Structural Steel

uksparks · Jan 15, 2015

Hi,

Following my threads about using structural steel for the earth...

Well, today was in the area and stopped by the office where the EV charger is going and they are building this building right next door to it, its exactly the same, I stopped and as it happens I managed to speak with the bloke who actually with his very own hands built the office the unit I will be working on.

Anyway, I thought you would like to see some photos of the construction of it so you can see how well its fixed to the ground.

He said there are well over 100 Bolts which are are massive bolts, not little things, they are connected to the ground with 400mm bolts into the concrete which each concrete chunk is 1000mm into the ground.

The Ra should be very good I would imagine. Ill be able to tell you on Saturday when I do the job.

[ElectriciansForums.net] Structural Steel

ImpededLoop · Jan 15, 2015

It'll be interesting to hear the value that you measure.

Geordie Spark · Jan 15, 2015

That's one Hell of a chicken shack bonny lad!

Engineer54 · Jan 15, 2015

He said there are well over 100 Bolts which are are massive bolts, not little things, they are connected to the ground with 400mm bolts into the concrete which each concrete chunk is 1000mm into the ground

Are you saying the steelwork is attached to separate concrete pads and not a common raft slab??

Darkwood · Jan 15, 2015

These pics are ringing alarm bells ... not seen ground work left like this with the building already up, Im no Structural Engineer but something just seems wrong. :juggle2:

PEG · Jan 16, 2015

Looks very much like base plates are rag bolted to a footing. This may be ring beam design,sat on piles,or may just be a footing. Its' ability to provide a decent Ra will not have been a design factor. Ironically,the more slap-dash,the reinforcing is,breaching the curtilage of the concrete sections,the better your readings will be :icon12:

Knobhead · Jan 16, 2015

uksparks said:
The Ra should be very good I would imagine. Ill be able to tell you on Saturday when I do the job.

What happens when you find out it isn’t up the job. If there’s any form of membrane around the plinths your idea goes out the window.

uksparks · Jan 16, 2015

Tony said:
What happens when you find out it isn’t up the job. If there’s any form of membrane around the plinths your idea goes out the window.

I did have a closer look and they do appear to be direct bolted to the floor with nothing in between, the bloke said no they sit direct on the concrete and get bolted to the 400mm bolts, I would imagine 100 x 400mm bolts = min of 40 meters of contact would provide a good earth.

Should it not give an acceptable reading I will not power it up and ill put earth rods in as am making provision for earth rods when installing just in case. What i am doing anyway is running a 25mm earth from the charge point to the steel and bolting it to it just as good measure, so if it does give a good earth, so be it, but if not, ill then hook it onto sufficient rods.

I have the ground plans and know 100% that there are no pipes etc in the ground too which is good.

uksparks · Jan 16, 2015

Engineer54 said:
Are you saying the steelwork is attached to separate concrete pads and not a common raft slab??

Correct, they are all just individual columns not on a slab.

uksparks · Jan 16, 2015

PEG said:
Looks very much like base plates are rag bolted to a footing. This may be ring beam design,sat on piles,or may just be a footing. Its' ability to provide a decent Ra will not have been a design factor. Ironically,the more slap-dash,the reinforcing is,breaching the curtilage of the concrete sections,the better your readings will be :icon12:

I asked about earth plates etc, and they said no, no such luck. It was helpful seeing this and actually speaking to someone who built it and bolted it all together, aleast I know enough about the structure now to give me some confidence in which was to go with it. Like I say, if it gives an acceptable reading, then so be in and my 25mm earth strap will just be a direct connection from the charger to the building, or if not, it will end up with rods.

uksparks · Jan 16, 2015

Oh and if you are wondering why I am going over board and using 25mm, I have about 30m spare of it I found on a job, funnily enough that job I posted up a while ago where the house got turned into a drug den... and they used 25mm earth tapped into the main supply to feed the loft.

I thought I might as well put it to some use as I have no other use for it and it save me spending money on 16mm etc.

Knobhead · Jan 16, 2015

uksparks said:
I did have a closer look and they do appear to be direct bolted to the floor with nothing in between, the bloke said no they sit direct on the concrete and get bolted to the 400mm bolts, I would imagine 100 x 400mm bolts = min of 40 meters of contact would provide a good earth.

Should it not give an acceptable reading I will not power it up and ill put earth rods in as am making provision for earth rods when installing just in case. What i am doing anyway is running a 25mm earth from the charge point to the steel and bolting it to it just as good measure, so if it does give a good earth, so be it, but if not, ill then hook it onto sufficient rods.

I have the ground plans and know 100% that there are no pipes etc in the ground too which is good.

That isn’t what I meant, a plinth can have a membrane between the substrate and the cast concrete. You could very well end up with a load of earth free blocks.

100 x 400mm bolts doesn’t equal 40m of effective electrode as they don’t go deep enough.

Talk to the construction engineer.

uksparks · Jan 16, 2015

Tony said:
That isn’t what I meant, a plinth can have a membrane between the substrate and the cast concrete. You could very well end up with a load of earth free blocks.

100 x 400mm bolts doesn’t equal 40m of effective electrode as they don’t go deep enough.

Talk to the construction engineer.

Very true, I think the only way to know is to measure it really.

uksparks · Jan 16, 2015

If I have to go back and put earth rods in, its not the end of the world, they don't exactly cost much, its more the hassle factor that the job is 30 miles away and not on my doorstep.

Engineer54 · Jan 16, 2015

uksparks said:
If I have to go back and put earth rods in, its not the end of the world, they don't exactly cost much, its more the hassle factor that the job is 30 miles away and not on my doorstep.

So long as you're not thinking about using those 3/8'' short thin twigs as earth electrodes!! You'll need at least two 5/8'' extendable rods coupled together at each rod location if you want to stand any chance of attaining a decent Ra value....

Going by the state of those photo's you posted of the other building under construction, you may well find that the ground around the building you're working on is full of rubble and building debris!! So be warned!!