Big tapered beams

[Welderpaul]

This will be of no interest to most

Need to form 21 tapered T sections (Large gantry canopy), 3m long. Starts off as a 457*152*52 UB, with the bottom flange stripped away leaving 450 ish at one end, and 300 depth at the other.
Cutting it is ok, hellofajob, but we can do it - whats the best way of keeping/getting it back straight once it arches its back?
Anyone stripped flanges of beams that big?

 

[Shox Dr]

This will be of no interest to most

It's us that need to be (ashamed) I'd love to work with that size of gear*









*although not for ever

 

[mike os]

dunno really.... can you cut & reweld the web?

 

[MarkMG]

Probably best to try an make jig to stop it distorting in the first place, that's if the distortion is cause by the heat of cutting.

If by stripping the one flange the internal stresses are going to distort the web of the beam and bend it out of shape then it is going to be a lot more difficult. Might have to cut the web bend back and re-weld....aarrgh. Hell of a job to stretch it otherwise.

 

[Tigman]

Can you clamp it to another beam before cutting to keep it straight ?

 

[morph]

No idea how to stop the distorsion but i know it will be a nightmare. I split some 6meter 300x150ish UBs once and they must have been 60mm out once done. There was no way they were going back straight.

Might it be more accurate to get the parts profiled out of plate then weld it all up??

All depends on what tolerances you are working to....

edit: I've always found the problem is nothing to do with heat and all to do with the different stress in the steel. I split Rsj's alot for shed gussets and even on a 1m length there could be 5-10mm of movement. I've even tried stilh sawing to stop distorsion with no luck. Clamping won't help in the slightest..

 

[TechnicAl]

Those ive seen have been fabricated from plate. Could you do that. They are welded both sides so the second side pulls back the distortion caused by the first. Any tighter tolerance than that and they get pressed.

 

[Welderpaul]

Tolerances not huge, the distortion is caused by the release of stresses in the beam. Toying with the idea of cutting then sending them to be rolled straight. No one seems to be able to roll them straight though ffs. No one wants the hassle i guess - from previous experience they all disort by different amounts.
Fabbing them from plate? rather avoid it, i think the heat distortion from welding will probably put us back in the same position, just bent the other way!

 

[mike os]

agreed Paul... always a barstuard of a job

I think I would put 3-5 cuts in the web then reweld.....still a right basket though

how straight do they need to be?

 

[Welderpaul]

They could be distorted upwards by a fair amount - i guess up to 50mm or so, as when they are loaded they will deflect back down to a more truer line. Just makes fabrication difficult if you are dealing with something that is bent.

 

[Paul.]

Yes I've made tee's from beams, we used to clamp them together back to back with spacers between them so that you can clamp them up to pre set them as you cut down the beam, can be a barsteward of a job though, bent quite a few big clamps!, we always ended up with a pepper pot on the top flange to shrink it back though.
I actually used to use an acetline sheet metal nozzle to make the cut,keeps the heat down.
the web on that beam is only 7mm so a steady hand will do it, there will be a fair bit of residual stress in the beam as well so its suck it and see really.

 

[Welderpaul]

we always ended up with a pepper pot on the top flange to shrink it back though.

That would bent it the wrong way though? - You would want the top flange longer once it had bent backwards? Thats half the problem, theres nothing to heat shrink it back with. Heating the web won't pull it back

 

[morph]

Yeah 25-50mm up sounds about right on 3m but it would take some serious weight to get them true again if at all possible.....rather you than me!!!

 

[snowcat]

Iv done a bit of this, mostly for trailers, Its a good way of reducing weight by keeping the beam large over the axles, so essentially Iv joined two beams together the part Iv used as the T Iv cut about an 1" from the web so there rigid enough to hold but week enough to pull (hopefully) back during welding...... to keep the cut straight Iv always flame cut with a pug...

distortion is life, and they will warp, the way iv pulled them back is to make a rectangular fixture to slide along the beam, inserted a ram or bottle jack welded and just kept sliding the jack along the beam works well probably only a few ton of force needed....

splicing beams like this BTW is dead common on commercial truck trailers.......

 

[Bsmith]

Cut them with a pad saw handle with a hacksaw blade in it

 

[Debs.]

Cut them with a pad saw handle with a hacksaw blade in it

A nice job for the new-start apprentice on his/her first day!

 

[Dune]

Sorry cant help you with the problem, but as an Structural Engineer I would be worried about cutting steel like this and what shape it would end up. Not only that any sort of heat cutting will impart stresses within the steel that as a designer I wouldnt want. I am doing a lot of work on bridges at the moment and flame cutting is not allowed as this can impart hard and soft spots. These cause trouble at later dates. Can you go back to the designer and talk through what he actually wants and whats going to happen once you start cutting?

 

[markthewelder]

The 52kgm light universal beam has a nice thin centre web, unfortuately, the flanges have internal stresses at the centre web fillet that are kept under control when joined together by the centre web, but released when the centre web is cut hence the flanges relax and arch away from the centre flange.

Once you get past a metre long, the 18 inch UB is a nightmare to keep plumb when the web is cut.

I first thought it was the heat from the gas torch that was causing the flanges to arch, but after starting the cut at the flange fillet then slitting with the stihl saw the promlem remained.

I tried slitting a mtr long section in a massive bandsaw at Howco, but the problem remained.

Once I had converted 20mtrs of UB into 4mtr tapered bananas, I then tried cutting the centre web at right angles at 300mm intervals with the still saw and pulling the flanges flat and welding back up the cuts, but the job was a very time consuming although it worked to an accptable degree.

I also tried bolting 100 x10 flat bar to both faces of the centre web at either side of the longditudinal cut to see if that would keep the flanges from arching? Nope, the stresses are too much even for that method.

I ended up using the 'cut and shut' method to get the job done, but even at that, the welding at every 300 along the 'nice looking shelf brackets' was a bit much to gain the end result and I abandoned the idea after I had made 20.

If I hadn't bought 100 tonnes of reclaimed UB in the first place ( a very cheap 'bargain' for me), then I would never have suggested to my customer that it would be a really good idea to use the UB slit long ways in the first place...!

I eventually made up the balance of 50 by fabricating them using 150x12 flat for the top flange, 60x12 flat for the bottom and the infill (to replace the centre web) I made from 16 dia solid round rebar (reclaimed) with them welded in at 60 degree zig zags.

The finished items were actually good looking and damn strong.

The fabing up was quite quick to do, (2.5hrs all in to cut and weld 1 in a jig) think it took longer to make a jig for them than anything else...!

I find that once you get past a mtr long, 'fancy shelf brackets' made from UB are not feasible for me.

If anyone has a solution to slitting UB lengthways over 2mtrs and keeping the flanges flat; I'm all ears.

The mtr long 'fancy shelf brackets' made from deep (over 400) UB is what I use for big storage rack arms on timber yard bulk storage racks and concrete lintel racks etc, as it's a great way to use up the mountain of UB offcuts that quickly take up yard space...!

But beware that the centre web of 450x150 UB will easily collapse downwards if a fully loaded forklift comes down and a fork tip catches the end of the 'fancy shelf bracket'. To get past this, I weld 50x12 flat at right angles to the lower edge of the centre web which creates a strong stiffener to maximise the load capacity.

A better option for the short 'fancy shelf brackets is to use UC (universal column) which has a 12 or 15 thk centre web depending on exact depth and kgm.

 

[Hitch]

Sounds to me like you need to invest in a precambering machine . Should make light work of straightening little beams like them Must be someone round your way with one...?

For staright splits, on smallish beams we work them through the ercorolls. The larger ones, get doinked in the press.

 

[markthewelder]

Yeah, I tried a bar straightening machine, but the centre web was buckling before the flange was straightening, all attempts to flatten out the flange was a dead loss using regular big press machines.

I was thinking along the lines of a shrinking machine which would have pulled the flange back down, but I couldn't locate anyone with one that would take the thickness of the centre web.