Module 6 : Framing Systems Flashcards
Longitudinal bending of the hull girder will induce stresses in the fore-and-aft direction
Caused by buoyancy and weight distribution of the vessel as well as wave action
Tranversely framed panel with have 1/4 of the strength of a longitundinally framed vessel of the same size and thickness
Due to thin shell plate being susceptible to buckling and due to the orientation of the stiffeners.
As a result, tranversely framed vessels tend to have thicker plating.
Hybrid / combined framing
Uses both tranverse and longitudinal framing within the same section. Generally longitudinal framing for some or all of the decks and the remainder is transversely framed.
Transverse Framing
Closely spaced frames, rule of thumb is 600 mm apart.
Used on vessels requiring considerable transverse strength and not overly prone to longitudinal bending like tugs, small utility vessels, general cargo vessels.
Used primarily for ships of less than 120 m in length. The floors, frames and beams form rings spaced closely together.
Longitudinal strength is provided by the keel, centre girder, side girders, deck girders, the entire bottom, deck plating and side shell plating.
Provides good cross-sectional strength to handle overall stresses, vertical loads, rolling, and dry docking.
However, on very long ships, sheer stresses can cause deformations between the rings.
Pillars will be used to tie the structure together vertically.
Deck beams are transverse members that connect the top ends of the frames, forming the transverse framing for the deck. The side shell framing is a combination of ordinary frames (offset bulb bar) and web frames (fabricated T section), supplemented by horizontal stringers and bulkheads.
Large brackets called beam knees are used to connect the side and the deck structure. Deck strengthening is transverse using ordinary beams (bulb bar or angle bar), strong beams (fabricated T shaped sections), and half beams (bulb bar or angle bar) with suitable longitudinal girders for extra support.
Gusset : bracket mounted horizontally
Double bottoms
- Maintain ship’s watertight integrity when the bottom is damaged
- Greatly increase longitudinal strength
- Forms a platform to carry cargo and machinery
Transversely framed double bottom
- No longitudinals
Will have appropriate strengthening in high stress areas (e.g. keel, round of bilge)
Composed of center girder, various number of side girders, three types of floors (solid, bracket, watertight), maybe a margin plate, many brackets and flat bars. If having a margin plate, will have a margin bracket for smooth transition between bottom and side structure. NO margin plate is safety, will prevent entry of water in the event of a hole in the turn of the bilge
Longitudinal Framing
AKA Isherwood system and used in vessels prone to longitudinal bending (> 120 m).
Mandatory for very large ships, oil tankers and bulk-ore carriers.
The rings are formed by floors, deck beams and web frames and are further apart than in transverse framing.
Longitudinal reinforcement members are deck girders, girders, the keel, bulkheads, the deck, and a large number of slender deck, bottom, and side longitudinals (bulb bar or angle bar). The longitudinals will end at plates called crutches.
Longitudinal framing and stiffening in the cargo area tends to trap liquid. Must take care to properly drain liquid from top side of longitudinals and stringers to avoid contamination and/or corrosion. May mitigate with ceiling or longitudinal bulkhead.
Longitudinal bulkheads fitted to provide side compartments in double hull construction. Will be fitted with a large number of web or diaphragm plates to construct very rigid transverse structure. Can also be used for ballast or to further segregate cargo.
The deck incorporates deck longitudinals, deck tranverses, and a system of longitudinal girders. Transition from the margin plate to the side structure as well as from side structure to deck will be in the form of large brackets extending to the first longitudinal.
Side shell stiffening uses a system of side longitudinals, side stringers, supported by web frames.
Longitudinally framed double bottom
Similar to transverse, has appropriate strengthening in high stress areas.
Torsion Box
Solid plate with a hole, located at every frame space for the length of the vessel. Connected through continuous longitudinals located within the box.
Increase strength (longitudinal and torsion).
Done to give smooth surface for TEU to slide down.
Combined / Hybrid / Mixed Framing System
Less cargo carrying, want to increase strength.
The most common combination is longitudinal framing for the bottom and the deck, and the transverse framing for the sides.
Often seen on ice and arctic class ships.
Bulk Carriers
Commonly fitted with a combined framing system since it provides the required longitudinal strength to the hull while preventing cargo from getting caught on the side structure.
Normally see wing tanks and hoppers fitted with large amounts of longitudinals to offset the longitudinal bending. May also fit web or diaphragm plates at regular intervals within the hopper or wing tank.
Wing tanks located at top and used for storage of liquid.
Hoppers located at bottom, form part of double bottom.
