In proportioning the web-members of such girders, the specified intensities of working stresses are to be reduced from ten (10) per cent for 6" X 3 1/2" angles to twenty-five (25) per cent for equal-legged angles, with proportionate amounts for angles of intermediate inequality of legs, so as to compensate for the secondary stresses due to the eccentric grip of the rivets. In no case will it be permissible to use flats instead of angles for web-members, but tees may be employed, provided their heads be wide enough to permit of satisfactory riveted connections.

At all intersections of web-members with chords, connecting plates are to be used; for it is not permissible to attach web angles directly to chord angles without using an intermediary plate.

The exact intersection at a point of all gravity lines of girder-members assembling at any apex must be adhered to in the designing of open-webbed, riveted girders.

In designing all riveted connections, the greatest care is to be taken to make connecting plates and groups of rivets balance about centre lines of stress, especially where passing from riveted work to pin-connected, as in the case of a riveted span with hinged ends at pedestals.

In all other particulars, the designing of open-webbed, riveted work is to comply, wherever practicable and proper, with the specifications for plate-girder and pin-connected spans.

DETAILS OF DESIGNS FOR PIN-CONNECTED SPANS.

The sections of the top chords and those of the inclined end posts of through-spans shall consist generally of two built channels and a cover-plate, each channel being formed of a web and two angles, the upper one small and the lower one much larger, so as to bring the centre of gravity of the entire box section of the member as close as possible to the midplane of the web-plates. In no case will more than one coverplate be allowed, and this is to be made as thin as is proper.   It is permissible to substitute rolled  channels  for  the  built