A question on spot-weld density on plates

[Angre]

Hi All,

I need a 6mm thick steel from strength point of view.
The fabricator does not have the capacity to bend 6mm thk plates.

Instead fabricator is proposing to use 2 nos. 3mm plates, bend them and use them on top of each other.
Spot welding will be used to ensure 2 nos. 3mm plates will act without slipping by each other, and thus shall have the strength of single 6mm thk plate.

How do I go about specifying the size and center to center distance of spot welds.

I have a good idea about calculation shear transfer in a I-beam, and know all about V.Q/I.t stuff, but Iam stumped when faced with a similar situation in case of plates.

Thanks

 

[kingnero]

What is the application, what are the loads?
For anything structural, it has to be raining in hell first before I would allow that.

 

[TehMightyEngineer]

Shear flow in plates is just the same as shear flow in two rectangular wood beams. Divide the plate up into small widths, equal to your weld spacing to make it simple. Also, rather than use spot welds (which I'm with kingnero on, they have zero design strength) use plug welds.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[Angre]

Hello KingNero

Your reaction is well justified.

The plates will be used for door frames. The doors are blast resistant and will resist 0.4 bar of overpressure , the design pressure being 0.4 x 4 = 1.6 bar = 16 tons/sqm.
The plates will be bent to produce a hollow box section.

To overcome the self-scepticism, I'm putting in a requirement, that the frame be filled with grout.The fabricator is willing to go along with grouting.
To keep things simple,I want to design the thing as hollow section, with grout being a extra measure of safety.
My judgement indicates that grout will add a lot of strength, but since it is not quantifiablle using standard calculations, I cant use it to my advantage in the design.
Hope that you have picture .

Thanks