INTERCOUNTY BRIDGE OVER THE WILLAMETTE AT SALEM.
BUILT BY MARION AND POLK COUNTIES IN 1917 AND 1918.
COST $250,000.00. TOTAL LENGTH 2,220 FEET.
With a view to securing the approval of this project by the Federal Office of Public Roads, and to undertaking the construction during the 1918 season, the necessary surveys were made in January and February, 1918, and the plans submitted to the Office of Public Roads in March, 1918. The final approvement by the Government was received June 15, 1918, and on June 25 proposals for the construction were received and opened. The lowest bid received was from Warren Construction Company, Portland, Oregon, but as it was in excess of the State Highway Engineer’s estimate, and in excess of the available funds, all bids were rejected.
The work would have then been started by the Highway Department with State forces, but it was just at this time that the shortage of labor, materials, transportation facilities, etc., became serious, and the Federal Government called for curtailment of road construction, and the Highway Commission was forced to order the discontinuance of preparation for this paving, as well as for all other proposed work in the State.
Now, that Peace is in sight, there is every reason to believe that the Highway Commission will order that construction begin on the Salem-Aurora Paving at the very earliest date, and its completion may be looked for during the 1919 season.
This paving is to be sixteen feet wide with a two-foot rock shoulder on each side. The type will depend upon the bids received. The paving will start about four miles north of the city limits of Salem and extend to the Marion-Clackamas County Line, just north of Aurora, the total length being eighteen miles. It is estimated that this work will cost $360,000.00.
The Salem Bridge
The [new bridge] over the Willamette River at Salem, designed and built under the supervision of the State Highway Department, is one of the largest strictly highway bridges erected in the United States in 1918. This structure has a total length of 2,220 feet, and consists of 352 feet of reinforced concrete approach on the Marion County end, six steel spans over the river aggregating 885 lineal feet, and 780 feet of high class pile trestle approach on the Polk County end.
To provide for the river navigation, the U. S. Engineers required a minimum horizontal clearance normal to the channel of 120 feet and a vertical clearance of at least sixty-six feet above low water, in case a high level type of bridge were adopted. After careful study it was decided to construct a high level bridge of the deck type, and to carry the pony channel span on cantilevers projecting from the adjoining spans, giving an arch effect over the channel. By this type of construction, a clear distance of about 145 feet between channel piers was obtained.
To minimize the cost of fabrication and erection of steel, four spans were made practically the same. The east span was necessarily shorter than the typical ones, since otherwise it would place the channel opening too far across the river. This span is not so deep as the adjoining one, and the difference in height is made up by means of a rocker under the small span, which, of course, also serves the purpose of movable shoes. The channel span rests on cast steel rockers on one end, which are carried by a shelf on the cantilever panel. The opposite end of the span was pin connected.
Previous to the design of the bridge, wash borings were made, which indicated in a general way that the bed of the stream was composed of a few feet of gravel, underlaid with sand for a considerable depth. It was accordingly decided to carry the foundations down below the probable point of future scour, and carry the loads entirely upon piling. The two channel piers were sunk about thirty-five feet below low water.