This section is from the book "Notes On Construction In Mild Steel", by Henry Fidler. Also available from Amazon: Notes On Construction In Mild Steel.
In Fig. 346 is given a cross-section of a jetty belonging to the first of those classes discussed on p. 339, being supported in the rear by a rubble mound, which may be supposed to resist, or share in resisting, the shocks to which the structure may be exposed by floating craft alongside, and to which mound the jetty forms a facing, having a sufficient depth of water alongside for the class of vessel for which it is intended.
Fig. 346. Scale 1 inch = 12 feet.
The jetty consists of two rows of cast-iron piles, as shown in the figure, the outermost sloping fender pile being of timber. The distance apart of the rows of piles lengthwise of the jetty is about 10 feet, while transversely they are pitched as shown in the figure.
The outermost cast-iron pile is 1 foot 6 inches internal diameter of l¾-inch metal. Two separate systems of joints of the pile are adopted, one for joints below the ground line, the other for joints above the ground line and below the level of the caps and sockets to receive the timber work.
Fig. 347. Scale ¾ inch = 1 foot.
The former joint is shown in Figs. 347 and 348, Fig. 348 being a section on line EF in Fig. 347. This method of jointing has been found satisfactory for mud and sand, offering no resistance to the sinking of the pile. As shown in the figures, it consists of a welded steel collar J inch thick, machined on the internal surface, and shrunk on to the machined surfaces of the cast-iron pile, to which it is attached by 1-inch diameter set screws.
Fig. 348. Scale ¾ inch = 1 foot.
The details of the joint above ground line are shown in Figs. 349 and 350, this being an ordinary flanged joint with machined faces and drilled holes for bolts.
Fig. 349. Scale ¾ inch = 1 foot.
The detail at the top of the outer cast-iron pile is shown in Figs. 351 and 352. This consists of a cast-iron cap specially shaped to receive the feet of the double timber verticals of the superstructure, and socketed into the top of the circular pile below, as shown. The timber work is bolted to the caps by l½-inch bolts, holes for which are provided in the castings, as shown.
The inner row of cast-iron piles is 12 inches internal diameter, of 1¼-inch metal, with joints similar in character to those of the outer row, and shown in Figs. 353, 354.
The caps of these piles are also arranged to receive the single timber verticals of the superstructure, as shown in Figs. 355, 356.
The deck or floor of the jetty is of 4-inch decking laid upon 14" X 7" joists, these latter resting upon the double timber girders shown in Fig. 346, which in their turn are carried by the timber verticals socketed into the caps of the cast-iron piles, as above described.
Horizontal and transverse walings, with struts, curbs, and capping pieces, complete the timber superstructure, as shown in Fig. 346.
Fig. 350. Scale¾ inch = 1 foot.
Cast-iron bollards are attached to the double timber girders, and are anchored back to concrete blocks set in the summit of the rubble mound by means of long steel straps with keys and cast-iron washer plates.
Where a crane road occurs, steel girders are frequently inserted under the decking, to which the rails are connected by through hook bolts, as shown in Fig. 357, which represents a crane road on a timber jetty arranged for 20-ton cranes working at 25 feet radius, with a gauge of crane road of 11 feet centres of rails, as shown, the total weight of the crane without the load being about 80 tons.
The use of floating booms alongside jetties of openwork construction is not uncommon. It may in certain cases be necessary to prevent small floating craft, such as boats or barges, from being blown or pushed in under the girderwork of a superstructure which is not sufficiently high above high water to prevent the risk of such craft being caught at the top of the tide, and by their displacement exerting an upward lifting force on the decking. Or, again, booms are used to mitigate the force of shock or rubbing as between the ship's side and the jetty face.
Scale ¾ inch = 1 foot.
In the case of large cast-iron cylinders, circular rings of timber, framed together, surrounding the cylinder and floating up and down with the tide, have been used, but are found to be severe upon the frames and skin-platiug of the ship; on the other hand, if the boom is made straight, the nip then becomes visited upon the cylinder to the relief of the ship.
We may now consider the other type of jetty previously referred to, consisting of heavy cast-iron cylinders supporting a superstructure of main and cross riveted steel girders with decking, the whole forming a facing in front of a rubble mound surmounted by a vertical wall in deep water, and adapted for the use of a heavy class of vessel of deep draught.
Fig. 352. Scale ¾ inch = 1 foot.
In the case before us the local conditions and the cost of sinking cylinders require that the latter shall be spaced as far apart as is practicable without unduly increasing the dimensions and weight of the main girders. This spacing is fixed at about 60 feet in the case shown in Fig. 358, which represents the upper portion of one cylinder and portions of the adjoining spans of main girders. An enlarged view of the upper portion of the cylinder, showing the capping, the junction of the main girders, and the bollard attachment, is given in Fig. 359.