(1)Byincreasingthe Dead Weight Per Foot of the Line And

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EFFECTSOFICEANDWINDLOADING

The span design consistsin determiningthe sag atwhich the line is constructed so that heavywinds, accumulations of ice orsnow, andexcessive temperaturechanges willnotstress the conductor beyondits elastic limit, cause aserious permanent stretch, or result in fatigue failuresfrom continuedvibrations, in other words,the lines willbe erected under warmer and nearlystill-air conditionsandyet must complywith the worstconditions.

EffectofIce

In mountainousgeographic areas, the thickness ofice formed on the conductor becomes verysignificant. Dependingon the circumstances, itmight be asmuch as several times the diameter of the conductor.Ice accumulations on the conductor affect the design of the line

(1)byincreasingthe dead weight per foot of the line and

(2)byincreasingthe projected surface of the linesubject to wind pressure. Mostlyused fordistribution lines.

Probableconfigurationoficecoveredconductorcross-sectionalarea.

Even though the more likely configurationofa conductor witha coatingof ice is as shown in Figure6,forthe sakeof simplicity, itcan be assumed thatthe ice coating, of thicknesst, inches, is uniform overthesurface of a conductor,as shown in Figure

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Then the cross-sectionalarea of the ice is

Assumedconfigurationofice-coveredconductorcross-sectionalarea.

If itieice loadisassumedto be uniformthroughout the lengthoftheconductor, thevolume

oficeper foot is

Theweightof theiceis57lb/It3,sothat theweightof iceper foot is

or approximately

Therefore,the total vertical loadon the conductorper unit lengthis

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wherewT= total vertical load on conductor per unitlength w= weight ofconductorper unit length

w1= weight of iceper unitlength

Effectof Wind

It is customarytoassumethat the wind blows uniformlyand horizontallyacross the projected area of the conductor covered with noiceand ice,respectively.

The projected areaper unitlength of the conductorwith no iceis

whereSni= projected areaof conductorcovered with no ice insquarefeet per Unit length

Ani= cross-sectional areaof conductorcovered with noicc in square feet l=length of conductor inunit length

fora 1-ft length of conductor withno ice,

whereaswith ice,it is

whereSwi= projected area of conductor covered withicc in squarefeet perunit length

Figure8.Forceofwindonconductorcoveredwithnoice.

Awi=cross-sectional area of conductor covered with icein square feet 1 = length of conductor inunitlength

fora 1-ft length of conductor,

Therefore, the horizontal forceexerted on the lineas a resultof thewind pressure withno ice (Figure 8)is

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fora 1-ft length of conductor,

whereP=horizontal wind force (i.e., load)exertedon linein pounds per feet p =wind pressure in poundsper square feet

whereas with ice(Figure9), it is

Figure9.Forceofwindonconductorcoveredwithice.

FIGURE10

FOR A 1-FTLENGTH OFCONDUCTOR,

THEREFORE,THE EFFECTIVELOAD ACTING ONTHECONDUCTORIS

ACTING ATAN ANGLEΘTO THE VERTICAL,AS SHOWNIN FIGURE 10.

BYREPLACING WBYWEINTHE PREVIOUSLY DERIVED EQUATIONSFORTENSIONAND SAG OF THELINEIN STILL AIR,THESEEQUATIONS CAN HE APPLIEDTO AWIND-AND ICE-LOADEDLINE.FOR EXAMPLE,THE SAG EQUATION BECOMES

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