The learning objectives of this section are to make shipboard operational
personnel familiar with how external forces act on the hel girder the effect
of local forces applied on internal structures in critical areas as a beam
the hel girder has to have sufficient cross-section material in the cargo area
in the midship area the longitudinal stresses in deck and bottom experience
in the plating as well in the longitudinal deck and bottom stiffeners
the highest stresses are experienced in flanges on top of longitudinal strengths
members
assessing local sea forces from the bridge is difficult basis for decisions
on appropriate speed and course are factors as bow impact green water on
deck bottom slamming exercising proper judgment does not prevent some
structural elements from being more exposed to sea forces than others making
damages more probable in certain areas as indicated above
you
we will now show you some examples of local strengths of structures the
transverse bottom web frame in a single skin oil tanker transverse bulkhead in a
bulk carrier transfers web frame ring in a single skin oil tanker horizontal
stringing we will now study the transverse bottom web frame in an oil
tanker the water pressure is acting at the bottom and a liquid pressure is
acting on the side of the tank the forces are distributed to the girders
and stiffeners the change of direction of the girder will result in a stress
concentration at the transition which may lead to cracks to avoid the stress
concentration brackets are introduced to smoothen the transition areas in a
construction
the hopper tank has the ability to withstand bending and torsion forces and
they support the flow of the Deborah bottom in bulk carriers constructed
without a single flaw the girders are supported by the transverse hold
bulkheads large forces are transferred to these panels instead of the size of
the ship normally through the lower stools
we will now study the transfers web frame of a single skin oil tanker
hardpoints would occur where stiffeners are crossing the web frames particular
hard points are found where cross ties are fitted
they are axially loaded in tension and compression but vertical forces and
bending moments will also occur
you
brackets must always be entering stiffeners and never end on open or not
stiffen plates
you
we will now study the transfers web frame of a single skinning oil tanker
hardpoints would occur where stiffeners are crossing the web frames particular
hard points are found where cross ties are fitted they are axially loaded in
tension and compression but vertical forces and bending moments will also
occur
brackets must always be entering stiffeners and never end on open or not
stiffen plates
you
horizontal stringer at the forward side of the cargo vessel is another example
of a highly stressed area frames are supported by the horizontal stringers
and transferring some of the forces acting on them the most stressed areas
of the stringers are at the intersection between frames and stringer web and in
the connections at the stringer ends
over pressurizing of a tank will lead to an excessive pressure inside the tank
this may happen if the loading rate is too fast or the pressure becomes too
high when the pressure on the tank becomes too high and the stress on the
structure Rises this will eventually lead to buckling of the structure in the
tank like tank top and bulkhead
the vessel is entering the port with ballasts in holes three and six in
addition to permanent ballast tanks hatch combing must be below cargo chute
loading is started without the ballasting tank three and six and the
vessel is slightly sagged the sagging is getting worse the deck is now in high
compression and the tension in the bottom structure is considerable the
deck longitudinal and deck plating start to buckle cracking starts in the bottom
structure and works upwards in side plating which finally will cause
collapse of the hell girder
you