Concrete lintel - which way up?
- Thread starter paulwf
- Start date
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When i first started in the trade pcc lintels did have a 'way up' indicator pressed into the concrete.
This, as far as i am aware, does not apply today. Lintels are ambidextrous....er...antibiotic....multifaceted.....or summat..!
You can lay them either way up unless otherwise stamped.
This, as far as i am aware, does not apply today. Lintels are ambidextrous....er...antibiotic....multifaceted.....or summat..!
You can lay them either way up unless otherwise stamped.
I have a 3metre concrete lintel (100mm wide). It has a rough side and a smooth side - which way up should it go?
And what would happen if it went the other way up
Cheers
Paul
ALWAYS put it with the wires at the bottom and that would normally be with the smooth side down.
If you put it with the wires at the top then the bottom will be under tension when loaded and it WILL fail.
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I would expect there to be a slight bow UPWARDS in the middle.
There are two ways these things work.
1. Pre tensioned. The steel wire is under tension before the concrete sets, they are made in long bits then cut. This means the steel is compressing the concrete (remember that concrete is only any good in compression and less than 10% in tension i.e.rate it zero in tension). As the lintel is loaded the tension is taken directly by the steel.
2. Plain reinforced. As the lintel beam is loaded the concrete brakes in lots of small cracks and as it does the steel takes the load. That's the way most reinforcing works.
So if its up-side-down the steel does not take the load when the concrete starts to crack and it splits along the steel line. I've had that happen from just having one roll over onto a bit of wood 2x2 with the lintel the wrong way up. Likewise I watched a neighboring farmer remove concrete cattle slats from my shed; he paid for them to use again. Despite of (because of?) my instructions how to lift them he did it the wrong way and half split. They had the steel in the bottom, being designed to take cows on top. Lifting them in the middle "broke their backs", at the ends did not because the load in the middle was still downward.
Hope that helps you understand how it works!
1. Pre tensioned. The steel wire is under tension before the concrete sets, . . .
Tha t would not work.
The steel is tensioned after the concrete sets so it compresses toe concrete - you can't do this when the concrete is wet.
Tha t would not work.
The steel is tensioned after the concrete sets so it compresses toe concrete - you can't do this when the concrete is wet.
Oh yes you can, its done all the time. The steel is held in tension by the casting mold until the concrete is cured, then when it all come out from the mold the tension compresses the concrete. Getting the turnaround of hardware fast was one of the drivers for high alumina cements and steam curing.
What you are thinking of is post tensioning. In that case its like the old idea of a steel or iron bar holding an old bulging building together. In that case the bars were put in hot and the nuts run up on the plates out side the building, as it all cooled the tension held it together. In post tension concrete the tendons ARE NOT bonded to the concrete.
Have a look at http://en.wikipedia.org/wiki/Prestressed_concrete
hillsider69 is spot on about pre and post tensioning. Post tensioned floors are now being used in the UK, but have been used in the States for years now. To cut in to one like you were talking about for your floor is really dangerous and there have been some serious accidents in the States doing this.
most concrete lintels are not load bearing as such,so if youre supporting a lot of weight then you could have troubles.
the reason why some of the old concrete lintels had to be the right way up is cos they had an extra steel rod in the top but ive not been able to get hold of these for yonks in this area
the reason why some of the old concrete lintels had to be the right way up is cos they had an extra steel rod in the top but ive not been able to get hold of these for yonks in this area
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