|March 2011 (-33.815 deg., 151.026 deg.) Camellia Bridges|
Alan commented in yesterday's blog that the superstructure of the Camellia Utility Bridge may originally have been on the Camellia Railway Bridge. The evidence suggests that he's right. We can see in the photo above that the piers of the two bridges are equally spaced, making the placement of the three spans onto the steel column caps of the utility bridge fairly straightforward.
I mentioned in a previous blog several reasons why we often see new and old bridges side by side. Alan brought up the additional point that a parallel bridge can be used as a detour during construction and that moving the superstructure onto an adjacent structure allows trains to cross the river while the new bridge is being built.
It is likely that the three trusses on the utility bridge were originally on the railway bridge. We can see how the railway bridge is narrow at the two ends. This matches the width of the trusses. The Heritage Council article mentioned that the original railway bridge had a wrought iron latticed truss. However, I think that may have been from an even earlier era (when the masonry abutments were first built). The laced and riveted Warren trusses must have replaced the wrought iron trusses when a stronger bridge was required. It's a little odd that there is no deck on the utility bridge, but perhaps it was removed as needless weight when they moved the trusses to their new location.
The new railway bridge is also an interesting structure. For one thing it is very wide for a single set of tracks. Perhaps they planned to widen the ends and add another track in the future? More likely the old abutments are considered of historic value and so they may not be allowed to widen the ends of the bridge. Also, it is a little unusual to build a truss bridge when box girders can provide longer spans at less cost. It's even more unusual to build a pony truss without any lateral support from cross-braces. It's also unusual to build a continuous three span truss that is over three hundred feet long. Was it shipped on a barge or somehow fabricated on the site? The steel pier legs that descend from the truss make it a much stiffer, almost rigid structure. Also, it looks like a very lightweight walkway is attached to the west side of the railway bridge.
Australia's Bridges: Camellia Bridges across the Parramatta River in NSW by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.