I returned to a section of temporary span to begin construction of proper bridges. The two track overpass seemed simple enough...just fabricate a skewed through girder type to serve the purpose. Simple couldn't be further from the truth. As it neared completion ( more rivets to add ) the focus shifted to the major span.
The nature of the duck under area meant building a bridge without central supports, and because the track here is curved, a prototypical railroad bridge type does not exist in the real world. Splaying the steel arch legs allows for ample support on the outside of the curved deck.
Construction began by forming the deck from steel curtain rod "I" beams tied together with short pieces of wood. Where the track crosses over lines on the other side it was simpler to continue the deck and tie it firmly to the benchwork.
The arches, again from curtain rod, produce the main support, and after a bit of maneuvering were anchored to the benchwork with screws. A single screw at the top of each arch fastens them to the deck. Notice the exaggerated lean to the inside arch, whereas the outside one is perfectly vertical. Further stringers and latticework can now be added at leisure in a sitting position without interrupting train operation.
Finally, for now, here's a shot that emphasizes the built in superelavation to the curved deck. String-lining here, a phenomenon that has yet to occur, could prove catastrophic. Fingers crossed.
Bruce
