Chalmers University of Technology
Contents - Lecture 1
• General introduction to ship structures and loads.
– Introduction.
– The anatomy of the ship: structural functions of elements.
• The hull girder.
• Primary strength elements.
• Secondary strength elements.
• Bottom structures.
• Deck structures.
• Side structures.
• Transverse bulkheads.
• Fore ship and stern.
• Details.
– Different types of loads that act on the ship.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 1 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
Introduction
• Cargo carrying ships are designed with optimum transport
work as the main design goal.
– The main dimensions of the ship, the general arrangement etc are
determined with this purpose and safety and environmental requirements
as boundary conditions.
• The structural design is made after the general
arrangement.
• The weight of the ship hull structure and the building
costs are very important for the total ship capital cost and
future earning capacity.
– Optimisation of the hull structure is usually made within the
classification rules, i.e. without endangering the safety.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 2 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
Introduction
• The design solution is more or less based on
experiences.
• The classification rulebooks are descriptions of
“survivors”.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 3 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
SSBC 2006
• Beam theory
Global structural (bending and twisting)
effects • Classification rules
• FE analysis
SSAC 2007
• Plate theory and
Local structural effective breadth of
effects stiffened plating
• Buckling
• FE analysis
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 4 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
Shell behaviour – effective breadth
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 5 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
Stiffened plate – effective breadth
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 6 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
• Skin plate of deck, sides and bottom:
– Geometric boundaries to the ship hull girder.
– Skin plates are supported by longitudinal or transverse stiffeners in
order to make them stiff to carry planeloads without buckling and also to
carry lateral load without too large stresses and deflections.
• Transverse bulkhead:
– Maintains the shape of the hull girder. It also subdivides the tanks in
different dedicated spaces, i.e. cargo holds or ballast tanks.
• Bottom plate:
– Takes lateral loads, e.g. water pressure. These loads are distributed and
transferred into the ship structure via longitudinal stiffeners to the
structural members of the hull girder.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 7 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 8 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 9 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
The hull girder
• The hull girder is the highest level.
– All local differences between external and internal loads will in the end
be seen as shear forces and bending moments in the hull girder.
– The hull girder can be seen as one large beam, where the side shell is
web plates and the deck and the bottom structures are flanges.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 10 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
The hull girder
• The design of the hull girder is normally
driven by the vertical bending moment.
• The longitudinally oriented stresses are
derived from the total bending moment.
– The longitudinal strength of the girder is
determined by its section modulus.
– All structural elements with continuous reach in
the longitudinal direction contribute to the
stiffness and strength of the hull girder.
• Deck and bottom structures have the most
significant influence on the section modulus as
they are far from the neutral axis.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 11 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
The hull girder
Bulk ship with
single skin
Dry cargo ship with
longitudinal framing
Tanker with
single skin
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 12 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
Primary strength elements
• Objective with primary strength elements:
– To maintain the shape of the hull girder on the local level.
• Deck transverse or deck beam.
• Web, main frame, vertical web side.
• Stringer.
• Longitudinal girder.
• Floor or bottom structure.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 13 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
Secondary strength elements
• Objective with secondary strength elements:
– To support the plates to maintain their shape and to limit the spacing in
order to keep plate stresses within reasonable values.
• Stiffeners.
• Beams.
• Longitudinals.
• Stays.
• Tripping brackets.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 14 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
Secondary strength elements – stiffeners
• The purpose of stiffeners is to prevent the plate areas of a
ship from distorting under the influence of the shearing
loads, bending moments, and local loads.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 15 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
Secondary strength elements – stiffeners
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 16 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
Bottom structures
• Today, most commercial ships are built with double
bottom.
– Beneficial from a strength point of view as the external bottom and the
inner bottom plating are effectively utilised as flanges to the primary
structural members (girders and floors).
– From environmental point of view, double bottom is preferred instead of
single bottom in order to prevent oil spill at e.g. grounding.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 17 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
Bottom structures
• The main (local) loads comes • Bottom girder (CL-and side girders):
from lateral pressure, e.g.: – The CL-girder supports the ship in the
– external hydrostatic load, and/or dry docking condition.
– load/pressure from cargo. – Girders redistribute loads on one floor
to neighbouring floors in the case of
very local cargo loads.
• Bottom longitudinals
contribute a lot to the global
hull girder section modulus.
• Floors reach between
longitudinal bulkheads and side
shells.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 18 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
Deck structures
• The total area of the deck plating and longitudinal
members of the deck are mainly determined by the
explicit contribution to the hull girder section modulus.
• The worst stresses of the hull girder will appear in the
“shear strake”, i.e. the plate that connects the side shell
and the deck plate.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 19 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
Deck structures
• Large container ships may have difficulties to achieve
enough material in the deck to get section modulus.
– This is due to the requirement of vertical load handling with very large
hatch openings.
• Local lateral load on Ro-Ro decks may be quite severe
due to wheel loads from e.g. trucks.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 20 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
Side structures
• When the hull girder is exposed to vertical loading, the
side structures are the shear elements of the structure.
– The plate thickness is needed to maintain reasonable shear stresses.
– The side structure must also be able to withstand external hydrostatic
and wave pressure loads.
– Torsion rigidity is enhanced by double skin structure compared with
single skin structure.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 21 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
Transverse bulkheads
• The function of a transverse bulkhead can vary:
– Subdivision into several tanks (tank bulkhead).
– Strength bulkhead: main function is to maintain the shape of the hull girder.
– Swash bulkhead to reduce problem with waves in cargo holds.
– Collision bulkhead (usually placed 0.05L - 0.08L aft of FP).
– Aft peak bulkhead.
– Engine room bulkhead.
Shear flow in single
skin structure
Single skin Double skin
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 22 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
Fore ship and stern
• Fore ship • Stern
– Is subjected to large pressure from – Is determined by stiffness criteria in
the waves and from the pitching order to avoid vibration from the
motion of the ship. The ship must engine room and the propeller.
be strengthened against these loads. – Web frames are deeper around the
– Slamming loads may also occur. engine and the floors are usually
– Ice strengthening may require located on each frame to increase
frames between the original frames, stiffness.
intermediate frames, in addition to a
thicker plate.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 23 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
Fore ship and stern
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 24 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
The anatomy of the ship
Details
• To avoid structural damage, all
details need to be considered.
• Details may fail due to overload
but more frequently die to
fatigue.
• Continuity and smooth notches
are the keys to low stress
concentrations in the hull girder
and in all members of the ship
that are subjected to dynamic
loads.
– Dynamic loads may come from
waves or from propulsion and
engine.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 25 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
Different types of loads
that act on the ship
• The deterministic load conditions • Dynamic loads (causes both local
given by the classification societies and global loads)
are to be seen as useful for – Wave induced loads:
assessment rather than real load • Variation in wave induced pressure
cases. due to waves and the ship motions.
• Variation in the inertia forces caused
by the motion of the ship in waves.
• Static loads • Vibration
– Still water loads: – Global vibration:
• Global (loads that affect the hull • The hull girder performs modal
girder). vibration like a beam the first ten
• Local (loads that affect the local modes being vertical hull girder
structures like plates, stiffeners and bending modes.
frames)
– Local vibrations:
– Frequency • From engine and propellers.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 26 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
Different types of loads
that act on the ship
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 27 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
Different types of loads
that act on the ship
Global static loads and
wave influence:
x1
V ( x1 ) = ∫ [b( x) − w( x)]dx
0
x1
M ( x1 ) = ∫ V ( x)dx
0
In engineering work:
∫ → ∑
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 28 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
Different types of loads
that act on the ship
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 29 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
Different types of loads
that act on the ship
Stress distribution and
deflection simulation using
the finite element method.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 30 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
Chalmers University of Technology
Different types of loads
that act on the ship
• Strength criteria:
– Collapse (buckling, yielding, brittle fracture).
– Fatigue.
Department of Shipping and Marine Technology Ship Structures Advanced Course 2007, p. 31 (31)
Division of Ship Design and Engineering LECTURE 1 Associate Professor Jonas Ringsberg
