Re: Movable span bridges

["chris 'fufas' grace" <chris@icos.net.nz>]

Derick Wuen wrote in message <37aafa29.0@iridium.webone.com.au>...

>A hinged movable span in Auckland, NZ was also reported.


[snip]
and:
>. Hinged, where one end of the span rotates vertically around a hinge at
the
>other end. Some in this NG have referred to this arrangement as a bascule
>bridge. The arrangement leaves a vertically unobstructed passage.
>


I'm sorry, I do not classify a hinged bridge as a bascule bridge, and the
one in Auckland was definitely a bascule.

I'll try and illustrate what I mean, within the limits of ASCII:
______________yy_________________
   *                             \
   *                              \          ^
    *                              \         | Direction of movement
     *                              \        |
       *                             \
       xx *                           \
--------------*------------------------ <- rail level

XX = Drive wheels

There is a geared quadrant at one end of the bridge (represented by *). A
Drive Shaft
engages with this (represented by xx). The bridge itself is a through truss.
pivoted
at yy. the bridge is opened by the drive shaft engaging the geared quadrant,
causing
the bridge to pivot around the yy point.

This arrangement is inherently self balancing, as the extra weight of the
geared
quadrant ( which was very substantial) balances the weight of the bridge on
the
other side of the pivot.

Quite a different thing from a hinged bridge.