Shear capacity - stainless thin sheet

[drscottuk]

Related to my previous post, im trying to scour for some way of calculating the shear capacity of stainless steel sheet. BS5950 doesn't cover it, neither does the BSSA (british stainless steel assoc), or the SCI. I have read through any relevant publication I can find on their sites.

I have also started checking through tables of the larger stainless suppliers like Eurosteel but they dont give shear capacity for thin sheet either. There must be some way to calc it?

I've heard (from the vine tree) that the shear capacity can be taken as around 80% of the yield stress, but cant find any book or other source that states this.

 

[Lion06]

I would venture to guess that shear in a thin plate will likely not control the design (flexure most likely will). That being said, if you feel the need to check it the basic allowable shear stress (I am not sure if SS is different) is 0.4Fy for shear yielding and 0.3Fu for shear fracture.
Like I said, I don't see this ever being an issue.
This is a plate laid flat, correct?

 

[bkal]

I assume that you have tried the SCI publication P291, Structural Design of Stainless Steel. Maybe you can try to combine it with the approach for the thin gauges sections, BS5950-5.

 

[rb1957]

i'd say the 80% value comes from the basic properties of steel (fsu = 0.8*ftu) ... but this shouldn't be applied to thin gauge structure because of buckling concerns. onset of shear buckling for a rectanguler web is easy to calculate (if you've got the right books, eg Bruhn) ... if you post the geometry (size of panel, thickness), I can give you an estimate.

 

[drscottuk]

Thanks for the speedy feedback!

rb1957 - dimensions of the flat 304L austenitic sheets are 2mx0.5m, the sheet is vertical, 3mm thick with a 2m water load acting horizontally against it (triangular UDL).

bkal - Ive read over the P291 a few times but cant seem to find a relevant section on dealing with thin flat sheets (without any folds). The BS5950-5 is for thin folded sections, so the buckling checks there are probably different than that for a flat thin sheet?

StructuralEIT - the deflection in the sheet arent too bad for the span size, I'm just a tad concerned on the shear capacity of the section at the max deflection point & at the bottom weld seam. Especially as the sheet is such a thin gauge.

 

[rb1957]

that doesn't sound like a shear problem to me (not the way i think of shear, being in-plane) ... it sounds like you have a panel with an out-of-plane load applied.

i guess you're thinking of the bottom edge of the panel being sheared off it's support by the water load ... in this sense the material fsu is reasonable (i remember it as 60% ftu). i'd be nervous about a single weld carrying the load, as well as the absence of any supporting angles (that'd help resist the bending deflection and carry some of the load across the weld) ...

 

[kelowna]

3 mm sheet?
I would be worried of calculating shear capacity of something so thin.

Maybe you could try a different approach. If the deflection is noticeable, you could consider membrane action on the plate, in which case the bottom weld would be working on tension and easier to calculate.

 

[csd72]

On plate loaded out of plane, the bending capacity always governs.

The value of 0.4Fy will be applicable in this case.

Loaded in plane, well that is a different matter. In plane shear for such a thin section wouldnt really exist, it would be more like a tension field action.

csd

 

[rb1957]

the panel sounds like it's 0.5m wide and 2m high ... in nay case, it's got to be supported on the vertical sides by something (channels or the like) which will help to carry the load (both shear and bending) away from the web

 

[drscottuk]

rb1957 - yes, the sheet is a total of 2m high and 3m long with angle sections welded every 0.5m along the length (acting as deflection stiffeners).

the problem im finding is choosing the appropriates BS section which covers shear and buckling of such a thin sheet.

On doing some research BS5950:1 gave huge deflections. I compared that with thick plate deflection analysis and the results were similar. Then by doing thin plate deflection analysis the deflections finally reduced to a realistic amount (8mm).

As part 1 of BS gave such way out deflections, it leads me to believe that the latter sections within part 1 (covering shear, buckling checks) arent designed for such thin profile sections.

BS part 5 is for folded sections. The "holy grail" seems to be finding a BS part that is accurate for clearing a simple thin stainless flat sheet of austenitic steel against shear and buckling.

 

[csd72]

drscottuk,

You still havent clarified if this is loaded in plan(parallel to the main surface) or out of plane (perpendicular to the main surface).

It is not possible to understand you issues without this answer.

csd

 

[drscottuk]

Hi cmb,

The loading is a water pressure load acting perpendicular to the vertical sheets (making up the container wall) - out of plane loading.

The water surface is at the top of the sheet, so the distributed water load acting against the sheet is triangular in form with worst magnitude at the base of the sheet (right on the bottom edge weld seam).

 

[drscottuk]

Argh the problem with posting while dealing with last minute friday rush... sorry cad72, mistyped then!

 

[Lion06]

oh, ok. Well, given this new information I might approach this differently. Depending on the spans, this might act more like a tension (cable) member than in bending.

 

[csd72]

The shear in this direction is fundamentally no different than that for a thicker plate. If you want to double check then look at the cold formed structures code. But as I said above the shear will not be an issue for a steel plate.

The difference in thin plates is mostly in how they act under in plane loading.

The deflection curves that give better results may assume that the supports give tension restraint the plate acts more like a membreane - check the assumptions. If this is the case then the restraint forces can be large (10 times the applied load is not uncommon) and your surrounding members need to be designed for this.

I doubt that you will find a specific reference for this, you may have to do some 'real engineering' backed up by some research.

csd

 

[drscottuk]

is there any approximation formula I can quote for gauging the (10 times load) reaction forces due to the membrane action? I dont want to have to resort to a full FE thin plate analysis, as that will add another week to the job.

 

[csd72]

drscott,

For oneway catenary action(like a cable) from Roarks.

Maximum deflection (ymax)= L(wL^2/(64EA))^0.33333

P = wL^2/(8ymax) where P=horizontal reaction.

Vertical reaction is the same as for a beam in bending.

If you take the load in each direction proportionate to the stiffness then you will get a good approximation of the restraint loads.

csd

 

[trainguy]

Another good way to check this would be a geometric nonlinear analysis with FEA software.

tg