Alternative to piers every 3m?

[tony1851]

Hi Tom,
My previous post was written from experience. Where I have gone outside the recommendations in AD A, I have usually been asked by Building Control to do calculations to prove stability.

Had you started this project under Full Plans, instead of Building Notice, I'm sure the inspector would have flagged this up initially.

All I can suggest is that if the inspector agrees to your choice of scheme, then all well and good, and go with that. Chances are you will be OK because the wind load we have to take into account is quite high and does not occur frequently.

On the otherhand, if he does ask for justifyying calculations, all I can suggest is that you post back here and ask chief-engineer-to-the-forum Woody what to do next.

 

[tony1851]

Hi Oldun,
With respect, I have to disagree with you on this one.

If the Council requested the OP to provide structural calcs for a 1/2 brick wall, say 2.2 or 2.3m high, supporting a load from only a 2.6m span roof, on a flexible dpc, no engineer would be able to prove that it would be OK under the specified wind load.

In practice, he may well be OK because the wind pressures allowed for only happen infrequently.

 

[Pallatrax]

Hi guys,

Thanks for the advice.

Please clarify what it is my hair-brained ideas (which I'd need to get past BC) need to do or combat though - I'm still a bit confused?

Do I need to make the wall more rigid or offer it more lateral support, treating it as a solid entity? To me piers do both, and that could by why a 6" block wall was offered as a compromise....

Cheers
Tom

 

[^woody^]

Stick with me Tony, I'll get you through your college building course with flying colours.

 

[tony1851]

Well just ask the inspector if you can use the 6" block - you might be lucky and have a reasonable one who doesn't ask you for any calcs.

If not, I'm sure Woody would be on hand to offer his usual expert advice

 

[^woody^]

OP, in essence bed reinforcement has the effect of stiffening the whole wall so that it performs, and has the resistance to loading of a wall of much greater thickness without reinforcement

If you get a bco of limited knowledge then they won't be aware of this, but that does not discount the fact that it is correct

 

[RonnyRaygun]

Err no. Horizontal reinforcement works in the horizontal plane which stop the wall buckling or deflecting in wind loading

Incorrect. The half-brick wall acts like a slab, and has to be reinforced in both directions if it is to be effective against horizontal wind pressure. This is basic stuff.

Where's Ronny?

Are you two still at it?!

I don't know whether bed joint reinforcement would completely eliminate the need for piers in the OP's situation, but according to the Brickforce brochure it does help improve the overall strength.

The fact is though, that it should be designed to ensure that the wall is strong enough. Just chucking in be joint reinforcement doesn't guarantee that the wall will be strong enough.

When I've got more time I might plough through the calc myself to see what difference it makes.

Brickforce Brochure in this link. Has load span tables and design guide but haven't had time to absorb any of it yet.

 

[tony1851]

OP, in essence bed reinforcement has the effect of stiffening the whole wall so that it performs, and has the resistance to loading of a wall of much greater thickness without reinforcement

I agree with that; the horizontal reinforcement (bricktor or suchlike) will enhance the vetical load-bearing capacity.
But it will do nothing to counter the tensile stress developed under wind loading, which is the critical aspect here.

Your comment suggests that you are not aware of the issue.

 

[tony1851]

I don't know whether bed joint reinforcement would completely eliminate the need for piers in the OP's situation, but according to the Brickforce brochure it does help improve the horizontal span.

Yes, it will improve horizontal spanning, but there have to be returns or piers to span between - OP doesn't want them.

 

[RonnyRaygun]

I don't know whether bed joint reinforcement would completely eliminate the need for piers in the OP's situation, but according to the Brickforce brochure it does help improve the horizontal span.

Yes, it will improve horizontal spanning, but there have to be returns or piers to span between - OP doesn't want them.

Yeah, I meant to say overall strength...gone crazy editing up there!

The calcs in the brochure suggest that it improves strength against lateral wind loads too.
I guess the theory is that if the panel is stiffer horizontally then less force will be taken spanning between vertical restraints

Agree though that it needs something to span between. If it could span end wall to end wall it might be OK. Needs to be looked at by an SE though...I wouldn't advise just throwing in some BJR and hoping for the best.

 

[Pallatrax]

I just phoned my LBC office and, - drum roll please
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there was no answer!

I'll try again shortly

Tom

 

[^woody^]

Your comment suggests that you are not aware of the issue.

Au contraire, my comments suggest I know more about it than you.

Reinforcement strengthens the wall in all three axes

 

[Pallatrax]

I just spoke with the office, and the chap was more than happy to dash off and confer with a colleague.

He cam back and said:

6" or cavity!

Well the cavity option seemed a tad daft, but there wasn't any interest in the bed reinforcing I put to him, so 6" blocks it is and no piers! That'll do

Thanks for all your comments chaps
Tom

 

[tony1851]

Reinforcement strengthens the wall in all three axes

No, it doesn't.
If you design an insitu reinforced concrete slab, you wouldn't just put bars in one direction. If you did, the slab would be ok in the direction of the bars, but it would fail the other way. That's why we use square mesh, which ensures it is reinforced in both directions.

Similarly with the thin garage wall; bed reinforcement will strengthen it in the horizontal direction but not vertically. Ronny noted that the mfrs brochure states that it would strengthen the wall against wind loading. But that would only apply if there were piers or returns for the wall to push against (that's the 'arching effect'). It would still not address the weakness in the vertical direction.

Woody - I've had to do a number of wind-load calcs over the years at the request of b/c when going outside AD A. The council's own engineers still look carefully at wind loading in these situations.
By that I/m not saying these things don't work - more often than not they do - it's just sometimes impossible to prove theoretically that they will. And I didn't write the codes

 

[tony1851]

@OP, well done and glad you got a result without too much hassle.
For my part, sorry about the debate with Woody

(he's a Brummy, you know................).