows:

When a single girder in a span containing at least four similar girders is strengthened then the following limit shall control:

where is the capacity of the existing member considering ONLY the existing reinforcement, SDL and SLL are the unfactored dead load and live load effects, respectively, that occur after the member has been strengthened. When multiple girders in a single span are strengthened then the following limit shall control:

If the existing reinforcement is insufficient to satisfy this equation, then alternative means of strengthening or replacement of the structure shall be implemented. This check shall be conducted using load factors and capacity reduction factors from the LRFD Bridge Design Specifications.

c) Modify Section 8.3.1 as follows:

An environmental reduction factor C E = 0.85 shall be used for all bridge applications.

d) Replace equation 9-5 with:

where c is the distance from extreme compression fiber to neutral axis when the section is at capacity and d t is the distance from extreme compression fiber to centroid of extreme layer of longitudinal tension steel.

e) Modify Section 9.4 as follows:

Stresses in existing reinforcement (using equation 9-6) shall be checked using Service I Load Combination from LRFD Bridge Design Specifications.

f) Modify Section 9.5 as follows:

Use the standard fatigue truck from LRFD Bridge Design Specifications to check fatigue stresses in CFRP composites. Allowable fatigue stresses in prestressing or mild steel shall be checked using Chapter 5 of the LRFD Bridge Design Specifications.

g) Modify Section 9.6 as follows:

Strength of nonprestressed concrete sections repaired with CFRP composites shall be calculated using the equations given in Section 9.6. Strength of prestressed sections repaired with CFRP composites shall be calculated using equilibrium and strain compatibility. Regardless of method, the strain in the CFRP composites at ultimate capacity shall not exceed the bond critical limit given in equation 9-3.

h) Modify Chapter 10 as follows:

Shear strengthening shall be restricted to one of the following methods. The first is with a completely wrapped element as illustrated in Fig. 10.1 of the ACI 440.2R-02. U-wraps may also be used only if the termination of the wrap is anchored to prevent debonding. The anchorage system shall have been tested to ensure the system will behave similar to the fully wrapped system.

i) Modify Chapter 12 as follows:

In addition to the requirements in Section 12.1.12, transverse CFRP reinforcement shall be provided at the termination points of each ply of CFRP flexural reinforcement. In addition, transverse reinforcement shall be provided at a maximum spacing of d along the length of the member from end to end of the CFRP reinforcement. Alternatively, 0-90 degree fabric shall be permitted, which when wrapped up into the web can provide simultaneous transverse and longitudinal strengthening. The width of the transverse reinforcement at the termination shall measure at least ¾d along the member axis and shall have at least 30% of the capacity as that of the flexural reinforcement. Intermediate transverse reinforcement shall have a minimum length of d/4.

### 7.8.3 Construction

The Engineer of Record shall develop Technical Special Provisions for Construction and quality control that conform to the specifications given in Section II of National Cooperative Highway Research Program Report (NCHRP) 514 (Mirmiran, A., Shahawy, M., Nanni, A., Karbhari, V., (2004) “Bonded Repair and Retrofit of Concrete Structures Using FRP Composites, Recommended Construction Specifications,” Transportation Research Board, 102 pp.) except as noted herein.

In wet layup systems, shear and flexural reinforcement shall have no more than three layers. This does not include anchorage requirements listed in 7.8.2.

Technical Special Provisions shall be non-proprietary, multi-vendor solutions (2 minimum), reviewed and approved by the State Specifications Offices and the State Structures Design Office.