Forming long re-inforced concrete beams

[Paul Andrews]

After extending our garage and house (so effectively some time away) we will need to move our garden wall 3m over.

The structural engineer has specified a pad and beam system (to help avoid problems with tree roots) for the base of our new garden wall, circa 20m long. The pads are concrete blocks - fine, but the beam is a long continuous beam reinforced with R8-150 links and spliced together T12 bars. It all sounds quite industrial to me. Anyone have any experience of this, or should I just admit defeat and get somebody else to do it, or change our wall plans completely?

Paul

[BigWallop]

Sorry to say this Paul, but if you have ask this, then it's time to get the pros' in mate. Creating a log for a heavy wall, which yours sounds as though it's going to be, really needs the proper foundation. This needs to be poured with the right mix and structural basket weave for it last any length of time. Steel fixers and civil works will probably do the job in a couple days, where it might take you weeks. So, it would be easier, and most likely cheaper in the long run, to have this done by the right squad.

[Paul Andrews]

That may be so, but building the wall is going to be one of the last things we do so it's some time off. The foundations themselves and indeed the beam itself are quite simple in shape. The pads are just 600x600x1.0m deep boxes (probably nine of them) with the beam construction running along the top (and through the pad itself) about 20m long. If it's going to be a really big deal, we might just change the existing plan and go for a lighter wall with brick piers and fencing between the piers, or even just a wood panel fence only. It certainly is a fun project though. Fortunately, it's not time critical since I can remove enough of the existing wall to allow for the building extension to happen first. At the time the construction was first suggested, I'd anticipated using prefabricated lintels to bridge the pads and didn't realise until later that it was a continuous beam rather than pads connected by separate lintels. Oh well, we live and learn.

So tying and cutting the rods/basket is a difficullt thing to do then? You can't blame me for being curious (I'm curious as to how it's done, even if I won't be doing it myself). Quite a lot of construction work seems to be shrouded in some mystery by those that do it for a living and us mere mortals who don't do it professionally are sometimes surprised at how people can build houses with bits of string and wooden sticks with lines on. Once it's explained it doesn't seem to be quite such a mystical thing after all. ;-)

Paul

[BigWallop]

LOL Nothing mystical really, just needs to be done properly for this type job. If you have loads of time to do it, then by all means get the gear and have a go at it. You'll need benders and things to form the rings that hold the stretchers in place while the pour is being done, and all to form the correct reinforcement needed. You'll need wire and hand tools to fix the stretchers in the right places on the formed rings which hold the mix in place when the shuttering is removed, and to make sure the reinforcement is all in the right places within the mix.

And all this on budget of a few pence. :-) LOL

[spakker]

I wonder how structural engineers sleep at night? They always have a 'belt and braces' solution and ,of course ,charge accordingly.A garden wall is not rocket science and your spec. sounds way OTT.

[Paul Andrews]

I kind of agree. When it was first suggested, I anticipated prefabricated lintels standing atop sturdy concrete pads. I hadn't expected the continuous beam at all and at the time we went forward with this I hadn't spotted the "cast monolithically" direction (I had no intention of building it at that time - it would be someone else's problem). There is an existing wall, circa

6' high at it's lowest end, rising over 7' as the ground drops away. The only reason for the pad and beam is that the wall is in very close proximity to large pine trees. It may be that we dump the idea altogether and go for a wooden fence instead - it would be much cheaper..

Paul

Paul

[bigcat]

or a standard brick wall, not especially difficult.

NT

[Paul Andrews]

prefabricated

Given the rather huge trees that are very close, I'm told that the council wouldn't have passed the planning regs. with a traditional wall (such as is already in place) because of the roots.

Paul

[Mike C]

I can't quite visualise what you want to do, but I remember my dad, 35 years ago, making reinforced concrete beams for a pergola. He built about 14 brick pillars in two rows, then put longitudinal beams across the tops of each row, and lateral beams across those. The longitudinals were heavier (from memory, about 4" wide and 10 ft long) and the laterals were lighter - probably about 2 1/2" x 8ft. Both must have been around 6" in depth. He made them by pouring 1/2" of concrete into a mould made of planks, laying a mild-steel rod on it, then filling the rest of the concrete on top. The longitudinals had two rods in them, and the rods (about 1/2" round section) were bent up an inch or two at each end, as they were smooth rods. Nowadays, however, you can get rods with ridges running around them, which would key much better to the concrete.

I know that the pergola is still standing, covered with plants.

Mike.