Taking down dividing wall

[marsaday]

I intend on removing a section of internal wall to make room for a kitchen / diner area. The opening will be about 1.3m wide and the wall is supporting the wall above it, but i dont think the roof (need to check though as not been in the house yet).

So can i use the strongboy needles and prop on one side only, or is it best to use 4 props and use some wood set between them ?

Do steel companies tell me what lintel will be appropriate or will BC advise what i need. Not getting an engineer for this.

 

[tony1851]

Only one strongboy needed for that span.
Use a 140 x 100 conc lintel, min. 100 bearing each end.

 

[^woody^]

Use a 140 x 100 conc lintel, min.

For a 1.3m span?

So what is the maximum span that you would recommend for a 65mm lintel, 600mm or so? Only they have some 65mm lintels up to 2.4m at the merchants

 

[tony1851]

A 65mm concrete beam won't span 2.4m.
Those thin ones crack very easily; they are only intended for being built-in as work proceeds, not for retro-fit.

 

[marsaday]

Hi guys are you saying i could use a 65mm lintel for this job ?

I much prefer to over spec, so will go with the bigger lintel, but just good to know this bigger size will easily be big enough. The opening may go up to 1.5m as well.

 

[tony1851]

Hi guys are you saying i could use a 65mm lintel for this job ?

No, not unless you wanted it to crack. Frankly, the 65mm lintels are rubbish and only suitable for bridging over drains below ground level, and similar narrow gaps.
Sure, some merchants may have 2.4m long lintels but they will crack before you lift them into place; they are intended for cutting into smaller lengths.

 

[^woody^]

65 is OK for that span.

It is nonsense to suggest that they are designed to be built in and not retro-fitted. Where the hell did that comes from? And as for only being good for bridging drains, I'll just shake my head slowly in dispair

Again, what spans are 65mm concrete lintels suitable for then Tony?

From my experience, 65mm is good for at least 1800mm of uniform loading in any domestic situation.

 

[marsaday]

Thanks for info. I would much prefer to over spec, so you have reassured me that 140mm is strong enough.

 

[tony1851]

65 is OK for that span.

It is nonsense to suggest that they are designed to be built in and not retro-fitted. Where the hell did that comes from? And as for only being good for bridging drains, I'll just shake my head slowly in dispair

Again, what spans are 65mm concrete lintels suitable for then Tony?

From my experience, 65mm is good for at least 1800mm of uniform loading in any domestic situation.

Are you aware of the difference between 'composite' and 'non-composite' lintels?

Some of these -particuarly the 65mm deep ones - are intended to be built-in as work proceeds and gain some of their strength from the compression of the masonry above. That does not work in retro-fit.
Furthermore, if they are only a few courses under the floor joists, they are not well-suited to any sudden impact loads.

As regards what spans they are suited for, I have already stated my opinion.

 

[cotswoldbuilders]

65 x 100 prestressed are available up to 3m long and some stockists have 3.6
Bearing 150mm each end, up to 1.2m and 200m over 1.2m.

When building in over 1.2m props are needed under the lintel until all works have set, ie minimum of 3 courses of solid brickwork.
This was requirements of our bco, ex old school brickie.

 

[tony1851]

Take a look at this, from a typical p/c concrete manufacturer's details.

http://www.stowellconcrete.co.uk/precast_concrete_lintels.php

Note that the 65 deep lintel is 'composite', ie taking a proportion of its strength from the masonry above by virtue of the fact that it is being built-in as work proceeds

The deeper lintels are non-composite, and can be used in both new work and alterations.

 

[^woody^]

..... gain some of their strength from the compression of the masonry above. That does not work in retro-fit.
.

Of course it does - the masonry has already gone off

 

[tony1851]

Of course it does - the masonry has already gone off

The masonry has of course gone off long ago. But there is still no bond between it and the beam, and it's the bond which helps reduce stress on the beam, by enabling the masonry to take some of the compressive force.

Spreading a bit of mortar on the top of the beam will not do either because hairline cracking will inevitably have formed in the masonry above. This will prevent the beam and masonry working together as an assembly.

Why do the manufactures I linked to say that these 65mm beams should be composite? Because they will not work on those spans otherwise.

 

[RonnyRaygun]

Take a look at this, from a typical p/c concrete manufacturer's details.

http://www.stowellconcrete.co.uk/precast_concrete_lintels.php

Note that the 65 deep lintel is 'composite', ie taking a proportion of its strength from the masonry above by virtue of the fact that it is being built-in as work proceeds

The deeper lintels are non-composite, and can be used in both new work and alterations.

This is interesting as it makes me wonder what is allowing the designer to take composite action into account.

Is it the bond created by the mortar between the lintel and the masonry above? Doesn't seem to be enough to give composite action.

I also noticed on the Robeslee Concrete website that a 100x70mm composite lintel with three courses of brick above has a higher load capacity than a 100x100mm non composite lintel.

Could the 100x100mm lintel be designed compositely and be capable of carrying a much higher load capacity?

 

[tony1851]

Is it the bond created by the mortar between the lintel and the masonry above? Doesn't seem to be enough to give composite action.

In theory, probably not. But the tops of these lintels are often very rough. Maybe the 1st mortar bed above the lintel binds into the little pock-marks and gives some shear resistance?

If you have a copy of Curtin's Manual there is a bit about composite action with thin beams on p247.