and ends are raised, thus making the entire lower lateral system with the bottom chords a continuous girder with four points of support. This case does not involve the presence of any live load on the span.

For lower lateral systems of through-bridges and upper lateral systems of deck-bridges—

Case No. 3. Greatest wind-load stresses when span is swinging.

Case No. 4. Greatest wind-load stresses when span is closed and ends are raised, and with live load on one arm only, thus making the loaded chords with their lateral system a simple span with supported ends.

Case No. 5. Greatest wind-load stresses when span is closed and ends are raised, and with the live load on both arms covering same either wholly or partially, thus making the loaded chords with their lateral system a continuous girder with four (4) points of support.

The greatest stress on any lateral member found by these five conditions of wind-loading is to be used in proportioning its section, and there is to be assumed no division of the wind load between structure and train, although the failure to make said division will cause small errors on the side of safety.

DETAILS OF DESIGN FOR PLATE-GIRDER
DRAW-SPANS.

Plate-girder drawbridges are to be divided into two types, viz.:

Type No. 1. Continuous girders, in which the girders act as continuous spans resting on four points of support; and

Type No. 2. Non-continuous girders, in which the two arms carry the live load independently of each other, the dead-load stresses over the pivot pier when the span is swung being carried by links.

For Type No. 1 the same combinations of stresses are to be used as specified for truss draw-spans, but it will generally be found that the wind loads do not affect the proportioning of the girders.