steels leads him to believe that when they are really worth considering for any case, the stronger metal should be used for the floor system so as to lighten the dead load, even if per se that portion of the structure were made slightly more costly, and that carbon steel should be substituted for the alloy steel only in such places where, without increasing the sectional

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area, the weaker metal would provide ample strength—for instance, in the lateral systems and lighter posts of moderately-light short-span bridges.

It was upon this assumption that the author many years ago accumulated the data upon which, substantially, the diagrams given in this chapter were prepared;  and  under  like  conditions  they  may  be  relied  upon  abso-