PREFACE 



THE use of influence lines for the determination of 

 maximum moments and criterions for wheel loads is pre- 

 sented in many modern text books. 



The object of these few pages is to bring attention to 

 the fact that for loads on all ordinary trusses, the influence ^ , J^ 

 diagrams for bending moments are drawn by following 

 a single simple rule, and that the diagrams so con- 

 structed require no computations for their direct applica- 

 tion. In addition to this the influence diagrams for loads 

 on continuous trusses, cantilever trusses and arches are 

 shown to be based upon the one general diagram for simple 

 trusses. 



While the diagrams, as a rule, are constructed for 

 moments yet they can be as easily drawn for stresses or 

 even areas of truss members. 



The use of the influence diagrams in the determination 

 of criterions for the positions of wheel loads which produce 

 maximums is explained and shown to be very simple. 



M. A. H. 



DECEMBER, 1913. 



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