Possible RSJ with welded under plate twisted

[mrgobby]

Doing a single storey extension with steel ridge beam, high collar and bifolds in gable with steel RSJ spanning opening of 3600 it's 203x102 with 6mm 250mm wide plate welded on underside to carry outer gable brick leaf (projects 275mm so mortars in okay). Inner leaf carrying medium density blockwork. The ridge rsj is 178 x 102 and roof pitch is 18 degrees so will have marley moderns as tiles.

External dimensions are length 6000 and 5850 wide. Calcs are borrowed if you like from other similar spec jobs, architect friend supplied them and I know the properties they were taken from, one in my street, an identical house and extension to mine for the ridge beam, just my opening was 3600 and theirs was 3000 so from another job of same design with a 3600 opening the 203x102 with 6mm plate had been specified.

SO It looks to me like the steel or more likely the welded plate was already or probably has since twisted in the middle as the gable has gone up and the load increased. The plate is level either end by the padstones but has tilted downwards a little in the centre towards the outside by about 10mm. Sort of a twist as I describe it. This means left to right there will be a 10mm bow effectively in the opening.

Maybe I'm being overly concerned about 10mm, but looking at bi folds for the opening and want them to work okay without binding. No more load will be going on the outer brick skin but the roof tiles are yet to go on. However The rafters were over specified at 200mm (150 would have done) and I'm thinking the loadings are multi directional with ridge beam carring a bit, the rafters are butted together as well as birdsmouthed into the bolted plate on the steel so force into each other for a load pushing against each other and load is transferred down onto the walls more than the gable really.

Has anyone seen or suffered similar issues or got any sensible advice as . I'm not going to be able to blame anyone for any of this other than myself as Im managing the job. IS there a remedial option other than tearing it down or am I over worrying about it, I'm a bit picky about the accuracy at times but then the carpenter said the walls were 30mm out of parallel when doing the roof and I thought he was being picky! I'm doing this myself albeit with qualified tradesman, I dug the footings with a chap I know, I drove the dumper he did the digging and we poured the slab after brickwork done up to damp all to specifications and with full building control approval. I've had professional brickie crew in at weekends who work in the week on main large housing developments and the roof was constructed by a professional carpenter who happens to live in our road.

Any reassurances welcomed as I'm about to felt up the roof and either have a go at that or more likely get a roofer in!

Thanks

Mark

 

[^woody^]

So to sum up, you ripped off someone else's calculations for a different loading situation on a different job, and your beam has bent, and you want to know if its OK?

 

[Notch7]

specifications and with full building control approval.

I hate to ask, but how will building control sign off the job if you dont have structural calcs?
If you dont have calcs for this project, my advice would be to get an engineer in and get some calcs done before going any further.

There a SE on here that might post -and give you a better understanding of what the problem is, but ultimately you have to have calcs done -which building control will accept because a SE is the qualified expert who will have PI backing his work.

Im guessing you have something like 1200mm brickwork either side of the bifolds -Im just wondering if the structure is ok for lateral stability.

Unfortunately structural calculations are more complicated than just simple loading, there is lot to consider

If you have steel ridge beam, is the extension having a vaulted ceiling -in which case the end of the ridge beam will be putting a load on something below -is that where the bifold lintel is fitted?

 

[mrgobby]

Your summing up is inaccurate Woody, nobody has been ripped off. A calculation paid for previously through an architect friend for the same set of parameters is hardly ripping anyone off. Some might conclude that to be paying someone twice for identical information would be a rip off but then you probably have an alternative view. What has happened here is the plate side should have been acro propped until the mortar set, making the mass all collectively set as one and not be tipped. I was looking to see if anyone had ideas for a solution otherwise I'll just get over it and perhaps you will get over yourself too

 

[mrgobby]

All is okay there Notch, building control are happy to accept the calculations, they show all the relevant load related information. The inspector has been round taken measurements and there wasn't any issue.

 

[Notch7]

All is okay there Notch, building control are happy to accept the calculations, they show all the relevant load related information. The inspector has been round taken measurements and there wasn't any issue.

Ah thats good

It seems surprising a 6mm plate has bowed with the weight of gable brickwork above -has the steel and plate twisted round because the outer brickwork was done and loaded the steel one side and not supported by acrows until the gable mortar had set?

if the steel twisted, I wouldve thought it would effectively drop all the way across the opening?

Im not sure its a problem -but you need to make sure your bifolds fit below the lowest mid point and you pack the frame head to keep it straight.

 

[mrgobby]

I think Notch there is a little bit of both gone on and yes it should have been propped while the mortar set is the bottom line on it. The steel is fine in that it's on the bubble left to right but yes has tilted a little front to back and the plate is slightly bowed but then tbh I didn't check it on arrival and welding sometimes causes a little distortion. Yes will need to measure the lowest points will be the outcome on the doors and a bit trim trickery externally to try and conceal the wandering level. I was just a bit peeved it happened at all when avoidable with a bit more thought but to tear it down now for this is probably overkill and causes more delay, the weathers turned a bit now too so making it a miserable thought but you know how it is when you know something isn't spot on and you've noticed it and it's niggling you a bit. I'll have to live with it I guess, when its all done I'm hoping the positives will outweigh it!

 

[tony1851]

If the original spec was for 3m, and you are 3.6m, it's no surprise that the beam has twisted and deflected. The deflection of a beam is proportional to the cube of the span, so your deflection on 3.6m will be getting on for twice that on 3m, and the offset loading will compound that.
A 203 x 102 on that span with a 6mm welded plate is IMO far too optimistic; a better solution would have been at least 203 x 133 x 30, with an 8mm plate (subject to the actual loading figures). If the plate has been tack-welded, it's unlikely that the distortion is due to the welding.
'I' beams are susceptible to torsion when loaded off centre, particularly those with a narrow flange; propping the beam while the mortar sets would have made little difference.
It's unlikely to come down, but the ridge beam will impart a little extra load on it, and you need to be aware of snow load if you are to tight tollerances with the bifolds.
If you want to do a proper job, replace it now or regret it for ever.

 

[mrgobby]

Thank you for your comments Tony, the SE specified for a 3600 span not 3000, yes the back was tack welded but not sure if the front wasn't continuous fillet.

 

[tony1851]

Thank you for your comments Tony, the SE specified for a 3600 span not 3000, yes the back was tack welded but not sure if the front wasn't continuous fillet.

I'd be surprised if he allowed for the torsion effect.
If you could post copies of his calcs (with your address/id etc redacted) it might be possible to see how he's come to such a slender section.

 

[mrgobby]

Thanks, I'll get back to the SE via the Architect about what torsion effect allowances were made in the calculations.

I should add for the benefit of those reading this that it really doesn't look dire or dreadful and in fact I'd have to point it out for someone to see it unless you were in the know and were looking for it, it's not in a state of collapse.

 

[pilsbury]

I feel your pain. I am not a pro in any sense of the word but for me I’d be asking myself the following questions. Is it safe? Will it affect the look or function of the build? Will the bifold work now and in years to come because of it? Will the homeowner know or be disappointed with this? Will it pass all the regs? Are you able to live with it?

then you’ll know whether to leave in situ or start the process of replacement.

 

[mrgobby]

Thanks pilsbury, all relevant questions and I'm sure you pro at something, so don't be so down on yourself lol. Yes it's safe, not a small piece of steel by any stretch (or twist). The local steel fabricator didn't wince when he delivered to site ready to go in, they made them to drawings of which they have seen a few over the years, they are pretty good at pointing out any issues before they happen as he was telling me! Looks wise no not really an issue, it's just that I know it's not perfection and regarding function well it does what it says on the tin. The bifolds will work just need measuring carefully and as the homeowner I'm more annoyed than disappointed. Regs are fine and if by the end of the weekend I haven't torn it down then I'll probably just live with a 10mm abnormality.

 

[pilsbury]

Well if you’re sure it’s safe, and you can work around all the cosmetics and still produce a good job, then I think you have your answer.

I had to bodge...... Sorry.... Manage.... a few issues on my project that if I were to have gone to the letter would have cost an arm and a leg in time and money to have been no better off at the end.

 

[John D v2.0]

as our structural engineer said to me on our extension/roof design when I asked about the existing roof, their job is to design something that they can prove won't fall down and will meet the performance and aesthetic requirements where applicable. Outside that realm there are a lot of things that can't be proven but wouldn't actually fall down, or meet a lower performance standard that would still be okay in the end. There is a certain element of natural selection (the houses that had issues have been underpinned or remedial works have been done, or as with pre 1930s houses the owners just treat the cracking as an aesthetic)
However you'd be well advised to listen to Tony rather than the person who delivered the steel as they don't really have any knowledge and he does!