Grounding for Building Foundation Structure

[Adnan Hasan]

The designer of my project (400 bed hospital) make Grounding to the steel structure of the building foundation using galvanized steel strip size 30x3.5 mm as shown in the attached picture.
My questions:
1- why do we need to make grounding to the foundation's structure?
2- can we use this grounding as EGC?

 

[Smart $]

The designer of my project (400 bed hospital) make Grounding to the steel structure of the building foundation using galvanized steel strip size 30x3.5 mm as shown in the attached picture.
My questions:
1- why do we need to make grounding to the foundation's structure?
2- can we use this grounding as EGC?

1) If you are talking about the strips, I don't know. Perhaps some form of equipotential bonding. Can you RFI the designer?

2) No, not as EGC or GEC* under NEC. At best, it could be considered part of structural steel electrode and used for permitted bonding.

*Appears there is a vapor barrier below rebar, perhaps gravel or other aggregate below that. The barrier/aggregate-fill would render such ineffective as a concrete-encased electrode, which has to be in direct contact with soil.

 

[Adnan Hasan]

1) If you are talking about the strips, I don't know. Perhaps some form of equipotential bonding. Can you RFI the designer?

2) No, not as EGC or GEC* under NEC. At best, it could be considered part of structural steel electrode and used for permitted bonding.

*Appears there is a vapor barrier below rebar, perhaps gravel or other aggregate below that. The barrier/aggregate-fill would render such ineffective as a concrete-encased electrode, which has to be in direct contact with soil.

steel rebar is not direct contact with soil because there is 50 mm concrete layer (blinding layer) between soil and rebars.
the strips clamped to the rebar in every 2000 mm span by galvanized clamp (please see the attached picture).
one end of the strip go to earth electrode and the second end suppose to go to electrical room and connected to equipotential (as designed).

strips form a matrix which cover all rebars (total area of land covered by rebars is 20,000 m²).
distance between columns/rows of matrix is 2000 mm.
with these additional information, can you please re-answer my questions? thank you..

 

[Smart $]

steel rebar is not direct contact with soil because there is 50 mm concrete layer (blinding layer) between soil and rebars.

You misunderstood... perhaps my fault for the way I wrote it... but what I meant was that the concrete would have to be in direct contact with the soil.

the strips clamped to the rebar in every 2000 mm span by galvanized clamp (please see the attached picture).
one end of the strip go to earth electrode and the second end suppose to go to electrical room and connected to equipotential (as designed).

strips form a matrix which cover all rebars (total area of land covered by rebars is 20,000 m²).
distance between columns/rows of matrix is 2000 mm.
with these additional information, can you please re-answer my questions? thank you..

1) As designed, not required by NEC. Rebar-reinforced slabs not in direct contact with soil (i.e. the concrete) do not qualify as a concrete-encased electrode. You mentioned one end of galvanized steel strap connected to grounding electrode. What kind of electrode?

2) No change to my first reply, but I'll add the NEC does not recognize steel strapping as a grounding electrode conductor or a bonding jumper, or as an EGC.

Are there any footings or is this structure entirely slab supported?

 

[Adnan Hasan]

You misunderstood... perhaps my fault for the way I wrote it... but what I meant was that the concrete would have to be in direct contact with the soil.


1) As designed, not required by NEC. Rebar-reinforced slabs not in direct contact with soil (i.e. the concrete) do not qualify as a concrete-encased electrode. You mentioned one end of galvanized steel strap connected to grounding electrode. What kind of electrode?

2) No change to my first reply, but I'll add the NEC does not recognize steel strapping as a grounding electrode conductor or a bonding jumper, or as an EGC.

Are there any footings or is this structure entirely slab supported?

1) type of grounding electrode is copper rod 20 mm diameter 2800 mm length.
Are there any footings or is this structure entirely slab supported?[/QUOTE]
sorry, I dont understand this question.please explain. thanks

 

[Smart $]

Are there any footings or is this structure entirely slab supported?

sorry, I dont understand this question.please explain. thanks

Footing, often referred to as footer, is a load bearing foundation pad set on undisturbed soil. It depends on weather conditions and soil bearing properties as to how designed... width and depth. In arid, temperate areas it may just be a thicker portion of the slab under walls. There may be none at all. Basically for your situation, I'm asking if there is any rebar-reinforced concrete directly in contact with undisturbed soil?

Will get back to copper electrode later, as answer to above question may have bearing on that.

 

[Adnan Hasan]

Footing, often referred to as footer, is a load bearing foundation pad set on undisturbed soil. It depends on weather conditions and soil bearing properties as to how designed... width and depth. In arid, temperate areas it may just be a thicker portion of the slab under walls. There may be none at all. Basically for your situation, I'm asking if there is any rebar-reinforced concrete directly in contact with undisturbed soil?

Will get back to copper electrode later, as answer to above question may have bearing on that.

there is no footing. all reinforcement steel rebars in contact with the 50 mm concrete.

by the way, can you teach me (after this question) how to divide the quot in two part as shown in below picture

 

[Smart $]

there is no footing. all reinforcement steel rebars in contact with the 50 mm concrete.

Forget about the rebar for now. Is there (or will there be, or even can there be) any concrete in direct contact with the soil beneath it?





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by the way, can you teach me (after this question) how to divide the quot in two part

Just put a quote inside a quote in your reply, like so....

[QUOTE=Smart $][QUOTE=Adnan Hasan]secondary quote[/QUOTE]main quote (i.e. the wrapping quote)[/QUOTE]

Below is what it looks like when posted...

secondary quote

main quote (i.e. the wrapping quote)

​

Disregard the "HTML Code" label. I just used the html code wrapper to show text formatting so you could see it.

 

[Adnan Hasan]

Forget about the rebar for now. Is there (or will there be, or even can there be) any concrete in direct contact with the soil beneath it?

**************************************************************************

Just put a quote inside a quote in your reply, like so....

Below is what it looks like when posted...


​

Disregard the "HTML Code" label. I just used the html code wrapper to show text formatting so you could see it.

No concrete in direct contact with soil (please see below picture) even in the future



layer beneath concrete (Plastobit) for water proof. Plastobit is a fibreglass-reinforced waterproofing membrane made of bitumen modified with APP (atactic polypropylene), coated with PE (polyethylene) film on the lower and upper surfaces and applied with an oxyacetylene burner

 

[GoldDigger]

No concrete in direct contact with soil (please see below picture) even in the future
layer beneath concrete (Plastobit) for water proof. Plastobit is a fibreglass-reinforced waterproofing membrane made of bitumen modified with APP (atactic polypropylene), coated with PE (polyethylene) film on the lower and upper surfaces and applied with an oxyacetylene burner

That means that the rebar in the concrete will not be of any use as a grounding electrode. On the other hand, if the rebar pieces are well bonded to each other (by tie wires, or similar) they will make a nice equipotential grid under the floor to minimize possible problems from voltage differences from one location to another. The strap is probably intended to set the potential of that grid by bonding it to the actual grounding system.

 

[Smart $]

No concrete in direct contact with soil (please see below picture) even in the future



layer beneath concrete (Plastobit) for water proof. Plastobit is a fibreglass-reinforced waterproofing membrane made of bitumen modified with APP (atactic polypropylene), coated with PE (polyethylene) film on the lower and upper surfaces and applied with an oxyacetylene burner

That means that the rebar in the concrete will not be of any use as a grounding electrode. On the other hand, if the rebar pieces are well bonded to each other (by tie wires, or similar) they will make a nice equipotential grid under the floor to minimize possible problems from voltage differences from one location to another. The strap is probably intended to set the potential of that grid by bonding it to the actual grounding system.

And as I said earlier, the NEC doesn't recognize the straps as a bonding jumper or GEC, so a copper GEC will have to be run to each of the rod electrodes. If the rebar would have been a qualified concrete-encased electrode, could have just used a bonding jumper between rod and rebar.

 

[Adnan Hasan]

That means that the rebar in the concrete will not be of any use as a grounding electrode. On the other hand, if the rebar pieces are well bonded to each other (by tie wires, or similar) they will make a nice equipotential grid under the floor to minimize possible problems from voltage differences from one location to another. The strap is probably intended to set the potential of that grid by bonding it to the actual grounding system.

And as I said earlier, the NEC doesn't recognize the straps as a bonding jumper or GEC, so a copper GEC will have to be run to each of the rod electrodes. If the rebar would have been a qualified concrete-encased electrode, could have just used a bonding jumper between rod and rebar.

GoldDigger said: "The strap is probably intended to set the potential of that grid by bonding it to the actual grounding system".

But you don't agree with him. So, is the strap ​useless?

 

[Smart $]

GoldDigger said: "The strap is probably intended to set the potential of that grid by bonding it to the actual grounding system".

But you don't agree with him. So, is the strap ​useless?

Not useless... but not useable with respect to establishing a grounding electrode system in compliance with NEC.

 

[Cavie]

there is no footing. all reinforcement steel rebars in contact with the 50 mm concrete.

by the way, can you teach me (after this question) how to divide the quot in two part as shown in below picture

View attachment 8277

Rebar is never allowed to be in ditect contact with the earth. It will rust and cause all kinds of bad things to happen. UFER requires the concrete to be in contact with the earth not the rebar.

 

[gndrod]

Roll Roofing

Roll Roofing

Adnan,

After checking the Plastobit product spec sheet PP3000 on the BTM website, the compound is used with a bitumin (tar) for torch down roofing. I am curious as to what building codes are used for this project and what the plan specifications call for this type of slab floating? As other comments on the validity of using a strap for an Earth Electrode, it is not compatible with NEC nor IBC standards AFAIK. The concrete outer footer according to IBC standards must be a monolithic concrete rolled perimeter pour that is in direct contact with the native hardpan soil footer trench.

The concrete BTM waterproofing isolates the foundation from earth thus preventing lightning imposed or any high-voltage transients to dissipate into the earth. If any result for this design, the steel slab and interconnected metal structure may cause a non-equipotential condition from the surrounding outside grade. The Ground System Grounding Electrode Conductor is not the same as the Equipment Grounding Conductor if that is what is being discussed.

I have no idea what is the code or design standards being used in your area. Please let us know what they are with plan specifications and maybe we can help.