questions about scantling (iso 12215 5-6 :2011)

Hello,

I have some questions concerning the interpretation of the ISO 12215-5:2011;

Question 1:

I have to analyze a panel (not rectangular) doing: 2300mm X 500mm
9.1.2 says that does not need to be taken higher than 330 LH

and also, 9.1.3 says that if I you convert a non-rectangular into a
rectangular it must have the same size as the actual panel

Knowing that the boat is a 6 metres, should I take l = 2300 or l = 1980

Question 2:

How to evaluate a stiffener (type omega high) with a variable height
having a inclined base (hull) ?

What value of h should I take?

question 3:

I have a panel l: 900mm and b: 600mm, so l/ b = 1.5

Under section H.2.1, the panel must be analyzed in the two directions,
What does it means?

thank you in advance !

 

Question 1: take l = 1980 mm.

Question 2: take b = 0.93 m2 / 2.3 m = 404 mm

Question 3: Annex H is for the uncommon case where the material is anisotropic (properties in both directions differing by more than 20%).
Plywood is quasi-isotropic; Annex H would apply in specific cases eg wood cold-molding or strip planking.
If really the case, l/b < 2 so the analysis can be done in the direction parallel to the small dimension only (=> apply H2).

 

First of all, this configuration of panel is to be avoided.
You will get stress concentrations at inside corner = formulas, derived far rectangular panels are simply not relevant to the task.

 

if l/b < 2 , the panel must be analyzed so as two-dimensional,
should I use H3 method for stiffeners ?
or H3 table in section H2.1.2, that is to say the panel is analyzed as orthotropic?

 

I shall have done a similar calculation
1.980 m* 0.404 m = 0.8m²
but the real panel measures 0.93m²

What is most important in this case?
panel surface or the length l ?

 

please, no one can help me ?

 

The equivalent panel would normally be 2300 x 404 mm. But length need not be more than 330 LH, so panel can be taken as 1980 x 404 mm.

 

Sorry my mistake. Indeed l/b < 2 => apply H.2.1.12 (analysis in the two dimensions)

 

thank you for your interest in my problems,

For calculating the panel (1980X404), I agree with you.

H3 but for I have some doubts
I think the panel should be Analysed in both directions using H3 (method for stiffeners), because we did not analyze for a band of 1 mm but for the length l.

we need to change and Fd and Md, and to calculate for the entire panel, replace b in all formulas in the table by "AD" (l x b)
this is what I understood, but I'm not certain of that.

we need to use h 2.1.12 for orthotropic panel, when the properties are different in the two directions.
(eg UD layer on panel), but my panel is quasi-isotropic.

please, could explain why you think the opposite ?

 

You can apply H.2.1.12 with EINAl = EINAb. You calculate the two tables H2 with the two bending moments Mdb and Mdl.

H3 is for stiffeners only.

 

LR, DNV, ISO, whatever method, you have to understand the basics of plate analysis.

Plate Analysis (plate bounded by firmly fixed stiffener)
The plate or panel is the area INSIDE the structure bounded by the frame and stiffener. If the sub structure is defined by the span of the frames and the spacing of the stiffener, the base width of the stiffener and frame is to be subtracted to arrive at panel size.

Panel aspect ratio is the length divided by the breadth with 2:1 being the optimal ratio. If the ratio is less than 2:1 or until it is square, a corresponding panel aspect ratio factor is applied to the bending moment.

There are two bending moment used. One is derived from the center of the panel and the second under the base of the stiffener/frame (or the very edge of the panel). Both are multiplied by the Aspect Ratio correction factor if the panel is less than optimum. The bending moment is further modified if the panel is significantly curved. The h is the distance measured perpendicularly from the chord length to the highest point of the curved plating in between two supports.

For simple plate analysis, the bending moment at the center will suffice.
A) It is the assumption that the pressure is delivered at the outer (wet) side with the outermost laminate in compression and the inner laminate in tension.

Plate with stiffener
For plate analysis with stiffener, the stiffener proportions, laminate schedules, and tabbings must be defined according to the rules.

When pressure is applied to the panel as defined in A, the fixed stiffener reacts in the opposite way by resisting as illustrated.

B) The stress of panel at the base of the stiffener is greatest and the outer laminate is in the region of tension and the inner laminate is in compression. The bending moment 2 is applied and the plate laminate is analyzed to INCLUDE the thickness of the stiffener tabbings.

This is the two way test. With A) pressure applied on the outside with the bending moment at the center of panel and B) pressure reversed and maximum bending moment calculated at the base of the stiffener.

Because the laminates are analyzed layer by layer ( I am assuming you are doing the tabulated format) you need to have two spreadsheet for this as the plate laminate schedule for test A is different for test B. Remember also to reverse all compressive/ tensile strength, compressive/ tensile modulus for each layer.

Hope that helps.

 

thank you
what you say is very interesting.
Indeed, it allows me to better understand the behavior of a plate.
for personal purposes, it is interesting to reverse compressive / tensile to see if the panel is ok.

therefore iso 12215-5, is only interested in analyzing the basis of the stiffener (wet ply is stressed in tension).
but does not include the thickness of the ply of the stiffener.


T0x1c,
What changes should I make to the table H2, to analyze this panel:
replace Md by Mdb and Mdl and what else ..?

 

Is it? Why does ISO have two bending moment Mdb and Mdl? What is its definition? I must admit I am not using ISO. Note the illustration I attached is from ISO. It is the same as LR.

LR has two bending moments, Mb (base of stiffener) and Mc (center of panel). At the fick of the button on the program, the laminate schedule automatically reverses. Quick and easy.

A plate with stiffener analysis is another topic. Quite interesting. I see the analysis of LR and ABS is more or less the same.

 

mdl et mdb is used to analyze an orthotropic panel,

it is the bending moment in each direction of the panel

 

someone has an idea to evaluate the stiffeners ...?
the deck is stuck on the top of the stiffeners,
should I evaluate as a bulkhead or a stiffener?