Taking down dividing wall

[^woody^]

But there is still no bond between it and the beam,

There you go again using terms in the completely wrong context. What do you mean bond?

Masonry is held in compression and aided by friction from the mortar. Full joints hold the units together in compression in the same principle as an arch. However as masonry courses are flat, it is friction (of the full joints) which makes the course self supporting.

It is this self supporting characteristic, which is the basis of the composite principle of support. Which is why the masonry above the lintel needs to go off before further load is placed on the lintel

It does not mean that a lintel designed for composite support can not be inserted into a wall where the masonry has already gone off. The nett effect is the same - a composite support

 

[tony1851]

[

It does not mean that a lintel designed for composite support can not be inserted into a wall where the masonry has already gone off. The nett effect is the same - a composite support

Yes, a composite-type lintel can be inserted into an old wall, but the safe maximum span will not be as much as if it was built in.

I was not using 'bond' in the wrong context. There is 'bond' as in English bond, and there is also 'bond' as in the attachment of the mortar to the brick.

Are you one of those folk who believe that old wive's tale that 'the mortar is there to keep the bricks apart, not to stick them together'?

I wouldn't want you advising on any structural aterations to my house.

 

[^woody^]

So the bricks actually bond to the concrete lintel, and this gives it some sort of enhanced strength? Not the masonry bond of the wall, just this one horizontal joint between lintel and bricks?

And by inserting the lintel retrospectively, with a fresh mortar bed on top, and then pressing it up to the bricks above, your claimed bond does not take place, and this enhanced strength does not occur?

Do you make this stuff up as you go along?

Oh incidentally, what happens if a cavity tray breaks this magical bond?

 

[RonnyRaygun]

I've been trying to find a definitive answer to this one.

EN 845-2:2003 (E) states the following:

B.3 Composite lintels
Composite lintels should be adequately propped in accordance with the manufacturer's
recommendation. The props should not be removed until the masonry element of the lintel has
achieved its design strength.
All masonry joints (horizontal and vertical) should be filled with mortar.
The bonding and the masonry work of the composite section should be in accordance with the
manufacturer's recommendation.
No chases or holes should be formed in the zone of the composite section.

It doesn't specifically state it, but to me this implies that the masonry should be new, not existing.

Similar information here including guidance that dpc (cavity tray too?) must be two courses above lintel.

I would think Tony is correct when he says hairline cracks due to slight movement in the existing masonry will prevent it acting as intended in composite design.

 

[^woody^]

Existing masonry had already achieved its design strength.

Propping is only necessary to support green masonry.

A lintel installed retrospectively will perform the same as one built in, and there is nothing in this thread to demonstrate anything to the contrary - just the usual dogmatic opposite view for the sake of it, with some random out of context terms thrown in to try and add credence were facts are absent

Ronny, yes that standard does not explicitly mention existing masonry, and that it's for a reason. It's not correct to imply meanings into a standard - standards are explicit

 

[RonnyRaygun]

Existing masonry had already achieved its design strength.

Yes, but you have no idea what that design strength is. Even if we take the view that the existing masonry is able to act compositely we have no idea if the design strength of the masonry is sufficient. Guidance states min 3:1 and 20N brick for composite action.

Propping is only necessary to support green masonry.

But again, even if we are of the view that the existing masonry can act compositely, we still need to ensure that the bond between masonry and lintel is achieved. Propping will help this to be achieved.

Ronny, yes that standard does not explicitly mention existing masonry, and that it's for a reason. It's not correct to imply meanings into a standard - standards are explicit

If only they were explicit. Sometimes they are so badly written with such little relevant information for a particular situation, it's impossible to ascertain what they mean.

 

[noseall]

Guidance states min 3:1 and 20N brick for composite action.

So "guidance" automatically rules out using pcc lintels in blockwork masonry then?

 

[RonnyRaygun]

Guidance states min 3:1 and 20N brick for composite action.

So "guidance" automatically rules out using pcc lintels in blockwork masonry then?

No, you can still use block work as long as there are a couple of courses above. The unit strength of blockwork doesn't need to be as strong to obtain the same masonry strength as there are far fewer joints in the masonry.

It would only prevent the use of blockwork in composite lintel design anyway.

 

[tony1851]

A lintel installed retrospectively will perform the same as one built in, and there is nothing in this thread to demonstrate anything to the contrary - just the usual dogmatic opposite view for the sake of it,

That is not so. Ronny's link to a manufacturer's spec. makes it clear that a given lintel which is intended to be composite will support a greater load with additional brick courses built at the same time.

The other references make it clear that the masonry should be built at the time the lintel is placed, and the latter propped.

And from a personal perspective, I would not disagree with anything someone writes, just to start a debate. There are many posts of yours with which I have agreed, whether or not I have contributed anything.

 

[freddiemercurystwin]

What's wrong with a good ol' 152?

 

[marsaday]

Hello again.

I have been into the house today and done some measuring and checked in the loft.

1) The span I want to create will be around 1.85m. Either side of this span will be 30cm of brick work.

2) This single skin wall (built 70-80 yrs ago) is pretty much dividing the house in 2 with the hallway and kitchen on one side and the lounge and dining room on the other.

3) This wall is taking a loading from the roof i think. I have been up there and seen the most beautiful back pointed tiled roof which hasnt been touched in all these yrs - great sight as normally the pointing drops out. On each side of the roof there is a post holding up the purlin in the middle. These posts on each side sit on a large central timber bearer which i think is sat on top of my wall.

4) So will i need a SE or do i just over spec it. I have some photos is needed.

 

[marsaday]

Just spoken to BC and an R9 215 x 100 will be fine for this.

The floor above is probably loading on this wall as well.