Loft Steel Query

[hamazz]

got calcs back from se, he has spec'd 2 203*203*71 beams spanning 7400mm carrying floor, purlins and roof for a loft conversion, thats a big beam at over 0.5t, there is a 152*152 spreader running in the middle between them to keep them from twisting im guessing. does anyone know is there is another size beam we can use or doubled up pfc channels, or a larger ub beam, that might weigh slighlty less and be easier to install, i know we could put 2 splices into it, bringing the weight down to about 180kg per section ?
i can give you the loadings if you need, it is about,
one carrying dormer, dead load is 24.35kn, live load 45.35kn
other side is dead is 18.16, live load 38.25kn

any advice would be appreciated

hamazz

 

[^woody^]

How the duck does he expect you to get that thing up there?

Go back to him and ask him to design something more realistic, or get the conversion designer to consider other options

 

[tony1851]

In his calcs, has the SE quoted unit dead loads for the various elements, such as roof, dormer front etc? Some SEs are lazy and will overestimate dead loads to avoid having to work them out carefully.
Also, have they worked out the loaded areas carefully (eg flat roof and floor)? Again, rough figures can lead to over-estimation.
Quick work can often result in oversized beams.

Having said that, 7.4m is a fairly long span; deflection may govern here. A deeper (but thinner and lighter) beam may solve that problem, though you might not have sufficient depth to get a deeper beam in? That may be why he's spec'd a heavy UC instead.

Finally, is the structural scheme itself economic? SEs usually just design beams around the architect's drawings, without suggesting that there may be easier ways which the arch. has not thought about.

Difficult to comment to deeply without knowing the figures.

 

[hamazz]

yes the se has provided a breakdown of the different loads, all done on superbeam, which is partially why i think it is a little over spec'd, another friend se mentioned i could get away with 254*146 beams, but the other problem i may has is that when the beam is sitting on the padstone, it may be higher than the pitch angle of the rafter and make for a messy looking finish as that area would have to be boxed out rather than tiled

just had a neighbour 2 doors down have their loft steel delivered today and it was a similar setup to what our engineer had spec'd 203*203*71's about 4 of them and a few 60kg ones..
so i think it may be as tony mentioned, the deflection issue which may govern.

hamazz

 

[^woody^]

If he has used Superbeam, then he is most likely not a structural engineer. He's thrown a few figures into the program. Crap in, crap out.

 

[jeds]

It is a big beam but it's also a long span. You could ask your eng to calculate a couple of splices which would allow you to take it up in sections and bolt together in situ.

 

[hamazz]

ok
went back to him, and he redesigned it with 3 beams, 2 parallels and a tie beam between them all at 203*203*60 kg, there is one more 151*152*30 but only spanning 3m, so can be lifted easily by hand.
he just included two flitch beams running 2 * 8x2 with a 6mm 180mm flat plate, will check about the splice details with the s.e


regards

hama