• The four cables support a dead load of 7140 tons and a live load of 4017 tons.

• The weight of main girders increases with the span, and there is for any type of bridge a limiting span beyond which the dead load stresses exceed the assigned limit of working stress.

• It was pointed out as early as 1869 (Unwin, Wrought Iron Bridges and Roofs) that a rational method of fixing the working stress, so far as knowledge went at that time, would be to make it depend on the ratio of live to dead load, and in such a way that the factor of safety for the live load stresses was double that for the dead load stresses.

• Let A be the dead load and B the live load, producing stress in a bar; p =B / A the ratio of live to dead load; f i the safe working limit of stress for a bar subjected to a dead load only and f the safe working stress in any other case.

• The distribution of total shear, due to a dead load w 1 per ft.

• For a train advancing from the left, the travelling load shear in the left half of the span is of a different sign from that due to the dead load.

• Then the bridge is designed, so far as the direct stresses are concerned, for bending moments due to a uniform dead load and the uniform equivalent load we.

• The practical limit of height was reached when the sectional area of the masonry of the piers of the exterior walls in the lower storey had to be made so great, in order to support safely the weight of the dead load of the walls and floors and the accidental load imposed upon the latter in use, as to affect seriously the value of the lower storeys on account of the loss of light and floor space.