Poured reinforced concrete lintel and French doors

[ianmc]

Hello - I would like to fit French doors into the back wall of our garage. It is concrete block, flat roof construction, tacked on the side of our ~1965 built bungalow. From what I can make out, the walls of the house and garage have been built with a concrete lintel poured in situ all the way around the wall tops with rebar over window openings and doors - or at least I am assuming that and it is not rebar all the way which is the nub of my problem! So I want to put 5' French doors in, by essentially extending the opening an existing standard single door, but I don't know how far the rebar extends from the original doorway. I am going to more than double it. There is no weight above it - the flat roof joints run the other way - so it just has to support it own weight. Here are my assumptions and what options I think I have:

1. The French doors (UPVC, steel frame) will not be strong enough to support the weight of the lintel on its own (?)
2. There is no way to check how far the rebar goes without destroying the lintel (?)
3. If there is a way, and the rebar is there, go ahead and knock out the blocks.
4. If no rebar or I have to assume this, find a way to reinforce it or replace it. I am assuming taking it will be a real b*stard, so I am hoping there is a way to reinforce it!
5. I was thinking I could use some angle iron on the front and back corners to reinforce it, but feels like a bit of a bodge...

Any thoughts or advice gratefully received!

 

[^woody^]

Post a picture. There several options, but it depends what you want it to look like

 

[endecotp]

You need an x-Ray machine. Or a big magnet.

Ah, I know - you want a metal detector. Seriously. Should easily be able to indicate if the rest of the concrete has steel in it or not.

 

[ianmc]

Thanks guys - I like the lateral thinking with the metal detector! I will see if I can whistle one up. Woody - here are some photos of the job. A 5' wide doorway would just overlap the window opening which I was going to block up with 9" hollow blocks (the rest of this wall is made of them with one row of normal concrete blocks running along the top of the poured lintel which the flat roof sits on). What would you say my options are?

Thanks, Ian

 

[Himaginn]

Your images appear to link to your email and are thus inaccessible.

 

[ianmc]

I'll try the pix again!

 

[Himaginn]

I think your pics are not sufficient to explain what is or isn't there.
You've uploaded them in a way that prevents further enlargement.

What is the wall construction? It looks like block work but the pics don't really confirm that.
What makes you suggest that there is a ring beam around the top of the wall, which I suspect it is (rather than a lintel)
If it's present it's possible that it is made up of what is known as "PARPAING DE CHAÎNAGE" blocks.
Here's a picture and the name is a link to these blocks used in Europe.

"
They are laid as blocks normally and reinforcement, "CHAÎNAGE TRIANGULAIRE" as shown, is laid in and concrete poured in situ.
I haven't seen them in UK.

 

[theprinceofdarkness]

Cor, cunning frogs!
(I think the steelwork should go in the other way up)
Frank

 

[Himaginn]

Cor, cunning frogs!
(I think the steelwork should go in the other way up)
Frank

Interesting comment, Franck, about which way up the steel goes, I mean.
Doesn't it depend on which direction you expect any forces to be. Whether it's a ring beam around the top, half way up, at the bottom, in a retaining wall, etc? I ask, 'cos I don't know the answer and I'm interested.

 

[ianmc]

Hi - I am not sure what I can do about the photos not enlarging. The wall is 9" hollow block. I think it is a ring beam cast in place. There are no joins running all the way around the top of the walls. I am assuming there is some rebar over the openings because when I removed an extension of the beam which formed a slab the chimney sat on elsewhere in the house that's how it was. Also, not that I am in any way an expert, wouldn't you expect some sort of reinforcing over the openings at least?

So, if we assumed it is a ring beam, what would you say my options are. I am erring towards cutting it out and have done with it, but it there is a trade tip that simplifies the job, I'm all ears!

Thanks, Ian

 

[Himaginn]

Hi - I am not sure what I can do about the photos not enlarging. The wall is 9" hollow block. I think it is a ring beam cast in place. There are no joins running all the way around the top of the walls. I am assuming there is some rebar over the openings because when I removed an extension of the beam which formed a slab the chimney sat on elsewhere in the house that's how it was. Also, not that I am in any way an expert, wouldn't you expect some sort of reinforcing over the openings at least?

So, if we assumed it is a ring beam, what would you say my options are. I am erring towards cutting it out and have done with it, but it there is a trade tip that simplifies the job, I'm all ears!

Thanks, Ian

I think, therein lies the problem. It's not sensible for anyone to offer advice based on what you assume or think is there.
You either need to ascertain more definitively what the situation is, probably by more intrusive investigation, or better pics, which might allow the pros to more accurately deduce what is there.

I would guess, that if it is a ring beam, then it's been cast straight across the openings. To provide a ring beam over sections of the wall is pointless, IMO.
To cut into this ring beam, or remove sections is to destroy any function of the ring beam.
If it is a ring beam, I would have thought you could safely work on openings underneath that ring beam, because it will act like a lintel.
But you need to ascertain definitively what the situation is, not start work on assumptions.
If you cannot, then you need to employ someone who can.

 

[ianmc]

Thanks Himaginn - I understand your logic. If I was sure the ring beam (it definitely is that) had reinforcement all the way around I would be very happy to leave it and cut out the opening. What I am trying to avoid is short lengths of reinforcing over the existing door and window opening which leaves a gap/weak spot right in the middle of my new opening for the French doors. Or, if there is a simple way to reinforce it, do that just to be sure.

Cheers, Ian

 

[Himaginn]

Because I've not seen that system that I referred to earlier, in use in UK, it would be purely speculative to suggest, if any and where, the rebar is.
Until you can definitively identify that you're taking chances.
Do the roof joists run parallel with the wall, in which you want to insert openings, or perpendicular to it? I.e. do the roof joists rest on top of this wall.
What would be the consequences of the wall collapsing from your openings to the top of that wall? I.e. is it a load bearing wall?

If there is to be any block work above the opening, and below any ring beam, if it's there, you will need a lintel, I would assume.

 

[ianmc]

Just to finish this off, I tried using various detectors with unclear results, so I ended up cutting out this section of the beam. As it turns out, there were 2 runs of rebar at one end, but this stopped well short of the end of the existing opening, so it was a bit if a lash up in the end as I had suspected and it was worthwhile going to the extra effort of chopping it out and replacing it in the end!