A Treatise On The Principles And Practice Of Dock Engineering

376 DOCK ENGINEERING. 26 inches. The tipper surface is of granolithic concrete to a depth of 2 inches. The main joists are 12 feet apart. The foregoing examples constitute very heavy types of floor, in propor- tion to their strength. With a view of minimising the amount of material, and reducing the cost of construction, various systems have been proposed in recent years, chiefly founded upon the intimate incorporation of iron or steel and concrete in one mass, and in such a way that each exercises its characteristic strength to the best advantage. One or two of the more important of these systems may advantageously be described, as there can be little doubt that the combination of these two fire-resisting materials is capable of effecting a great and useful saving in structural weight. .............t’A" Staffordshire tiles Fig. 361. —Shed Upper Floor. Gran°Mhic Surface Finishing 2 to 1 °; Cement ?'.° B to 1.^ Concrete 6"x3" Rolled Steel Joists^ Fig. 362. —Shed Upper Floor. Monier System.—The Monier system consists of a network of metal bedded in a concrete slab, the network being formed by two rows of bars or wires crossing one another at right angles. The lower row are the stressed bars. They are intended, in flat floors, to relieve the concrete of its tensile stress, and consequently are proportioned in number and size to the load to be carried and the amount of span. In arched floors they assist in taking up the compressive stress. The function of the upper row of bars is merely to distribute the pressure evenly, and they are generally made three-fourths of the diameter of the lower bars. The floor is divided into bays by a series of iron joists, upon which the network is laid. It is recom- mended that the width of the bays should not be too small. “Fairly large spans enable the supporting joists to be more economically designed, on account of a better proportion of depth to length being obtained.”* At the same time, the floor must not be made unduly deep or it will prove an arrangement of dubious economy. “The minimum thickness of the concrete, * Beer on “ The Monier System of Construction,” Min. Proc. Inst. C.E., vol. cxxxiii.