Steel column pad base questions

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31 Jan 2022
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Hello,

I am in the process of building an extension to the rear of my house. Part of the project involves opening up the rear of the house by installing a 8 metre steel beam which will be supported by a column either side to form a portal/goal post system. This has been designed by a structural engineer and building control have approved it. The main foundations for the walls have recently been poured and brickwork up to DPC complete.

My next task is to install the columns before the main floor slab can be cast. The engineer has specified a concrete bad base of 1200x1200mm wide/long and 700mm deep, there will be one of these under each steel column. I am struggling to understand how exactly these will be located as the engineer has not been very specific. I have limited experience with something like this so was hoping someone on here could help point me in the right direction.

I have spoken to building control who seems to think the pads will need to as deep as original house foundation, this is fine expect the location of the pads will interfere with that original foundation, below is a sketch showing how I think the portal will look. Note nothing is to scale.etc:

portal.png


Here is a more detailed look at the foundation:

Foundation detail.png


If the above sketches are accurate, this would mean that I must cut and dig out a portion of the original house foundation in order to install the pad base in that location. Obviously the pad base will be much wider than the foundation (which is around 600mm). can anyone confirm if this is correct and if so is there anything I need to be aware of when doing this as currently the original wall is still in place and not supported?

Also on the second sketch I have marked the column away from the remaining wall as the pad base will need to be butted against this foundation, is it possible to dig under the remaining walls foundation in order to move the steel closer to the wall and maximise the opening?

As above I have limited knowledge of this so may be asking obvious or stupid questions but I am just trying to get a better understanding of how these pads need to be built.

For reference, here is an extract from the structural engineers drawings which shows the pad base detail:

Screenshot 2026-01-06 114148.png


Appreciate any suggestions.
Thanks
 

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