DETAILS OF DESIGN FOR ROLLED I-BEAM SPANS.

Rolled I beams used as longitudinal girders shall have preferably a depth not less than one twelfth (1/12) of the span. They shall be proportioned by their moments of inertia.

I beam spans may have either one or two beams per rail. In the former case the spacing should be six (6) feet six (6) inches, and in the latter case two (2) feet six (6) inches between contiguous girders. With two lines of stringers per track, there will be required a bracing-frame at each end of span and diagonal bracing between the top flanges, unless the span be less than ten (10) feet in length, in which case the diagonals may be omitted.

With four lines of stringers per track, no diagonal bracing will be required, but three (3) bracing-frames at each end will be used, with three (3) more at mid-span when the span length exceeds ten (10) feet.

Each I beam is to have at each end a pair of stiffening angles, one of which will form a portion of the end bracing-frame. These are to fit tightly at both top and bottom against the flanges.

Under each end of each I beam there is to be riveted a bearing plate of proper area and thickness to distribute the load uniformly over the masonry, said plate being bolted effectively to the latter with due provision for expansion and contraction.

DETAILS OF DESIGN FOR PLATE-GIRDER SPANS.

Plate girders shall have preferably a depth not less than one tenth (1/10) of the span.

All plate girders, whenever it is practicable, shall be built without splices in the web; and, when such become necessary, the smallest possible number of same shall be adopted. The splice-plates and rivets for the splices shall be such as to develop in every respect the full strength of the net section of the web, the main splice-plates extending from flange to flange and having at least two (2) rows of rivets on each side of the joint. In addition to these, each flange shall  be  spliced  by two cover-plates on top of the vertical legs of