Hull – Superstructure Interaction

Types of Interactions
 Flush Deckhouse
 No bulkheads at ends
 Bulkheads at ends

Research and Analysis (FEA)

Expansion Joints

Aluminum Superstructures
 Joining techniques
 Case Studies
Types of Interaction (House flush with side)

The superstructure bends with the hull as one
hull-girder
 May consider contribution to longitudinal strength
through Moment of Inertia
Types of Interaction
(House not flush/no intermediate bulkheads)
Stress
Risers!



Deck beams are flexible; deckhouse acts independent of
hull
Hogging and sagging puts large stresses on connection
points
Best to terminate deckhouse with WT bulkhead (and/or
longitudinal bulkhead or significant deck girders)
Modes of Interaction
(House not flush, intermediate bulkheads)
Full
bulkhead
maintains
shape



Intermediate bulkhead forces superstructure
to undergo same deflection as the hull
Between bulkheads the strain diminishes
Can cause large “lift off” forces at bottom of
deckhouse (particularly the ends)– must be
considered in design (fatigue analysis)
Design of Deckhouses

ABS Rules require that deckhouses with lengths
greater than 10% of ship’s length located at midships
have longitudinal members large enough to give a
hull-girder section modulus in the deckhouse equal to
that of the hull girder.
 Usually design hull girder alone to withstand
bending moments without the deckhouse
 Method is sound but conservative
Research and Analysis


Non-linear stress distributions in deckhouse – Bleich
Shear and shear lag effects at deckhouse/hull –
Schade

Full scale tests on SS President Wilson – Vasta

FEA (only area currently active)
Expansion Joints


Joints are cut in the superstructure above the main
deck (strength deck). Bolted joints with slots
sometimes used, or simply slit with waterproof cover.
Relieves deckhouse longitudinal bending stress so
that it acts independent of hull.
 Allows deckhouse to be designed for vertical loads
and racking stresses.
 Saves significant weight topside
Expansion Joints
HOUSE DECK
Cover strip outside
HOUSE DECK
HOUSE SIDE
STRENGTH DECK
SHELL
PLATING
Flat bar face around
circular cut at bottom of
expansion joint
Use of Expansion Joints



Must be spaced close enough to relieve deckhouse
bending stresses
They introduce severe concentrations of stress at the
bottom of the joints
Can lead to creaking and leaking in seaway if joining
details not properly designed.
Aluminum in Deckhouses

Advantages
 As strong as steel but Elastic Modulus 1/3 that of steel  stresses
are 1/3 of that in steel  may eliminate need for expansion joints
 Almost 2/3 reduction in weight over mild steel  lowers weight of
structure and KG  improves stability

Disadvantages
 Coefficient of thermal expansion almost double that of steel  may
cause distortions with temperature variations in service
 Aluminum loses strength at elevated temperatures  detrimental to
damage control
 Can lead to galvanic corrosion with steel
 Difficult to join to steel structures (explosive or biweldable joints)
 More expensive than mild steel
 Potential brittleness of high strength aluminum
Aluminum Steel Joining Techniques

Rivets/Bolts

Explosion Bonding
 Process uses an explosive detonation as the energy source to produce
a metallurgical bond between metal components. One of the metals is
accelerated by explosive detonation at a very high rate over a short
distance resulting in a progressive collision of the materials.
 The metals are forced together under several million psi pressure
creating an electron-sharing bond that is typically stronger that the
weaker of the parent metals.
 Due to its use of explosive energy, the process occurs extremely fast;
unlike conventional welding processes, parameters cannot be finetuned during the bonding operation.
 The bonded product quality is assured through selection of proper
process parameters: material surface preparation, plate separation
distance prior to bonding, and explosive load, velocity, and detonation
energy.

Biweldable strips (2002)
Source: Clad Metal Division - Dynamic Materials Corp.
Aluminum in Naval Warships

U.S. Warships
 Prior to DDG-51 most warships used aluminum in their
superstructures for its various advantages
 1975: USS Belknap collided with USS John F. Kennedy and
a major fire broke out on Belknap that melted most of its
superstructure
 1991: USS Princeton detonated an Italian-made MRP
acoustic mine under the ship’s quarterdeck. The blast
detonated another mine three-hundred yards off the
starboard beam.
» A six-inch crack opened in the Princeton’s aluminum
superstructure running up one side and down the other. More
than 10% of the superstructure separated from the main deck.
USS Belknap - 1975
NAVSEA Inspection Procedure
Inspection Guidelines
USS Radford (DD 968) collision (1999)
Split at bi-metallic joint in deck house frame 174