Deck Beams

Deck Beams

• athwart ship member located under the deck plating

• usually fitted on every frame• more desirable to fit extra beams then to increase

thickness of deck plates• fastened to the frames by beam brackets

– frames act as pillars (vertical members) – carry load downward, where it is distributed over the

bottom by the floors

Three Primary Functions of Beams

• acts as a beam to support vertical deck loads

• acts as a tie to keep the sides of a ship in place – sagging (sides want to

move away from each other)

– hogging (sides want to move toward each other)

Three Primary Functions

• acts to keep the deck plating from wrinkling due to the twisting action on the vessel as the ship sails at an angle to a heavy sea– the twisting action is called racking

Deck Beams

• beams act as tie (top)

• keeps deck plating from wrinkling (bottom)

Racking

• concentration of stress occurs at the beam brackets (the upper corners of the ship)– beam brackets

– transverse bulkheads

– web frames• all help to resist

this stress

Racking

• concentration of stress also in bottom corners during racking– tank side brackets help

resist this stress

Beam Brackets

• fix end of beam to frames– uniformly distributed loads on a fixed-ended

beam• at ends: BM=WL/12

• in middle: BM=WL/24

• helps explain need for beam brackets

Beam Brackets

• a bracketed beam tends to check racking (twisting) of the hull

Beam Size

• depends on beam spacing– more beams translates to smaller beam size

• less depth of beams = more headroom

– fewer beams translates to larger beam size• more depth of beams = less headroom

Weather Deck Beams

• beams under the deck exposed to the weather (weather-deck) are of heavier scantling then would be used elsewhere– due to tremendous weights involved when the

vessel ships green water over the weather deck• tanker’s weather deck is the main-deck

http://www.flickr.com/photo_zoom.gne?id=370320910&size=o

Beam Size

• also depends on the number and size of other structural members of the vessel– pillars– girders– thickness of plating– height between deck

Camber

• water on deck will run toward the stringer strake (outboard) and into the scuppers (drains) and falls overboard

• measured at the centerline

• beams and plating are arched upward

Standard Camber

• standard camber is 1/50 of the beam– vessel with 150 foot beam will have 3 feet of

camber• camber is measured in inches per beam of ship

– 36 inches per 150 foot beam

» I will see only half of you if we each stand on the stringer strakes on opposite sides of a vessel whose beam is 150 feet!