I have just exposed the existing RSJs to which new load is to be applied to support my roof. The BCO said the bearings may need to be exposed but has said nothing more. For peace of mind I probably need a structural engineer to check things, but can anyone give a rough feel for the loadings here ?
Old fashioned RSJ, width 125mm, height 150mm, flange thickness 10mm at the edges, 15mm at the web, web thickness 10mm. Span is 2800mm. Can anyone tell me what type of loads this beam can take (assuming bearings are OK). Also, what type of point load could it take near the middle of the span ?
Provided it's not rusty and full of holes - it will more than do the job. I have seen one half that size (height and width) and around 10 foot long holding up two bedroom floors.
This was part of an old miners diy job when he knocked two rooms into one - and when I asked if it would take the weight, he said that if that girder was strong enough to hold the pit roof up, it'll certainly hold the bedroom floors, even when I'm f*****g my wife (a very true tale by the way, those Yorkies were tough then). LOL
Nice story ;-) A very fine dusting of rust on the surface, overall seems very sound. Trouble is, there may need to be almost a point load of 250kg on it near the middle, but I can add some support from a new wall that runs right under it. I've got my first kiddy on the way and its making me a bit paranoid about safety ! Simon.
Believe it or not, that story really is true and it took place around 1988 - and that girder (a couple of straightened out pit rings with a couple of bolted on fish plates either side) is still there holding up those floors with nary a sag), and I still say that's a bloody miracle.
As for you job, even without structural calcs, (and I have long forgotten the 'bending moment' formula) that RSJ will hold whatever you can throw at it with a standard roof - and there's no need for "parania".
Mmmm.... 150mm height, 15mm web, 250kg... ... equivalent to 2 rather large people ... equivalent to another largish RSJ sitting on it ... equivalent to 0.3m wide crap upstairs block wall
I think the RSJ is likely to say "that all you got" :-)
The BCO is more interested in the bearings. That is, crumbly crap mortar vs tightly packed slate or padstone.
We would need more detail of the roof construction...
Clay tiles are about 0.77 kN/m^2 for example.
Quite substantial!
I had a little play in SB4, and assuming I selected the appropriate beam (i.e. please don't take my word for it - try it yourself!), it looks like it would cope with a point load of just over 57kN in the middle of the span!
Also taking in snow weight and high wind loading, in both pull and push directions, your calculations would drop that figure to around 49 - 50 kN in the centre. But it isn't so much the RSJ itself that needs calculating. The RSJ is only as strong as the platforms it rests on. If the existing wall pads are crumbling and dried out, then they may cause slip or sag to the ends of the beam. This is not a good thing to have, under any loading circumstances.
Also, Fire regulation now say that the steel must have a minimum of three hour protection from direct heat along the full length of any structural works. So allow for the BCO to add that equation once the works have begun. Each Building Control Person seems to have their own particular way to create an adequate heat barrier on these things, so ask them first about this, before getting pads and other things done.
The loading it can take is what it can take - that obviously needs to include static, live, and wind etc. loads. The thrust of what I was saying however is that there is a fair chance this steel is more than "adequate"!
Three hours seems like quite a lot in a domestic situation. Do you have a reference to the relevant section of the ADs?
Thanks guys. The roof dead load is 1 tonne (very close to), including snow load is 3 tonnes (roof is quite shallow). Roof is bearing on several purlins such that each purlin end is carrying just over 200kg, including snow load. I can add an extra support under the RSJ, reducing span to about 1.8 metres (aircrete loadbearing wall passes under, whereI could easily add a padstone - replace an aircrete block with 7N block). The bearing I can see on one end looks like the RSJ is dry on a thick quarry tile bedded on strong cement mortar (most of house is lime mortar), and I assume all bearing are around 4" (t'other end must be, its in a 9" wall). To check the bearings properly you'd need to remove a brick next to it and have a look.
Other issue is how to support the purlin on the RSJ. RSJ is inset against 9" wall above it by 2". FIrst row of bricks on RSJ are dry laid headers (2" overhang off RSJ), don't think it would be wise to bear a masonry hanger direct on one of these. I could drill the RSJ and bolt timber bearer and use a jiffy hanger, but I'm not sure how drilling some 10mm holes through the RSJ affects it, or how hanging weight off only one side could unbalance it. When I say I'm not sure about all this, I could make a educated guess, but a struct eng could insure it ! Simon.
Well, the struct eng that validated my roof design says they would want 150+vat for a site visit to confirm some drawings I do for them and to check end bearings etc, then about 105+vat for calcs to confirm and also design an acceptable way to hang a purlin from an existing RSJ. Does that seem reasonable ? Question is - do I bother ? Only thing as regards purlin on RSJ, is its loading on one side that could try to twist the RSJ. I'm sure I'd get away with just doing it, but for insurance purposes, etc it may be a good idea. Simon.
I can't answer your question numerically - but, in a domestic situation, you're unlikely to be able to throw anything at that RSJ which it *can't* support.
When I recently made some structural changes to my house, the BCO said that as long as I used a 7x4 RSJ over a similar span to yours (ok, yours is 6x5 - but a pretty beefy one) he would be happy because it would be sufficiently over-engineered that there couldn't possibly be any problems. On the other hand, if I wanted to use anything less, he would need to see calculations done by a structural engineer.
It will be money well spent for the peace of mind you get with a proper job. I'd say "go with the struct' eng" and make sure the whole thing lasts the years you want it to.
I do the same as you. I look at it for months, then decide I can do the work without problems, then change my mind and ask someone I know, with a greater experience of the actual calculations, to come in and tell me I am correct. But it seems to have been a good way of doing things, just for the peace of mind I get knowing the work is done properly.
I was being a little bugger. Your calcs' are spot on. :-) Just added a little bit to them. lol
I think the reference to the new amendum BS 476 parts 20 and 22, IIRC, give guidance to both full steel structural builds and any internal new steel supports testing requirements. But it is definitely somewhere in the BS 476 : 2009 book.
I've had a look at the RSJ over the other side of the house (the kitchen), and that is interestingly two parallel RSJs 3.5" by 7" with similar flange and web sizes to the other 5" x 6" RSJ. I'm guessing the parallel ones start with stretchers rather than headers. It would be interesting to have seen these houses being built. Massive gobs of lime mortar and beefy RSJs being thrown around everywhere would be quite a sight ! Simon.
It may also be possible to do the same technique on the beam you're working on. If the load can be spread across two similar sized RSJ's, then it might make life a bit simpler for you.
You should see the size of the steels under our floors. We are in an old (112 years) four storey tenement in Edinburgh, and have shops on the ground floor, with our flat directly above. Actually, it's a five storey building if you count the in-ground cellar spaces. The steel RSJ's are 22 inch X 9 inch and have been rolled to half an inch thick all round, with each being
11 yards in length.
I tried to calculate the weight that the four ground level ones are carrying, above the cellar space, and gave up at the 200 ton mark. Thank goodness there are a few spreading the loads throughout the whole building. These old sandstone tenements were built to last. :-)
Right, I've thought of the best solution now, assuming the RSJ can take the point load (struct eng ?) Fix some timber into the web both sides of the RSJ by bolting throught the flange M10 bolts every 600mm or so. Then remove a single brick from the headers that are bearing directly on the RSJ (could there be some slippage ??), and wrap a long leg hanger up the timber, over the top and down the back and nail in. Will hang below the RSJ like is often done in loft conversions. Joist may need to be notched at the top if it ends up just a little higher than the top of the RSJ.
Variation: no brick removal just fix hanger up and over the timber infill and bolt this to the flange.
Only question - this is an RSJ with tapered flange, so I guess the timber should be shaped at the bottom to follow the flange, and bear in mind the bolts will be doing more than in a UB with flat flanges. Up and over RSJ probably best, since force is more direct onto RSJ and less the timber infill.
If these timber joists are hanging on only one side of the RSJ, then you have a twisting action as the loads increase and begin pulling on that side. Is this something you are allowing for?
Timber is at least fifteen time weaker than steel, so any infill of the web of the RSJ will mean nothing to actual load bearing properties of the steel. Drilling into or through the steel can change its loading character dramatically. Holes under stress can allow cracking to take place through the rolled grain of the RSJ in certain circumstances. 600mm spacing sounds like one of these circumstances.
I still think spending a little time talking to, not hiring, a proper engineer will help out on your project and let you do the works without any faffing about. Even if you give the engineer a retainer for their consultation, it's better than trying and failing with this type of job.
I agree about considering the effects of torsion, but can't see that drilling holes in the beam will have an effect on the steel that's left. I am though a little puzzled at the OP saying he wants to drill holes in the flange rather than the web. Running the same calc through our ProSteel program shows that even a 50mm hole through the web is quite OK - smaller ones for through bolts will have a negligible effect.
No argument there. We do have SuperBeam users who offer a calcs by mail service and others who will not do them without a site inspection. If I were offering engineering services I would definitely be in the latter camp.
Whoops, drilling through the web of course - I "mis-wrote" ! The torsion thing I mentioned in an earlier post - yes it is a concern. I'm not sure how you talk to a struct eng without hiring one (unless you have a mate)
- please let me know ! As far as 10mm holes at stated intervals - I cannot see a problem with that. However, I would probably drill them just either side of an exact central line. The timber infill is not adding strength to the RSJ - it just gives a connection method and stabilises the hanger. If hanger is wrapped over, the top of the RSJ takes up some strain. Method I mentioned is standard for loft joists - at least it has been mentioned several times in web searches. Not always with joists hanging from both sides. If hanger is up close, leverage is only over half the RSJ width =3D 2.5 inches. Only question is added point load on RSJ, and torsion. I believe I will have to hire a struct eng for this - unless I meet one round the shops to talk to ! I guess the weight above the RSJ and side restraint will need to be a factor in counteracting the twisting forces. However, torsion would be an issue on any beam supported off the side of another.
I've drawn some plans for the struct eng, and he will need to do a site visit (look at bearings). The bearing on one end of the RSJ is quite a lot, and new support can be offered 1/3 along the RSJ via aircrete wall and padstone if required.
I'll let you know what the struct eng says. And if I have to pay him ;-)
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.