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I've got a couple of 3.5m c-section (100mm x 50mm x 8.5mm) galvanised steel 'girders' lying around and was wondering if I could use these suspended between brick/concrete pillars to support one edge of a conservatory? The other edge is going to be sistered to a joist bolted to a brick wall.

Actual span would only be 3m and my red-neck test of standing (I'm 125kg) in the middle of a beam supported at each end shows no visible defelection - possibly 1mm??? - so I'm guessing it would be ok???

I've found various tables on line but nothing that actually states the maximum loading for a given span. Anyone got any clues?

10x50 PFC by the sounds of it, parallel flange channel....pretty light weight stuff really when it comes to building work...
If its just holding up a bit of plastic....

100x50 PFC .... I found a document that showed the maximum span for its use for a 'building' - and that gave a figure of 2.2m - but that design indicated the building to be 'proper' i.e. solid walls, full constructed roof (rafter, joists, tiles etc) whereas the conservatory I intend is not exactly plastic but just a wood frame side with simple box profile plastic roof.

I could build pillars at 2.2m intervals but given the 'lightweight' use I thought stretching to 3m wouldn't be an issue.

Here are some caps of the document - it's a little confusing to me but for the 3m 'depth' (load width?) I want you can see the 100PFC figures for the timber/tile construction as 2.2m.

I've got figures for A, C and D and all are '3' or near as damnit.... I think this gives me a load width value of 1.5 and according to the tables (I need to take the next higher load width value which is 1.8) which gives an allowable span of 2.6m (not the 2.2 I stated above, wrongly ).

So, given the much lower construction quality - especially the roof - I was hoping that along with the exaggeration afforded by using 1.8 for the load width value when the actual is 1.5 - I might be ok having a span of 3m rather than the 2.6???

Now I've plugged the figures in I seem to be convincing myself I'm probably right but some more experienced advice is welcome - thanks for your input so far hitch

I'm also assuming the figures for the beam are based on the beam being used in the [ direction rather than the U or n position???

I'm no expert in working out loadings for beam, usually done for me where its important, use experience where less important... pick a size then get the next one up

Whats it holding then, just a bit of timber and polycarb roof? Sounds like itll be okay judging by your your table...

That table doesnt say if its taking end restraint of the beam into consideration, if the ends are fixed solid, the actual loadings generaly can be increased slightly.

If youve got a couple, bolt them back to back to be extra sure, like ][, M12 bolt at 400 centre or something like that, be proper solid

Assuming that the beam is simply supported at each end and based on a centre load with a span of 3000, then allowable deflection is 1/500 of the span; so 6mm in this case.

You can then work out the maximum allowable load via bending moment equations as you know span, deflection, modules of elasticity (steel in this case) & area moment of inertia of cross section (based on PFC X section - check steel section tables).

Yes, I have 'spares' so I could bolt a couple together. If I'm reading the tables right (anyone?) then given the less-than-heavy purpose I think I'll give it a shot on that basis (fingers crossed ).

I do know that my 120kg+ lard arse stood centrally on the beam supported at each end (3.5m span) moves it less than a couple of mm - in fact I can't see movement at all....... but I'll try to measure it!