DETAILS OF DESIGN FOR TRUSSES.

The details of trusses for draw spans shall comply in general with the specifications given for trusses of fixed spans.

In trusses having broken top chords, that portion of said top chords between outer and inner hips is to be made of rigid members, and that portion between the inner hips and over the tower is to be made of eye-bars.

In pin-connected trusses with parallel chords rigid members will be required throughout the top chord, except for the centre panel, in which eye-bars are to be used. In riveted trusses stiff top chords from end to end of span are to be adopted.

The bottom chords are to be of rigid sections throughout for all spans; and for spans over three hundred (300) feet in length provision must be made near the panel points at feet of tower-posts for adjusting, by means of shimming-plates, the height of the ends of the trusses. These shimming-plates must provide an end, vertical adjustment of one (1) inch for each one hundred (100) feet of length of one arm of draw. For spans shorter than three hundred (300) feet shimming-plates beneath the end bearings will give sufficient adjustment.

Rigid portal-bracing must be used between the two inclined posts at both the inner and the outer hips. These portals are to be carried down as low as the specified clearance over tracks will permit.

In heavy spans the portal-bracing must attach to the upper and lower flanges of inclined posts, instead of lying in the gravity-planes of same.

The tower must be rigidly braced in all four faces. In the transverse planes all the diagonals and horizontal struts must, generally, be made of stiff members of box or I sections, so as to take hold of the exterior of the posts; and this sway bracing must be carried down as low as the specified clearance will permit, so as to hold the tower-posts firmly to place and line.

In the planes of the trusses the diagonals are to be made of