Is it safe to drill holes in concrete lintel?

I have read most of the messages regarding drilling into concrete lintels above a window and saw the recommended various tools (SDS drill etc) but one post has a comment stating that this can weaken the lintel and cause structural damage. Anyone have any experience of these problems? Thanks

Reply to
jjc001
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In message , jjc001 writes

No, but obviously in principle drilling holes into lintel will potentially weaken it.

But for a few small holes to mount a curtain track etc. then I can see that that is going to really weaken the lintel.

Reply to
chris French

In article , jjc001 writes

I've seen those posts too and it's not something I would do, I have installed some pre-stressed concrete lintels and they are only 2 1/2" tall to I wouldn't want to be any of such a weeny thickness.

Reply to
fred

I'd like a definitive answer myself. A few thoughs however;

There must be a million drilled lintels happily holding up both walls & curtain rods - I've done it myself many times without any visible problem.

I would guess that a lintel is designed with a huge safety factor included - in other words, if it's sold as being able to hold a ton it will probably hold two ton.

Thinking about it, would a hole actually weaken a lintel anyway? What are the physics?

I've also done a Google search on 'drilling concrete lintels' and found several sites (inc Wickes) that give advice on how do do so and none has any kind of warning about weakening the lintel - if it was a common problem surely there would be something out there somewhere?

I'd be happy to keep doing it.

Dave

Reply to
david lang

In article , fred writes

Lets try that again: I've seen those posts too and it's not something I would do, I have installed some pre-stressed concrete lintels and they are only 2 1/2" tall so I wouldn't want to lose any of such a weeny thickness.

Reply to
fred

Yes it will weaken a lintel. However, to a very small margin IMHO less than the variance between individual lintels and batches.

A million is almost certainly an underestimate. I am unaware of any lintel failure caused by affixing a curtain rail.

The mathematics of this are astoundingly complex, but I think that the factor of safety lies somewhere about 10. There are normally 3 or 4 reinforcing rods in a cast concrete lintel, and they reside near the bottom, the better to resist flexural loads, the rods being at their best advantage, in tension. Most lintels are (often unclearly) marked "top" on the side which is supposed to be uppermost. I wonder how many have been installed upside-down and still perform their purpose.

How scary do you like your mathematics to be?. Using a spreadsheet, it is possible to do finite element analysis in 3 dimensions, although the imposed load is somewhere between point load and uniformly distributed. Even finding the bending moment will be a nightmare, probably a few years of skullsweat. Then finding a suitable model for a lintel with a few holes drilled in it (perhaps others have done this and papered over) will take another chunk out of your life expectancy. To crown it all nobody in particular will give a toss. There is no Nobel prize for Boring Pointless Research.

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wot I rote.

Me too. As well as drilling into lintels.

John Schmitt

Reply to
John Schmitt

Thanks all for your replies, I will go ahead and put up my curtain rail, once I manage to beg/borrow a suitable drill to do it.

Reply to
jjc001

The prestressed plank lintels that Fred referred to work (if installed properly) compositely with the masonry above. The cable(s) are in tension and the masonry over in compression. In theory (don't try this at home, children) you could remove all the concrete except that between the cable and brickwork and that at the ends which provides an anchorage.

Reply to
Tony Bryer

Why not just stick a strip of timber to the lintel, and screw into that?

Reply to
Rob Morley

That is an idea but basically there is about 1cm plaster in front of lintel, I could chase out a slot to the lintel and then glue some wood as you suggest. However I am then left with a choice (1cm) fix depth which i doubt is enough or have the wood protrude from beyond the plaster depth, lets say (2cm) which leaves me with a 3cm fix depth. However the brackets from the rail extend the rail by a further 5cm which in turn will push the curtains to 7 cm from the window (too far) in my opinion.

Reply to
jjc001

If I remember correctly, reinforced concrete beams are typically analysed ignoring any concrete under tension, simply analysing the steel. Hence any holes toward the bottom of the beam won't weaken the beam beyond the theoretical strength (any cracks that do appear won't propagate beyond the centroid of the beam), and any holes in the top won't result in any crack propagation at all.

Please don't go drilling holes into lintels on the basis on this though, I've absolutely no practical experience, and didn't take structural mechanics any further than the 2nd year.

Chris Key

Reply to
Christopher Key

The physics (or engineering) is quite simple. A hole in the centre of the side of a beam will not weaken it. If you look at steel beams you will see that they are often cut in a zig-zag pattern and rejoined to produce a beams with holes. The central part does not carry load. As you move away from the centre the material carries more and more tension or compression. The centre simply acts as a rigid spacer to the load bearers. That's the theory and is why 'I' beams carry the highest load for a given weight.

However concrete is slightly different. If you bashed large holes in with a hammer drill you might weaken the adhesion between the concrete and the steel reinforcing if there is any. You might even crumble a significant volume which definitely could weaken the structure.

I wouldn't worry about drilling small holes for screw plugs unless the lintel was very shallow. If you hit a stone don't switch to hammer. Just drill in a different place.

Reply to
Peter Scott

: If I remember correctly, reinforced concrete beams are typically analysed : ignoring any concrete under tension,

There is, however, a huge difference between reinforced concrete (steel bars take the tensile load instead of the concrete) and prestressed (steel bars apply a preload so that the live load never does put the concrete in tension). And even if the concrete is cracked and taking zero tensile load it will still be contributing to sideways buckling resistance.

Ian

Reply to
Ian Johnston

I wouldn't like to drill into one of these brick height lintels, they're a bit of cheap "wire rope" in a sludge of (albeit carefully concocted) "concrete".

Reply to
Chris Bacon

A little more than "cheap wire rope": a prestressed cable held under a lot of tension while the concrete cures.

Reply to
Tony Bryer

Really? In what way?

So? Why is it any more than "cheap wire rope"?

Reply to
Chris Bacon

It is often high-tensile steel. Boring old steel yields at about 250 MPa, High tensile has a .2% deformation stress of 1650 MPa. The different expressions of strength are due to the different failure modes of the alloys. However, I think it is clear which is the stronger.

Greater strength, a useful property in something supporting a load.

John Schmitt

Reply to
John Schmitt

Not quite sure how this is a 'huge' difference. In the both cases, the steel is taking all the tensile load, just in the latter, the steel is taking additional load as the beam is in a state of self stress to keep the concrete under compression.

In the former case, a crack could propagate through the section of concrete under tension, which although not affecting the maximum moment the beam withstand, would reduce it's strength in shear, and against horizontal buckling. Not sure how important those would be in practice though.

In the latter case, there should be no crack propagation (unless the prestressing put the concrete under very high compression), and the very small loss of material should have minimal effect on the strength of the lintel.

As I said earlier though, I've absolutely no practical experience with these, and have no idea of typical loads / size of lintels etc.

Chris Key

Reply to
Christopher Key

It's wire rope.

So what's used in these lintels, then?

Reply to
Chris Bacon

There's a big diffeence between drilling into the lintel and right through the lintel. There's a very big difference between drilling a 6-8mm fixing hole and a

40mm waste pipe hole right through.
Reply to
Ed Sirett

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