Shell Stiffeners

[naserrishehri]

Is It A RULE That Shell Stiffeners Must Be Normal To Shell Plate?

[gonzo]

I think you mean "rule". No, they can be at an angle other than 90 degrees.

[naserrishehri]

But I Think Software For Modelling Shell Stiffeners ,model Them Normal To Shell.

[gonzo]

Are you asking about framing for hull plating?

[Ad Hoc]

Originally Posted by naserrishehri

Is It A RULE That Shell Stiffeners Must Be Normal To Shell Plate?

They should be as normal to the plate as possible. Anything less may require an increase in its modulus. Each Classification society is different with the minimum angle the stiffener has with the plate.

Originally Posted by naserrishehri

But I Think Software For Modelling Shell Stiffeners ,model Them Normal To Shell.

That is a software issue. Nothing to do with a "rule requirement".

[ancient kayaker]

It is more efficient from an engineering point of view, making maximum use of the stiffener material and avoiding creation of lateral forces that have to be considered and controlled. But if there is a reason for doing otherwise, just be sure to do it right. Most hull frames and bulkheads, for example, are not normal to the skin, they are normal to the centerline, so it's hardly unusual.

[johngilpin]

Hi there

I think there aren't any right answers to such a broad question.
Structural engineers use tables that give them the bending strength
(modulus) of various sections(z-tables). These are for when load is simply supported, like standing is the middle of a plank supported at either end.
This is strength on one plane only.

Obviously if the ribbing is angled, there is no longer bending in a plane, but other more complicated things to consider. It depends on what is connected to what.

Anyhow right angles stiffeners would seem the most logical.

Please see my stiffener plates.

Cheers

[nemo]

Originally Posted by naserrishehri

Is It A RULE That Shell Stiffeners Must Be Normal To Shell Plate?

No, there isn't a RULE. They are just more efficient if placed normal to the shell plate. If they are placed at a different angle, the bending plane is no longer aligned to a principal axis of Inertia, so generally it means that the scantling of the stiffener will be larger.
However, on large ships it is sometimes preferable to have bigger horizontal side shell stiffeners, rather than normal to shell plate, as they need only to be bent and not twisted, hence there is a building advantage.

[naserrishehri]

dear nemo
thanks a lot for your reply.really i want to make a 3d model of a ship and i want to start with shell and stiffeners on it.i have only approval plans as reference and the software (foran) don't ask me the angle of stiffeners and designer don't show that angle .
what should i do?

[naserrishehri]

Originally Posted by gonzo

Are you asking about framing for hull plating?

yes i ask about longitudinal profiles on shell.

[naserrishehri]

Originally Posted by Ad Hoc

They should be as normal to the plate as possible. Anything less may require an increase in its modulus. Each Classification society is different with the minimum angle the stiffener has with the plate.



That is a software issue. Nothing to do with a "rule requirement".

i think softwares model longitudinal shell profiles normal to shell automatically .do you believe it?

[gonzo]

Then you need new software. A ship designed like that may be correct from a computer programmer's viewpoint, but from a shipwright's it it an expensive nightmare.

[Ad Hoc]

Originally Posted by naserrishehri

i think softwares model longitudinal shell profiles normal to shell automatically .do you believe it?

Depends on the software and how it copes with stiffeners and frames. But you should be able to do what you want. If the software wont let you..it is crap software.

[Perm Stress]

Originally Posted by naserrishehri

i think softwares model longitudinal shell profiles normal to shell automatically .do you believe it?

Normally there should be stiffener orientation settings: relative shell (angle), relative to baseline (angle), or similar. Probably default setting is 90 "degrees to shell". But it should not be the only one.

Read the manual!