Duane Phillips, MPM Director of Project Management

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Duane Phillips, MPM Director of Project Management

Transcript of Duane Phillips, MPM Director of Project Management

Page 1: Duane Phillips, MPM Director of Project Management

Duane Phillips, MPMDirector of Project Management

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Understand what structure deflection is and the impacts to design & construction

Understand the mechanisms behind what drives structure deflection and its design implications

Discuss the construction impacts of structure deflection and construction considerations

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Deflection is the degree to which a structural element is displaced under a load.

Measure of the amount of movement from unloaded (resting) position

Components: pole top, arms

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Some deflection is inevitable in any structure materials

Manufacturing cost savings with a reduction in steel (significant)

Shifts further away from brittle fracture point (stress & strain resulting in failure)

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Reliability› Recurrence Interval/Return Period› Operational Contingencies

Safety› Construction› Operation› Maintenance

Existing Codes› 2012 NESC

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Maximum un-factored loads

Should not cause damage to structure

Based upon the facility configuration & resulting loads

Maximum factored loads

Should not cause failure of structure

Based upon the ultimate strength of installed components

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Among Sub-Systems› Tangent Structures› Angle Structures› Dead End Structures› Conductor

Within Sub-Systems› Structure› Foundation› Hardware

Weakest

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Strongest

Weakest

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Strongest

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Types of Structures Monopole H-frame/Multi-pole Lattice

Deflection Points Structure Shaft (pole top - vertical) Arms (arm tip – vertical & transverse)

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Various loads act on structure simultaneously

Very unlikely that every load will reach ultimate load at once

For ultimate loads, design specifications provide factors for load magnification

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Conductor Point Loads› Wire Tension & Wind› Vertical Load Weight Span NESC Ice Load Local Utility – Extreme Ice

Pole Self-Weight Wind Acting on the Pole Hardware Construction

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Weight Span Concept

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Continental Winds› NESC Rule 250 C [Based on ASCE 7-05]

Not applicable if structure or attachments does not exceed 60 feet above ground

Load (lbs) = .00256*(Vmi/h)2*kz*GRF*I*Cf*A(ft2)

V → Basic Wind Speed kz → Velocity Pressure CoefficientGRF → Gust Response Factor I → Importance FactorCf → Shape Factor A → Projected Area

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Sag and tension are inversely proportional.As one increases, the other decreases.

Tension = span2 x weight/foot of wireSag x 8

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Transverse & Longitudinal Load due to Conductor Tension› Changes in Line Direction› Span Length Variation› Unbalanced Ice› Broken Wires› Dynamic Loads

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Based on total loads applied to structure & components

Comparison to design specification limits (allowable deflection)

Considers total load vs. vibration impacts› Some deflection is fine – too much is not

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Determine forces & associated stresses

Apply each load combination

Define critical demands

Max Load Demand ↔ Design Load Limits

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Used to optimize design (situational)

Operational or ultimate limits may govern specific feature

Should include both strength and fatigue design loading

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Clearances → additional sag › Other facilities & electrical ‘window’

Adjacent span sag/tension

Moment impacts to foundation

Constructability› Wire sag/tension specifications› Aesthetics

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Safety → understanding deflection & potential energy

Wire installation → properly sag/tension› Alternate means of sag verification› Shift installation sequence› Temporary guying deadends

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‘Up front’ discussion on means & methods of wire installation

Clear specification requirements

Review/approve wire installation methods

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Manufacturing cost reductions (quantity of steel)

Shift in field aesthetic perspective

Changes in means & methods of wire installation

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Duane Phillips, MPMDirector of Project Management