Steel Bearer size

[DSJC]

We are considering replacing a bearer supporting one side of a bedroom floor. Yes I know that we will have to engage a structural engineer for formal calculations etc., but for now, I just want to get an idea of practicalities, sizes etc..

A builder has suggested using hollow rectangular steel 150mm x 100mm x 5 mm thick. Is this overkill, adequate or insufficient?

Dimensions are – unsupported span 4.2M, and taking what seem to be normal assumptions of 0.5kN/m^2 dead load and 1.5kN/m^2 imposed load, then the bearer would be subject to uniform load of 3.7kN/m. Although actual loading will be much less than that especially as it will not be supporting any walls or partitions.

Any thoughts welcome.

 

[tony1851]

Why use a box section? - a 152 x 89 'I' beam would be OK and probably cheaper and easier to plaster over.

 

[^woody^]

but for now, I just want to get an idea of practicalities, sizes etc..

Whats the point planning for something that you don't know will be, unless an engineer tells you what is needed?

 

[DSJC]

Whats the point planning for something that you don't know will be, unless an engineer tells you what is needed?

If a much bigger (deeper) section is likely to be required, then once boxed it will just look silly and engaging an engineer would just be a waste of time and money

 

[tony1851]

If it is just for supporting floor joists, it is possible to notch the underside of the joists by a designed amount to set the steel beam up higher.

 

[DSJC]

If it is just for supporting floor joists, it is possible to notch the underside of the joists by a designed amount to set the steel beam up higher.

Both your suggested 152 x 89 and builder's 100 x 150 would end up looking OK. But if something much deeper (say 250) is required then the project is a non starter. Using joist hangers is not really a practical option in this case.

 

[^woody^]

If a much bigger (deeper) section is likely to be required, then once boxed it will just look silly and engaging an engineer would just be a waste of time and money

But you can't rely on a bloke on the internet or a builder's opinion.There only way to know is for the beam to be calculated.

 

[tony1851]

You are obviously knowledgable on loadings and spans - can you not do the figures yourself? There's plenty of info on the internet, with lots of worked examples.

 

[^woody^]

I suspect he's after a freebie.

 

[DSJC]

You are obviously knowledgable on loadings and spans - can you not do the figures yourself? There's plenty of info on the internet, with lots of worked examples.

..... this morning I have done just that .... but I don't really trust my results ... because they suggest a far larger beam - either 152 x 152 x 23kg/m or 203 x 102 x 23kg/m

 

[designinsteel]

If you want some guidance on working out loads and calculating a steel beam size, I've put up a four part tutorial on youtube. I do steel beam calculations all the time, and have worked out what I think is one of the easiest methods for working out a preliminary steel size. You will still need someone like myself to provide you with the final calculations to satisfy building control, because you need to be covered by PI insurance and ideally done by a chartered engineer.

How to do a steel beam calculation.