2. OBJECTIVES:
Specific:
To define what is point load and distributive load.
General:
To know how the load was spread and the
important of distribution of load to the loading
system on-board the ship.
3. What is a point load?
-In the field of engineering, a point load is a
load applied to a single, specific point on a
structural member. It is also known as a
concentrated load, and an example of it
would be a hammer hitting a single nail into a
beam.
4. What is an uniformly distributed load?
-A uniformly distributed load has a constant
value, for example, 1kN/m; hence the
"uniform" distribution of the load. Each
uniformly distributed load can be changed to
a simple point force that can be used to
determine the stresses in an object.
5. The alternative to a point load is a distributed
load. As the term implies, the force in a
distributed load is applied across a given area
rather than at a single point. An example would
be water in a river that comes up against a dam;
the pressure or force of the water is distributed
fairly evenly over the entire width of the dam.
The differences between point loads and distributed
loads become important in the analysis of a
structure. In simple construction, the joist is a beam
that distributes weight across the length of the
beam.
6. . An unsupported beam-to-beam connection
is a point load and a potential weakness in
the structure. If too much weight or force is
concentrated on a specific point, it can cause
a beam to snap, and there can be other
catastrophic damage to the overall structure.
In construction, a point load is reserved only
for lighter structures or other cases in which
the load or force is relatively light and not
subject to undue stresses.To maintain
structural integrity, designs and blueprints
are engineered to avoid the use of point loads
in other situations.
7. Point-loading and uneven distribution of
cargo weight can, and frequently does, cause
unnecessary damage to decks and hatch
covers. Unless the weather-deck has been
specially strengthened, it is unlikely to have a
maximum permissible weight-loading of
more than 3tonnes/m².
8. Similarly, unless hatch covers have been
specially strengthened, it is unlikely they will
have a maximum permissible weight-loading
of more than 1.8tonnes/m².The ship’s
capacity plan/or general arrangement plan
should always be consulted. If the
information is not there, try the ship’s
stability booklet.
9. In the event that specific values are not
available onboard the ship, allow no more
than 2.5tonnes/m² for weather-deck areas;
and no more than 0.75tonnes/m² for hatch
covers in small vessels; 1.30tonnes/m² in
vessels over 100m in length. (The word tonnef
used later in this article means tonnes force.)
10. •The adverse effects of point-loading are
not always fully appreciated. On the other
hand, a 6 tonne machine with a flat-bed
area of 3m² will exert a down-load of
2tonnes/m².
11. When exceptionally heavy weights are to
be carried, it may be necessary to shore-up
the weather-deck from below ; but, again,
care must be taken to spread the load on
the tween decks so as not to overload that
plating.
12. In the not so dense range of cargoes, units of
20 to 40 tonnes weight are common today,
and stacking of unit weights is widespread. If
a piece of machinery weighing , say, 30
tonnes with a base area of 6m² is placed
direct on the weather-deck the point-loading
will be 30/6=5tonnes/m².
13. If, however, the deck plating has a maximum
permissible loading of 2.5 tonnes/m² then the
minimum area over which that 30 tonnes load
must be spread is 30/2.5=12m².
14. Good dunnage must be used to spread the
load, and it is always good practice to add 5%
to the weight to be loaded before working
out the dunnage area. For the 30 tonne
weight, for instance, 31.5 tonnes would be
used and the dunnage area would go from
12m² to 12.6 m².
15. Dunnage timber is often no more than 6”×1”
(150×25mm) rough planking; but where
weighty cargo items are involved dunnage
should not be less than 50mm(2”) thickness ×
150mm(6”) width and preferably 75mm(3”) ×
225mm(9”). It is acceptable, however, to used
two dunnage planks nailed together securely
to make up the thickness.
16. A dunnage width greater than 150mm is
always acceptable-225mm(9”) to
305mm(12”), for instance; but where the
thickness goes to 75mm(3”) care must be
taken to choose straight-grained timbers of
as great a width as possible, and to ensure
that they are laid with the grain horizontal
and parallel with the deck.
17. There have been incidents in the past where
what appeared to have been a soundly
dunnaged and well-secured item of deck
cargo broke adrift and was lost overboard
due to a sequence of events commencing
with the collapse of 3”×3” dunnage timbers
along the curved grain used on its edge,
followed by consequential slackness in
otherwise adequate lashing arrangements,
followed by increasingly accelerated cargo
movement and finally breakage of the
lashings.
19. Because of the random nature of grain
configurations in the thicker dunnage timbers
it is acceptable to achieve thicknesses by
nailing planks together. A 2” thick dunnage
timber can be made up using 1” thick planks,
and a 3” thick dunnage timber can be made
up using 2” and 1” thick timber planks, all
securely nailed together.
20. To a large degree, this will correct the
tendency for separation in timber with a
bably-alligned grain. And remember, it will be
as important to install good lower-level foot
lashing as it will be to install downward-
leading lashings if load-spreading dunnage is
to remain fully effective.
21. A lashing is an arrangement of rope wire or
webbing with linking device used to secure
and fasten two or more items together in a
somewhat rigid manner. Lashings are most
commonly applied to timber poles, and are
commonly associated with the cargo,
containerisation, the Scouting movement,
and with sailors.
23. SUMMARY:
Proper loading and distribution of cargo
weight can maximize the strength of the
ship. Point loading is necessary to avoid
damages to deck and hatchcovers and it also
prevent accidents.When exceptionally heavy
weights are to be load, it may be effective to
spread the weight of the load on the decks as
to not to overload that plating. In spreading
the load, we can used lashing to secured the
load for the equal distribution, effective and
safe loading of cargoes on-board the vessel.
24. QUESTIONS
1. What is point loading?
2. What is its importance to the loading of
cargoes?
3. Define uneven distribution of cargo weight?
4. How does lashing secure the load?
25. ASSIGNMENT
1. Give other examples on how to avoid
damage on decks due to uneven distribution
of cargo weight.
2. Site some incidents that was caused by
uneven loading of cargoes.
