. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools, and a hand-book for the use of engineers in field and office . hange of flexure at two points between the this stress the floor is subjected to compression when,the cars are suddenly stopped and to tension when in ordinary jmotion, the tension being greater as the train resistance is igreater and as the car is nearer the engine. The shocks, jars,and sudden strains to which the car-frames are subjected arevery much harder on them than the mere static strains due to
. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools, and a hand-book for the use of engineers in field and office . hange of flexure at two points between the this stress the floor is subjected to compression when,the cars are suddenly stopped and to tension when in ordinary jmotion, the tension being greater as the train resistance is igreater and as the car is nearer the engine. The shocks, jars,and sudden strains to which the car-frames are subjected arevery much harder on them than the mere static strains due totheir maximum loads if the loads were quiescent. Consequentlyany calculations based on the static loads are practically value-less, except as a very rough guide, and previous experiencemust be relied on in designing car bodies. As evidence of theincreasing demand for strength in car-frames, it has been re-cently observed that freight-cars, built some years ago andbuilt almost entirely of wood, are requiring repairs of woodenparts which have been crushed in service, the per-fectly sound as regards decay. 418. The use of metal. The use of metal in car construction. Fig. 201. is very rapidly increasing. The demand for greater strengthin car-frames has gro-v\m until the M^ooden framing has becomeso heavy that it is found possible to make steel frames andtrucks at a small additional cost, the steel frames being twiceas strong and yet reducing the dead weight of the car about5000 lbs., a consideration of no small value, especially on roadshaving heavy grades. Another reason for the increasing useof metal is the great reduction in the price of rolled or pressed
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