The west approach is carried on fir piling treated in an open vat with carbolineum to a temperature of about 220 degrees F.
Lumber being comparatively cheap, the entire roadway deck of the bridge and wooden approach is composed of fir, three by seven inches and twenty-six feet long on edge, spiked together, thus projecting a foot outside the curb on either side, the roadway being twenty-four feet between curbs. An asphaltic wearing surface three and one-half inches thick effectively waterproofs the wood, and the small interstices between the pieces will allow sufficient circulation of air to preclude any possibility of attack of dry rot. The ends of the floor members were painted with hot carbolineum, as were also the wooden members contiguous to openings in the floor occasioned by expansion joints between spans.
The two five-foot concrete sidewalks are carried on brackets beyond the trusses. The curbs serve as reinforced concrete beams to carry half the sidewalk load to the trusses, there being small concrete struts extending up from the top of the top chords at panel and midpanel points. Between the bottom of the curb and the top of the wooden floor is a three-quarter-inch cushion of “Sarco.” Since the bridge is on a grade, it was necessary to precast this in sheets the width of the curb. When the material hardened, it was rolled up in convenient lengths and placed. It will thus be possible in the future to renew the wooden floor with comparatively little difficulty, although it is believed that the wood floor base, protected as it is now, should last at least fifty years.
On account of the rather extreme length for pony trusses of the channel span, 123 feet between end pins, it was decided to tie the trusses together, and this was accomplished by means of two arched lattice struts placed each twenty feet and six inches from the center of the span.
A final coat of battleship gray paint was applied to the steel work, and has evoked considerable favorable comment, being an innovation from the black paint commonly used in this part of the country.
The bridge was built by the Coast Bridge Company and Robert Wakefield of Portland. The cost of the structure complete was $250,000.00, of which Marion County paid approximately $200,000.00 and Polk County $50,000.00.
The engineering cost for the work is remarkably low. It includes surveys, borings, inspection of cement and steel fabrications, resident engineer’s salary, cost of design, blue prints and supplies and stenographic work, and amounts to $4,600.00, or about one and eight-tenths per cent of the total cost.
Surrey—Salem to Jefferson
A reconnaissance between the city limits of Salem and the Linn County Line (Santiam River) just south of Jefferson, was made in the spring of 1918, and the following facts developed, as regards the comparison of three possible routes between these points: