Universal beams

Does anyone know how to work out the load capacity of a universal beam for a set length with evenly distributed loads?

I want to build an extension and span the first floor on the beams.

Brian

In the UK you will need to comply with building regulations and they will require calculations from a structural engineer. The costs are not too bad mine for the roof structure on the garage workshop extension were £400.00 and that was using 270 x 90 glulam beams. Although you may well be able to build an extension under permitted development it still needs to be signed off by the local building inspector failure to do so will present problems if you try to sell the property. Calculations are quite complex as it is not just a case of knowing the beam will support the loads and that assumes you know how to calculate the load but also the bending moment. The beam will have a limit to how much it is allowed to bend under the load applied. Throw in wind and snow loads..................

Bob

Brian,

If you have not contacted the council building people, then speak to a local "approved inspector" who will be far more helpful and knowledgeable for your building control statutory requirements. They only used to do commercial projects at one time but they are normally very competitive and a lot more helpful than the council departments.

As for calcs, you will find what you need on the Internet (search for a beam as you describe, "uniform loading stress beam calculation". They are not hard to do (no calculus only "normal" maths that you can do on a calculator). When it comes to "competent person", try and find a definition! As long as you can demonstrate that you understand the bounds of your knowledge, you are probably a "competent person". There are huge amounts of misinformation around on these subjects....

As for problems selling property later, it is now common to take out indemnity insurance against this sort of problem and most conveyances will advise you to take this route - it costs about £100 ish and against all the other costs is almost stupid not to consider it.

Mark

Brian

Some info that may be of help ... ref... Newnes Mechanical Engineers pocket manual.

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George.

You will find the "I" (second moment) value in the steel stockist catalogue or search for your section on the Internet rather than working it out.

Mark

Most likely area for error is mixing different type or magnitude of units!

Edited By Mark C on 09/08/2015 20:57:54

The other area that is often overlooked is the bearing conditions - normally engineering grade bricks in buildings. You need to m match your total loading to the bearing material and size. Building control will threaten to check the calculations but in reality, they probably have neither manpower or skilled people to do it - your certificate of compliance really means nothing if anything gets to litigation. They make a big point of ensuring that they do not provide any guarantee.....

Mark

Thank you all. The beams have to sit on concrete for our local inspector. So I will build in a 6 x4 concrete lintel

Brian

When i built my extension i used a fair bit of steelwork including columns to support the main load bearing beam (rather than building brick piers) my architect used a friendly certified structural engineer who for about £80 did the necessary calcs. These came hand written on three sheets of plain A4 and were duly submitted to building control.

There was no covering letter or anything to suggest the bloke who produced them had any qualifications or idea of what he was doing, but they looked mightily impressive, i doubt anyone at building control would have had the knowledge to decipher if in fact they were beam calculations or moon landing trajectory calcs.

Being a good lad I did however follow them to the letter, and it cost me a small fortune in steel, the main span beam was only 16ft long and weighed a shade over a tonne as specced. Flipping ridiculous for what it was holding up. I reckon something half the size would have been adequate. Luckily i managed to borrow a tractor to lift it into place.

Calcs must have been ok though as its not fallen down yet......

It always makes me wonder what they think the 3.5 means when they talk about concrete blocks. 3.5 Newton/mm2 are only suitable upto two storeys after which they should be 7 Newton but if you think you are going to be asked what block strength you are using, think again. The idea that steels should be on concrete is also a bit of a joke, just 'cos it's concrete does not mean it is right - what happens if the concrete was mixed by some bloke with a mixer and a shovel (how a lot of concrete gets mixed) ? As I said, the bearing should be designed properly and some consistency should be used with materials and the method of transferring the loads into the surrounding structure. this does not mean that a concrete bearing will automatically fit the bill (probably on the assumption that it will be 30 N/m2 strength at 30 days if it came readymix)

I have found that a commercial building control firm (approved inspectors) will be both knowledgeable and supportive unlike council building control who are often re-trained staff from the building trades working to prescriptive instructions.

Mark

As I said mine was for the roof structure which included 5 glulam beams and all the rafters which is more than a single beam is likely to cost in terms of calculations which should be around £100 to £150. Not forgetting if the structural engineer gets it wrong you can claim and a good one will have professional indemnity insurance.

Although it is probably true that the council have no liability they can stop work and make you make changes if they think it does not meet the standards.

Indemnity insurance is normally taken out buy the seller, a buyer will have to wait 12months after completion before they can take it out.

Bob

Bob,

I had meant the seller when I mentioned insurance, I had no idea you could take it out as a purchaser. As for the council poking around on site, it is my understanding (from building control themselves) that once you have taken one route or the other then you can't change your mind afterwards and neither has any jurisdiction on the others project. In other words, once building control are on the job you cant then change to an approved inspector and if approved inspectors are running the show, building control have no authority.

Mark

Re, Structural engineers insurance, it would be prudent to check what his indemnity covers and how much. It is entirely possible to get a 3 or 4 thousand pound insurance cover which is hardly worth having given potential risk!

Edited By Mark C on 09/08/2015 22:27:46

If you opt for the approved inspector route and they are not happy with what you are doing as they can only advise and withdraw,they have no powers, then unless you appoint another the council will take over automatically and can force changes if they do not comply even to the point of doing the work them selves and present you with the bill.

Bob, the point being that unless you fall out spectacularly with the approved inspector then council building control are off the job - if you can't get along with the approved inspector your chances of getting along with council BC are pretty slim.

Mark

When I have been down this route and this included both extending sideways a built-in garage and also whole house construction including a double width garage, I did the full calculations of loads and steels required. The Building Regs Departments on both cases approved the actual calculations. When a friend and neighbour who happened to be a Lecturer in Building Technology submitted plans for his garage with an insitue cast roof, they threw the book at him and made him produce test cubes of the mix as well!!