Site: Bridge Deck Strengthening Demonstration Site
Hanshin Expressway
Kobe, Japan
Date Visited: October 1996
Contact: M. Uemura, General Manager, Tonen Corporation
Summary: Carbon fiber sheets were used to retrofit deck slabs using a variety of sheet types, thicknesses and reinforcement patterns.

ACTIVITIES OF INTEREST

Under the aegis of the CFRRA (Carbon Fiber Repair and Reinforcement Research Association), Tonen Corporation, Mitsubishi Chemical and Toray undertook a joint demonstration project to showcase the use of carbon fiber sheet based external reinforcement as a strategy for the repair and rehabilitation of bridge decks. The project was conducted on a span of the Hanshin Expressway in Kobe and was funded by the CFRRA and the Hanshin Expressway Corporation. There were 3 primary objectives:

  1. To demonstrate field applicability of bridge deck strengthening through the use of external sheets
  2. To provide a means for establishing cost effectiveness of the method as compared to more conventional repair/retrofit strategies
  3. To provide a site for monitoring

The different sheets were all applied to the soffit of the concrete deck using wet layup procedures with epoxy. They were cured under ambient conditions. The goal was to increase load carrying capacity from 20- to 25-ton trucks. The project was conducted in bays separated by longitudinal and transverse steel supporting girders (Fig. B.88) between piers 426 and 427. The overall span consisted of 12 such sectors of equal size, each containing a different reinforcing strategy (material, design method and layup ) as shown in Figure B.89 and in Tables B.9 and B.10 . The lattice pattern was utilized to facilitate easy visual inspection for cracking and to allow for movement of moisture out of the slab which otherwise might have been trapped at the resin-concrete interface.


Fig. B.88. View of retrofitted slab bottom.

 

 

A Type IV

A Type V-II

A Type I

A Type V-I

A Type II

A Type III

B Type V-I

C Type V-I

B Type II

B Type III

C Type II

C Type III


Fig. B.89. Distribution of types of strengthening. Each cell represents an area of retrofit (A,B,C relate to the manufacture of the carbon fiber sheet).
Table B.9
Details Related to Layup of Fabric Sheets

Reinforcement

Type

Number of Reinforcing Sheets

Reinforcement

Pattern

Lateral Direction

Longitudinal Direction

Type I

Type II

Type III

Type IV

Type V-I

Type V-II

8

3

4

2

3

2

2

2

3

1

2

1

All over

All over

Lattice

All over

Lattice

Lattice


(All over=full coverage, Lattice=cross pattern leaving open gaps as in Fig. B.90)
Table B.10
Comparison of Methods Used for Design

Method of Design

Reinforcement Pattern

All Over

Lattice

Allowable Stress Method

Allowable Stress in Reinforcing Bars

Limit State Method

Type I

Type II

Type IV

-

Type III

Type V

After construction wheel load tests (25 ton) were conducted to assess overall deflection and strains in the carbon sheets. Strain levels of 150 to 160 microstrain were measured subsequent to the retrofit procedure and deflections were reduced by 30 to 40% with Type I showing the best performance. The overall response appeared to be largely independent of the number of layers used to strengthen a section, emphasizing the fact that even small amounts of carbon fiber reinforced overlays can be very effective in keeping cracks closed. The project, including initial monitoring, was completed in early 1996, and draft design guidelines have been prepared. These will be reviewed after a period of a year, subsequent to further testing. Then guidelines will be officially published. It was reported that on average the total retrofit cost was $15/ft2.


Fig. B.90. Close-up of a lattice pattern showing open areas and Tonen tow sheet fabric in the longitudinal and transverse directions.


Published: October 1998; WTEC Hyper-Librarian