Page:Final Report - The Columbia River Interstate Bridge.pdf/38

 Where I 2 percentage. L = Length of load on bridge producing maximum stress.

N = Number of loaded tracks for street car loading, or number of lines of traiﬁc for highway load- ing.

The above ﬁgures will convey to an engineer the permissible loads to be allowed to cross the bridge, but a more detailed state- ment may be of service to the Commission. The bridge was not designed for heavy locomotives or heavy railroad trains. Light trains, of course, can be operated across it with safety. The following limitation, which is included in your franchise to the only railway company now operating, sets out the maximum weights of locomotives, cars and trains which should be per- mitted to operate across the bridge. This should be your guide for granting permission for operation of trains or cars on the bridge:

“No car or locomotive of any character weighing in excess of 100,000 pounds gross load, or having any single axle load in excess of 25,000 pounds, shall be pemlitted on the structure; and no cars weighing over 80,000 pounds having a length of less than 20 ft. c. to c. of trucks shall be pemiitted on the structure. Two coupled locomotives or cars shall not weigh in excess of 180,000 pounds gross load; three coupled locomotives or cars shall weigh not in excess of 190,000 pounds gross load nor more than 1,600 pounds per lineal foot; four coupled cars or locomotives shall weigh not in excess of 210,000 pounds, nor more than 1,300 pounds per lineal foot; five coupled locomotives or cars shall weigh not in excess of 230,000 pounds, nor more than 1,200 pounds per lineal foot. Trains composed of more than ﬁve loco- motives or cars, or both, shall weigh not more than 1,100 pounds per lineal foot.”

The limitation on the roadway of a truck with load totaling 24 tons as given above needs no special explanation. The speci- fications for design employed have not been published and space does not permit their inclusion here, but if the Commission should at any time need information concerning unit stresses and details of design your Engineers will make a supplementary report to give that information.

33