Some movement during extension work-ok?

[indus]

Hi

I'm having some 'major' work done on my 1902 built house including a double storey extension. Significant parts of the original supporting walls have been removed and steels put in. (and more of the same to come)

All calcs were done by a structural engineer and going by past experience he always over specs things. Parts of the original walls, which would become piers to support steels, were underpinned with 1m x1m x 1m concrete pads.

I watched all the steels go in and temporary support was provided, they were well packed in, steel plates used etc.

However it seems as though there has been some movement of the building at the rear (where most of the existing rear wall has been removed)

There are no significant cracks appearing but the two upvc windows on the first floor of the rear wall now don't close properly. You can close them but they need hard yanking rather than the previous smooth operation.


Is it reasonable for there to be some movement like this when structural walls are removed, foundations are underpinned etc?

Thanks for your advice

 

[skotl]

Err no. That's not usual.

You should get the structural engineer out again.

 

[tony1851]

It could be one of two things; excessive deflection of the beam(s), or slight settlement of the support to the beams.

For deflection of the beam, the SE would have assumed a safe amount (usually around 1/360th of the span) and checked that his chosen beam
would not deflect more than this. But the figure of 1/360 is fairly arbitrary, and it could be more or less than this, depending on the state of the structure above the beam. His calcs will show what allowance he made for deflection.
The only point mitigating against excessive deflection is that it usually (though not invariably) occurs more or less straight away; how long has the beam been in?

The other possibility - settlement - would be caused by excessive loading on the sub-soil. Again, if your pad is 1m x1m, your SE will have calculated the load on it. In the absence of any specific ground-bearing figures (was there a test?) the SE will have assumed a safe bearing capacity and worked back from there.

I shouldn't jump to any conclusions just yet, but at least let the builder and SE know of the problem, and monitor it.

 

[Deluks]

Did that pad really need to be 1m thick?

 

[indus]

Hi Tony

The movement seemed to have happened BEFORE the steels went in ie when they were removing the wall and prepping it for the steel.

It was supported by a technique that I think is called 'needling'? Two rsj beams were inserted through the wall upstairs and supported outside by acros.

Deluks, I have no idea whether they needed to be 1m thick, it's what my agent specified and I don't have the knowledge to question it. And to be honest when it comes to my own home I'd rather things were over specifief than under.

Thanks for the advice

 

[^woody^]

They have jacked the wall up too much, and then the panel has distorted when it came back down to is original level

 

[indus]

They have jacked the wall up too much, and then the panel has distorted when it came back down to is original level

Aha! This is what the builder said had probably happened when I first noticed it. But I thought if that was the case it would have gone back to normal once the acros were removed.

 

[jeds]

It is also common practice to dry pack a steel beam under no load and then let the load onto it. I don't allow this on my jobs. I have the beams loaded with wedges and the temporary support let off before it is packed. That way all design deflection is taken up before the temporary support is finally removed and there is no possibility of subsequent movement.

 

[noseall]

I don't allow this on my jobs. I have the beams loaded with wedges and the temporary support let off before it is packed.

Ahh, you're one these on site types that like to finger point and stand in the way or do you actually give the builders a hoik up with the beam rather than get in the way?

Bet you prefer bark your orders from the sanctity of your office when it's -5°C though.

 

[indus]

Thanks Jeds, I'm not sure which my builders fitted the beams.

 

[^woody^]

It is also common practice to dry pack a steel beam under no load and then let the load onto it. I don't allow this on my jobs. I have the beams loaded with wedges and the temporary support let off before it is packed. That way all design deflection is taken up before the temporary support is finally removed and there is no possibility of subsequent movement.

I don't understand the point of what you are describing, as there is no difference between the two

You wont load a beam with wedges, because you will never get the same load as the wall above while the temp supports are in place

All you are doing is packing the beam and releasing the temp supports, so whether its packed with slate, mortar or wedges before the temp supports are removed, there is no difference at all

 

[jeds]

I don't allow this on my jobs. I have the beams loaded with wedges and the temporary support let off before it is packed.

Ahh, you're one these on site types that like to finger point and stand in the way or do you actually give the builders a hoik up with the beam rather than get in the way?

Bet you prefer bark your orders from the sanctity of your office when it's -5°C though.

Don't be an idiot. I have a very good relationship with the builders I work with. And I've lifted more beams up than you've had hot dinners.

 

[jeds]

It is also common practice to dry pack a steel beam under no load and then let the load onto it. I don't allow this on my jobs. I have the beams loaded with wedges and the temporary support let off before it is packed. That way all design deflection is taken up before the temporary support is finally removed and there is no possibility of subsequent movement.

I don't understand the point of what you are describing, as there is no difference between the two

You wont load a beam with wedges, because you will never get the same load as the wall above while the temp supports are in place

All you are doing is packing the beam and releasing the temp supports, so whether its packed with slate, mortar or wedges before the temp supports are removed, there is no difference at all

It's not the same. Wedge the beam and let off the temp support. The wedges are then doing all the work and the deflection is full on before packing. When you wedge up you can measure the deflection.

 

[^woody^]

What is the difference between a "wedge" and a "packing"? I don't understand.

They are both doing the same function, except one is temporary

I wedge with slate packing and the wall above does not move

 

[Pallatrax]

I'd like to stick my nose in and ask where you wedge the beam - above the beam along the entire span, or under each side on top of the pad stone?

Tom