It is economical sometimes to increase the diameter of a cylinder between top and bottom, but in such cases the lower twenty feet should be made plumb so that the cylinder can be sunk with ease and accuracy. This detail was adopted for the Jefferson City bridge, the variation in diameter being obtained by telescoping some of the lengths and putting in filling-rings. This required a trifle more metal than truly conical piers would; but the shop-work was much simpler.

The proper load for large piles inside of cylinders is about thirty tons each, although with very large piles and solid material to hold them it may, be increased to forty tons. On the other hand, in case of bad foundations, it is sometimes necessary to reduce the load to ten tons per pile.

The proper distance for piles to project into cylinders is about fifteen feet, and should never be less than ten feet or more than twenty feet under any circumstances. With less than ten feet there will not be enough grip for the concrete, and with more than twenty feet it is difficult to place the concrete properly under water between the piles. Piles in cylinders should be driven as closely as possible, and precaution should be taken to prevent the lifting of piles already driven by the sinking of the last few piles. When large piles are employed, the designer can figure upon six square feet of pier section for each pile.

The bracing between the up-stream and the down-stream cylinders of a pier should invariably be of solid webs properly stiffened, extending from high water to near low water, in case there be any drift; but for cylinder piers on shore an open bracing of struts and ties will suffice.

Concerning braced steel piers but little need be said, except that they should conform in their design with the specifications given in Chapters XIV and XVI. It is advisable, if practicable, to avoid battering more than two faces of a braced pier on account of the troublesome shop-work that would be involved with a four-face batter; nevertheless it is often necessary to adopt the latter, especially for high piers. A possible objection  to  this  type  of  pier  is  that  for cantilever bridges it increases  the  deflection  of  the  span  because of  the compression