Ground Beam dimensions?

[Delinquent]

According to a (very, very) old copy of the building regs, the reinforced ground beam needs to be only as wide and deep as the width of the wall going on it - the wall is 300mm but before I start digging I was wondering if anyone could confirm this?

The S.E. notes are hand written and I can't make out what on earth he's written!!! Looking at the calcs that I can make out it could be either 300mm, 400mm or 450mm depending on which squiggle you look at and how you squint your eyes

Many Thanks

 

[jeds]

When you say 'ground beam', do you mean a reinforced concrete beam sat on piles or are you talking about a strip foundation?

If your talking strip foundation, the width depends on the loading and ground conditions. It could well be the width of the wall or it could be more.

If you talking reinforced ground beam, this should be calculated and designed by a structural engineer.

 

[Shytalkz]

It's not one of my calculations, is it?!

An rc beam need only be as wide as the wall for obvious practical purposes, but the required width depends on the design; 400 would be an unusual width for design purposes, though. We normally use 300/450/600/750/900/1000/1200 etc (the first three for domestic!)

Note that there is a minimum cover requirement to the rebar, which should also be scrawled on there somewhere. However, that cover requirement will assume that the bottom is blinded with lean mix and the sides are shuttered. If you are casting against an earth face, the cover to the links at the side must be 75mm (to allow for wibbles in the excavation), so depending on how you're doing this, you might need to add another 70-80mm to the beam width.

Can you scan and post the calc (hide the name, obviously) and I'll see if I can decipher for you?

Edited to add: you're not just talking about a strip footing with some rebar in are you?

 

[Delinquent]

LOL no not one of yours. definitely not strip footings - the large quantity of 8m deep pilings that are being driven in rule that out I think!

Thanks for the info - I'm intending to shutter all round with that corrugated plastic stuff (LOL technical me, eh?) so I can leave it in situ and put the noted heave protection in place. (supposedly clay soil, though in shifting 70+ tonnes of it so far we've found nothing but gravel and sandstone...)

I've managed to get an explanation, and they are 400x400 (which going on the info appears to be odd in itself!) now I've just got to try and get a stone cutter and kango to task before the sun goes down as they are starting piling in 4 days and I'm a VERY long way off being ready!!! Also trying to get some calcs done to work out if a tiny extension would be plausable adding just a couple of further piles and starter bars keyed in to the designed ground beam - S.E. sounded a bit huffy when I suggested it, but I'm not sure I want to put any more money his way at the moment!

 

[Shytalkz]

Ah, ok! Strange beam size...

Understand the "plastic stuff" description - presume you mean this?

If the piling guys are still on site, you'll just pay EO metreage for the extra piles; however, if they've gone, you'll have mobilisation costs to add in again as well.

Can't see what the SE's problem is, it's not complicated after all.

 

[Delinquent]

That's the stuff Even better, I don't have to go asking for "plastic stuff" on the phone now which will hopefully see me looking less of a plank.

That was the reasoning behind trying to get the extra bit of piling done now - they've agreed a good price, but obviously the less I can add the better, so if I can get away with just 2 it would be very handy.

I think the SE isn't very happy with me after I was.... erm... "slightly less than polite" about the bill! I was given a price prior to work commencing, only the bills that came through were more than double that. I'm very hesitant to ask about this new part as I can see some ridiculous figure come floating through the door on a bit of paper.

Still, I doubt he'll be very happy when I suggest replacing the beam and block with hanson jetfloor either

 

[Shytalkz]

How much was the bill, ooi? Presume it's a house/garage kinda arrangement and he just did the design/detailing of the beams and pile loads?

Nothing wrong with changing to Jetfloor btw, it's a variation on a theme, won't make any difference to his calculations.

 

[Delinquent]

it was supposed to be "around £600", ended up being £1300. He did the beam and pile loads + the roof loads (and put steel in the roof, which I'd specifically requested not be put in)

I did manage to get bending calcs done eventually as well though only took a couple of months for those to come through.

Good news on Jetfloor - we are on a site with difficult access so the fewer blocks I can get away with the better!

 

[Shytalkz]

Still cheap tbh: I charge typically £2-2.5k for design, detailing and rebar scheduling of ground beams with pile loads for piles by others, for a house. £600? No way, unless it's one of the blokes from the office doing a "foreigner" (not advisable, from PI pov as well!)...

 

[Delinquent]

interesting - and has made me feel slightly better, ta TBH if I'd been told £1300 up front, I wouldn't have batted an eyelid, I just don't like surprises, and the sudden hike was certainly a surprise.

Unfortunately I'm having to do a lot of reworking as there are a few things that neither I nor the building regs bloke are very happy with, but that's another story!

 

[Shytalkz]

I don't know why some engineers say a cheap price to start with, they just drop themselves in the cart if they want more...at an average charge out rate for engineer (design) and technician (detailing/scheduling) of say £60/hr , that original quote was only 10 hours and that's pushing it to get it designed (4 hrs say), leaving only 6 hours to get it detailed, scheduled, calcs and drawing collation, in-house checking and issued...not saying it couldn't be done, but it would be at a speed where goolies would be likely to be dropped...