building brick walls on "propped" structure ? Now it cracks after de-propping

[lolobau]

Hi, I have some problem because the contractor was building brick walls on propped structure.
Now what happens after they "de-propped" the slabs, the bricks started to crack here and there.
How can I prove to the contractor that this was wrong? Obviously he is now arguing that why was he not supposed to build the brick walls on propped structure.
Where can I get some written proof that this is not allowed? Do the building regulates and codes mention it?

 

[BAretired]

Building codes don't cover every eventuality, but it stands to reason that a structure which is loaded while propped will deflect when the props are removed.

BA

 

[PEinc]

I agree with BAretired. Everyone involved with the job should have seen that one coming!

http://www.PeirceEngineering.com

 

[cvg]

at least in the US, the contractor is responsible for his means and methods, safety, quality control and protection of the work. it is not up to the owner or engineer to direct any part of the work. so it is entirely his problem to deliver a wall that is not cracked. it doesnt really matter how or why it cracked

 

[oldestguy]

Unless this is so bad and the contractor doesn't fix things, it may be cheaper to hire someone to replace it than to hire a lawyer. However with an attorney you will have the best way to solve it.

 

[WARose]

I've got into this before (i.e. about when to remove forms/supports). A lot of people just cover it with a note on the drawings saying do not remove until concrete gets its 28 day strength. But contractors always want to move on ASAP.

Probably one of the first things you need to do (if you don't already know) is figure what the deflection of the "slabs" would be long-term and what they would be at the point he removed the supports/forms. If the former is in excess of the latter.....you don't have a leg to stand on. You may not have one anyway if the long-term deflection exceeds something like L/600. (IIRC that's the requirement for supporting masonry under some circumstances.)

If he's not following your directions (or the drawing notes) and the deflection meets the criteria I was talking about in the previous paragraph.....it's time to talk to the owner/PM about getting him off the project.

 

[rapt]

Been telling consultants about this one for years in my RAPT training sessions.

Specifications and design drawings should specifically require that slabs and beams be unpropped before masonry and brittle finishes are added.

Any engineer who does not specify this cannot base their design on the deemed to comply deflection / span/depth ratio rules in design codes because they assume unpropped conditions and "incremental" deflections are controlling the design, not total deflection.

 

[dik]

It's been my experience when doing modifications to existing structures that involves any change to the existing load regime that you can have 'unexpected' consequences and other issues. You may not be able to pass this off as a contractor's 'means and methods'; courts in these environs also put a requirement of 'reasonable' to contract work.

Can it be remedied in a simple and cost effective manner?

Dik

 

[lolobau]

that you guys, you all say the same basically, you all are also experts in this field but now an weak contractor wants to argue and I would like to show it to him somewhere written down. I need something to relate to.

 

[TehMightyEngineer]

There's a requirement in the MSJC for beams supporting masonry to have a maximum service deflection of L/600. My MSJC is at home so I don't have the section number in front of me but I can get it tonight.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[rapt]

Lolobau,

It is the designers responsibility to both specify it and check that it is done correctly in my opinion.

The contractor is supposed to do what he is told.

 

[dhengr]

Lolobau:
Maybe the brick wall should have been designed as a deep beam, with a substantial bond beam, tension reinfr’g. region at the bot. of the wall height, to distribute the tension forces and provide some self spanning ability, and better distribute the wall DL. You might have been better off waiting to build the wall until the slab didn’t need to be propped for early strength, deflection and curing reasons. Thus, some deflection would already exist when starting the wall and some added deflection due to wall weight might be accommodated by a softer wall which was still compliant. Maybe the slab should have been formed and built with some camber in this wall area so that it would still have a bit of camber after the wall was built. Some of this problem falls back on the EOR for not designing the wall and the slab in anticipation of this sort of potential problem.

 

[dik]

TME: It's unlikely that the Contractor knows about L/600 deflection and how to create it...

Dik

 

[rapt]

dhengr

Sorry, Precamber does not help! It is the amount of movement that affects brickwork, not the final deflected position. Precamber has no effect on the amount of movement, only on the visible deflection, unless you make it an arch, and I doubt that you want that much Precamber!

Otherwise, yes some Engineering input into it as you have described might have been useful.

 

[lolobau]

@dhanger: you right could have been done this way but not needed.

I just regrade that I did not have a note on my drawings which clearly stipulates that this is not allowed to built walls on a propped structure :-(

 

[BAretired]

I just regrade that I did not have a note on my drawings which clearly stipulates that this is not allowed to built walls on a propped structure

I assume "regrade" should read "regret". The question is, if the props had been removed before building the walls, would there have been a cracking problem?

BA

 

[P1ENG]

You may not be able to pass this off as a contractor's 'means and methods'; courts in these environs also put a requirement of 'reasonable' to contract work.

I agree with this, so the question is defining "reasonable". What knowledge should a contractor have? He is competent enough to know that he wouldn't build his wall 3 hours after pouring, so why not expect him to know that shoring affects the structure? Is building a masonry wall on a shored floor a common knowledge no-no? I would think so. Who told him he could build the day that he did? Was it his own decision? Wouldn't he have to coordinate his presence with the project manager in order to not conflict with the other possible trades there?

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[briancpotter]

L/600 requirement for vertical deflection of masonry veneer is in section 6.2.2.3.1.5 of ACI 530-05. Not sure newer versions.

Brian C Potter, PE
Simple Supports - Back at it again with the engineering blog.

 

[cvg]

if it cracked because of the specific means and methods used in the construction, than it is likely that most courts would place the liability on the contractor. If it cracked because the structure was not designed adequately to handle the load without excessive deflection than the engineer would be to blame. I wish I could anticipate every dumb thing a contractor might do and place a note on my plans to warn him not to do it, but I don't have a crystal ball. I don't expect them to read all the specs either, because they rarely do. A qualified contractor acting reasonably should have known better than to lay bricks on a structure that is temporarily propped up. Of course the engineer could not know ahead of time how much it would deflect after removing the props. It appears that this contractor may not have been qualified, due to lack of experience.

 

[rapt]

CVG

" Of course the engineer could not know ahead of time how much it would deflect after removing the props"

Why wouldn't the designer know. It is part of the design calculations, if the designer wants to put in the effort to do them properly.

"I wish I could anticipate every dumb thing a contractor might do and place a note on my plans to warn him not to do it, but I don't have a crystal ball."

That is normally what Notes are for. So that the designer can tell the builder the limits on how he wants it built to suit the design. It is possible to design the floor to allow the brittle wall to be built on a shored floor if you want to do the calculations and pay the extra cost for the improved deflection control.