2 NOTES ON PI .ATI M.IKUER DESIGN 



such as minimum thickness of material in web plates, 

 and minimum edge distances for punching, they fix a limit 

 10 size of certain pa 



The correct design of plate girders therefore requi 



. tical knowledge and cither practical experience or 

 formulated rules, based on practical experience, and so 

 carefully and closely drawn as to prevent a pnnr de.-ign. 



Plate Birders are used for bridges anywhere from 18" 

 and 1.V long to 126" deep and 130' long, and even 

 beyond these limits: they are also used in buildings and 

 other important engineering work to a great extent. In 

 general, the lower limit of their use is the I l>eam, which 

 will furnish the proper strength at a less cost per pound 

 of material: their upper limit is the truss, whose total 

 cost b less than the heavier but cheaper per pound girder. 



In order to design properly any structure it is necessary 

 to understand the composition and relation of each to 

 each of the various parts. The following drawings are 

 meant to illustrate some of the most essential features of 

 plate-girder construction. They are therefore not meant 

 to be casually inspected, but thoroughly studied, and tin 

 function of the various parts in carrying a load to the 

 supports, the makeup of the parts and their connection, 

 !i clearly understood. 



Fig. la shows a single-track deck plate-girder bridge. 



Fig. 16 shows a single-track through plate-girder bridge. 



The computation of the stresses in any structure is 

 the preliminary step in the design. The stresses themselves 

 are a function of the weight of the structure, and hence 

 an early estimate of the weight of each portion of the 



