overloading, assure ground clearance is sufficient at all points along the right-of-way, and minimize
blowout or uplift under cold weather conditions. To do this, catenary constants are typically found for: (1)
the maximum line temperature; (2) heavy ice and wind loading; (3) wind blowout; and (4) minimum
conductor temperature. Under any of these loading conditions, the catenary constant allows sag
calculation at any point within the span.
14.5.2 Wind Span
The maximum wind span of any structure is equal to the distance measured from center to center of the
two adjacent spans supported by a structure. The wind span is used to determine the maximum
horizontal force a structure must be designed to withstand under high wind conditions. Wind span is
not dependent on conductor sag or tension, only on horizontal span length.
14.5.3 Weight Span
The weight span of a structure is a measure of the maximum vertical force a structure must be designed
to withstand. The weight span is equal to the horizontal distance between the low points and the vertex
of two adjacent spans. The maximum weight span for a structure is dependent on the loading condition
being a minimum for heavy ice and wind load. When the elevations of adjacent structures are the same,
the wind and weight spans are equal.
14.5.4 Uplift at Suspension Structures
Uplift occurs when the weight span of a structure is negative. On steeply inclined spans, the low point of sag
may fall beyond the lower support. This indicates that the conductor in the uphill span is exerting a
negative or upward force on the lower tower. The amount of this upward force is equal to the weight of the
conductor from the lower tower to the low point in the sag. If the upward pull of the uphill span is greater
than the downward load of the next adjacent span, actual uplift will be caused and the conductor will swing
free of the tower. This usually occurs under minimum temperature conditions and must be dealt with by
adding weights to the insulator suspension string or using a strain structure (Fig. 14.9).
14.5.5 Tower Spotting
Given sufficiently detailed plan-profile drawings, structure heights, wind=weight spans, catenary con-
stants, and minimum ground clearances, structure locations can be chosen such that ground clearance is
Min. SagMax. SagUplift at TowerMin. SagMax. SagFIGURE 14.9 Conductor uplift.