ABS Part 3 - Aluminum Hull

Hi,
According to Part 3 , Ch. 1, Sec. 2, 1.3.3
Design Consideration
Where scantlings are reduced in association with the use of higher-strength steel or where aluminum alloys are used, adequate buckling strength is to be provided. Where it is intended to use material of cold flanging quality for important longitudinal strength members, this steel is to be indicated on the plans.

How exactly do I reduce the scantlings when the hull and its framings are in aluminum? As I understand most of the formulas in this ruleset is made for Steel.

or is there any other Rules By ABS that I just have not seen.

 

You don't reduce it, because the rule says so.
What it means is that when you use materials that are of a strength higher than the 'standard' strength of the material, such as HTS rather than Grade A steel, any reduction in scantling - because of the higher strength material - you must check for buckling.
Since going thinner, to save weight, by using a higher strength material comes at the expense of buckling...as a thinner structural member becomes more prone to buckling.
That's all it means.

 

Hi Ad Hoc! Thank you for your reply.
When you frame it like that. It is that way, my bad.
But what I mean is I am going to use an aluminum alloy with a min. yield of 125mpa. as opposed to the standard steel which is about 235 mpa.

 

You use the strength of the alloy/metal that is given.....so the question is, what material are you using?
And there is your answer.

 

Hi Ad Hoc,
I have to clarify. Because I am still quite confused.
in ABS rules (For Building and classing marine vessels)
Part 3, Chapter 1, Section 2, 1.3
It does state that
"The use of aluminum alloys in hull structures is to be considered upon submission of a specification of the proposed alloys and their proposed method of fabrication. "

Just to give an example. in Part 3, Chapter 2, Section 3, 5.1 (Deck Thickness). The formula is just stated without any modifiers for Stl or aluminum. But I would imagine a commonly soft material like aluminum would require a thicker requirement.

Thank you again for spending time on this.

 

Once you calculate the deck pressures, using their rules, and then which material you will use and then the formula associated with said deck pressure to arrive at a thickness for the deck,.... if that thickness you just calculated, is less than the minimum requirement noted in 5.1, you default to that minimum requirement.
It is basic Class rules cross checking...to ensure a calculated thickness, does not fall below a minimum required standard.

It is a minimum thickness requirement, nothing else.

 

Hi Ad hoc.
This clears that up. Thank you.