ARAMID FIBER BASED LINEAR REINFORCING ELEMENTS

Although a majority of projects discussed in this chapter involve the use of carbon fiber reinforced tendons and/or cables, considerable work has also been conducted with aramid fiber reinforced tendons, bars and cables. Aramid fiber reinforced composites are increasingly popular in Japan because of their high toughness/tenacity, high elongation at break (significantly exceeding that of carbon fiber based elements) and nonmagnetic/nonconductive characteristics. Three main classes of aramid fiber based reinforcing elements are currently available:

The first was not included in the draft document on "Design and Construction Guidelines for Prestressed Concrete Highway Bridges Using FRP Tendons" issued by PWRI in March, 1994. In this section, brief descriptions of each of these types and applications using these elements are discussed. Additionally, descriptions of the use of these elements can be found in the Akashi Kaikyo Bridge, the Kamiooka Station Parking Structure, the Rainbow Bridge, the Sone Viaduct and the Sumitomo Bridges site reports in Appendix B of this report.

Arapree Elements

Arapree, or Aramid Prestressing Elements, are fabricated from high modulus Twaron fibers (a product of Aramide Maatschappij vof, a joint venture of Akzo and N.V. Noordelikje Ontwikkelingsmaatschappij), which are a form of aramid developed through the combination of p-phenylenediamine and terephthaloydichloride (Fig. 3.42).


Fig. 3.42. Chemical structure of aramid.

The prestressing elements, which are available in the form of rectangular bars, or circular rods (Table 3.9), were initially developed through a collaboration between HBG-Hollandsche Beton Groep and Akzo Fibers. The elements are formed by passing non-twisted Twaron fibers through eyelets and combs. This enables the simultaneous impregnation of the bundles and the structure such that 35-45% by volume consists of the almost 100% paracrystalline, highly oriented, unidirectional rigid chain type molecule based fibers, and 65-55% consists of a chemically resistant epoxy resin. The surface of the element has a knobbed topography, which facilitates good mechanical interlock for stress transfer. Except for the two smallest sizes, all tendons are formed in multiples of 100,000 individual Twaron high modulus filaments. Overall properties for individual circular tendons are given in Table 3.10.

Table 3.9
Types of Arapree Elements

Element Type

Shape of Cross-Section

Size-Nominal (mm)

Cross-Sectional Area of Fiber (mm2)

f 20,000

f 100,000

f 200,000

f 400,000

Rectangular

20 x 0.3

20 x 1.5

20 x 3.0

20 x 5.0

2.2

11.1

22.2

44.4

f 20,000

f 100,000

f 200,000

Circular

2.5 diameter

5.0 diameter

7.5 diameter

2.2

11.1

22.2

These elements have a creep coefficient of 0.2 after 106 hours and exhibit a 15% drop in prestress level due to relaxation after 106 hours in air, as well as a 20% drop in level after exposure to alkaline solution. Service temperature above 100°C is not recommended due to the low melting point of Twaron fibers. At 60% of ultimate strength (short term) the elements have a predicted life of 105 hours (11.41 years). Twaron manufacturers recommend that the elements be stressed to a level no greater than 50% of their ultimate short-term strength levels.

Table 3.10
Average Mechanical Properties of Individual Circular Twaron Tendons at 20oC

Property

Unit

Value

Axial Tensile Strength

N/mm2

2800 - 3000

Tensile Modulus (measured between 10% and 50% of ultimate strength)

kN/mm2

125 - 130

Failure Strain

%

2.4

Density

kg/m3

1250

Transverse Compressive Strength

N/mm2

» 150

Interlaminar Shear Strength

N/mm2

» 45

Poisson's Ratio

 

0.38

Coefficient of Thermal Expansion

10-6 /K

1.8

Electrical Resistance

- in air

- saturated with water

Ohm · cm

 

7 x 1015

7 x 107

Wedge type anchorages are employed for short-term use (Fig. 3.43). For long-term use, anchorages in which steel tubes are filled with cement mortar are used (Fig. 3.44).


Fig. 3.43. Short-term tendon anchorage assembly.


Fig. 3.44. Anchorages for long-term use.

A listing of sample application projects is given in Table 3.11. Except for the last case, Arapree was used in conjunction with another reinforcing element.

Table 3.11
Examples of Application of Arapree Elements

Structure and Location

Date

Description

Birdie Bridge

Southern Yard Country Club

Ibaraki Prefecture

September

1990

Flat Arapree elements were used in the deck slab. Bars were 20 x 5.0 mm nominal type

f 400,000, 8 sets were used for a total length of 7,150 m.

CFCC & Leadline tendons were also used.

Kikumoto K-4 Berth

Sumitomo Chemical Co., Ltd.

Ehime Prefecture

October 1991

Arapree f 400,000 elements were used for pretensioning of the main girder of the berth slab. A total length of 3,200 m was used on a 8.76 m x 13.8 m slab.

Prestress at jacking = 80% of ultimate

Stress at transfer = 70% of ultimate

Stress under design load = 60% of ultimate

Kamiooka Station Parking Structure Entrance Slab

Keihin Kyuko Railway Co.

Kanagawa Prefecture

August 1995

470 m of Arapree was used to reinforce an approach slab of size 8.4 m x 6 m

FiBRA Elements

FiBRA (meaning Fiber in Portuguese) elements are available using glass, carbon or aramid fibers in a braided form, although in most cases aramid fibers are used as the reinforcement. Aramid-based FiBRA is available in two varieties based on the type of resin systems used - flexible/elastomeric and rigid. In both cases, ultimate elongation is restricted by the strain capacity of the fiber, which gives a composite elongation level of 2%. The tensile modulus of FiBRA elements is 68.6 kN/mm2 and the linear coefficient of thermal expansion is -5.2 x 10-6/°C. Specifications of standard FiBRA elements are given in Table 3.12.

Table 3.12
Specifications for Standard FiBRA Elements

Type

Designation

Nominal Diameter (mm)

Effective Cross-Sectional Area (mm2)

Unit Weight (kgf/m)

Assured Tensile Load Capacity (kN)

Flexible

FA11

FA13

FA15

10.4

12.7

14.7

85

127

170

0.108

0.162

0.216

117.7

176.5

235.4

Rigid

RA7

RA9

RA11

RA13

RA15

RA18

7.3

9.0

10.4

12.7

14.7

18.0

42.0

63.0

85.0

127.0

170.0

254.0

0.053

0.080

0.108

0.162

0.216

0.324

62.8

94.1

125.5

188.3

251.0

380.0

These elements have a relaxation ratio of 25% and retain 95% of their tensile strength at 220°C. At 280°C, despite the braid, strength retention is only 55%.

In general, two types of anchorages exist for FiBRA elements, the wedge type and the resin-cone type. The first type is more popular and consists of a three- or four-section inner conical wedge that is forced into a sleeve with the tension rod in the center. Figure 3.45 gives schematics of some of these anchorages depicting their use for multi-rod configurations.


Fig. 3.45. Schematics of wedge type anchorages.

In the bonded resin type anchorage, the tension rod is placed at the center of a conical hollow in a stainless-steel sleeve and resin is poured around it (Fig. 3.46).


Fig. 3.46. Bonded anchorage.

Limited use is made of non-metallic sleeves and anchor wedges. A listing of sample application projects is given in Table 3.13.

Table 3.13
Sample Application Projects using FiBRA Elements

Structure and Location

Date

Description

Talbus Bridge

Talbus Country Club

Tochigi Prefecture

October 1990

FiBRA FA15 elements used for the post-tensioning of a girder. Bridge length = 36 m, width = 2.4 m. A total length of 2020 m of FiBRA was used.

P1 = 0.50, P2 = 0.45, P3 = 0.37

Beams of a Club House

Sunland Golf Club

Gunma Prefecture

July

1991

FiBRA FA15 elements were used for post-tensioning with a total length of 1430 m.

P1 = 0.65, P2 = 0.60, P3 = 0.48

Compass Check Apron

Haneda Airport, Tokyo

Ministry of Transportation

April 1992

FA15 elements were used to post-tension part of a concrete apron. 1970 m of FiBRA was used on a 40.0 m x 16.0 m section, in conjunction with CFCC and Leadline bars. Multiple rod (3) anchorages were used.

P1 = 0.50, P2 = 0.43, P3 = 0.34

Pontoon Bridge

Takahiko Three Country Club

Takahiko, Ibaraki Prefecture

May

1992

FA13 and FA15 elements with total lengths of 600 m and 360 m respectively were used in post-tensioning of the deck of 56.4 m x 4.0 m size.

P1 = 0.50, P2 = 0.45, P3 = 0.37

Girder - M.C. Heights

Kashiwa

Mitsui Construction Co.

Chiba Prefecture

August 1992

RA13 and RA11 elements were used for pre- tensioning of girders, with lengths of 150 m and 270 m, respectively

P1 = 0.65, P2 = 0.60, P3 = 0.48

Yamanaka Bridge

Tochigi Prefecture

May

1993

FA15 and FA13 elements were used for the pre-tensioning of the main girder and post-tensioning in the transverse direction. Lengths used were 1460 m and 160 m respectively.

P1 = 0.50, P2 = 0.44, P3 = 0.37

Prestressed Concrete Deck Slabs Rainbow Bridge

Tokyo Metropolitan Expressway Corp.

Tokyo

August

1993

Slabs at an anchorage site were pre-tensioned. 9000 m of FA9 200 slabs of 5 m x 0.91 m size were used.

P1 = 0.65, P2 = 0.60, P3 = 0.48

Stress Ribbon Bridge

Nagasaki Park Country Club

Nagasaki Prefecture

October 1993

Deck of 73 m overall length and 3 m width was post-tensioned using FA15 elements, total length of which was 2630 m.

P1 = 0.65, P2 = 0.60, P3 = 0.50

Reinforcement in Heading Kisaki Tunnel

Nagano Prefecture

November 1994

RB28F elements were used as reinforcement.


P1 = stress level at jacking as a percentage of ultimate strength
P2 = stress level at transfer as a percentage of ultimate strength
P3 = stress level under design load as a percentage of ultimate strength

Technora Elements

Technora elements are made from PPODTA (poly-para-phenylene-3,4-oxidiphenylene terephthalamide) and vinylester resin. The PPODTA fiber is a type of polyaramid with slightly lower density and higher performance than conventional polyaramid fibers. They are available in the form of round rods, deformed rods, twisted strands (Fig. 3.47), and occasionally as flat bars. The fibers are produced by Teijin, Ltd. and the Technora elements are developed by Teijin, Ltd. and Sumitomo Construction Co., Ltd. Generic materials characteristics are given in Table 3.14.


Fig. 3.47. Types of Technora elements.

Table 3.14
Specifications for Generic Technora Material

Characteristic

Unit

Value

Density

g/cm3

1.3

Guaranteed Tensile Strength

kgf/mm2

180

Tensile Modulus

kgf/mm2

5400

Elongation

%

3.6

Net Relaxation

%

7 - 14

Coefficient of Thermal Expansion

/ o C

-3 x 10-6

Specific Gravity

 

1.30

Poisson's Ratio

 

0.35

Specifications for the most commonly used varieties of the round rod and spiral wound (deformed) bar/rod elements are given in Table 3.15.

Table 3.15
Characteristics of Typical Technora Elements

Type

Nominal Diameter (mm)

Nominal Cross-Sectional Area (mm2)

Unit Weight (g/m)

Specified Tensile Strength (kgf)

Round

3.0

4.0

6.0

8.0

7.07

12.56

28.26

50.24

9

16

37

66

1330

2320

5090

8790

Spiral Wound/Deformed

3.0

4.0

6.0

8.0

7.07

12.56

28.26

50.24

10

18

41

73

1330

2320

5090

8790

Technora rods are often used in multiples, with groups of rods loosely held together but anchored within the same anchor sleeve. Characteristics of these groups are given in Table 3.16.

Table 3.16
Characteristics of Multi-Rod Technora Combinations (Deformed Bars)

Tendon Composition (# of bars - diameter - mm)

Nominal Cross-Sectional Area (mm2)

Weight (g/m)

Assured Tensile Load Capacity (ton force)

1-f6

0.283

41

5.1

3-f6

0.848

123

15.3

4-f6

1.132

164

20.4

7-f6

1.981

287

35.7

12-f6

3.396

492

61.2

19-f6

5.377

779

80.0

1-f7.4 (8 nominal)

42.4

73

7.6

2-f7.4

84.8

146

15.2

3-f7.4

127.2

219

22.8

9-f7.4

381.6

657

68.4

12-f7.4

508.8

876

91.2

Anchoring of Technora elements is enabled through the use of either wedge type (Fig. 3.48) or bonding type (Fig. 3.49) anchorages. Although non-metallic/composite anchorages are still not widely used there is considerable interest in this development, with composite bonding type anchorages being used on some demonstration sites. A schematic cut-away of a bonding type anchorage is shown in Fig. 3.50.


(a) single wedge type anchorage


(b) multi-wedge type anchorage
Fig. 3.48. Wedge type anchorages.


(a) metallic bonding anchorage (19 - 6? rods)


(b) non-metallic/composite bonding anchorage (7 - 6? rods)
Fig. 3.49. Bonding type anchorages.


Fig. 3.50. Schematic cut-away of a bonding type anchorage.

A listing of sample projects is given in Table 3.17.

Table 3.17
Examples of Projects Conducted using Technora Elements

Structure and Location

Date

Description

Girders of Prestressed Concrete Bridge

Sumitomo Construction

Tochigi Prefecture

July

1990

Pretensioning of the main girder (L = 12.5 m, W = 4.6 m), transverse prestressing and use of Technora as stirrups and secondary reinforcement.

Project used 2800 m of 6 mm diameter bars and 600 m of 8 mm diameter rods.

P1 = 0.80, P2 = 0.70, P3 = 0.60

Girders of Post-Tensioned Concrete Bridge Adjacent to a Prestressed Girder Bridge

Sumitomo Construction

Tochigi Prefecture

February 1991

Use of 6 mm diameter Technora rods for post-tensioning of the main girder (groups of 19 cables, L = 4800 m) and for external post-tensioning of the girder (groups of 7 cables, L = 1100 m)

P1 = 0.80, P2 = 0.70, P3 = 0.60

Table 3.17 (cont.)
Examples of Projects Conducted using Technora Elements

Structure and Location

Date

Description

Deck of the Kikumoto K-4 Berth

Sumitomo Chemical Co., Ltd.

Ehime Prefecture

October

1991

Technora rods of 6 mm diameter (in groups of 4) were used in conjunction with Arapree elements to pretension the main girder. Overall length of Technora elements used was 8000 m.

P1 = 0.80, P2 = 0.70, P3 = 0.60

Girders for Linear Motor Tracks

Japan Railway, Sohken, Tokyo

November

1992

7.4 mm diameter, deformed Technora rods in groups of 2 were used to pretension 12.5 m long girders. Overall length of Technora elements used was 400 m.

P1 = 0.80, P2 = 0.70, P3 = 0.60

Concrete Water Channel Flood Prevention Scheme

Central Saga District

Kyushu Board of Agriculture

Saga Prefecture

May

1993

6 mm diameter, deformed Technora rods in groups of 3 were used to post-tension precast channel sections. Overall length of Technora elements used was 400 m.

P1 = 0.80, P2 = 0.60, P3 = 0.50

Box Culvert

Nakagoh Drainage Works

Kyushu Construction Bureau

Saga Prefecture

November

1993

25 m length of a box-culvert was post-tensioned using 6 mm diameter, deformed Technora rods in groups of 4. Overall length of Technora elements used was 1200 m.

P1 = 0.80, P2 = 0.70, P3 = 0.60

Curtain Wall

Koami-cho Communal Building, Chugoku Electric Power Co.

Hiroshima Prefecture

March

1995

16,370 m of 3 mm diameter rods and 5030 m of 7.4 mm diameter rods were used as horizontal reinforcement in reinforced concrete curtain walls as replacements for steel rebar.

Sone Viaduct

Japan Highways Public Corp., Osaka Office

Hyogo Prefecture

May

1995

7.4 mm diameter, deformed Technora rods in groups of 9 were used to transversely pretension (and thereby connect) external anchor block to 28 girders. Overall length of Technora elements used was 3020 m (including length cut away after post-tensioning - see site report, Appendix B).

Seisho Bypass Bridge

Japan Highways Public Corp.

Kanagawa Prefecture

January

1996

Couplers installed to prevent bridge collapse. 7.4 mm diameter rods were used in groups of 9, with a total length of 110 m.

Kaiten Base

Tokushima City Government

Yamaguchi Prefecture

March

1996

13 m diameter Technora deformed bars were used as reinforcement during the repair to slabs of the historic marine base.

Water Channel Saga Chuba Farmland Safety Project

Kyushu MAFF Regional Office, Saga Prefecture

March

1996

6 mm diameter Technora deformed bars were used in groups of 3 to connect precast concrete sections of the water channel lining

Yamanashi Linear Test Track

Railways Research Center

Yamanashi Prefecture

May

1996

7.4 mm diameter Technora deformed bars were used as pretensioning reinforcement along with CFCC tendons for the main girder.

2233 m of Technora elements were used.

Kaken Pharmaceutical Hon-Komagome Building

Kaken Pharmaceutical Co.

Tokyo

May

1996

3 mm diameter Technora deformed bars were used as transverse reinforcement in curtain walls to make them electro-magnetically transparent


Key:
P1 = tensile stress level at jacking as a percentage of the ultimate strength
P2 = tensile stress level at transfer as a percentage of the ultimate strength
P3 = tensile stress under design load as a percentage of the ultimate strength

Examples of Applications

As described earlier in this section, aramid fiber based linear reinforcing elements have been used in a large variety of applications in structures ranging from bridge decks and girders to precast irrigation channel sections. Descriptions of their use in the Kamiooka Station Parking structure entrance slab, the Rainbow Bridge, the Sone Viaduct, and the Sumitomo Bridges at the Oyama Works are in the site reports (Appendix B). Two additional examples are discussed below.

Use in a Prestressed Concrete Berth

Due to their non-corrosive nature, aramid fiber reinforced Arapree and Technora rods were used to reinforce the prestressed girders making up the concrete berth at the Ehime Works of the Sumitomo Chemical Corp. Girder geometry and placement of the prestressing tendons are shown in Fig. 3.52. The berth consists of 17 hollow girders, each of which is 8.72 m in length. Ten used Technora elements and 7 used Arapree bars (Table 3.18). The girders were designed as simply supported beams with a TL-20 live load rating.


Fig. 3.51. Overall view of the prestressed concrete berth.

Table 3.18
Reinforcement Bar Details

Characteristic

Technora Elements

Arapree Elements

Shape

Spiral Wound

Flat

Dimensions

6 mm diameter

20 mm x 5 mm

Cross-Sectional Area

28.3 mm2

88 mm2

Material Density

1.30

1.25

Matrix Material

Vinylester

Epoxy

Tendon Grouping

4 rods

2 bars

Tensile Strength of Tendon

20.4 tons

20.1 tons

Tensile Modulus

5400 kgf/mm2

6000 kgf/mm2

Stress Level at Jacking (% of Ultimate)

0.80

0.80

Stress Level at Transfer (% of Ultimate)

0.70

0.70

Stress Level Under Design Load (% of Ultimate)

0.60

0.60


Fig. 3.52. Details of girder geometry.

Use in Irrigation Channels

Irrigation channels consisting of precast concrete sections are commonly used in Japan. The channels are often built on soft ground, which is likely to settle unevenly and cause cracks, especially at joints. Sections are precast using aramid tendons, both as reinforcement and for connecting adjacent sections, avoiding the need to undertake costly ground improvements or support the channels using piles.

The use of these aramid based elements enables the sections to undergo some relative movement at joints without significant distress to the concrete. (Aramid tendons have about 25% of the stiffness of steel cables.) In the Nakagoh drainage works, precast culverts in the form of hollow boxes 25 m long were used. Both steel cables (32 mm diameter at corners) and groups of four 6 mm diameter Technora rods were used, as shown in Fig. 3.53. The Technora rods were laid continuously with prestress levels of 80%, 70% and 60% of ultimate strength, at jacking, transfer and under design load, respectively. L shaped precast segments (Fig. 3.54) were used in conjunction with a cast-in-place concrete bed to form an irrigation channel in the central Saga district on soft ground. The use of aramid Technora tendons on a 30 m test section was undertaken to demonstrate their use in connecting the precast L wall sections.


Fig. 3.53. Schematic of the culvert at the Nakagoh Drainage Works.


(a) cross-section


(b) view of the L sections
Fig. 3.54. Use of Technora for connection of precast linings.

The Technora elements were used in groups of three 6 mm diameter rods, two per L section, with stainless steel anchorages. The cable assemblies were designed to withstand differential forces due to the movement of the adjacent sections. The Kubota trunk line project used U-shaped precast units of 1.5 m in height by 1.8 m in width by 2.0 m in length. Units connected through the use of 6 mm diameter Technora rods. A schematic of the section is shown in Fig. 3.55a, and an individual unit is shown being placed in Fig. 3.55b.


(a) schematic of precast units


(b) placement of a precast unit
Fig. 3.55. Precast units on the Kubota trunk line for irrigation.


Published: November 1998; WTEC Hyper-Librarian