hips, none of the wind load on the upper lateral system is carried down the tower-posts, excepting that which comes on the centre panel and the two adjacent panels. In order to ensure such a distribution of the wind load it is necessary to put no diagonals in those panels of the upper lateral system which are adjacent to the inner hips and between same and the tower.

When the draw is closed, one half of the wind load on the upper lateral system of one arm is to be assumed to travel down the end inclined posts, and one half down the inner inclined posts.

The transferred-load stress on an inclined post is to be found by multiplying the wind load going to it by the average height of the top-chord panel points to which said wind load is applied, dividing the product by the perpendicular distance between central planes of trusses, and multiplying the quotient by the secant of the angle that the inclined post makes with the vertical.

The transferred-load stress on a tower-post is to be determined by multiplying the wind loads carried by the two opposite posts by the respective heights at which these loads are applied, and dividing the sum of these products by the perpendicular distance between central planes of trusses.

COMBINATIONS OF STRESSES.

In ascertaining the stresses in the trusses of swing-bridges the following conditions are to be considered:

Case No. 1. Greatest stresses, dead load only acting, bridge swinging open.

Case No. 2. Greatest stresses from assumed uplift at end of span.

Case No. 3. Greatest stresses from live load on one arm only; each arm being considered to act as a simple span on two supports.

Case No. 4. Greatest stresses from live load on both arms, the live  load advancing  from  both  ends toward the centre