Foundation expert (steel frame)?

[imsparticus]

Hi, we are in the process of building a new orangery/conservatory and wanted a green oak look to it but without the cost and potential problems re shrinkage/movement etc. We decided to opt for a steel framed structure and infill the walls with floor to ceiling oak windows and doors, capping any exposed steel with oak.
Our designer and structural engineer have come up with a design for the foundations which are strip foundations with a brick outer and block inner leaf up to damp proof course. The idea is that each steel post will rest on the outer leaf and have a foot which would be bolted down on the inner leaf block work.
This has been passed by building control but the problem is that the steel erectors have said that doing it this way it is very likely to crack the inner block work and crack the mortar joints of the blocks. They have suggested that the posts need to be bolted to a poured/cast concrete pad stone which would be part of the foundation.

The question is, as I have been told that I still need a cavity up to damp proof course is it practical do shuttering to pour the inner leaf along with the strip foundation and then build the outer leaf in brick? Or are there alternatives?

Many thanks.

 

[tony1851]

Your designer and engineer seem clueless; you cannot bolt a steel frame to the top of a 100 wide concrete block and hope that it does not crack.

You need a proper poured concrete pad for the supports, preferably with holding-down bolts cast in.

Your 'engineer' should design the fixings, and your 'designer' should detail the wall construction to ensure dampness is not a problem.

 

[pinenot]

Knowing steel workers as I do, they are assuming the steel will take a load, but if that's the case, you could build the inner leaf with deeper blocks, say 140-150, and use reputable chemical anchors. The holes are drilled bigger than the bolts (no pressure) and fixed by the cured resin, thereafter the steel flanges are fixed down via nuts with washers to spread the load. This is a well used and tested method for fixing down steel columns, the only thing you need ensure is sufficient compressive strength in the blocks used (7n) and sufficient size of footing for the steel flanges...pinenot

 

[themiddleagedun]

Just done something like this. The 75x75mm posts went down to the footing, and the cavity was widened to allow insulation round it.
Posts were galvanised BTW.

 

[tony1851]

@pinenot - I'm not sure that would work - it's not just compressive strength that is required, but wind load would apply some bending moment to the fixings and I doubt 7N block even 140/150 wide would be sufficient.

Can't understand why the council's building inspector has approved this, unless it was not passd on to their own engineer for checking?

 

[Static]

If its even done under building regs..

Bear in mind also that steel reacts bad with contact to green oak and will need protecting.

 

[pinenot]

If its even done under building regs..

Bear in mind also that steel reacts bad with contact to green oak and will need protecting.

Taking a cue from this, you could paint out the steal with an intumescent coating, which would kill two birds with one stone so to speak. For bye giving you fire spread protection, it would provide a separation barrier between the steel columns and the Oak...pinenot

 

[imsparticus]

Many thanks for your replies, it looks like the steel erectors know more about what I should have rather than what has been designed and passed so far. So I know more of what I should expect does anyone have any advice experience of what my foundations should look like up to damp proof course?

themiddleagedun I don't suppose you have any drawings/rough sketch that show what yours looked like?

re the reaction of green oak with steel as the oak we now intend to use is relatively thin we had intended to use kiln dried oak which I'm guessing will not react in the same way? Also we would be painting the frame before hand and any fixings into it would be stainless steel.

 

[themiddleagedun]

No, no drawings, but the spec was nothing special, just a post with a plate
with four bolt holes, welded to each end...

 

[loply]

No, no drawings, but the spec was nothing special, just a post with a plate
with four bolt holes, welded to each end...

How exactly do you weld a bolt hole to a plate?

 

[tony1851]

No, no drawings, but the spec was nothing special, just a post with a plate
with four bolt holes, welded to each end...

How exactly do you weld a bolt hole to a plate?

He put the comma (.) between the words 'holes' and 'welded', so he's grammatically correct and the meaning is perfectly clear!