. The railroad engineer's practice . fact thatthe effect of the wind on the train is to raise the windwardside and so increase the load on the leeward side, decreas-ing and increasing the loads on the respective columns asgiven r-bove. Similarly the effect of tbe v-ind on tbetrusses when tbe top chord rests on the pier is to decreasethe load on tbe leeward side, and increase it on the wind-ward. Tbe effect produced by the difference of theseshould therefore be subtracted or added (as the momenton the train or truss is the greater) to that produced by Pabove. Tbis may bo accomplished by writing
. The railroad engineer's practice . fact thatthe effect of the wind on the train is to raise the windwardside and so increase the load on the leeward side, decreas-ing and increasing the loads on the respective columns asgiven r-bove. Similarly the effect of tbe v-ind on tbetrusses when tbe top chord rests on the pier is to decreasethe load on tbe leeward side, and increase it on the wind-ward. Tbe effect produced by the difference of theseshould therefore be subtracted or added (as the momenton the train or truss is the greater) to that produced by Pabove. Tbis may bo accomplished by writing P± 2 t tan. «for P and ^V + t for TFfor tbe leeward, and W— t for tbewindward column, in the formulas above, t being equal to H h — n hI in which //is the pressure of tbe wind on the train cover-ing tbe adjacent half spans, and h is tbe height of thecentre of pressure above the point of connection of thetruss with tbe piers, and II and K are similarly tbe total 87pressure of the wind ou the half spau and the depth of the A B. centre of pressure below the point of connection of thetruss with the pier, and I is the distance IIB in the figure. In a direction parallel to the centre line of the bridge,the pressure on the braces is due to the action of the driv-ing-v,hcel of the locomotive, and is found as follows : Let y ■=■ the angle made by the brace B G with thehorizontal. If :?is the horizontal force exerted by thesteam in the cylinder, and ^S is the stroke of the piston,and I) is the diameter of the driving-wheel, the stress on A B, CI), etc., will be T^, and that on A I), &c., equal to S TBros, y To find T, if the cylinder of the locomotive is d inches 88 in diameter, and the pressure of the steam in the boiler140 pounds per square inch, T — 140?r-^ = imd-4 The value of ^ is about two-fifths in the heaviest en-1) gines on the ordinary gauge. The strain on A D resolved on A C must be added tothe compression due to the weight of the train and bridge,and the effect o
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