594 



REPORT — 1884. 



the moving load with the least amount of wear, and at the bottom so that 

 it may be securely attached to the snpportH upon which it rests, at tho 

 same time transmitting tho load cRectively to them. It must be designed 

 with the greatest possible economy in weight, to carry with safety its load 

 between the points of support, acting as a continuous girder of a span 

 equal to the distance of the points of support apart, or rather twice that 

 distance, so that in case any one should fail or give way, the rail would 

 still be able to carry over the increased span with safety. Theory there- 

 fore points to a deep rail having a comparatively thin web, witli upper 

 and lower flanges, the upper flange being rounded to the proper shape to 

 receive the wheels of the moving load, allowing suflicient width of bear, 

 ing surface to prevent crushing under the action of the wheels, but not 

 more than necessary, as the friction would otherwise be increased ; and 

 the lower flange shaped to adapt it to the mode of support adopted. In 

 England, where iron chairs of peculiar kind are used to carry the rail, 

 the lower flange is made of a similar form to the upper, while on the 

 Continent of Europe and in America the lower flange is made flat to rest 

 on a timber tie or sleeper. The width of this flange should be such tlmt 

 the load will not cause the rail to sink into the timber. The web of the 

 rail must be sufiiciently thick to give stiffness sideways, and prevent 

 the load bending the top of the rail over and crushing it. The section 

 of the rail is made symmetrical about a vertical axis, allowing of re- 

 versal, if desired, when the inner edge has become seriously worn by tbo 

 wheels. 



As to the proper depth and weight of the rail, it will readily be seen 

 that this depends upon the distance that the supports are placed apart 

 and the load carried. The loads carried on first-class American railways 

 are no lighter than those carried on European railways. Class K engine, 

 as used on the Pennsylvania Railroad, has a total weight in working order 

 of 92,700 pounds, distributed on a wheel base of 22 feet 7^ inches, and 

 a weight on the first pair of drivers of 33,600 pounds. Class L engine, on 

 same road, has a total weight of 124,100 pounds, on a wheel base of 31 

 feet 4 inches, with a load on the main pair of drivers of 32,500 pounds. 

 Class M engine has a total weight of 87,500 pounds, on a wheel base of 

 only 10 feet 8 inches, and a weight on the first pair of drivers of 33,400 

 pounds. But in Europe, where timber is expensive, the ties or sleepers 

 are placed farther apart than they are in America, and therefore heavier 

 rails are required. So long as timber is cheap in this country light rails 

 will be used, but there is a tendency on some lines to heavier rails. 



In assuming the proper load to be used in calculating the proportions 

 and weight of rail, it is not suflicient to take the static weight from tlio 

 heaviest wheel, but an amount mast be added to this on account of the 

 load being a live or moving load, and also for impact, the tendency of a 

 rapidly moving train, particularly with the driving wheels of the engine, 

 being to pound down as it were upon the track, making sudden applica- 

 tions of heavy loads. The percentages of addition thus required to the 

 dead load cannot be determined theoretically, but must be assumed more 

 or less empirically, depending upon the results of practical experience. 

 The rails, when fastened firmly to their supports, must also possess sutfi- 

 cient lateral stiffness to resist all deflection sideways from the swinging 

 motion of the train, centrifugal force on curves, &c. 



The author is indebted to the courtesy of the Cambria Iron Company, 

 Johnstown, Penn., for the standard sections of steel rails shown on Plates 



