LIVE LOADS.

The live loads for the various parts of the structure are to be taken from the "Compromise Standard System of Live Loads for Railway Bridges," in the same manner as previously specified for fixed spans.

The live load for trusses with only one arm loaded is to be taken from the live-load curves for a span equal to the distance between the centre of the end-pin and that of the pin at the foot of the nearer tower post; but for both arms loaded the live load is to be taken for a span equal to the distance between centres of end-pins.

For only one arm loaded, the half-span is to be considered to act as a simple span on two supports; and, for both arms loaded, the entire span is to be considered continuous over four supports. The stresses due to the live load, with both arms wholly or partially loaded, are to be determined by the balanced-load method. For convenience in determining the reactions at ends and at centre supports for balanced loads the curve given on Plate IX can be used. This gives the percentage of any balanced load which is supported at the outer end of a half-span.

DEAD LOADS.

In spans over two hundred and seventy-five (275) feet, the dead load per truss is to be increased properly from the ends towards the centre of span in order to cover the weight of the heavy truss-members, which increase in size toward the centre of the span. The division of the dead load between top and bottom chords is to be the same as specified for fixed spans.

The dead loads from tower, drum, and turntable are not to be considered as affecting the stresses in the trusses.

ASSUMED UPLIFT LOADS.

There will be a considerable uplift at the ends of the span, for they are to be brought to a firm bearing by means of the endlifting device. The amount of this uplift per truss or girder is to be assumed  as  a certain proportion of the entire dead load