Hull

1
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

2
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

3
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)

4
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)

5
Design of Deckhouses

• ABS Rules require that deckhouses with lengths
  greater than 10 of ships 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

6
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)

7
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

8
Expansion Joints
9
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.

10
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

11
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
  fine-tuned 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.
12
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 ships quarterdeck. The
  blast detonated another mine three-hundred yards
  off the starboard beam.
• A six-inch crack opened in the Princetons
  aluminum superstructure running up one side and
  down the other. More than 10 of the
  superstructure separated from the main deck.

13
USS Belknap - 1975
14
NAVSEA Inspection Procedure
15
Inspection Guidelines
16
USS Radford (DD 968) collision (1999)
Split at bi-metallic joint in deck house frame 174