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Special Forces Appendix C
Snow and Ice Loading Appendix EE
Robert Lake
Senior Development Engineer
Transpower NZ Ltd.
Special Forces
Forces due to Short-Circuit
Currents;
Creeping Snow (on
foundations/lower part of
structure);
Earthquakes; and,
Mining Subsidence.
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
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Forces due to Short-Circuit Currents Different for simplex or bundled phases;
IEC60865-1 provides simplified method;
Based on initial/everyday tension in system;
Terminal or landing spans, short strain spans
critical, but may affect several spans from
substation;
Produces increased conductor tensionswhich may be greater than wind or other
loading induced tensions.
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
Forces due to Short-Circuit Currents
Only 2-phase short-circuit current considered;
Pinch tensile force from sub-conductor
attraction;
Swing tensile force due to phase to phase
attraction;
Vertical drop tensile force due to phase to
phase attraction;
IEC60865-1 provides some example
calculations.
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
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Forces due to Short-Circuit Currents
Wn Coincident wind pressure of 25%
ultimate;
Ft tensions for non short-circuit spans;
Fsc* maximum tension from 3 cases in
IEC60865-1;
1.25 factor for exceptional load; Loading considered to be too quick to affect
foundation significantly.
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
Creeping Snow
Loading will probably be
different in all situations;
May involve taller pedestal
outstands on foundations
designed to accommodate
lateral loading.
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
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Earthquakes Very topical;
Generally not a major issue with loading for
transmission lines;
Location relative to fault line is important;
Distribution poles with mounted transformers
can involve significant impact;
AS1170.4-2007 Australian actions; and, NZS1170.5-2004 New Zealand actions.
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
Earthquakes Need to allow for potential settlement,
rotation and/or translation movements;
Seismic mass to include all permanent
attachments; Fundamental period;
Ductility factor by material/structure type;
Cables/conductor behaviour linear springs.
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
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Earthquakes Types of analysis:
Equivalent static force method symmetrical and
consistent stiffness and mass, relative low
structure height;
Modal response spectrum analysis significant
mass or stiffness variations; and,
Time history analysis method large guyed
structures.
Combination of effects multiple directions;
Second order effects P- effects.
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
Earthquakes
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
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Earthquakes
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
Earthquakes
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
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Earthquakes
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
Earthquakes
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
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Earthquakes
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
Earthquakes
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
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Mining Subsidence Areas subject to underground mining, close to
large excavations of weaker material, or de-
watering activities e.g. geothermal activity
Likely to be more significant for towers than for
poles;
Tie-beams can be used between all four legs
to minimise differential settlement;
Loading will depend on potential for differential
settlement, extent of settlement etc.
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
Snow and Ice Loading
With or without coincidentwind;
Variation with altitude/location;
Australian requirements: Ice above 800m;
Ice above 500m in Tasmania.
New Zealand requirements: Snow and Ice varies widely.
Guidelines only. Use local
knowledge e.g. BoM ifavailable.
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
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Snow and Ice Loading Australia generally:
12mm, 900kg/m3, 100Pa wind, -5 C;
Assumed 50yr return period;
Unbalanced loading should be
considered.
Tasmania:
All areas;
Structure ice area;
Defined wind Pa; Apply 100m lower
in some areas.
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
Snow and Ice Loading
New Zealand:
Based on 50yr return period loading;
Uses a reliability multiplier instead of varying return
period as used for wind;
Allows to apply higher
factor for special assets;
Snow and ice loads from
Table EE3 multiplied by Mrel;
Conductor temperature under snow 0C;
Conductor temperature under ice varies with altitude.
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
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Snow and Ice Loading New Zealand:
As per IEC60826,
unbalanced tensions based
on 70% of full loading on one
side and 30% on other side;
Large deviations/
terminations suggest full ice
on one side only;
Care with post or pininsulators which limit flexibility
of system.
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
Snow and Ice Loading
New Zealand:
Wind load from
AS/NZS1170.2 for
relevant return
period;
Only SW, S, or SE
wind directions;
Snow 400kg/m3;
Ice 700kg/m3;
Differential snow/ice
for torsion and longl.
Australian Panel B2 Overhead Line
Design Seminar AS/NZS 7000:2010
Overhead Line Design Sydney 28 & 29
March 2011
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Special Forces Appendix C
Snow and Ice Loading Appendix EE
Questions ?