The weight of metal in the panel over the pier is, according to the directions on the diagram,

1.8 X 3.0W = 5.4W.

Let us assume that there are only five panels in the anchor-arm, then the trial weight T will be

0.75W + 1.75W + 2.1W + 2.5W + 3.0W = 10.10W.

Substituting in the formula gives

It will be seen from these calculations that the full percentages given for the end panel points of cantilever and anchor arms are to be used, although in reality there is but a half panel length for each point. This is caused by the heavy details required at these points for adjustment and anchorage. All erection metal at the end of a suspended span is assumed to belong to the cantilever arm.

Should in any case the panel lengths be unequal in different portions of the structure, it will be a simple matter to use the curves by finding average weights per foot for two assumed cases of equal panel lengths, one making the arm greater and the other making it less in length than it actually is, and interpolating properly between the results for the required average weight per foot for the arm.

The total weight of metal in the two anchorages of any three-span cantilever bridge can be taken at five per cent of the grand total weight of metal in the said three spans, and the weight of metal in the pedestals on main piers at four per cent of same. Of course, conditions vary for different cases, nevertheless these percentages will give results sufficiently close for all practical purposes.

If the bridge be so long as to require an anchor-span, its weight of truss and lateral metal per lineal foot will be about 3.25 W, irrespective, strange to say, of the length of said anchor-span, W being the weight per foot of the trusses and laterals in a suspended span,  whose  length  is  three  eighths  of