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Comparisons were made for swing bridges giving two 150-foot channels
and two 200-foot channels, as against one channel of 150 and one of 200
feet for the vertical lift and the bascule. It was found that the swing was a
trifle more expensive than the bascule for the 150-foot channel, and of
about the same cost for the 200-foot channel. For clear heights less than
160 feet, the vertical lift was cheaper than the swing. There was some
variation with the depth of the foundations, the swing being more expensive
for deep ones.
The Mystic River, Brown-Balance-Beam bascule is a through, plate-girder, highway bridge 215' 3" long, consisting of a fixed span of 68' 6", a
tower span of 23' 9", a bascule span of 88' 0", and a fixed span of 35' 0". The clear channel is 75' 0". This layout was compared with one for a
vertical lift, consisting of one 92' 3" fixed span, one 88' 0" lift span, and one 35' 0" fixed span. It was found that the two were of equal cost when the required vertical movement of the lift span was 61', corresponding to a
clear height of 64', since there is only a three-foot clearance when the span
is down. If the clearance with span down had been the usual one of 15 or
20 feet, the two types would have been equal for a clear height of 75 or 80
feet. This Brown bascule rotates through 90°, so that the moving span
never needs to be any longer than that of the vertical lift.
The Housatonic River Bridge is a concrete-arch structure, with a simple-trunnion, double-leaf-bascule span giving a clear waterway of 125', the distance from center to center of trunnions being 175'. The bascule piers were necessarily quite heavy and massive; and while much lighter ones would have sufficed for the vertical lift, it was decided to make a compari-
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