Steel calculations

Hi

Just a quick question, im awaiting structure engineer to reply to email, but it's bugging me now.

The council BC attended today all work fine but have questioned why this timber spec on drawing.

It's just randomly on there and confused everyone, the calcs are only for steel in rear wall, but the engineer has included timber spec, see attached.

Thanks

 

Looks like he's sent you the output from a timber beam design in the software package TEDDs. It's nothing to do with steel beam design.

Do the forces match with what been used for the steel design? Unless they're in there as an alternative to a steel they probably accidentally included.

 

Unsure of how to read the force correctly, but I hope the attached helps

 

Wouldn't say a alternative, spam of rear to house 5 metres

 

Can't see the timber included in the final drawing.

 

Where would they be without their spreadsheets?

 

Looks like the timber beam and steel beam calcs are totally unrelated.

I'd assume the timber beam calc is in there by accident.

 

Thanks guys, engineer emailed back he's looking into it hopefully a mistake.. I'll let u know when he responds.

Thanks again

 

He'll probably invoice you for the extra timber beam.

 

Thread drift Q. Do calculations for structural needs, beams etc HAVE to be done by a structural engineer; or like electrical work, by a competent person? Surely these days, most calcs are done by sticking the parameters into a computer?

 

Structural calculations don't have to be undertaken by a chartered SE; that may change in the near future after Grenfell.

 

What parameters? The relevant ones or the ones to get the result you want?

That's the difference.

 

Of course, but I am looking to find stuff out here, not to be contentious. I assume.... that there would be a number of values the person asked to calculate the size of a beam will need in advance? Width of opening, bearing material under the beam ends, type and extent (no of floors) of material above the beam etc. Once you have all those, I further assume that it's about using a formula? Is that not the case?

 

That's what people tend to think when they download a dodgy copy of superbeam or get a copy of someone else's calculation and just want to change the address.

The loadings have to be known and any site specific factors need to be taken account of. So things like point loading can drastically alter what beam is required, as will the position of windows and doors alter whether the load is distributed across the beam or partially.

So its not just a case of working out an area of floor or roof and wall, and then putting those into some formula - well different formulae for bending, shear, buckling, deflection with potential differing factors to add or not add.

Yes a beam under a simple wall or floor may well be easy to work out, but its knowing whether it is actually easy to work out or if there are factors to be taken in to account - that is where competence comes in.

Then comes the wall below the beam and how is the load to be transferred down to the ground. Are the foundations suitable, are posts required for stability etc.

It's the old "crap in, crap out" scenario.

 

Spreadsheets can do the 'heavy lifting' of the calculations required to design a beam, bearing in mind that there are a number of checks which need to be done before a specific size of beam is declared satisfactory.

But the loadings the beam is carrying have to be evaluated by the SE to input the figures into the program. This is where engineering judgement comes in, because it can often be difficult and time-consuming for the SE to identify all the loads. Because of this, a less experienced SE will just pick a large figure off the top of his head to save the effort of more accurately calculating the loads. On the basis of GIGO, this often results in a much heavier/bigger beam than is strictly required, and the client has to pay more than necessary.

A wider issue concerns the on-line calculation sites. They can give a beam section size for a specific load/span - if the user knows how to input loads - but never see the wider picture of the overall stability of the building, and the effect removing a wall might have.