Pile and Groundbeam Design

[carson321]

Hi all. 

 

I feel like im losing the plot going back and forward with building control over my foundation design. 

 

Lot of history to this but right now, I have a screw pile and groundbeam design for my single storey rear extension. Screw piles are in and the rebar in place waiting for the concrete to be poured. BCO has complained about various things first of all thinking that the cage was misplaced, misaligned and all sort of other things. Visit from her supervisor and some setting out by my builder made it clear that this was fine. 

Now for my current predicament, BCO have said they have consulted with their engineers and received a response stating

 

"It’s not entirely clear from the foundation calculations, but it appears that the groundbeam design is to BS8110. If so they do not have sufficient links in their groundbeam as no bar in tension should be more than 150mm from a vertical leg. (clause 3.4.5.5). Bars in tension should be no more than 155mm apart and no more than 77.5mm from the outside face (clause 3.12.11.2)."

 

Piling engineer response was basically  that he believes the spacing is correct but if they wanted extra steel, then stirrups could be placed halfway between the links to reduce the vertical spacing. 

 

BCO further response was then " I have spoken to our consulting structural engineers regarding the design and there are fundamental errors with the calculations and the question that our engineers have posed to your piling contractors has been misunderstood. Therefore, we require a design from a competent structural engineer that provide a coherent justification for the foundation design on site."

 

They never raised any issues with the calculations in the first response, and im not really sure how many different ways their comments on the number of links could be interpreted. 

 

I have attached the original beam design and a photo of the installed rebar. 

 

Any help interpreting this mess or helping me understand if my piling engineer is doing the right thing or not would be greatly appreciated. 

[Oz07]

Sounds like your job has become a bit of a battle for the bco. It's a tough one. Maybe in the first instance copy your piling engineer in on their concerns and get him and them to sort it between them. You want to try to de escalate if you want to get the job moving might need some skillful diplomacy when talking to both sides.  

[ETC]

What centres are your links?

[Gus Potter]

33 minutes ago, carson321 said:

 I have spoken to our consulting structural engineers regarding the design and there are fundamental errors with the calculations and the question that our engineers have posed to your piling contractors has been misunderstood. Therefore, we require a design from a competent structural engineer that provide a coherent justification for the foundation design on site."

That is a bold statement to make!

 

The design of the links can be complex, depends on the level of shear stress, usually in and around the pile heads. I won't comment further as I don't know what loads are on the beams / piles. 

19 minutes ago, Oz07 said:

Maybe in the first instance copy your piling engineer in on their concerns and get him and them to sort it between them.

Plus one to that, good advice. This is what often happens, sometimes a quick phone call between the engineers can sort it all out. Oh, it's ok to design to BS 8110, so long as you are aware of any parts of the more modern Eurocode that superceed the older BS 8110 code.