Lintel orientation.

[Pocster]

Google suggests some lintels are marked ‘ top ‘ . Other than that it suggests the application determines the orientation. No markings on mine . Steel is central …

This is to support some walk on glazing ( cough cough ) - so I’m guessing I can orientate to suit ??

[Carrerahill]

22 minutes ago, pocster said:

Google suggests some lintels are marked ‘ top ‘ . Other than that it suggests the application determines the orientation. No markings on mine . Steel is central …

This is to support some walk on glazing ( cough cough ) - so I’m guessing I can orientate to suit ??

I wondered the same, brickie looked at them it and said, "that's the top" after rolling them a bit, all I could see that he used to differentiate it was that the top was a vibrated, or simply a naturally settled finish but the bottom and sides were smooth from being in formwork. 

 

From what I can remember, the prestressed wire/rod is biased towards the bottom, so when loaded that steel is in tension and gives the strength, however, you also get plain ones... I think if the steel is mid, then its plain and can indeed go anyway.

 

I have been left scratching my head looking at them too.

 

Where is @Gus Potter - he will know for sure!

 

Edited August 23, 2022 by Carrerahill

[Pocster]

41 minutes ago, Carrerahill said:

I wondered the same, brickie looked at them it and said, "that's the top" after rolling them a bit, all I could see that he used to differentiate it was that the top was a vibrated, or simply a naturally settled finish but the bottom and sides were smooth from being in formwork. 

 

From what I can remember, the prestressed wire/rod is biased towards the bottom, so when loaded that steel is in tension and gives the strength, however, you also get plain ones... I think if the steel is mid, then its plain and can indeed go anyway.

 

I have been left scratching my head looking at them too.

 

Where is @Gus Potter - he will know for sure!

 

I assume it’s stronger ‘up on end ‘ …

[Gone West]

1 hour ago, pocster said:

Google suggests some lintels are marked ‘ top ‘ .

I was checking this out a few weeks ago for making a new window opening. I think the Naylor economy lintels can be fitted either way round but the pre-stressed ones are marked top.

 

https://naylorlintels.co.uk/products/

 

 

[Pocster]

Ah (expletive deleted) it - I’ll bed it the way that suits me !

[nod]

Concrete lintels are fine either way 

The reinforcement bar runs through the middle 

[Gus Potter]

6 hours ago, pocster said:

so I’m guessing I can orientate to suit ??

Hi pocster. That looks like a typical lintel that may be produced by say Robslee, they call it a type A lintel which is what we call a composite lintel. It has the rod in the middle.

 

For all they are two types of generic lintels, one is called a composite lintel, the other a non composite lintel. They are two different animals. The composite lintels tend to have the rod in the middle and a bit of prestress in the rod to keep the concrete in compression, also helps it not to fall apart while you are laying the bricks above. Long composite lintels need to be propped until the brickwork cures so read the manufacturer's instructions. If you have a good height of brickwork above they can span quite a long way if you are careful.

 

If you think about a reinforced concrete beam. It has steel in the bottom with a bit of cover to the steel to prevent corrosion (plus often fire protection) and provide bond between the concrete and the steel rod / wire. Concrete is good in compression, steel good in tension so when you load up the beam from the top the bottom goes into tension (resisted by the steel) and the top into compression (resisted by the concrete).

 

Now for a composite lintel you can mix up materials. You can have a rod encased in a bit of concrete, like your's pocster. If you make sure the top of the lintel is clean and put say 5 -7 plus courses of brick (see manufacture's spec) on top then you now have a deep beam.. (the top 80 odd % is of brick if you have 5 courses or more of brick) .. the depth of the lintel plus the brickwork above and that works quite well in places. In fact surprising well.. What happens here is the courses of brick above acts in compression and the rod in the lintel is in tension. The concrete in the lintel is not doing that much. In other words the brickwork acts compositly with the steel rod / wire in the lintel.. like say a SIPS panel where the sheeting and internal timbers act together and to make this work the sheeting has to be well fixed to the internal timbers..  thus the brick work has to be well bonded to the top of the lintel and the perpendicular ends of the bricks fully filled with mortar.

 

In summary the lintel per say does not act to resist the majority of the bending effects.. the concrete around the rod / wire just acts arguably as a medium to transfer the horizontal shear forces (tension) in the bottom side of the brick to the rod in the lintel, which happens to be encased in concrete.

 

A big mistake folk make is to put a DPC (cavity tray) between the top of a composite lintel and the brickwork above. Here you create a slip plane and the whole system stops working.. please don't do this.

 

Now a non composite lintel acts much more like a reinforced concrete beam. The major difference is that it does not rely on having masonry above. This lets you introduce say cavity trays and put floor joists on it for example... maybe a bit of point load.

 

The rods are more heavily prestressed and are in the bottom. They are marked top. If you can't see the mark, (sometimes the lintel may have been cut down) then look for the rods and put them at the bottom.. unless your SE tells you otherwise. Sometimes you can use a lintel upside down to create a cantilever / corbel but this is not that common.

 

Prestressing? An ordinary precast reinforced concrete beam has say steel in the bottom, a rebar cage is made and the concrete poured round about it. It all cures and you load it up. Now steel is quite a stretchy material so when you load up the beam it drops (deflects) a bit before the steel really starts to work. The concrete is also a bit elastic so it has to "shorten" on the top of the beam and this gives rise to more deflection. Also concrete shrinks so that relaxation has to be taken up and that can manifest as more deflection.

 

When they make lintels they don't make them one at a time. Commonly they have a very long mould and run a long wire near the bottom. The wire is put under tension and the concrete poured and cured. Then they release the tension blocks at each end of the wire and saw up the long prestressed beam into common lintel sizes. Once they release the tension blocks the wire in each section of lintel it wants to shrink, but it can't as it's bonded to the concrete in the bottom of the lintel. What happens here is that the wire compresses the concrete in the bottom of the lintel and this makes it bow up a bit.. which is good as when you build it into your house it bows back down. the idea is that the bottom of the lintel ends up about flat... in an ideal world.. just like us on BH!

 

If you are curious if you take a longish non composite lintel.. say a 145 high x 100mm wide (type C that look like a concrete beam higher than it is wider) and lay it flat with the rods near the bottom you should see a bit of a bow upwards.

 

But @nod some non composite lintels do have the rod in the middle!! and !!! The explanation for this is very lengthy but so have left it out. These tend to be wider and flatter.

 

There you go.. hope this helps to give you a flavour of how the different type of lintels work and hopefully this will help you select the right lintel and use them in the right way.

 

For me I tend to stay away from composite lintels on longer spans even if I have a good few courses of brick above as the workmanship / site supervision is often so poor these days. Yes I know the heavier non composite lintels cost a bit more but they are more "idiot proof" to some extent. Also, on self builds we often make late changes so non composite lintels give you a bit more flexibility here.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Pocster]

@Gus Potter that’s a Muv of an answer !

[Russdl]

35 minutes ago, pocster said:

 that’s a Muv of an answer

Wasn’t it just. What an amazing place this is. 

[Gus Potter]

3 minutes ago, Russdl said:

Wasn’t it just. What an amazing place this is. 

It is indeed. @pocster.. thanks for the response.. it took me a bit of time to write that while trying not to sound too much like an.. @pocstercan fill in the expletives.. I maybe failed as concrete lintels are not that sexy..

 

The thing  I like is that there are folk here on BH that have forgotten more than I know an don't mind sharing their knowledge and experience.