joint use pole overloading - psc.state.fl.us...july 18, 2005 florida public service commission staff...

new stratagem consulting

Joint Use Pole Overloading Joint Use Pole Overloading

Tallahassee, FLJuly 18, 2005

Florida Public Service CommissionStaff Workshop on Electric Utility Infrastructure

Factors Contributing to Pole Failures Factors Contributing to Pole Failures

Structural Pole Failures

Aging/

Maintenance

Factors

Extreme

Weather

Factors

Accidental

Factors

Overloading

Factors

Extent of Overloading Extent of Overloading

• Research suggests up to 5% of the poles on average may be overloaded

• Another 10% may be marginal, approaching overloaded conditions

• Overloading is most likely to occur:o In urban areaso Along main communications corridors (back-bone)o In areas where multiple, facilities-based communications

service providers are operating – cable, telecom, fiber, etc.• Heavy loading and overloading are significant contributing factors

in pole failures due to weather, rotting, aging and accidents • Continuing demand for expanded communications services is

likely to contribute additional loadings on poles

Evolution of the Problem Evolution of the Problem

• Pole overloading has developed slowly over decades• Poles originally installed had sufficient excess capacity to avoid

overloading for anticipated uses at the time• Proliferation of communications applications increased demand

for access to poles• Some attaching entities failed to fully record facilities installed,

often during rapid network build-out periods, resulting in incomplete inventories

• FCC sanctioned over-lashing without prior engineering review and approval is an additional source of loading uncertainty

• FCC policies designed to expedite network build-out by limiting the time to process applications may unintentionally exacerbatedoverloading

Defining Defining ““Pole OverloadingPole Overloading””

• “Overloading” occurs when poles are stressed to levels that exceed standards set by the company in accordance with National Electric Safety Code, IEEE, state agencies, and/or other regulatory or professional organizations

• Departure from the standards may adversely affect the safety of workers and the general public, as well as service reliability

• Contributing factors are loads induced by electric, cable, telephone, and fiber conductors – as well as streetlights, signs, traffic signals, and other uses

• Bending-inducing stresses are the predominant factors contributing to pole failure, far exceeding vertical stresses inmost cases

Specialized Loading Model for Specialized Loading Model for Evaluating Programs and PoliciesEvaluating Programs and Policies

• Comprehensive models for pole line design and loading analyses are commercially available

• To support policy analysis, a screening model was designed that:

o Considers only the dominant forces – conductors and guys

o Identifies the nature and extent of the safety and program issues

o Provides a tool to develop mitigation tactics and a remediation strategy

o Documents pole characteristics under normal “measured” conditions in the field and inventory data

o Projects loadings under “design” conditions by attaching entity and cumulatively

Case Study ACase Study A

Case Study A: Measured Load ConditionCase Study A: Measured Load Condition

Stress In Pole

-500

0

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1 29 57 85 113

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Elevation (inches)

Stre

ss (p

si) Guy LocationForce LocationBending Stress In PoleMaximumDesign Stress

Stress In Pole

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Force LocationBending Stress In PoleMaximumDesign Stress

NewPole

WithAgingEffects

Case Study A: Design Load ConditionsCase Study A: Design Load Conditions

Stress In Pole

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ss (p

si) Guy LocationForce LocationBending Stress In PoleMaximumDesign Stress

Stress In Pole

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Stre

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NewPole

WithAgingEffects

Case A: Separate Stresses Case A: Separate Stresses -- Design Load Design Load

Stress In Pole

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Elevation (inches)

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ElectricOnly

Stress In Pole

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Elevation (inches)

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CableOnly

Stress In Pole

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TelcoOnly

Case Study A: FindingsCase Study A: Findings

• Aging would significantly increase the likelihood of pole failure given the heavy loading of this pole

• Cumulative stresses exceed maximum threshold under design loads making structural failure likely in “design” storm conditions

• Loading of electric, telecom, cable and fiber counter balance each other to some extent

• Taut cable conductor is significant contributing factor.

Mitigation Options• Reconfigure guying to reduce stress• Increase cable conductor sag• Replace pole with larger pole when opportunity is afforded.

Case B: Broken PoleCase B: Broken Polefrom Auto Accidentfrom Auto Accident

Case Study B: Combined Measured Load Case Study B: Combined Measured Load

Stress In Pole

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Elevation (inches)

Stre

ss (p

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Force LocationBending Stress In PoleUltimate Stress

Case B: Separate Measured Loads Case B: Separate Measured Loads

Stress In Pole

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1 29 57 85 113

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Stre

ss (p

si) Guy Location


Stress In Pole

-1000

0

1000

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1 29 57 85 113

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Stre

ss (p

si) Guy Location


Stress In Pole

-1000

0

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1 29 57 85 113

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Elevation (inches)

Stre

ss (p

si) Guy Location


Electric

Cable

Telecom

Case B: Combined Design LoadCase B: Combined Design Load

Stress In Pole

-2000

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2000

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1 29 57 85 113

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Stre

ss (p

si) Guy Location


Case Study B: FindingsCase Study B: Findings• Measured loads bordered maximum design load under

normal conditions and were imbalanced• Age of pole was likely a contributing factor – estimated 35 to

45 yrs• Cumulative stresses exceed maximum threshold under design

loads and would be vulnerable in a severe storm• Heavily loaded condition was the “the straw that broke the

camel’s back” contributing to the structural failure after the collision

Mitigation Options• Improved load-balancing of conductors• Review poles with similar characteristics in nearby area for

aging and potential overloading

• Loading problems are often precipitated by larger conductors that are more susceptible to extreme wind loadings

• The tautness of conductors installed by non-utility users are a major source of structural stress on poles.

• Pole failures in storm conditions are heavily influenced by loading characteristics and aging as well as pole maintenance

• When aging is considered, maximum allowed stresses must be reduced to maintain the same safety margin

• Poles with overloading and safety problems o Often occur in clusters along popular “corridors”, but may

also occur in isolationo Usually have more complex facilities than average.

Overview Findings Overview Findings

Examples of Financial Impacts of Examples of Financial Impacts of NonNon--Utility Loadings on PolesUtility Loadings on Poles

• Capital investment - pole inventory sizes increased by one class to accommodate joint use

o Estimated rise in pole costs of 15% o Labor and installation costs another 15%

• Capital investment and revenues – pole height increased to provide additional space for communications

o Increased capital costs for poles placedo Decreased revenues under FCC formulas when “usable

space” on pole is increased (cable -6.9%/ft; telecom -2.6%/ft)

• Operating costs – Second “truck roll” to remove poles stubs after non-utility transfers to replacement poles

o Second roll can cost $500 to $1,000 per pole

Impacts on Utility OperationsImpacts on Utility Operations

• Heavily loaded poles impact operations by:o Requiring additional time to perform routine maintenance

due to increased pole complexity, taller poles, etc.o Increasing cost of repairs – more extensive, time consumingo Creating additional reliability and safety risks that demand

attention o Increased administration and monitoring to deal with

overload situationso “Hidden costs” on entire distribution organization can add to

overall carrying charges• Loss of “good will” due to:

o Increased number of outages of longer durations o Unnecessarily unsightly poles, conductor configurations,

guying, etc.

Options for Utilities Addressing Options for Utilities Addressing Overloading Issues Overloading Issues

• Assess nature and extent of overloading due to non-utility uses.

• Conduct “root cause” analyses on sample of pole failures across service territory

• Design remediation programs that offer benefits/cost ratios thatresponsibly balance consumer rates against reliability and safety considerations.

• Develop pole loading monitoring criteria for use in routine maintenance and repair activities, and more thorough “spot checking” programs

• Request funding for necessary capital and operating costs of overloading remediation programs in routine rate adjustments.

• Establish information base on the direct and indirect costs of non-utility use of infrastructure

Options for State Regulators Options for State Regulators Addressing Overloading Issues Addressing Overloading Issues

• Evaluate the nature and extend of overloading across the stateo Compile readily available data from all parties using utility

infrastructure o Based on findings regarding severity and location of problem,

determine what programs are needed

• Create incentives/penalties for all non-utility pole users that ensure compliance with engineering and safety standards

• Require notification and approval before access to poles by non-utility user to assure safety..

• Allow cost recovery for programs that identify and remediate overloading associated with non-utility uses.

For more information contact:

Mary Wolter GlassDr. Martin Skeer, Ph.D.

new stratagem consulting1655 North Fort Myer Drive, Suite 350

Arlington, VA 22209Office: 703-738-9260

[email protected]@newstratagem.com

Joint Use Pole OverloadingFactors Contributing to Pole FailuresExtent of OverloadingEvolution of the ProblemDefining “Pole Overloading”Specialized Loading Model for Evaluating Programs and PoliciesCase Study ACase Study A: Measured Load ConditionCase Study A: Design Load ConditionsCase A: Separate Stresses - Design LoadCase Study A: FindingsCase B: Broken Polefrom Auto AccidentCase Study B: Combined Measured LoadCase B: Separate Measured LoadsCase B: Combined Design LoadCase Study B: FindingsExamples of Financial Impacts of Non-Utility Loadings on PolesImpacts on Utility OperationsOptions for Utilities Addressing Overloading IssuesOptions for State Regulators Addressing Overloading Issues