calculation of all stresses, excepting only such unimportant cases of ambiguity as that involved by using two stiff diagonals in a middle panel.

All lateral bracing and other sway-bracing shall be rigid both above and below, i.e., the sections must be capable of resisting compression, adjustable rods for such bracing being allowed only in towers of draw-spans and in lower lateral systems of deck-bridges.

The stiff diagonals of lower lateral systems, which shall be of double cancellation, shall be riveted rigidly to the stringers where they cross them, so as to transfer in an effective manner the thrust of braked trains to the truss-posts without causing a horizontal bending on the cross-girders.

All through-spans shall have stiff portal bracing at each end, connected rigidly to the inclined end posts. The said portal bracing shall be made as deep as the specified clear headroom will allow.

When the height of the trusses is great enough to permit it, there shall be used at each panel point a rigid bracing frame riveted to the top lateral strut and to the posts, and carried down to the clearance line. When the truss depth is not great enough for this detail, corner brackets of proper size, strength, and rigidity are to be riveted between the posts and the upper lateral struts.

Deck-bridges shall have stiff, diagonal braces between opposite vertical posts, which bracing, as a matter of precaution, shall have sufficient strength to carry one half of a panel-truss live load with its impact allowance; and the transverse bracing between the vertical or inclined posts at each end shall be sufficiently strong to transmit properly to the masonry one half of the wind-pressure and centrifugal load (if there be any) which is carried by the entire upper lateral system of the span.

The lower lateral systems of deck-bridges shall be made of adjustable rods in alternate panels, thus leaving every other panel unbraced, and forcing the wind-pressure from below up the vertical bracing and to the ends of the span by the upper lateral system.