. Cranberries; : the national cranberry magazine. Cranberries. Figure 1. Sand spreader crossing a pair of aluminum bridges with 1 Vz cu. yards of sand. rivets should be used. The lower surface was riveted at 4-inch intervals. Testing Bridges Obviously a truck size vehicle could not cross a ditch on a single bridge, such as the one just de- scribed, so a second bridge of the same construction was made. The bridges were subjected to labora- tory tests to determine their poten- tial for use in place of the rail-plank assembly described above. The test consisted of subjecting the bridges to succes
. Cranberries; : the national cranberry magazine. Cranberries. Figure 1. Sand spreader crossing a pair of aluminum bridges with 1 Vz cu. yards of sand. rivets should be used. The lower surface was riveted at 4-inch intervals. Testing Bridges Obviously a truck size vehicle could not cross a ditch on a single bridge, such as the one just de- scribed, so a second bridge of the same construction was made. The bridges were subjected to labora- tory tests to determine their poten- tial for use in place of the rail-plank assembly described above. The test consisted of subjecting the bridges to successively heavier loads until the deflection increased without any increase in load. The ultimate load at mid-span, for both bridges, was 4500 pounds. The test procedure is illustrated in Figure 4. A bridge was placed top side down, on supports directly below the track of a chain hoist. Columns were erected between the ends of the bridge and the track. The columns were set on 4" x 1-5/8" x 2' steel channels which were placed across the ends of the bridges to prevent local crushing of the bridge under the columns. A short length of 3" steel pipe was suspended by a chain across the underside of the bridge at mid-span. A dynamometer scale was sus- pended from the hook of the chain hoist and attached to the chain which supported the 3" pipe. The hoist was then raised, bringing the 16 3" pipe into contact with the underside of the bridge (actually the top side in field use). An initial load of 1000 pounds was applied to assure firm contact between the columns and the bridge. The height from the floor to a reference point on the side of the bridge was recorded for the initial load and for each subsequent load. The load was increased in 500 pound increments and deflections from the initial loading position recorded. After reaching the 2500-pound load the tension was relaxed to the initial 1000 pound level and the height to the reference point checked to determine
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