. Electric railway journal . d members shall bear directlyagainst or be attached directly to longitudinal members ateither top or bottom, the assumed reactions shall be con-sidered as loads applied to whatever construction is usedat end sill or end plate, and both these last members shallhave section moduli, respectively, sufficient to prevent theirfailure horizontally before that of the vertical end members. Other specifications make allowance for oscillation,either by assuming as high as 25 per cent additionallead or by reducing the allowable unit stress as low as12,500 lb. per square inch.
. Electric railway journal . d members shall bear directlyagainst or be attached directly to longitudinal members ateither top or bottom, the assumed reactions shall be con-sidered as loads applied to whatever construction is usedat end sill or end plate, and both these last members shallhave section moduli, respectively, sufficient to prevent theirfailure horizontally before that of the vertical end members. Other specifications make allowance for oscillation,either by assuming as high as 25 per cent additionallead or by reducing the allowable unit stress as low as12,500 lb. per square inch. The Postal specifications may be taken as represent-ing good practice for electric car service as far as unitstresses are concerned, and also for buffing strains forcars in rapid transit service where speeds are lower speeds and light trains the buffing strainsmay be reduced, as these will vary with the speed andwith the energy of the moving mass. Thus if 200,000lb. is considered to be sufficient for a maximum speed. Fig. 4—Loading, Moment and Shear Diagrams of Side Sills of 60 , then for a city surface car whose speedwill not exceed 15 , the maximum end force wouldprobably not exceed 12,500 lb., which for a car weigh-ing 50,000 lb. with load is equivalent to a retardationrate of between 5 and 6 , and would permit ofapproximately double that amount before the elasticlimit of the material would be exceeded. In the design of parts under compression particularattention should be paid to proper bracing, and in factit may be stated that, throughout, care must be takenthat the structure is sufficiently rigid. It must be re-membered that strength and rigidity are not necessarilysynonymous, and the latter quality must be obtained bythe proper reinforcement against buckling of parts incompression, and gusseting of joints subject to wearingaction. On this point the Master Car Builders Associa-tion has ruled that the length of center or draft-sillmembers b
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