Site: Sumitomo Bridges, Oyama Works
Sumiken Concrete Industry Co., Ltd.
Technical Research Institute
Sumitomo Construction Co., Ltd.
Tochigi Prefecture, Japan
Date Visited: October 1996
Hosts: Shin-Ichiro Kumagai, Deputy General Manager, Sumitomo Construction Co., Ltd.
M. Kamiyoshi, Project Manager, Teijin, Ltd.
Atshushi Sumida, Manager, DuPont Toray Kevlar, Ltd.
Summary: Two parallel bridges were built using aramid fiber reinforced composite tendons. The first bridge was a pretensioned bridge of 12.5 m span, whereas the second was a post-tensioned box girder of 25 m span.

ACTIVITIES OF INTEREST

The aramid fiber-reinforced polymer (AFRP) rod reinforced demonstration bridges are two parallel bridge structures, each having a lane width of 4 m, and designed for 20-ton truck loads. The shorter span consists of 3 pretensioned box girders (each of 12.5 m length) whereas the longer span is made up of a single-cell post-tensioned box girder of 25 m length (Fig. B.68).


Fig. B.68. Plan and cross-section of the AFRP reinforced bridges.


Fig. B.69. View of the AFRP bridge.

Table B.6

Design Criteria

Pretensioned Span

Post-Tensioned Span

Structure

Bridge Length

Girder Length

Span Length

Width

 

Longitudinal Gradient

Lateral Slope

Live Load

 

 

Impact Coefficient

Composite Girders

12.50 m

12.39 m

11.79 m

0.6 m + 3.99 m

(side + roadway)

2.9%

2%

TL-20

(20 tons)

 

Single Box Girder

25.00 m

24.88 m

24.10 m

0.6 m +3.99 m

(side + roadway)

2.9%

2%

TL-20

(20 tons)

 

Horizontal Seismic Coefficient

Stress Limits in Tendons

(a) During tensioning

(b) At transfer

(c) Under design load

0.2

 

0.80 Pu

0.70 Pu

0.60 Pu

0.2

 

0.80 Pu

0.70 Pu

0.60 Pu

Pretensioned Girders

The pretensioned girders were constructed using procedures similar to those used in conventional precast construction, with tensioning carried out in one operation through a movable tensioning plate. Each girder was reinforced in two layers with 12 aramid fiber reinforced tendons at the bottom and 4 similar tendons at the top that were pretensioned. Each of these tendons consisted of 3 strands of 6 mm diameter each. Eight millimeter aramid fiber reinforced bars were also employed for stirrups and reinforcement on the top (2 bars, one at each corner) and at the sides (3 bars per side). The initial stressing force for the tendons was 0.75 fpu assuming a 7% relaxation/prestress loss. Figure B.70 shows positioning of the prestressing tendons and Figure B.71 depicts the overall reinforcement arrangement (including stirrups). The overall fabrication diagram is shown in Figure B.72.


Fig. B.70. Prestressed configuration with tendons installed and pre-tensioned.


Fig. B.71. Overall reinforcement configuration.


Fig. B.72. Diagram of prestressing configuration.

Secondary reinforcement and stirrups were post-tensioned. The entire girders were reinforced with Technora tendons, with appropriate surface deformations. Total length of 6 mm diameter tendons was 2.82 km and that of the 8 mm diameter tendons was 0.6 km. The bridge was completed in July of 1990.

Post-Tensioned Girder

The single-cell cast-in-place box girder of 1.9 m depth is post-tensioned with both external and internal tendons. Internal post-tensioning is through ten 19-strand AFRP tendons of 6 mm diameter each with locations as shown in Figure B.73.


Fig. B.73. Location of internal tendons.

Tendons are anchored using a special bonding anchorage as shown in Figure B.74. The anchorage is designed for a tensile strength of 80 tons, has a cross-sectional area of 5.372 cm2, and is made of stainless steel. Anchorages are mortar filled. Six additional external tendons were also used, each consisting of seven 6 mm diameter AFRP rods in a plastic sleeve (Fig. B.74) and using a nonmetallic anchorage (Fig. B.75). The anchorages were made of short fiber reinforced composite with square threads machined into them. A close-up of a 12 strand anchorage is shown in Figures B.76 and B.77.


Fig. B.74. Sheathed external tendons.


Fig. B.75. Nonmetallic anchorage for post-tensioning.


Fig. B.76. Close-up of 12 strand nonmetallic anchorage (side-view).


Fig. B.77. Close-up of 12 strand nonmetallic anchorage (end-view).


Fig. B.78. View of external post-tensioned tendons at girder end.


Fig. B.79. View of external post-tensioned tendons at girder mid-span.

An automatic tensioning jack was used for post-tensioning, bearing in mind that aramid tendons show significant elongation (0.5 m in a 25 m length), necessitating frequent resetting of the tensioning jack. Views of the tendons at the ends and at midspan are shown in Figures B.78-B.79. The overall length of the deformed Technora rods in this girder was 5.9 km (4.8 km in the internal tendons) and 1.1 km in the external tendons. The AFRP bridge was completed in February 1991.

Tendon Characteristics

Technora rods are made by Teijin, Ltd. using aramid fiber and vinylester resin. The aramid fibers are made from PPODTA (co-poly-paraphenylen/3,4-oxidiphenylene telephthal amide). Basic properties of the fiber and resin are listed in Table B.7.

Table B.7
Basic Properties of Constituents

Property

Fiber

Resin

Tensile Strength (MPa)

Young's modulus (GPa)

Elongation to Break (%)

Relaxation (%)

Coefficient of thermal expansion (10-6/C)

Specific Gravity

3430

72.6

3.7-4.6

10

-3

1.3

90

3.53

4.5-5.5

The rods are fabricated using the pultrusion process with 65% Vf and deformations where applicable are created using a secondary spiral winding process. The general appearance of the rods is shown in Figure B.80 and the geometry of deformations is depicted in Figure B.81.


Fig. B.80. AFRP rods.


Fig. B.81. Deformed bar geometry.

A comparison of rod characteristics is given in Table B.8.

Table B.8
Comparison of Reinforcement Characteristics

Type

Nominal Diameter (mm)

Nominal c/s area (mm2)

Unit Weight (g/m)

Guaranteed Tensile Strength (kgf)

Round

Spiral Wound

Round

Spiral Wound

6 mm

6 mm

8 mm

8 mm

28.26

28.26

50.24

50.24

37

66

41

73

5090

8790

5090

8790

ADDITIONAL POINTS OF INTEREST


Published: October 1998; WTEC Hyper-Librarian