Lesson eleven Structural Design, Ship Stresses Structural design un fter having established the principal dimensions, form. and general arrangement of the ship, the designer lertakes the problem of providing a structure capable of withstanding the forces which may be imposed upon it The hull of a steel merchant ship is a complex structure, unique in the field of engineering structures in that it is primarily a plate structure, depending for its major overall strength on the plating of the shell, decks, and in most cases,also on the inner bottom and longitudinal bulkheads. The framing members, each of which has its own function to perform, are designed primarily to maintain the plate membrances to the planned contours and their positions relative to each other when subjected to the external forces of water pressure and breaking seas, as well as to the internal forces caused by the services for which the ship is designed. Unlike most other large engineering structures, the forces supporting the ship's hull as well as the loads which may be imposed upon it vary considerably, and in many cases, cannot be determined accurately. As a result, those responsible for the structural design of ships must be guided by established standards Basic considerations The problem of the development of a satisfactory structure generally involves the following considerations 1. It is necessary to establish the sizes of, and to combine effectively, the va that the structure, with a proper margin of safety, can resist the major overall stresses resulting from longitudinal and transverse bendin 2. Each component part must be so designed that it will withstand the local loads imposed upon it rom water pressure, breaking seas, the weight of cargo or passenger, and other superimpose loads such as deckhouses, heavy machinery, masts, and so on, including such additional margins as sometimes may be required to meet unusually severe conditions encountered in operation Rules of classification societies The various classification societies have continued to modify and improve their rules to keep pace with the records of service experience, an increasing amount of research, and the constantly growing understanding of the scientific principles involved. In the modern rules of the societies, the designer has available to him formulas and of scantlings, dimensions of framing shapers, and thicknesses. These are directly applicable to practically he ordinary types of sea-going merchant vessel being built today, and contain a flexibility of appli vessels of special types The design of structural features of a merchant ship is greatly influenced by the rules of classification societies in fact, the principal scantlings of most merchant ships are taken directly from such rules Scantling are defined as the dimensions and material thicknesses of frames, shell plating, deck plating and other structures, together with the suitability of the means for protecting openings and making them sufficiently watertight or weathertight The classification society rules contain a great deal of useful information relating to the design and construction of the various component parts of a ship's structure. Scantling can be determined directl from the tables given in these publications. In many cases, a good conception of the usual"good-practice construction can also be gleaned from the sketches and descriptive matter available from the classification societies From"McGraw-Hill Encyclopedia of Science and Technology",Vol 12. 1982 Ship stresses The ship at sea or lying in still water is being constantly subjected to a wide variety of stresses and stra which result from the action of forces from outside and within the ship. Forces within the ship result from structural weight, cargo, machinery weight and the effects of operating machinery. Exterior forces include the hydrostatic pressure of the water on the hull and the action of the wind and waves. The ship must at all times be able to resist and withstand these stresses and strains throughout its structure It must therefore be constructed in aLesson Eleven Structural Design, Ship Stresses Structural design After having established the principal dimensions, form, and general arrangement of the ship, the designer undertakes the problem of providing a structure capable of withstanding the forces which may be imposed upon it. The hull of a steel merchant ship is a complex structure, unique in the field of engineering structures in that it is primarily a plate structure, depending for its major overall strength on the plating of the shell, decks, and in most cases, also on the inner bottom and longitudinal bulkheads. The framing members, each of which has its own function to perform, are designed primarily to maintain the plate membrances to the planned contours and their positions relative to each other when subjected to the external forces of water pressure and breaking seas, as well as to the internal forces caused by the services for which the ship is designed. Unlike most other large engineering structures, the forces supporting the ship’s hull as well as the loads which may be imposed upon it vary considerably, and in many cases, cannot be determined accurately. As a result, those responsible for the structural design of ships must be guided by established standards. Basic considerations The problem of the development of a satisfactory structure generally involves the following considerations: 1. It is necessary to establish the sizes of, and to combine effectively, the various component parts so that the structure, with a proper margin of safety, can resist the major overall stresses resulting from longitudinal and transverse bending. 2. Each component part must be so designed that it will withstand the local loads imposed upon it from water pressure, breaking seas, the weight of cargo or passenger, and other superimpose loads such as deckhouses, heavy machinery, masts, and so on, including such additional margins as sometimes may be required to meet unusually severe conditions encountered in operation. Rules of classification societies The various classification societies have continued to modify and improve their rules to keep pace with the records of service experience, an increasing amount of research, and the constantly growing understanding of the scientific principles involved. In the modern rules of the societies, the designer has available to him formulas and tables of scantlings, dimensions of framing shapers, and thicknesses. These are directly applicable to practically all the ordinary types of sea-going merchant vessel being built today, and contain a flexibility of application to vessels of special types. The design of structural features of a merchant ship is greatly influenced by the rules of classification societies; in fact, the principal scantlings of most merchant ships are taken directly from such rules. Scantling are defined as the dimensions and material thicknesses of frames, shell plating, deck plating, and other structures, together with the suitability of the means for protecting openings and making them sufficiently watertight or weathertight. The classification society rules contain a great deal of useful information relating to the design and construction of the various component parts of a ship’s structure. Scantling can be determined directly from the tables given in these publications. In many cases, a good conception of the usual “good-practice” construction can also be gleaned from the sketches and descriptive matter available from the classification societies. (From “McGraw-Hill Encyclopedia of Science and Technology”, Vol.12.1982) Ship stresses The ship at sea or lying in still water is being constantly subjected to a wide variety of stresses and strains, which result from the action of forces from outside and within the ship. Forces within the ship result from structural weight, cargo, machinery weight and the effects of operating machinery. Exterior forces include the hydrostatic pressure of the water on the hull and the action of the wind and waves. The ship must at all times be able to resist and withstand these stresses and strains throughout its structure. It must therefore be constructed in a