As the mainline begins the climb up the mountain RR-West of
Oakridge, it immediately crosses Salmon Creek. The mainline bridge is a four-span ballasted-deck girder
bridge. Very nearby is a lower
bridge and trestle that serves the Pope and Talbot sawmill. The immediate concern, though is for
the mainline bridge.
The mainline bridge was built around a core composed of the
three splines in the middle of the spline roadbed used for the mountain
grade. I use nominal ¼ inch hardboard
cut into one inch strips for splines.
The core bridge splines were depressed below grade to account for the
thickness of the deck. The
ballasted deck was located on top of the spline core. Girders were attached to the underside of the deck, concealing
the spline core. Piers and
abutments will be fitted to this assembly (deck and girders), completing the
bridge. The spline core maintains
roadbed continuity and a modest curve through the bridge.
Construction of the bridge began with a template tracing of
the spline core. Using this
template, I planned the deck base sections, using two segments for each
girder. The deck width is 16
scale feet, per SP Common Standard plans published by Steam Age Equipment
Company. In contrast to the deck
on a pile trestle, this deck uses 4 inch thick longitudinal boards supported by
transverse (across the girders) 12x12 beams. I cut out the scale 16 feet wide deck base segments from
0.040 inch thick styrene. I used
my NWSL Chopper to cut the 12x12 (1/8 inch square) styrene beams, making every
eighth beam 18 feet long to support the railing posts.
Ballast deck under construction.
Once the basic deck and its support beams were assembled, I
attached the handrail posts and handrails. Note there was a lot of styrene cement used on the
deck. While the primary bond occured
fairly quickly, it took quite a while for the remaining solvent to
evaporate. I did fairly well with
getting weight on the assembly to hold it flat, but I still got a little bit of
warpage. That complicated the
handrail construction and subsequent handling, but was well within bond
strength of the girder attachment and eventual use of adhesive caulk to hold
the deck flat as roadbed.
Ballasted deck with handrails installed test fit into
location.
The girders were cut from Central Valley plate girder bridge
kits (210-1903). Only the rounded girder ends of two center girder sets were
cut off. The outer girder sets
were cut shorter by a panel on each end, just as the prototype bridge. The top and bottom plates were attached
and trimmed to length, followed by the bridge shoes. The rest of the Central Valley kit is surplus to this
bridge. I painted the girder
sections Grimy Black. Rust weathering was done with Bragdon powders, followed
by a light overspray of Tarnished Black.
The bridge deck was placed on the spline core and the spline
outline scribed on the bottom (cross-beam) surface. The front
girder segments were attached to the deck assembly using gap-filling acc cement. Once this set, the bridge assembly was
removed from location, inverted and the back girders attached, staying outside
the scribed lines for the spline core.
Once all of this set up, the deck and girders were placed in position again,
awaiting piers and abutments.
Ballasted deck in place with front girder segments
attached. Rear girder segments are
laying on the “creek” surface below.
Cans of beans are very handy weights!
Completed ballast deck and girder assembly in place,
spanning Salmon Creek.
