If in any bridge design the dead load assumed should differ from that computed from the diagram of sections and the detail drawings by an amount exceeding one (1) per cent of the sum of the equivalent live load and actual dead load, the calculations of stresses, etc., are to be made over with a new assumed dead load.

WIND LOADS.

For railroad bridges the wind loads per lineal foot of span for both the loaded and the unloaded chords are to be taken from the curves given in Plate VII.

The wind loads for the loaded chords include a pressure of three hundred (300) pounds per lineal foot on the train, the centre of which pressure is applied at a height of eight (8) feet above the base of rail.

For determining the requisite anchorage for a loaded structure, the train of empty cars shall be assumed to weigh one thousand (1000) pounds per lineal foot.

In trestle towers the columns and transverse bracing shall be proportioned to resist the following wind-pressures in addition to all other loads.

1st. When the structure is loaded, four hundred and fifty (450) pounds per lineal foot on stringers and cars, and two hundred and fifty (250) pounds for each vertical foot of each entire tower.

2d. When the structure is empty, three hundred and fifty (350) pounds per lineal foot on stringers, assumed to be concentrated one foot above the centre of stringer, and three hundred and fifty (350) pounds for each vertical foot of each entire tower.

The wind loads for longitudinal bracing are to be taken as seven tenths (0.7) of those for the transverse bracing.

In figuring greatest tension on columns and anchor-bolts, computations are to be made for both the loaded and the un-