Site: Technical Research Institute
Sumitomo Construction Company
Oyama Works Site
Tochigi Prefecture, Japan
Date Visited: October 1996
Hosts: Shin-Ichiro Kumagai, Deputy General Manager,
Sumitomo Construction Company, Ltd.
Atsushi Sumida, Manager, DuPont Toray Kevlar, Ltd.
M. Kamiyoshi, Project Manager, Teijin, Ltd.
Summary: Seismic retrofit tests of columns using aramid fabric.

ACTIVITIES OF INTEREST

In an effort to increase the use of aramid fibers in the civil construction area, tests were conducted on rectangular columns at 50% scale of actual "Shinkansen" columns using aramid fabric and tape. Aramid fibers were considered more suitable than carbon fibers for use with rectangular columns because of their toughness, which would allow tighter wrapping at corners without damage to the fibers themselves. Similar tests were also conducted on columns reinforced with carbon and steel jackets and with combined carbon-steel jackets. In this application a steel layer on inside is separated from the carbon outside by a thin layer of resin.


Fig. B.35. View of test columns.


Fig. B.36. Close-up of steel jacketed test column.


Fig. B.37. Hybrid steel-carbon jacketing.


Fig. B.38. Close-up of hybrid steel-carbon jacket showing the thick resin layer between concrete and steel.

The use of aramid cloth or tape (unidirectional or braided, 75 mm to 300 mm wide) is reported to be advantageous for four reasons:

  1. Aramid fibers have a higher elongation capacity than carbon
  2. They are non-conductive and can be used wherever electrical supply is in the vicinity
  3. Aramid fibers are tough and hence retrofit of rectangular/square columns needs no rounding of corners
  4. The aramid fibers impregnate better and faster than other fibers

Properties of aramid fibers and sheets used are shown in Tables B.2 and B.3.

Table B.2
Basic Characteristics of Aramid Fibers Used in Column Retrofit

Characteristics

Class of Aramid Fibers

 
 

Aramid-1

Aramid-2

Brand Name

 

 

Density (g/cm3)

Tensile Strength (kN/cm2)

Tensile Modulus (MN/cm2)

Strain to Failure (%)

Kevlar - DuPont Toray

Kevlar, Ltd.

Twaron-Nippon Aramid Co.

1.45

284

10.9

2.6

Technora -Teijin, Ltd.

 

 

1.39

343

7.3

4.6

Table B.3
Characteristics of Aramid Sheets

Characteristics

Classification of Force

 

40 tf/m-width

60 tf/m-width

Guaranteed Force * (kN/m)

392

588

Tensile Force (MN/m)

Unit Weight (g/m2)

Aramid Class

23

280

Aramid-1

14

235

Aramid-2

34

415

Aramid-1

20

350

Aramid-2


* Guaranteed Force = Average Force - 3 x Standard Deviation As detailed in Table B.2

The FITS system, which is an aramid tape based system (Fig. B.39), is used by Mitsui Construction Co., Ltd. commercially and has been used on 10 projects to date. The basic procedure is shown in Figure B.40. A small consortium has been formed with goals similar to that of the CFRRA, but with a focus on the use of aramid fibers in rehabilitation and retrofit. The "Association of Aramid Reinforcement for Concrete Structures" is headed by Kajima Construction Co., Ltd., and consists of members from DuPont Toray Kevlar, Ltd., Nippon Aramid Co., and Teijin, Ltd. as suppliers, and Kajima Construction Co., Ltd., Mitsui Construction Co., Obayashi Construction Co., Sumitomo Construction Co., Tokyu Construction Co., and Sho-Bond Construction Co. as members from the civil construction industry.


Fig. B.39. Example of the FITS tape.


Fig. B.40. Procedure for use of the FITS system.


Fig. B.41. Use of the FITS systems on columns. Examples of the use of the FITS system on columns and chimneys are shown in Figures B.41 and B.42, respectively.


Fig. B.42. Use of the FITS systems on chimneys.

The consortium is aggressively pursuing opportunities to prove the viability of aramid as an alternative cost-effective material; Mr. Atsushi Sumida provided the example shown in Figure B.43 to demonstrate the potential for economic savings from the use of aramid sheets rather than carbon for the retrofit of columns.

Purpose

Zone

Number of Layers

Required

  

Aramid

Carbon

Shear

Bending

2

1 and 3

3

6 each

2

10 each

Total (m2)

 

156

242


Fig. B.43. Example of competitiveness (provided by A. Sumida).


Published: October 1998; WTEC Hyper-Librarian