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II. 



ON THE GEAPHIOAL CONSTEUCTION OF MAXIMUM BENDING- 

 MOMENTS ON SHOKT GIEDEES DUE TO A LOCOMOTIVE. 



By T. ALEXANDEE, M.A.L, 



Professor of Engineering, Trinity College, Dublin. 



To which is added the description of a new Kinematical Model, 

 By J. T. JACKSON, M.A.I., Assistant to the Professor. 



Read June 24. Published August 31, 1912. 



Much attention has recently been given to the bending effects upon bridges of 

 short span, due to the concentration of the loads on the wheels of locomotives. 

 The subject assumes special importance on account of the ever-increasing 

 weight of the rolling-stock. In a paper by W. B. Farr, read before the 

 Institute of Civil Engineers in 1900, the subject was discussed at great length, 

 as at that time the Board of Trade had required all the railway companies to 

 strengthen their bridges. Farr, in his paper, contends that a period has 

 arrived when the weight concentrated on any wheel cannot further be 

 increased, so that any further increase of weight must be spread over a longer 

 wheel-base and a greater number of wheels. This would, he held, narrow 

 the problem to that of finding the maximum bending-moment for a span 

 accommodating a locomotive and tender, and a like moment for a series of 

 decreasing spans accommodating portions of the locomotive. Then, for each 

 span, an equivalent uniform load was calculated and the rate of this uniform 

 load tabulated for use in designing. Much of the discussion on this paper 

 turned upon the question as to what was the best method of estimating such 

 an equivalent uniform load. 



Each type of locomotive and tender gave a special table of its own ; and 

 these tables were given in the paper for a large series of locomotives, and were 

 amplified to allow for shock and other important practical considerations, 

 again leading to much important discussion. 



It was suggested, too, that each railway company might use a table 

 derived from a hypothetical locomotive, which was an average of their actual 

 passenger engines. 



