Railway-and-Highway, all metal being carbon steel (excepting in one set of estimates where nickel steel was employed), the railway floors being open, the highway floors being paved with creosoted blocks resting on a reinforced-concrete base, the foot-walks being slabs of reinforced granitoid, and the handrails being of steel.

The highway bridges considered are all of the author's adopted standard type, viz., carbon-steel trusses, laterals, and floor-system with a 42-foot paved roadway supported on a reinforced-concrete base, two 8-foot side- walks of reinforced granitoid carried on cantilever brackets, and two steel handrails, making the deck about sixty feet wide from out to out, exclusive of the space occupied by the trusses in through bridges.

All pier-shafts are of plain concrete with a coping, the batter being 1" to 1' for low-level-railway and low-level-combined bridges, 3/4" to 1' for high-level-railway and high-level-combined bridges, and 1/2" to 1' for highway bridges.

All caissons founded on sand are of timber with concrete filling and having steel bases and cutting edges; and they are made as light as is legitimate by omitting to fill a large proportion of the excavating shafts. But when the caissons reach bed rock they are assumed to be filled solid. The depth of water in each case is taken as one-third of the vertical distance between extreme low water and caisson footing.

In the pile piers the piles are seventy-five feet long and project sixty feet below the bases, which are assumed to be twenty feet high, the piles being spaced three feet from center to center.

The character of the materials passed through during the sinking is assumed to be the ordinary mixture of silt, quicksand, soft gumbo, and other river deposits, overlying either coarse sand suitable for foundations, or bed rock.

Methods of Pier Sinking

The methods assumed for sinking the caissons are those of open dredging and the pneumatic process, the former being employed when the bases are to rest on sand and the latter when they are to reach bed-rock. In the case of pile piers, the open box is first to be sunk by dredging to the required depth, then the piles are to be driven inside of it, and finally the remaining space is to be filled with concrete.

Specifications for Designing

The specifications for the designing of superstructure are those given in Chapter LXXVIII of "Bridge Engineering," and those for the designing of substructure are to be found in Chapters XXXIX to XLIII, inclusive, of that treatise.