Introduction of Fiber Reinforced Polymer

(FRP) Materials

John BuselAmerican Composites Manufacturers Association

January 9, 2007Orlando

Towers, Poles & Conductors Meeting

• What is FRP ?

• FRP benefits

• Current Status of FRP Utility Structures

• Installations

• FRP performance

• Changes to 2007 NESC code

Outline

Compared to other

engineering materials

composites have

different properties

What is FRP ?

Metals - Homogeneous &Isotropic

Composites -Inhomogeneous & Anisotropic

What is FRP ?The Difference Between Composites and Other Materials

Definition:

Composites are a combination of a reinforcement fiber in a polymer resin matrix, where the reinforcement has an aspect ratio that enables the transfer of loads between fibers, and the fibers are chemically bonded to the resin matrix.

Creates a material with attributes superior to either component alone!

What is FRP ? Fiber Reinforced Polymer (FRP) Composites

Products made for utility structures are manufactured several ways

• Pultrusion

• Filament Winding

What is FRP ?

Pultrusion Process

Resin

Heated DieCuredProfile

Bridge decks, rebar, structural profiles, concrete & masonry structural strengthening, sheet piling, dowel bars, utility poles, grating

What is FRP ?

Filament Winding

Resin

Utility poles, columns, bridge girders, pipe, missiles, aircraft fuselage

What is FRP ?

• Lightweight – easy to handle and transport

• High Strength to weight ratio

• Corrosion resistant – will not rot or corrode

• Non-conductive (essentially a large hot stick)

• Non-magnetic

• Impervious to pests and woodpecker attack

• Design – Tailor material properties, some systems are modular

• Compatible – use standard hardware

• Environmentally safe – no leaching of toxic chemicals into soil

FRP Benefits

• FRP utility structures include poles, crossarms, stand-offs and now conductor reinforcement

• Composite, or “fiberglass” poles, were installed in West Oahu in 1962 and were only recently taken out of service

• Composite lighting poles have an extensive history of use dating back more than 40 years

• The use of FRP utility structures throughout the U.S. is widespread and still growing

• The use of FRP utility structures in Canada is growing• Some larger installations...

• 8,000+ FRP poles at large California utilities starting 1995• 1,500+ FRP poles at Rural Coops since 2000• 300+ FRP poles at Northwest Territories since 2003• 100,000+ FRP crossarms across virtually every state

Current Status of FRP Utility Structures

Installations

Residential Backyard Installations

Remote Installations

Deadend Crossarms

Joint Use with Transformers

Claim by Manufacturers…”Since FRP structures are engineered like steel and prestressed concrete, and manufactured, they result in good initial strength consistency” Question: Is this true?

FRP Performance

Answer: Yes EDM has performed numerous proprietary bending strength tests on FRP utility poles and crossarms for several manufacturers. 

Conclusion:  the poles and crossarms yielded very consistent (low COV) as manufactured strength properties

FRP Performance

3,100

3,5003,300

3,0003,150

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

Pole 1 Pole 2 Pole 3 Pole 4 Pole 5

Lo

ad a

t F

ailu

re (

lb)

3,100

3,5003,300

3,0003,150

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

Pole 1 Pole 2 Pole 3 Pole 4 Pole 5

Lo

ad a

t F

ailu

re (

lb)

COV = 6.1 %

Actual 40' Filament Wound Pole Bending Strengths (Tested by EDM)

FRP Performance

Actual 40' Pultruded Pole Bending Strengths(Tested by Manufacturer)

COV = 3.4%

Load-Deflection very nearly linear

FRP Performance

The first FRP poles for overhead line application were designed using a net overload factor (“Application Safety Factor”) of 4.0, the same as required for (Grade B) wood construction

Question: What factors are now being employed for FRP Utility Poles and Crossarms?

FRP Performance

The use of overload factors as applied to FRP utility poles is all over the map

• Some utilities using a factor of 2.5

• Some using 3.0

• Some using 3.85

• Some still using 4.0

FRP Performance

The use of overload factors as applied to FRP crossarms is more consistent

• Most utilities use a factor of 2.5

FRP Performance

Cantilever Loading

• Load-deflection curve very nearly linear

• Typical break is due to local stress rupture on the compression face and is most often associated with local buckling

• Kinematics of pole deflection cause loss of cross-section inertia as the pole begins to oval which means EI decreases

• Failure in area where applied stress first exceeds allowable stress

• Typical allowable stresses in the range of 25,000 psi to 45,000 psi

FRP Performance Failure Mechanisms of FRP Poles

Tangent and Deadend Loading• Load-deflection curve very nearly linear

• Typical break is due to local stress rupture on the compression face and typically propagates from the attachment to the pole

• Crossarm breaks can also be snap breaks, or crushing breaks if crossarm mounted directly to pole without a bracket

• Failure in area where applied stress first exceeds allowable stress

• Typical allowable stresses in the range of 25,000 psi to 45,000 psi.

• FRP crossarms are typically pultruded and perform like pultruded poles

FRP Performance Failure Mechanisms of FRP Crossarms

• Subcommittee 5: Strength & Loading• Sections 24, 25, 26, 27

• Taskforce 5.1.7: FRP Structures• Change Proposal accepted in 2005

• Reduced Application Safety Factor

• Material Strength Factors same as STEEL provided that FRP pole and crossarm strengths are published as 5% LEL values (5th percentile strength)

Changes to 2007 NESC

• Added NOTE References

• ASCE-104, Recommended Practice For Fiber-Reinforced Polymer Products For Overhead Utility Line Structures

• ASCE-111, Reliability-Based Design of Utility Pole Structures ….. (provides 5% LEL)

• ASCE/SEI Task Committee – develop FRP Manual of Practice

Changes to 2007 NESC

Table 253-1 -- Load factors for structures,1 crossarms, support hardware, guys, foundations, and anchors to be used with the strength factors of Table 261-1A

Load Factors

Grade C

Grade B At crossings 6 Elsewhere

Rule 250B Loads Vertical Loads 3

1.50

1.90 5

1.90 5

Transverse Loads Wind Wire Tension

2.50

1.65 2

2.20

1.30 4

1.75

1.30 4

Longitudinal Loads In general At dead-ends

1.10

1.65 2

No requirement

1.30 4

No requirement

1.30 4

Rule 250C Loads 1.00 0.87 7 0.87 7

Rule 250D Loads 1.00 1.00 1.00

........................................... 5 For metal prestressed concrete, or fiber-reinforced polymer portions of structures and crossarms, guys, foundations and anchors, use a value of 1.50.

Changes to 2007 NESC

Table 261-1AStrength Factors for Structures

  Grade B Grade C

Strength factors for use with loads of Rule 250B    

Metal and Prestressed-Concrete Structures 6 1.0 1.0

Wood and Reinforced-Concrete Structures 2,4 0.65 0.85

Fiber-Reinforced Polymer Structures 6 1.0 1.0Support Hardware 1.0 1.0

Guy Wire 5,6 0.9 0.9

Guy Anchor and Foundation 6 1.0 1.0

Strength factors for use with loads of Rule 250C    

Metal and Prestressed-Concrete Structures 6 1.0 1.0

Wood and Reinforced-Concrete Structures 3,4 0.75 0.75

Fiber-Reinforced Polymer Structures 6 1.0 1.0Support Hardware 1.0 1.0

Guy Wire 5,6 0.9 0.9

Guy Anchor and Foundation 6 1.0 1.0

Changes to 2007 NESC