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)

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)

StressRisers!

Modes of Interaction (House not flush, intermediate bulkheads)

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)

Full bulkheadmaintains

shape

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

SHELL PLATINGSTRENGTH DECK

HOUSE DECK

HOUSE DECK

HOUSE SIDE

Cover strip outside

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 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.

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