"SANDY RIVER BRIDGE AT TROUTDALE
The Sandy River Bridge at Troutdale is one of two beginning points of the Historic Columbia River Highway (HCRH). The other is the Sandy River Bridge (Stark Street) (HAER No. OR-36-B), which connects Stark Street with the Historic Columbia River Highway at milepost 16.7.8 Both Sandy River bridges are the only steel truss spans on the highway. Constructed in 1912, the Sandy River Bridge at Troutdale is the oldest structure on the Historic Columbia River Highway and the oldest state-owned metal truss bridge in Oregon.9 Multnomah County built it as part of a large farm-to-market road improvement campaign of the 1910s. The bridge initially served nearby rural residents from the rolling fields high above the Columbia River east of Troutdale. Just east of the bridge, the county road rose steeply, with 10 to 20 percent grades to reach an elevation nearing 700 feet in the district near Chanticleer Inn, 22 mites from downtown Portiand.10
In 1916, well after other, more eastern sections of the HCRH were completed, Multnomah County cut a new, 1 ½ mile long road through 200-foot rock bluffs, along the south side of the Sandy River. This new route eliminated excessive grades and achieved a water-level road from the Sandy River Bridge at Troutdale to the new Sandy River Bridge (Stark Street) completed in 1914.11 Both bridges served as a feeders for traffic along the Historic Columbia River Highway, which in this part of Multnomah County was simply a realignment over gentle grades of existing county roads.12 Estimated construction cost was $23,600.13
DESIGN AND DESCRIPTION
The Sandy River Bridge at Troutdale, from west to east was constructed of one 40'-0" steel plate girder span and two nine- panel 162'-0" Pratt through-truss spans (9 x 18'). Its 18' roadway was constructed of a tongue-and-groove deck covered with asphalt. A four-foot plank sidewalk with timber railing cantilevered out from the south elevation on a continuation of the wooden deck beams. Horizontal clearance was 17'-5" and vertical clearance was 14'-5".14
Waddell and Harrington, a well-known Kansas City bridge engineering firm, designed this structure shortly after they completed the 1912 Steel Bridge, a telescoping vertical lift structure spanning the Willamette River in nearby downtown Portland. The main spans of the Sandy River Bridge at Troutdale appear to be standard riveted steel Pratt through-truss structures. Inclined end posts and upper chords were made from rolled steel channel and plate with latticed bracing. Truss vertical chords consisted of rolled angle steel and lattice. Portal bracing was made from angle steel, lattice, and gusset plates. Sway bracing was angle steel and gusset plates arranged in a lattice form. Diagonal bracing for the Pratt trusses consisted of angle steel and intermediate bracing plates. Lower chords were made from heavier rolled steel with bracing. The lower chords were pin-connected to shoes affixed to the piers.
Truss protection barriers, or steel guard fences, about 3' high and consisting of steel angle frames with intermediate lacing, were placed inside the truss panels above the deck curbs to prevent vehicles from damaging the superstructure. A sidewalk was placed on the upstream or south elevation of the bridge and consisted originally of 2" x 8" planking and 3" x 8" stringers on 6" x 6" cantilevered deck beams that also supported tongue-and- groove deck planking. A standard highway guard-rail type barrier constructed of timber posts and 2" x 6" stock was placed horizontally serving as the sidewalk handrail.15
Designers used two types of piers in constructing the Sandy River Bridge at Troutdale. The west pier of the plate girder span and the east pier of the east Pratt truss are simple reinforced-concrete batter structures founded on bedrock. The west pier of the west Pratt truss and the intermediate pier shared by both Pratt trusses consist of pairs of battered circular bents connected by solid web walls. Stream foundation conditions no doubt dictated the types of piers used on the bridge. The use or arrangement of piling is unknown but the Sandy River, as its name implies, is a wide stream with a gravel bed, with bedrock most likely some distance below the stream floor.
Masonry guard walls consisting of ashlar basalt with a screened concrete cap served as entryways at both ends of the bridge. These features were probably not original to the bridge's construction but were added latter in the 1910s while masons were constructing retaining walls and guard fences along nearby sections of the Historic Columbia River Highway." - Historic Columbia River Highway website