No eye-bars less than three (3) inches deep or five eighths (5/8) of an inch thick shall be employed; and the depths of eye-bars for chords and main diagonals shall not be less than one sixtieth (1/60) of the horizontal length of same.

No adjustable rod shall have less than three quarters (3/4) of a square inch of cross-section.

The shortest span length for trusses with polygonal top chords shall be one hundred and sixty (160) feet.

The limit of span length in which steel stringers can be riveted continuously from end to end of span shall be two hundred (200) feet. Beyond this limit sliding-bearings must be used at one or more intermediate panel points; and in no span shall there be a length of continuously riveted stringers exceeding two hundred (200) feet.

For all compression-members of trusses and for columns of viaducts the greatest ratio of unsupported length to least radius of gyration shall be one hundred and twenty (120), excepting those members whose main function is to resist tension. In these the limit may be raised to one hundred and fifty (150).

The corresponding limit for all struts belonging to sway-bracing shall also be one hundred and fifty (150).

GENERAL PRINCIPLES IN DESIGNING ALL HIGH-
WAY STRUCTURES.

See Specification for Railroad Structures.

RIVETING.

In general, the specifications for riveting given for railroad structures shall apply also to highway structures, except that in the latter the diameters for rivets may be reduced to three quarters (3/4) of an inch for ordinary work.

DETAILS OF DESIGN FOR ROLLED I-BEAM SPANS.

Rolled I beans used as longitudinal girders shall have, preferably, a depth not less than one fifteenth (1/15) of the span. They shall be proportioned by their moments of inertia. The spacing shall generally not exceed three (3) feet six (6) inches.