STRESSES FROM WHEEL LOADS. Art, 143- 



that is, by assuming a number of positions, calculating the stress 

 for each position, and then comparing the results. This is indeed, 

 in some cases, the quickest as well as the simplest way of arriving 

 a I the result, because the usual engine loadings are rather simple 

 systems of concentrated loads. Certain simple criteria will, how- 

 ever, be developed whose employment will, in most cases, save time 

 and enable us to determine if a certain assumed position will, or 

 will not, give a maximum. 



It will be noted that, in general, it is not only a question of 

 finding the position of a definite set of wheels on the span, but of 

 finding what set of wheels must ~be on the span. This can only 

 6V; done ~by trial. To determine what set of wheels to try in any 

 particular case certain- fundamental principles will help. 



1. To find the maximum shear at any section of a solid 

 beam, there should be as much load as possible between the section 

 and the further support, and its. center of gravity should be as 

 near the section as possible. There may be some load on the oppo- 

 sits side of the section, as is explained in Art. 151. 



2. To find the maximum, shear in any panel of a truss, there 

 should be as much load as possible between a support and the 

 nearest panel point of the panel in question, and its center of 

 gravity should be as near to this point as possible. There will 

 usually be some load in -the panel as shown in Art. 147. Loading 

 the longer segment gives the maximum positive shear and loading 

 the shorter segment gives the maximum negative shear. 



3. To find the maximum moment at any point of a beam 

 (includes truss) there should be as much load as possible on the 

 span, and its center of gravity should be as near tltfc center of 

 moments as possible. 



These principles -are applied roughly, of course, that is by 



10 30 50 10 90 103 110 129 142 152 172 102 212 232 245 258 271 284 Sum of the Loads. 



10 20 20 20 20 13 13 13 13 10 20 20 20 20 13 13 13 13 Loads In 1000 Ib. units. 



'-Q COCOCD fJi) (?) fs) (JD ^.P") @@@ (H) tjij) (H) 



fjs) I 



Ibs. per 



heel spacing. 



8 13 18 23 32 37 43 48 5fi 04 09 7.4 7!l 8 93 99 104 109 Sum of the distances. 



llO 120 30 I | 40 I 150 I 60 I |70 80 1901 100 Y 110 120 130 140 150 



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COOPER'S #40 LOADING FOR ONE RAIL. 

 Fig. 199. 



inspection. A diagram of the loads should be made to scale 

 on a piece of good paper or on tracing linen, as shown in Fig. 

 MM). By moving this "loading strip" along a diagram of the 

 beam or truss drawn to the same scale, and keeping in mind the 



