in the form of an I with a single line of lacing. When two angles are used, a single plate must not be depended on to form the splice at the intersection of the diagonals, but two angles, each not less than two (2) feet long, are to be placed beneath or on top of the spliced angles, so as to form a full splice in respect to rigidity as well as strength.

Diagonals for upper lateral systems and vertical sway-bracing shall, preferably, be built of four angles in the form of an I with a single line of lacing; but, for structures where this section would involve an extravagant use of metal, two of the angles, one at top and one at bottom, may be omitted, thus making each strut consist of two angles laced, provided, of course, that where the struts cross they shall be rigidly connected by two plates of ample size. This unbalanced section for such diagonals is to be avoided whenever it can be done without undue use of metal. In no case, though, will it be permissible to use angles in tension that are not capable of resisting properly the possible compressive stresses, with due regard for the specified limit of ratio of unsupported length to least radius of gyration.

In designing transverse lateral and overhead struts and their connections it must be remembered that their main function is to hold rigidly the chords or posts to place and line, and not merely to resist as columns the greatest calculated direct stresses to which they may be subjected. For this reason such struts should have ample section for rigidity, and the connecting plates at their ends should grip both connected members effectively.

Stringers for truss-bridges shall invariably be built of plates and angles, and no cover-plates will be allowed for the flanges. Their depths shall be made not less than the most economic ones in respect to weight of metal required, provided that the bridge clearance will permit, and never less than one twelfth (1/12) of the span. No splices will be allowed in their flanges nor any in their webs, provided that sufficiently long web-plates  are  procurable.  The  compression-flanges  shall  be  made of the; same gross section as the  tension-flanges;  and  they  shall