feet. For clear heights much exceeding these, the bascule leaf will have to be longer than the vertical-lift span, unless an encroachment on the clearance at one corner be permitted, which is not usually the case. For a clear height of 150 feet, this excess length will generally be at least 10 or
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![](fig30cd.jpg)
12 feet, and often still more. This limitation does not apply to the Brown balance-beam type, which can be rotated 90°.
In making the comparisons, it was necessary to consider two cases—first, when there are long flanking-spans, and, second, when there are not. Typical layouts are shown in Figs. 30c and 30d. It will be noted that in
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