Re: Movable span bridges

["John Wayman" <trecker@bigpond.com>]

Pyrmont Bridge was never used by trams, although you drive the bridge like a
tram. I have been in the drivers cabin when the bridge was opened. The gates
on the bridge are also driven with tram style controllers. One set of gates
has spur gears and sounds "like a tram on  Bellevue Hill"!

Cheers
John Wayman

Derick Wuen <cullend@webone.com.au> wrote in message
37aafa29.0@iridium.webone.com.au">news:37aafa29.0@iridium.webone.com.au...
> Thanks to all those who posted replies or emailed. Corrections welcomed.
>
> 1. Summary of Movable Span Railway Bridges, so far
>
> Location        Waterway                Type            Comment
> NSW
> Shea's Ck   Alexandria Canal     Hinged
> Menindee    Darling River            Hinged
> Grafton        Clarence River         Hinged
> Pyrmont       Darling Harbour       Swing        Tram then Monorail
> Glebe Is.      Sydney Harbour       Swing        Tram
> Gladesville   Sydney Harbour      Swing        Tram
>
> NSW-Vic
> Tocumwal    Murray River            Vertical Lift
> Murrabit       Murray River            Vertical Lift
> Robinvale    Murray River            Vertical Lift     never used for rail
> Yelta            Marray River            Vertical Lift      never used for
> rail
>
> S.A.
> Paringa       Murray River            Vertical Lift
> Jervois        Port River                 ?                        see
note
> (a)
> Robinson    SA Co Basin            ?                        see note (a)
> Fisher         SA Co Basin            ?                        see note
(a)
>
> Tasmania
> Bridgewater    Derwent River    Vertical Lift
> Bridgewater    Derwent River    Swing                replaced by lift
bridge
> Hobart             Constitution Dock Hinged(?)
>
> Note (a) SA Port Adelaide area bridges details unclear. See ARHS Bulletin
> July 1970 for photos of Robinson and Fisher bridges. Both look immovable,
> but enclosed tallish sailing vessels. Jervois Bridge carried Semaphore
> branch and/or trams?
>
> Is there really nothing in Qld?
>
> The old road bridge over the Swan at Fremantle was a timber swing bridge I
> dimly recall, and so there was a chance that the rail bridge may have been
> at one time. But my references only bemoan the fact that the rail bridge
> obstructs navigation of the Swan. So none for WA.
>
> A hinged movable span in Auckland, NZ was also reported.
>
> 2. Concepts
>
> The suggestion that the scope of the enquiry into "movable spans" might
> include those bridges which had collapsed caused a little flurry of
thought.
> But once it was clear to me that the next logical step after collapsed
spans
> was potentially movable spans, I stopped worrying. Even the Sydney Harbour
> Bridge is potentially movable, and thus the term "movable spans" covers
all
> bridges. But we all know what is "really" meant.
>
> Likewise the suggestion that the Spit tram punt might be a movable span.
> Same function; different solution, as far as I'm concerned.
>
> In the summary I have added movable span type. I think there are 3 broad
> types:
>
> . Swing, where the span rotates horizontally to clear a passage
unobstructed
> vertically;
>
> . 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.
>
> . Vertical lift, where the span lifts vertically to clear a passage but
only
> to a limited amount.
>
> Each type has advantages and disadvantages.
>
> From a mechanical engineering point of view, the swing and hinged types
> require precision only at the point of travel where the road or rails have
> to line up for on-bridge traffic. Furthermore, both can give unlimited
> overhead clearance when opened, a big advantage.
>
> But both tend to obstruct clear passage horizontally:
>
> . for example the big central pier on which the Pyrmont swing span is
> located.
>
> . hinged types have to rotate almost 90deg to provide a clear passage, and
> complicated systems of counterbalances are needed as the moment around the
> hinge decreases the more vertical the span rotates to. For example the
> curved counterweight tracks on the Sheas Creek bridge decreased effective
> counterbalance the more the span rotated. Additionally some designs of
> hinged bridge provide for the hinge to move away from the waterway to
> increase clearance, causing further complications.
>
> The vertical lift bridge can only provide a limited amount of vertical
> clearance. Furthermore, the lift mechanism is required to be accurate for
> the whole lift. Each corner of the lift span must be lifted at exactly the
> same rate, otherwise the span will jam in the tracking of the four lift
> towers.
>
> It is therefore a mild surprise to find so many vertical lift spans. These
> spans are closely related to many road only vertical lift spans, so the
> clearance and engineering accuracy disadvantages of the type were well
> understood and under control.
>
> 3. Safeworking
>
> A movable span bridge in a section of railway is a serious obstacle to
> safeworking. Study of safeworking methods is likely to prove rewarding.
>
> 4. Trams
>
> When trolley equipped trams crossed movable spans, what were the
> arrangements for mechanical and electrical continuity for the trolley
wires?
>
> Regards
>
>
>