The POSIs Picnic: a solution is in sight.

[ToughButterCup]

Some of you will be aware of this thread. It itemises a series of errors on my part. 

The wet-fish slap in my face was provided by @mvincentd. For which I am sincerely  grateful. Cutting through the clutter of a five page thread and seeing the core of the problem is not easy. Thanks @mvincentd.

 

POSIs ordered were 100mm or less too short. The thread explains how I made the error. It shows quite how much support you can muster on BH by making one simple post. At one stage I was resigned to re-ordering a new set and hawking the old set of POSIs on eBay. Many technically savvy people pitched in: it became very obvious how much experience is packed into this little Discussion Group. Technical resolutions to the problem were offered and, truth to be told, I didn't take much notice of them. Thats the problem with my German extraction: your instinct is to do it right or not at all.

 

Perhaps because I'm old, with the supplier, I tried to apply the conflict resolution techniques I taught for so many years. I say tried because its a damn sight easier teaching others how to do it than to apply it to yourself. And, slowly the possibility of a technical solution became clearer in my disappointed brain. So this thread is about looking forward to a sensible way of solving this little problem.

A series of people @PeterStarck , @scottishjohn, @joe90, @Russell griffiths, @Nickfromwales all supported the idea of lengthening the  body of the joist. And when @JSHarris pitches in and supports those saying that I ought to consider the idea, I did what I should have done ages before. Picked up the phone.

 

Steve Grice of Cheshire Roof Trusses has been dealing with my orders for joists. He's patient. Has to be.?

He suggested he talk to Cullens the hanger manufacturer. And a certain Nicola Small came up with this idea

 

In the way of things on BH, one idea - fifty opinions. Most pointed to the issue of unsupported top and bottom chords. Anyway, I read through them all and had a chat with Steve Grice (manufacturer) this morning.

 

He agreed to talk to Nicola (Cullens, hanger manufacturer) to see if we could pack out  the top and bottom chords. (The area immediately above and below the purple-shaded area above)

 

Cant say I hadn't heard the exact same idea  from @joe90 . Why he even supplied a diagram.

 

Hey Joe! Did Nicola ring up yesterday and  ask you ? ?

[joe90]

@recoveringacademic no, but she’s welcome ?. Glad this issue is being resolved, did you see my PM.

[Guest Alphonsox]

Good to hear you've found a resolution to this problem - Onwards and upwards !

[Mr Punter]

The proposed solution shows 2 vertical pieces and new 3" block. The photo on @recoveringacademic's original post just has a single upright and I can't see how this will work.  Maybe just screw length but a new drawing may be needed.

[joe90]

I think you will find that some joists only have one end vertical piece and others have two. I still think it depends on what the BCO will accept. Like others I don’t like the 3” block idea and prefer my “T” piece idea, again it’s down to what the BCO will accept. On reflection rather than try to make lots of “T” pieces, (which I could do with my woodworking machines but more difficult without) I think two pieces glued together might be simpler. If @recoveringacademic wants me to I will draw a diagram of what I propose and he could send it to Nicola, if they accept it (in writing) that will keep building control happy.

Edited November 29, 2018 by joe90

[ToughButterCup]

Thanks folks. 

Here's a copy and paste from the manufacturer

 

I spoke to the engineer who calculated the detail at Cullen and have had this response below.

“Hi Steve,

They are welcome to put blocks in above and below but they are not required. 

If they feel they want to do this it’s fine as long as the screws are in and the middle block is tight first.

Regards,”

So yes, if you want to fill the areas above and below then not a problem but it is not required for the floor performance.

Best regards,
Steve

 

In other words, the top and bottom chords can be supported. One by one we're knocking them down.............

 

Now then, how to handle the BCO? Advice please.

If the manufacturer has designed and signed off a solution to the problem, has the BCO the authority to refuse to allow the modification? 

If he / she were to refuse (and in this case a refusal really would offend) surely  it would have to be on the basis of reasoned argument? Put another way, this solution enables the BCO to argue that it's nothing to do with him (in this case it is a him).

 

For the sake of completeness, I attach the relevant document for review.

104 18 - Cheshire Roof Truss_28-11-2018_R-104 18_RevA.pdf

[joe90]

In my experience BCO,s cover their backs with documents given by suppliers, they don’t usually disagree  with them. I would just present the BCO with what you have been supplied with by the manufacturer and get him to agree that you can do this (I would be extremely surprised if he disagreed). Then I will do you a diagram (if you want) of what I would do that would satisfy the manufacturer and your BCO. and is easy to do.

[ToughButterCup]

1 minute ago, joe90 said:

In my experience BCO,s cover their backs with documents given by suppliers, they don’t usually disagree  with them. I would just present the BCO with what you have been supplied with by the manufacturer and get him to agree that you can do this (I would be extremely surprised if he disagreed). Then I will do you a diagram (if you want) of what I would do that would satisfy the manufacturer and your BCO. and is easy to do.

 

Thanks Joe. The cheque is in the post......

 

I like the sound of the last bit... the diagram and .... easy to do. I like that a lot.

[joe90]

I would make up the “T” piece using two blocks A and B as per below, glue all in place with d4 expanding glue, I would countersink the screws in a little that gives you some timber to plane off in case it’s too tight in the hangers. Also drill pilot holes in A and B so you don’t split them. Make sure the blocks are the same width of the joists. Using two blocks saves you having to cut a “T” section if you don’t have woodworking machines. Shame I am not closer, I would help you out with this, it’s right up my street this woodworking malarky.

Edited November 29, 2018 by joe90

[Mr Punter]

I think you could just double up the timber ledger on the wall.  Just like when you trim a stair opening.

[Declan52]

Instead of long screws would something like coach bolts not be stronger. 

 

[joe90]

3 minutes ago, Declan52 said:

Instead of long screws would something like coach bolts not be stronger. 

 

 

As everything is in compression I am not sure it would add anything, plus, the manufacturer stipulated screws and the BCO would want that followed.

[mvincentd]

I really don't understand why they are saying the filler block (particularly at bottom) isn't necessary, given its so easy to achieve and surely good practice at least even if not critical at an engineering level.

 

Their drawing shows a single block reaching from back of joist hanger to joist vertical.  Might they baulk at splitting that into two blocks...suggesting a shear line is introduced as per pink on drawing below left.  In which case does drawing right mitigate.

[joe90]

@recoveringacademic Actually I think the above is better than my solution and easy to do. 

[Nickfromwales]

I assume (  ) this is all fortified with a good lashing of glue? 

[ToughButterCup]

Thanks boys... only just seen this.

I sent the drawings and email exchange to the BCO yesterday. He's visiting on Monday.

 

Would it make sense to put another block tight up against the top chord - in the same way that there's a yellow block on the bottom chord in your drawing @mvincentd ?

 

I'll try a mock-up over the weekend.

[joe90]

Yes I would also block the top, but then again my wife says I am OCD .

[scottishjohn]

18 hours ago, Mr Punter said:

I think you could just double up the timber ledger on the wall.  Just like when you trim a stair opening.

suggested that 4 pages ago ..double up the thunder bolts+ screw wall plates together --job done -

he would be doing the flooring by now--maybe even the carpets.LOL

 

[ToughButterCup]

Key issue ( @scottishjohn ) is sign off....... by the SE at Cullens, and the BCO.

 

@mvincentd, I have asked directly whether I may put blocks in top and bottom because I thought - given all the posts by you @JSHarris and others about compression, shear and bouncing POSIs.

I'm surprised you make the point above -  

 

'...and surely good practice at least even if not critical at an engineering level....'

 

I thought it was critical. But then what do I know? [ A whole lot more than I did on Monday]

[joe90]

20 minutes ago, scottishjohn said:

suggested that 4 pages ago ..double up the thunder bolts+ screw wall plates together --job done -

he would be doing the flooring by now--maybe even the carpets.LOL

 

 

But that had not been sanctioned by either the joist company or the BCO for signoff, personally I would rather extend the joists in an engineered fashion.

 

oops, cross posted with @recoveringacademic (Great minds think alike ?). Frankly it is critical, there is nothing worse than a bouncing of flexing floor that can’t be put right after the build is finished.

 

 

Edited November 30, 2018 by joe90

[scottishjohn]

27 minutes ago, joe90 said:

 

But that had not been sanctioned by either the joist company or the BCO for signoff, personally I would rather extend the joists in an engineered fashion.

 

oops, cross posted with @recoveringacademic (Great minds think alike ?). Frankly it is critical, there is nothing worse than a bouncing of flexing floor that can’t be put right after the build is finished.

 

 

we seem to be getting a bit anal now--next your going to tell me you used a torque wrench on all the thunderbolts --

16m  thunderbolts should be 100nm  before you ask

not that i,m a fan of them --used too many bolting down ramps and things in a garage -very critical on pilot size and do not like being taken out and refitted--hole gets bigger--its a one fix bolt --good old expansion  types are way stronger +can be removed =refitted  

its a building not space rocket not a vehicle that has all sorts of other dynamic loads -no earth quakes -so good straight forward engineering is all that needed--that why i said just double up the number of thunder bolts --I understand the idea that being further away from way it could try to twist beams from walls --simple solution--pack ends of joist out sideways so there is no space for the beams to move from twisting off wall motion -,

[scottishjohn]

14 hours ago, mvincentd said:

I really don't understand why they are saying the filler block (particularly at bottom) isn't necessary, given its so easy to achieve and surely good practice at least even if not critical at an engineering level.

 

Their drawing shows a single block reaching from back of joist hanger to joist vertical.  Might they baulk at splitting that into two blocks...suggesting a shear line is introduced as per pink on drawing below left.  In which case does drawing right mitigate.

this is why isuggested if you really want to over engineer it

to use plywood and glue a few layers together and jigsaw to exact shape ,then a bit of goorilla glue and predirlled holes +screws make it bullet proof.

so many simple ways to sort this problem  and by the time the floor is glued+screwed  its going no where.

If you get floor bounce ,then your engineer didn,t spec it right to start with 

[Jeremy Harris]

15 minutes ago, scottishjohn said:

we seem to be getting a bit anal now--next your going to tell me you used a torque wrench on all the thunderbolts --

16m  thunderbolts should be 100nm  before you ask

not that i,m a fan of them --used too many bolting down ramps and things in a garage -very critical on pilot size and do not like being taken out and refitted--hole gets bigger--its a one fix bolt --good old expansion  types are way stronger +can be removed =refitted  

its a building not space rocket not a vehicle that has all sorts of other dynamic loads -no earth quakes -so good straight forward engineering is all that needed--that why i said just double up the number of thunder bolts --I understand the idea that being further away from way it could try to twist beams from walls --simple solution--pack ends of joist out sideways so there is no space for the beams to move from twisting off wall motion -,

 

What about the increased shear stress in the doubled wall plate then?  Not a good engineering solution at all to double up the wall plate, far, far better to adopt the properly designed end extensions, that includes both a thick shear web, plus an end block that will restrain the lower member that is in compression when loaded.

[mvincentd]

19 minutes ago, recoveringacademic said:

I'm surprised you make the point above -  

 

'...and surely good practice at least even if not critical at an engineering level....

 ...point below presumably?

 

1st- I'm pleased to have been able to be of some help....but please don't mistake me for someone in any way qualified to make engineering judgements....at the end of the day I was just chewing the fat with you and all.

 

Cullens said you could block the top and bottom sections but that it was not necessary....so i took from that my assumption of not critical at an engineering level.

However I thought surely good practice to replicate the original intended 'shape' of the joist as far as possible given those parts surely provide some enhancement to performance (for one  example don't the hangers have holes for twist nails going into those areas and aren't ALL holes supposed to be nailed).

 

I only drew in the bottom yellow block out of laziness but yes it would make sense to do this at top too, but i'd think the bottom is the most important bit to remediate, and this is why;

Remember that unlike your earlier joists these were designed not to be top hung, so here the bottom chord is the primary bearing point onto the hanger and without the addition of the bottom yellow block the 'too short' bottom chord is only catching maybe half of the hanger base.  I know the hanger base isn't the be all and end all because of the twist nails through the sides....but my instinct has me more comfortable utilising all the hanger base, just as @joe90's design does.

 

 

 

 

 

[scottishjohn]

Just now, JSHarris said:

 

What about the increased shear stress in the doubled wall plate then?  Not a good engineering solution at all to double up the wall plate, far, far better to adopt the properly designed end extensions, that includes both a thick shear web, plus an end block that will restrain the lower member that is in compression when loaded.

it will be minimal but to be super sure  i said double up on bolts and if ends of joists are packed after fitting they can go nowhere --no space means even if there is a twisting force it can,t move cos theres no where for the plates to go.

Isaw original spec was  one bolt every 600 but joist were 400 spacing --i would have done bolts at same as joists anyway ,and if you still worried about something that can,t happen apply a layer of no nails or whatever behind wall paltes then load is pread over total area

how many diff solutions do you want to a simple problem 

i suggested a soltion to fix it that way aswell

take your pick both will work fine and with double wall plates you got twiice the area to glue + double screw the floor too if you want

  engineers  have said you don,t need full support on the end of the joist anyway --so can,t be much load anyway--=if you believe them  

me igo for belt and braces always