Structural engineers assemble! Steel sheet to hold 200kg...

Russinating · 1 Jun 2020 at 19:58

If I had a 2200mm x 800mm sheet of steel bridging a gap length-ways, how thick, what type, and how far should it overlap the supports at either end, to safely hold 200kg in the middle, evenly distributed over a 300mm circle? Outdoor use, if that makes a difference.

OcUK is amazing and I'm sure someone can help me with this! May even be simple if steel is a lot stronger than I think it is.

robfosters · 1 Jun 2020 at 20:02

I don’t know but I’m gonna guess around 40mm.

let’s see how close I am when someone with half an idea answers.

Russinating · 1 Jun 2020 at 20:11

Fair, if it's anywhere near that then yeah, it's not as strong as I thought. May need to look a RSJs.

robfosters · 1 Jun 2020 at 20:19

What exactly is it if you don’t mind me asking?

DB_SamX · 1 Jun 2020 at 20:19

How wide is the gap?

I could run some calcs tomorrow. I've put my calculator down for the day.

Orionaut · 1 Jun 2020 at 20:21

Are you strictly "Bridging a gap" with this or can/are you providing support along the long sides? (Even a small timber section down each side would make a massive difference)

Actually.

What is the purpose of this. This matters too.

Even old school corrugated steel roofing is incredibly strong (Despite being quite thin), depending on what you want it to do.

jpaul · 1 Jun 2020 at 21:46

D/P OP's too smart to do maths

Russinating said:
I didn't know if I'd just get pointed at a formula but deflection is a fair point.

if you look up youngs modulus of typical steel, below will tell you deflection ... previous ikea desk flex discussion

jpaul said:

interesting - if you do the calculation using https://www.physicsforums.com/threads/determining-youngs-modulus-by-bending-a-piece-of-wood.783911/
if there is no bracing/longitudinal support benath a piece of chip-board of worktop length I got 28.2 mm droop with legs in 4 corners and 50kg in middle
[based on chip board E=2000Nmm2]

Click to expand...

Diddums · 1 Jun 2020 at 21:56

You won't need an RSJ.

Go to a scrapyard, they've always got those massive steel sheets that are always lying around on construction sites as ground covering (not sure what they're called, @Maccapacca might know).

Ask them to chop a few up in to your desired size & 50 cm extra, then take them home, bridge the gap (you may need a few layers) and chop off the excess with an angle grinder (be safe please, gloves n stuff, those things cam be nasty).

This is about as accurate as I can guess with the info provided. How long does it need to hold the weight for? How often? Always exposed, or taken indoors?

If you just tell us what it's for we can give you a better idea but with the info you've given we don't even know if you need ferrous or non ferrous.

Hagar · 1 Jun 2020 at 22:45

Diddums said:
You won't need an RSJ.

Go to a scrapyard, they've always got those massive steel sheets that are always lying around on construction sites as ground covering (not sure what they're called, @Maccapacca might know).

Ask them to chop a few up in to your desired size & 50 cm extra, then take them home, bridge the gap (you may need a few layers) and chop off the excess with an angle grinder (be safe please, gloves n stuff, those things cam be nasty).

This is about as accurate as I can guess with the info provided. How long does it need to hold the weight for? How often? Always exposed, or taken indoors?

If you just tell us what it's for we can give you a better idea but with the info you've given we don't even know if you need ferrous or non ferrous.

Road plates I think?

Anyway they are generally 25mm thick to cover trenches 6-800mm wide. Usually for loads greater than 200kg (2kN). The answer depends on the allowable deflection as quite a thin plate would support the loading but would deflect a lot.

Russinating · 1 Jun 2020 at 23:13

Yeah fair, I didn't know if I'd just get pointed at a formula but deflection is a fair point.

So it's for the garden, to effectively make a custom surface for a cast iron pizza oven to sit in. The oven weighs 100kg so I was going double.

It'd be supported by brick walls at either end (rendered planters) and we'd probably want partial shelving underneath anyway so a vertical support directly underneath the oven is an option.

The road plates are certainly an interesting thought! Need to be carried through the house though...

builder22 · 1 Jun 2020 at 23:14

how stable the supports are and if the sheet will be fixed (rivets/bolts/weld etc) or just resting on the supports will make a big difference

edit...just saw your post....what are pizza ovens usually 'mounted' on..seems like steel would soak the heat from them? maybe just use the norm and support it (in the middle) if that's an option

Hagar · 2 Jun 2020 at 06:35

Russinating said:
Yeah fair, I didn't know if I'd just get pointed at a formula but deflection is a fair point.

So it's for the garden, to effectively make a custom surface for a cast iron pizza oven to sit in. The oven weighs 100kg so I was going double.

It'd be supported by brick walls at either end (rendered planters) and we'd probably want partial shelving underneath anyway so a vertical support directly underneath the oven is an option.

The road plates are certainly an interesting thought! Need to be carried through the house though...

How about rectangular or circular section bars or strips, built into the end walls and supported on a central pier? Even scaffolding tubes have a decent capacity in bending if spaced at say 100mm (48mm diameter) then you have few issues carrying them. These could be surfaced by a custom non ferrous thin sheet, ally or brass for a non corroding professional finish.

famas · 2 Jun 2020 at 07:30

What pizza oven is it? Do you have a link?

I'm currently building a WFO and a metal support is generally not recommended as it will act like a heat sink and suck the heat out of the oven making it hard to get up to temp and need a lot of fuel, though this is in regard to a brick pompiee oven so maybe different for yours.

Normally the support slab is made from concrete and rebar with a 4" thick insulation layer on top made from calcium silicate board or a 5-1 mix of vermiculite and cement. Do not put an oven directly onto concrete as this acts like a heat sink as well.

Russinating · 2 Jun 2020 at 11:32

So the oven is this: https://morsoe.com/en/product/outdoor/outdoor-fireplaces/forno_uk
This is one of their official tables which is made of steel, so I don't think the material is an issue re: heatsink properties: https://morsoe.com/en/product/outdoor/accessories/outdoor-tables/morso-terra-outdoor-table

I'm effectively re-creating their bigger version of the table - https://morsoe.com/en/product/outdoor/accessories/outdoor-tables/morso-garden-outdoor-table - but cheaper, longer and more intergrated. My Sketchup below:

Mods, feel free to move this into Home & Garden at this point...

Gav_r26 · 2 Jun 2020 at 11:52

As previously suggested I'd be using small section RSJ's or tube of some sort spanning between the walls asn then clad the top with 8 or 10mm We use 8mm at work for welding bench tops and they are damn heavy. We sit them on 40mm aluminium extrusion frames and a 1.8m long one can safely support 300kg with a safety factor of 2. 8mm x 1.8m x 0.8mm is heavy enough to try and lift, let alone anything thicker.

D.P. · 2 Jun 2020 at 12:04

I would definitely go about creating a frame with supporting beams. Will be much easier and much cheaper than buying super thick and heavy steel plate.

dl8860 · 2 Jun 2020 at 12:13

From an engineering design point of view looking at your sheet acting as a beam spanning two supports, you've got about 1kNm of moment and 1kN of shear. To resist each of those, if you assume an effective width of 300mm (as this is the central bit loaded) then you need a depth of 9.2mm if you use 235N/mm2 steel. That's using no safety factors.

How your sheet behaves in reality will depend on a lot of things like how it's restrained at the ends, but if you manage to make it work effectively in bending then steel is often stronger than you might think.

dl8860 · 2 Jun 2020 at 12:17

robfosters said:
I don’t know but I’m gonna guess around 40mm.

let’s see how close I am when someone with half an idea answers.

40mm is serious steel! If the OP is using the word 'sheet', if you looked at a piece of 40mm steel plate then the word sheet wouldn't be springing to mind, trust me.

Russinating · 2 Jun 2020 at 12:38

gav_172 said:
As previously suggested I'd be using small section RSJ's or tube of some sort spanning between the walls asn then clad the top with 8 or 10mm We use 8mm at work for welding bench tops and they are damn heavy. We sit them on 40mm aluminium extrusion frames and a 1.8m long one can safely support 300kg with a safety factor of 2. 8mm x 1.8m x 0.8mm is heavy enough to try and lift, let alone anything thicker.

Yeah, I was looking at these: https://www.metals4u.co.uk/materials/mild-steel/mild-steel-universal-beams-rsj/7553-p. £97 for 2.5m. Two of those and then a sheet of steel ~1.5-3mm powder coated for another ~£150.

I love the look of corten steel but it's probably not the best as a food prep surface so might just use as a heat splashback and elsewhere in the garden.

dl8860 · 2 Jun 2020 at 14:21

Two of those 127x76x13s are giving you 35kNm of bending resistance when you've got 1kNm, so it's certainly huge overkill in terms of capacity, but the key thing to think about is how you fix it all together.

In your sketchup you've got a vertical propping up under the oven, is your 2200mm span ignoring that?