THE SHI P AS A BEAM It was seen ea

THE SHI P AS A BEAM It was seen earlier that the ship bends like a beam; and in fact the hull can be considered as a box-shaped girder for which the position of the neutral axis and second moment of area may be cal- culated. The deck and bottom shell form the flanges of the hull girder, and are far more important to longitudinal strength than the sides which form the web of the girder and carry the shear forces. The box shaped hull girder and a conventional I girder may be compared as in Figure 8.3.In a ship the neutral axis is generally nearer the bottom, since the dbottom shell will be heavier than the deck, having to resist water pressure as well as the bending stresses. In calculating the second moment of an area of the cross-section all longitudinal material is of greatest importance and the further the material is from the neutral axis the greater will its second moment of area about the neutral axis. However, at greater distances from the neutral axis the secti'onal modulus will be reduced and correspondingly higher stress may occur in extreme hull girder plates such as the deck stringer, sheerstrake, and bilge. These strakes of plating are generally heavier than other plating.Bending stresses are greater over the middle portion of the length and it is owing to this variation that Lloyd's give maximum scantlings over 40 per cent of the length amidships. Other scantlings may taper towards the ends of the ship, apart from locally highly stressed regions where other forms of loading are encountered.

THE SHI P AS A BEAM It was seen earlier that the ship bends like a beam; and in fact the hull can be considered as a box-shaped. Girder for which the position of the neutral axis and second moment of area may be cal - culated. The deck and bottom shell. Form the flanges of the, hull girder and are far more important to longitudinal strength than the sides which form the web. Of the girder and carry the shear forces. The box shaped hull girder and a conventional I girder may be compared as in Figure 8.3.In a ship the neutral axis is generally nearer the bottom since the, dbottom shell will be heavier than, the deck having. To resist water pressure as well as the bending stresses. In calculating the second moment of an area of the cross-section. All longitudinal material is of greatest importance and the further the material is from the neutral axis the greater will. Its second moment of area about the neutral axis. However at greater, distances from the neutral axis the secti onal modulus. ' Will be reduced and correspondingly higher stress may occur in extreme hull girder plates such as the deck stringer sheerstrake,,, And bilge. These strakes of plating are generally heavier than other plating.Bending stresses are greater over the middle portion of the length and it is owing to this variation that Lloyd s give. ' Maximum scantlings over 40 per cent of the length amidships. Other scantlings may taper towards the ends of, the ship apart. From locally highly stressed regions where other forms of loading are encountered.