General remarks - Design of iron piers or jetties - Classification of jetties - Those which are backed up by solid structure in the rear - Those which are isolated - Types of design of the second class - Accessories of jetties - Exposure and "fetch" - Height of deck - Details of pilework as influenced by conditions of soil or sea bottom - Modes of sinking piles - Difficulties as to finished lengths and levels of top of piles - Make-up lengths - Objections to make-up lengths - Sawing off of steel or iron sections - Composite structures of cast iron and timber - Example and description - Bollards - Crane roads - Floating booms - Description of cast-iron cylinder jetty with superstructure of steel girderwork - Cylinder spacing - Main box girders - Cross girders - Details of cylinders - Flange joints - Cap - Make-up lengths - Lowermost rings of cylinders - Cutting edge - Further adaptations of steelwork in marine engineering works - Tie-rods to wharf walls - Accessories to jetties or wharves - Bollards - Strength of bollards - Details to suit special cases - Anchorage - Examples - Fairleads and capstans - Position and arrangement - Foundations - Caissons - Varied applications of the term - Caissons for dock entrances - For foundations - For the commencement or completion of breakwater structures - Practical example of a caisson for breakwater construction - General description - Dimensions - General arrangement - Compartments - Bulkheads - Details of construction - Valves - Mooring rings - Method of erection and launching - Launching ways - Completion after launching - Ballasting - Weights - Conditions of stability - Composition of ballast - Subsequent operations - Towing into position - Sinking - Programme for concreting and successive conditions of stability - Titan cranes for block-setting - Caissons for closing dock entrances - General comparison between lock-gates and caissons - Types of caissons - Sliding - Floating - Comparison of types - Advantages and disadvantages - Functions as a bridge and as a dam - Watertightness - Design of keels and stems - Arrangement of sealing timber for floating caissons - For sliding caissons - Width of water seal - Details of timber keels and mode of connection, etc. - Consideration of pressures, reactions, and general stresses due to water pressure - Position of decks and air-chamber - Effects of corrosion and considerations of minimum scantlings - General description of internal arrangement of floating caissons - Bilge - Air-chamber - Stability and pendulum - Upper and end chambers - Scuttling tanks - Upper deck and top tanks - Dangers arising from excess of buoyancy - Critical conditions - Holding-down apparatus - Frictional resistance to uplifting - Coefficient of Friction -

Calculation for buoyancy and weight - Rivet heads - Percentage to be allowed - Weights of immersed timber - Subsidiary items - Table of the weights of recently constructed caissons - Ballast and stowage - Composition and densi-ties of ballast - Burr concrete ballast - General description of sliding caissons - Arrangements of upper deck and camber deck - Sliding ways - Hauling mechanism - Additional resistances due to currents or differences in water level - Culvert area - Extra sluices - Position of hauling gear - Tilting moments - Sledge runners and rollers - Combination of the two types in recent caissons - Keels - Roller paths - Rollers and rams - Mode of operation during inward and outward journeys - Details of roller path and roller - Of hydraulic rams and mud-scrapers - Handrailing - Hauling chains - Description and manufacture - Tests - Tables of results of tests - Modulus of elasticity of hauling chains - Table of the weights of sliding caissons.

The contents of this chapter are devoted to a brief reference to that branch of construction in mild steel or iron which may be entitled marine, as it deals with structures (other than ships or shipping) which are constructed either in the water, such as jetties or piers, or with reference to the requirements of navigation and commerce, in docks and dockwork generally, with their accessories, such as caissons, lock-gates, bollards, penstocks and the like, while an important branch of this subject is occasionally found in the application of steelwork to certain structures connected with the construction of breakwaters, an example of which will be illustrated and described later on.

The details of design of iron piers or jetties will vary greatly with the conditions which such structures are called upon to meet.

Thus, for wharves constructed for the loading or unloading connected with an extensive shipping industry, and alongside which ships of deep draught and heavy displacement have to lie, will have their details largely determined, amongst other ruling considerations, by the amount of resistance to be offered to the shock of heavy vessels coming alongside, in addition to the heavy strains brought to bear upon the structure through the bollards, capstans, or fairleads, by the hawsers used in bringing ships alongside, or getting them away.

In this respect piers or wharves may, for convenience, be classed under two heads - those in which the jetty or wharf is backed up by a solid structure, such as a wharf wall or rubble mound, and those in which no such supports are found, the structure having to resist the shocks or bumps of floating craft alongside without the aid of any such accessories, these stresses being in the former class transmitted to and absorbed by the solid structure in the rear.

It is obvious that in the second class much more consideration will be necessary as to the means by which such stresses are to be resisted, and the designer will usually find himself called upon to select either one of two types, that in which the supporting columns are numerous, spaced fairly close together, and connected by numerous braces, both transverse and longitudinal, converting the entire structure into what may be termed a basket-work of more or less elastic members, tending to absorb, by reason of their number and connections, the shocks or bumps of craft alongside, or the stresses caused by hawser connections.