Steel box section size

[Chrisinspain]

Hi, we live in Spain are at the planning stage of converting a warehouse into a house. I want to put in a mezzanine floor and was going to use timber, but I’m now thinking of using steel box section instead. The floor size will be 5 meters x 8 meters with the maximum span being 5 meters. It will be bolted and set in to the wall along two sides so support on these sides won’t be a problem. On the “free” end I can put in 3 or four supporting uprights to carry the leading edge of the floor. I’ve just done a quick sketch so hopefuly it makes more sence.. A + B will be set into the wall.. C + D will need support. So my questions are.. what size steel box section will I need for the beans marked G and G1 on my drawing and what spacing would I need between the beams.. also how many support beams (marked E) would I need for the size of the floor. And finally is it better to weld spacing beams between the bars marked G ? The floor above is going to be clad above in timber and the new mezzanine will be used as a bedroom at one end and an office at the other. I hope this makes sence ?? I’ve confused myself drawing the bloody thing..

 

[MetalMonkey]

I could be wrong, but I think you will find most people will be unwilling to commit to providing any sort of advice or specification for making a structure like that.

I don’t know what the building regulations are like in Spain, but it is something you really should be consulting with a structural engineer for a design that will be correctly calculated and meet any legal local building requirements.
All I would say is you will probably find you need to use steel beams (I beams) and columns rather than box section.

 

[winchman]

As above really never seen a box section floor its I beams you would need. Not being a structural person you really need to ask and expert but I feel the box would have to be massive so as not to bend over 8M
I would check the Spanish rules for building this sort of thing
I am certain someone will be along in a moment with more knowledge than me.

 

[Agroshield]

Go here:

Beam Calculation Examples - Steel Beam Calculator

www.steelbeamcalculator.co.uk

Go through all the free examples until you understand what information you need to input to receive any meaningful output.

Then pay for a month's subscription, put in some numbers and see what it tells you. It is to Eurocode so should be Euro-applicable.

Otherwise, pay a structural engineer to do the calculations for you.

Generally, what governs structural member size in these cases is allowable deflection rather than structural strength. I think it is something like span/360, so about 14mm. A simply supported beam over that length will sag more than one with moment connections at the ends, so you can trade off design complexity for shallower beams if headroom below is an issue.

 

[gaz1]

your drawing is all wrong and so is your posts

your posts should match the cross sections whilst also supporting the structure itself

remember one thing when building a floor like that its designed on the weight you intend to put on it too much and the whole lot will collapse

if you was planning a post every 2.5m then it would give you an idea what your playing with if you want strength and to be able to well support the structure

 

[Welderpaul]

Hot rolled is very inefficient for floors. Think about utilising a cold rolled mezzanine product which only need a small amount of hot rolled section.
There's online design tools to size it up too.

 

[Shedendman]

I'd do that all in timber(cheaper) if me,A's and B's fixed into the walls(brick?),G's hung from B by hangers onto C,but the support for C is a main factor,are you running these up to ceiling height?
My main concern would be the bottom left E,that would need to be not floating(ie stand alone),whats the underneath used for?

 

[Erie Fred]

Hi, we live in Spain are at the planning stage of converting a warehouse into a house. I want to put in a mezzanine floor and was going to use timber, but I’m now thinking of using steel box section instead. The floor size will be 5 meters x 8 meters with the maximum span being 5 meters. It will be bolted and set in to the wall along two sides so support on these sides won’t be a problem. On the “free” end I can put in 3 or four supporting uprights to carry the leading edge of the floor. I’ve just done a quick sketch so hopefuly it makes more sence.. A + B will be set into the wall.. C + D will need support. So my questions are.. what size steel box section will I need for the beans marked G and G1 on my drawing and what spacing would I need between the beams.. also how many support beams (marked E) would I need for the size of the floor. And finally is it better to weld spacing beams between the bars marked G ? The floor above is going to be clad above in timber and the new mezzanine will be used as a bedroom at one end and an office at the other. I hope this makes sence ?? I’ve confused myself drawing the bloody thing..

View attachment 475706

While that's all well & good, you need to figure out your floor loading
to do any kind of calculations.

 

[Agroshield]

...you need to figure out your floor loading to do any kind of calculations.

...and the first question any competent SE will ask is how much of the area is office and how much is bedroom because the imposed loadings differ between the two. If that info. is not known, the SE will design conservatively with the whole area using the higher load.

A different part of the same site above has a timber beam calculator, and it includes what are called filtch beams, which is a steel plate sandwiched between two timbers. That can be a way to increase span while maintaining acceptable deflection. You can keep much of the economic benefit of timber but have the greater strength of steel in as minimal (cheap) way as possible.

 

[Shedendman]

...and the first question any competent SE will ask is how much of the area is office and how much is bedroom because the imposed loadings differ between the two. If that info. is not known, the SE will design conservatively with the whole area using the higher load.

A different part of the same site above has a timber beam calculator, and it includes what are called filtch beams, which is a steel plate sandwiched between two timbers. That can be a way to increase span while maintaining acceptable deflection. You can keep much of the economic benefit of timber but have the greater strength of steel in as minimal (cheap) way as possible.

hes in spain

 

[Agroshield]

he's in Spain...

How is that relevant? I hope you are not implying that Spain has no competent structural engineers.

When the UK was in Europe, the whole of Europe moved to Eurocodes for design. Each country has a national annex, specific to that nation (so Welsh roofs have to be sheep-proof) but the design codes are the same.

 

[Chrisinspain]

I'd do that all in timber(cheaper) if me,A's and B's fixed into the walls(brick?),G's hung from B by hangers onto C,but the support for C is a main factor,are you running these up to ceiling height?
My main concern would be the bottom left E,that would need to be not floating(ie stand alone),whats the underneath used for?

Unfortunately here timber is a lot more expensive compared to steel. Plus because I’ve only just got enough roof space for the mezzanine every cm counts, and I’m guessing that I won’t need as thick steels as I would timbers. I know in timber I’d be looking at 6x2 at 16 inch centers but I don’t know what size steel I would need.

 

[Chrisinspain]

As above really never seen a box section floor its I beams you would need. Not being a structural person you really need to ask and expert but I feel the box would have to be massive so as not to bend over 8M
I would check the Spanish rules for building this sort of thing
I am certain someone will be along in a moment with more knowledge than me.

The longest span would be 5 meters. But I have no idea as to what I would need. I thought that box section or oblong as it were, something like 120mm x 80mm would be stronger than I section, but as I said I really don’t know. At this stage it’s just finding out what I can to see how feasible it is

As above really never seen a box section floor its I beams you would need. Not being a structural person you really need to ask and expert but I feel the box would have to be massive so as not to bend over 8M
I would check the Spanish rules for building this sort of thing
I am certain someone will be along in a moment with more knowledge than me.

 

[Chrisinspain]

your drawing is all wrong and so is your posts

your posts should match the cross sections whilst also supporting the structure itself

remember one thing when building a floor like that its designed on the weight you intend to put on it too much and the whole lot will collapse

if you was planning a post every 2.5m then it would give you an idea what your playing with if you want strength and to be able to well support the structure

The drawing is literally a rough sketch I did in the middle of writing the post just so it was easier to explain. I don’t know how many supports I would need or size. At the moment it’s just trying to get an idea of what I may need

 

[gaz1]

Unfortunately here timber is a lot more expensive compared to steel. Plus because I’ve only just got enough roof space for the mezzanine every cm counts, and I’m guessing that I won’t need as thick steels as I would timbers. I know in timber I’d be looking at 6x2 at 16 inch centers but I don’t know what size steel I would need.

your wrong at that number even for 5m length

 

[gaz1]

if your playing with house weight alone per floor its 12x4s for 5m length at 12s/14s in wood

 

[Chrisinspain]

if your playing with house weight alone per floor its 12x4s for 5m length at 12s/14s in wood

View attachment 475743

The structure is already there built of double skinned block and brick. The only weight it’s got to take is the floor itself and bedroom/office furniture. If needed I could also put in supports in the 5 meter span, as it’s just going to be a seating area. But I was hoping that I could use smaller steel trusses than I would need if it was timber

 

[Erie Fred]

The structure is already there built of double skinned block and brick. The only weight it’s got to take is the floor itself and bedroom/office furniture. If needed I could also put in supports in the 5 meter span, as it’s just going to be a seating area. But I was hoping that I could use smaller steel trusses than I would need if it was timber

Put a number to it.
Pounds per sq. foot is what code is over here, yours is probably metric.

 

[skotl]

The structure is already there built of double skinned block and brick. The only weight it’s got to take is the floor itself and bedroom/office furniture. If needed I could also put in supports in the 5 meter span, as it’s just going to be a seating area. But I was hoping that I could use smaller steel trusses than I would need if it was timber

I'm definitely not a structural engineer, but it's not just weight and length that need to be taken into account, but stress and flex (and other terms I'll likely get wrong). Even a massive section of 5m box is going to flex and the danger is that it will crumple along its length with even a moderate weight applied. With wooden trusses you would have spars supporting them every 16 inches or so and I'd expect you would need similar with steel box section.

This is, I believe, due to the shape of box and why structural steel tends to be I-beam in cross section.

Is all that steel really cheaper than timber?

 

[Chrisinspain]

I’m obviously going to have to do a lot more research, but everything I’ve read says that box section is stronger than I beams. I’m meeting with an architect next week so I’ll put the problem to him.,
Timber prices here are ridiculously expensive. Plus we get the long horned house beetle so all timber is at risk.