Universal beam calculation

[nafuk]

Universal beam calculation Posted: Jan 18, 2006 10:57 AM Reply

Hi, I'm replacing a section (2.2m) of first floor internal suporting wall with a universal beam (2.5m). The beam will have to support floor joists, p/b, flooring only (no walls etc.) Rooms above whose floor joists will be supported by the universal beam (ub):

1. have an area of 13.6 m2
2. dead load (0.75 kN/m2) + live load (1.5 kN/m2) = 2.25 kN/m2
3. load is 13.6 x 2.25 = 30.5 kN
4. beam only suports half the load (one end of joists supported by wall so load is 0.5 x 30.5 = 15.25 kN

I've looked on the Corus site at

there are lots of specs for different sized universal beams. Looking at a 152(h) x 89(w) x 16(kg/m) beam the spec is:

1. buckling resistance for a 2.5m ub = 19.8 kNm
2. Compression resistance for a 2.5 m ub: Pcx = 529 kN, Pcy = 222 kN etc.

Please can someone tell me what are the factors I need to look at to meet my loading requirements.

Thank you,

Neil

[Jonathan Pearson]

> and there are lots of specs for different sized universal beams.

When I was a lad, you applied all your loading, plus any additional specified in BS5950 and applied 1.6 to the live load & 1.4 to the dead load, then calculated my shear forces and bending moments and checked for deflection, then selected the appropriate beam

Jon

[Tony Bryer]

Your bending moment is WL/8 = 15.25 x 2.5/8 = 4.77 kNm v. 19.8 limit

so a 152x89 is more than ample. A 127x76 would also be OK. Alternatively consider a pressed steel box lintel - probably a little more expensive but easier to handle.

[Christian McArdle]

I am not a structural engineer. Do not use my suggestions directly, as I could well have cocked up the calculations. Ensure that any real calculations are done by a structural engineer (complete with liability insurance) and checked with the building control department.

Using Superbeam and your figure of 15.25kN, evenly distributed over 2.5m, I make it:

Section Size: 127 x 76 x 13 UB Grade 43. Total deflection = 3.2mm.

However, some shallower sections are available if you don't limit to UB sizes (this is the minimum UB size that SuperBeam has programmed in).

In particular, it suggests:

89 x 89 x 19 RSJ Grade 43 Total deflection = 4.9mm

Would be acceptable. RSJ is a "rolled steel joist", the forerunner to UB "Universal Beam".

If you can't get hold of that a 90 x 90 x 6.3 HF SHS (Square Hollow Section) complies at 6.4mm deflection and is probably easier to come by.

If you are trying to keep weight down, then the lightest beam it suggests will cut the mustard is:

120 x 60 x 3.6 HF RHS Total deflection = 6.7mm

No wooden beam is suitable. However, you could consider a flitch beam, which is easier to install and fireproof than steel.

It suggests 50 x 170 C16 with 10 x 145 flitch plate deflects by 5.1mm.

Christian.

[none]

Remember the corus tables quote buckling resistances for effective length which can be a good bit more than actual length, this is dependent on end conditions and wether the load is considered destabilising or not. Often but not always lateral torsional buckling is the limiting factor in beam design, which is why UC sections are commonly used. Would suggest for the sake of probably £200 or so you get the calcs done by an engineer.