The learning objectives of this section are to make shipboard operational
personnel familiar with stresses in a hull of structure illustrated by the
behavior of a simple beam be able to recognize failure modes and damages to
the vessel during inspection hull girder showing beam theory for longitudinal
strengths problem areas to be given special
attention on board a bulk carrier our upper and lower connection of main side
frames
boundaries of transverse bulkheads and bulkhead stools
cross deck structure
hatch corners and hatch combing brackets
localized cracking and buckling of web frames and breakdown of coating in water
ballast tanks
in there bottom plating and hopper plating intersection
in the system of structural elements of the ship hull a plate represents the
lowest and the hull girder the highest level in between there are in raising
order stiffener girder panel tank
every element serves a local purpose with separate dimension and requirements
and plays roles in various combined systems which finally make up the
complete system in hold and global system of the cargo area all of which
have to meet applicable strengths criteria
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the structural integrity of any ship should be achieved through design
considerations is new observing special requirements to design of areas prone to
significant external or internal forces from cargo or sea maintenance of steel
work particularly in areas with corrosive cargo or ballast water
operation requirements in other words seaworthiness during transport and
loading and or unloading of cargo if poor maintenance one may experience
corrosion cracks buckling of plating
click at the underline words to get more
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we can compare ship to a structure built up of many small beam elements that are
continuously subjected to sea forces and stresses in addition to exposure from
the harsh sea environment and corrosive cargos and ballast water ship strengths
problem through the behavior of simple beams the ship health can be compared to
a beam when assessing the longitudinal strength of the ship the purpose of the
assessment of the ship's longitudinal strengths is to ensure that the ship
will withstand the applicable forces in stillwater condition wave action at sea
the highest longitudinal stresses in deck and bottom structures will normally
take place when the ship is in a loaded condition at sea
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when forces are acting in a longitudinal direction of a beam it will give stress
in tension or compression if a force is acting vertically on the same beam it
will give a bending stress and a shear stress if forces are acting both
longitudinally and vertically on the same beam it will give a combination of
stresses
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examples of types of stresses on a beam are pension
compression bending shear and combination tension and compression
stress in a beam our bending stresses in outer fibers of a beam or in deck or
bottom of a held girder click the different beams to get more information
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the sum of all the forces acting on a beam has to be taken up by the end
support for a beam loaded symmetrically the reaction forces at the supports are
of equal magnitude when the loading of the beam is unsymmetrical the reaction
forces at the supports are of any curved magnet
forces acting on a beam have to be transferred along the beam to the end
supports as a result the beam has to have sufficient cross-sectional area of
the web to take up forces as one moves either way from the mid-span
area or from the position of concentrated forces towards the supports
the distribution of the stress caused by the transferred force show that the web
is the important part and that the middle of the web has maximum stress
when a beam is loaded it will Bend depending on the stiffness of the beam
and whether the ends are prevented from rotating or free to rotate the extreme
bending stresses are experienced in the outer layer of the beam these layers
will either be in compression on the load side or in tension on the other
side the middle layer of the beam is unaffected by the bending
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for a simply supported beam the bending effect is zero at the support since the
ends are free to rotate the inner layers of the beam will be stressed in
compression on the load side and in tension on the opposite side for
built-in beams the effect of bending may be significant at the ends however here
the outer layers of the beam will be stressed in tensions on the load side
and compression on the opposite side
take a look at the hierarchy of the health strengths members we find the
bell girded being built up with plates stiffeners girders panels and finally
tanks comprising the hell girder with fore and aft ship click the house
strengths members to get more information
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a plate is divided into rectangles limited by two parallel stiffeners and
girders the distance between the stiffeners is much less than between the
girders the most significant portion of the pressure forces will be transferred
to the stiffeners only a small force is transferred directly from the plating to
the girders
a strip of the plate will react like a beam this beam will be supported by the
applied stiffness acting like fixed supports the clay is bent between the
fixed supports
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each of the tools supporting stiffeners takes half of the forces transferred
from a strip of the plating all forces apart from the forces transferred
directly to the girder a taken up by the stiffeners
each stiffener functions as a single beam with fixed ends and uniformly
loaded by the forces transferred through the plating
in addition to force is acting perpendicular to the plating
there are also forces acting the plane of the plate as a result of bending of
the hel girder
forces are acting as shown
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when the hell is acting as a beam the applied forces are transferred via
strengths members to the hull girder longitudinal stresses are experienced in
deck and bottom structures at sea when the ship is in hog position the deck
plating will be in tension and bottom plating in compression when the ship is
in Sag position the deck plating will be in compression and bottom plating in
tension the stress distribution will be at a minimum and the hell girder neutral
axis being approximately 1/2 depth and maximum a deck and bottom