Abstract
Partly from theoretical considerations, but mainly from practical data, an empirical formula is derived giving the approximate weight of any tower in terms of its height and maximum working overturning moment at the base. The tower weight above ground line is shown to be satisfactorily represented by kH√M tons, where H is the overall tower height above ground line, in feet; M is the overturning moment at ground line, in thousand lb-ft; and k is a “constant” which varies within an extreme range of about 0.0014 to 0.0029 throughout the whole series of towers; most towers have k values well within this range.The towers investigated covered ranges of about 16 to 1 in height, 3 000 to 1 in overturning moment, and 1 200 to 1 in tower weight.Design factors which explain variations in the “constant” k are discussed at some length on a qualitative basis.It is shown that an economic value for the base width of any tower is in the neighbourhood of 0.5√M ft.On the assumption that, for any given general type of tower, the total erected cost may be regarded as proportional to the aboveground weight, the tower-weight formula, kH√M, can be used with convenience and reasonable accuracy for a wide field of cost estimations, especially those involving comparisons of a number of alternatives of a generally similar nature.Such investigations include the following:Ordinary transmission lines: (a) Economic span lengths. (b) Relative costs of lines for different voltages, conductor sizes and conductor materials. (c) Number of circuits. (d) Number and height of earth conductors. (e) Abnormal wind and ice loading assumptions and/or actors of safety. (f) Different clearances between conductors and ground. (g) Suspended auxiliary cables. (h) Hypothetical “dogleg” lines. (j) Hypothetical “super e.h.v.” lines.Navigable river crossings: (a) General layout. (b) Clearance to high water; Air Ministry height restrictions. (c) Span lengths and river bank configuration. (d) Foundation conditions. (e) Number of circuits. (f) Long spans; economic conductor. (g) Narrow waterways; economic number of towers. (h) Terminal-type crossing towers; economic conductor tension.
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