pillars

[mind_huntr7]

how do i know i need to use pillars although i have webframes,deck girders?

[rxcomposite]

you must know the elements of boat strength. A pillar supports the girders and/or the load above the deck it is supporting. It is used to reduce the "size" of the girders. So if your girder span is capable of supporting the load, you don't need a pillar.

A pillar is not necessarily a post (round, rectangular, or H beam) because if the bulkheads are close together, a pillar can be integrated into a bulkhead commonly known as the bulkhead pillar.

[gonzo]

Basically, as rxcomposite said, it depends on the structure you designed. It can be either.

[mind_huntr7]

well, lets say i have ship her breadth 24 meter, 3 deck girders, each girder depth is 600mm and thickness is 10mm, webframes every 3 meters 600mm depth and thickness is 10mm, load on deck 3t/m^2, i will need pillars?

[rxcomposite]

24 meter breadth? Is that a VLCC tanker in the seawaymax class of 60,000 DWT?

[mind_huntr7]

barge

[rxcomposite]

The classic bending stress (σ) at any point in the beam is σ=M/I x y where
M= bending moment
y= distance of point considered from the neutral axis
I= second moment of area of cross sectional area of beam about the neutral axis

To be sure we are on the same page, we are talking of transversely framed (strength) deck 24 meter wide with three primary stiffeners (girders) spaced 6 meter apart (or slightly less), with deck beams spaced 3 meter apart. The web depth is 600 mm., 10 mm. thick. I added a flange (T web) 200mm wide, 20 mm. thick mild steel.

1 MT = 9.8 kN, so 3 MT/m2=29kN/m2 pressure on deck.

There are many variables, and I got lazy so I fed it the data into a stress analysis program. With the section stated above, you need to support the girder every 4 meters, 6 meter if you reduce your cargo (deck) pressure by 18kN/m2.

Question. Since this is a barge, there will be an opening. What will the center pillar support if you cut open the deck for the hatch? Seems three primary longitudinal is not a good number unless your hatch is less than 4/6 meter on the long side.

[mind_huntr7]

well, did u calculate the transverse web frame every 3 meters same section as main deck girders, it supports the girders!

[rxcomposite]

Sorry it doesn't work that way. The pillar supports the girder, the girder supports the deck beams, and the deck beams in conjunction with the deck plating supports the deck load.

You must be confused with longitudinaly framed craft where the deck transverses (the big ones running accross) are the ones supported by the pillars. with the smaller deck longitudinals (not girders) running along the length of the boat.

[mind_huntr7]

well,
deck longi framed spaced 0.750 meter section equal L 150x10 , supported by transverse webfame T section web 600mmx10 mm every 3 meters, 3 deck girders T section web 600mmx10 mm every 6meters

[rxcomposite]

That is a longitudinally framed deck. The calculations remains pretty much the same. With your 24 meter span and 3 meter spacing, you need to support it with at least 2 pillars. Good design practice requires that the pillars be allgined with your girders which does not appear so.

With very little information, I would assume it is a deck barge, no hatch opening,

[mind_huntr7]

so, it will b the same if i change the deck girders by longitudinals?!

[rxcomposite]

The fixed beam formula remains basically the same the same. If you analyze the longitudinals, it is now supported by the transverses 3 meter apart. So the span of the longis are now only 3 meter with closer spacing.

Of course when you cut the deck to make way for an opening such as a cargo hatch, the transverses will be reduced in length and the formula for the transverse will change to a partially fixed beam. The ends fixed to the side frames by brackets and the other end partially supported by the hatch coaming or bigger longitudinals (or girders if you like to call it).