Shoring Existing Masonry Wall

[IceNine]

Hello-

I have a situation where a building is being renovated, and the 5th floor has been removed in an area, causing the exterior wall to be unbraced between the fourth floor and the roof (20'). This is an older building, with the walls constructed of clay tile masonry.

At the time I became involved, the contractor had the wall shored at a height of 6'-6" from the fourth floor. The original fifth floor slab was at 8'-10". Due to the fact that the exact construction of the unreinforced clay tile wall isn't known, and I'm not comfortable trying to analyze a wall of such construction, I told the contractor he had to brace the wall at the original height of the fifth floor, and of course he through a fit.

I'm calculating an increase of moment due to wind of approx. 30% due to the shoring height of 6'-6" as opposed to 8'-10". Since I don't know the cross sectional area of the wall and section modulus of the wall, I can't calculate if there will be any net tension on the wall.

I feel like I need to stick to my guns, and make him brace the wall at the original floor height.

Anybody have and other thoughts?

Thanks

 

[Lion06]

How is he bracing it at 6'-6" and what is preventing him from bracing it at the original slab height (8'-10")?
I would tend to agree with you about needing to brace it at the 8'-10". Don't you run into problems if the stress changes by more than 5% unless you can show by calcs that it is ok? It sounds like you might have a hard time showing it is ok.

 

[IceNine]

StructuralEIT,

Good question. The new fifth floor calls for steel beams to be pocketed into the wall, and the detail provided by the EOR shows the grout pocket extending 1'-4" below the new steel beam. So, the contractor put a horiz. steel angle below this pocket, with diagonal angles welded to it. He claims that if he'd put the angle any higher, he wouldn't be able to install the beams.

I think at this point, he just really doesn't want to spend the time or money moving the angle and cutting new diagonals, so he's pressuring us to make it work as he's installed it.

 

[jike]

What is your contractual relationship with the GC and with the Owner? Do your drawings require shoring at the floor and he did not provide it at that location? Is it even practical to put it at the floor line or did you need to install one below and one above the floor?

Sounds like he is determined to take the risk. How long will the wall be unbraced by the floor? Chances are probably very good that you won't see a full wind load during that time but it is anyone's guess.

All you can do at this point is tell him and get it in writing with a copy to the Owner and building inspector. Let them deal with him since the Owner has the direct contractual relationship with the GC.

 

[csd72]

Can you put a second line of braces up to the roof to reduce the span length?

I can see the contractors point, how does he install the floor if the bracing is already there?

That said, if you are in a hurricane zone and it is out of hurricane season then it is very unlikely that the wind will approach the design wind anyhow.

csd

 

[IceNine]

Thanks for the replies.

I'm not the EOR for this job. The contract documents didn't anticipate removal of the 5th floor. (architect thought the floor spanned full length, but interior partitions slated for removal turned out to be load bearing)

The EOR is passing this off to the contractor. The contract has hired us to sign off on his bracing.

I've come up with a plan of putting horizontal angles between the future beam pockets at the fifth floor level, with diagonals at each end bracing to the floor below. This way, they can install the beams, poor the slab, and remove the bracing. However, since this is a lot more work for the contractor, he isn't happy with it.

I'm at the point of telling him that I'm sorry he's not happy, but this is the way it must be. Just looking for any other ideas I may have missed.

Another line of bracing to the roof may be a possibility.

Thanks again for your replies

 

[lkjh345]

IceNine:

The floor needed to be removed because the orginal EOR and AOR didn't know the interior walls were load bearing, and now they are telling the contractor its his problem??????

Your kidding?? Right??

That sounds like a fairly serious error on the orginal professionals parts, and to pass it off to the contractor seems very irresponsible to me.

JMHO.

 

[IceNine]

It is a strange situation. The EOR designed a new floor system, but won't take responsibility for shoring the wall until the new floor is in place. He claims it's a conflict of interest?

 

[lkjh345]

Wow!

I guess some of us would have been embarrassed by a mistake like that on a project we were responsible for and would have been falling all over themselves trying to help resolve the problem.

Others, appearently not.

 

[jike]

I wouldn't be to quick to second guess the EOR. Perhaps the original drawings weren't available and the Owner may not have allowed exploratory work at the time of design (perhaps due to occupancy). I have been there.

The only thing the EOR is passing off is "means and methods" which fall under the contractor's responsibility. I am certain that most insurers would recommend against an EOR from taking on "means and methods". In fact if something goes wrong, you may not be covered! The EOR was right in requiring the contractor to develop his own shoring scheme for the wall.

 

[Lion06]

I agree with jike, we often say on drawings something to the effect of "contractor to provide temporary shoring until slab is cured", or "contractor to provide temporary bracing until diaphragm is in place and attached to framing".
If you get into telling the contractor how to brace or shore, then you are prescribing "means and methods".

 

[lkjh345]

I'll have to respectfully disagree.

If the situation was such that the EOR could not do adequate investigation to even determine which members are load bearing, then he/she should have respectfully declined the job.

Determination of which members are laod bearing seems to me to be at least the very basic 'standard of care' expected of a design professional.

JMHO.

 

[csd72]

lkjh345,

I agree with you in principle, but these days there are a lot of jobs where the client tries to fast-track the job.

For example there are existing tennants that cannot be disturbed and the client wants to start construction as soon as the tennants move out.

If this was the case I admit that the EOR should have visited the site on the first day to confirm their assumptions prior to demolition. Maybe this was the intention and the builder did not notify the engineer when they started.

I have taken the same stance when the builder has got into a problem through not consulting me. I would not want to spend my time fixing their mistake if I may not get paid for it.

Just a thought.

csd

 

[lkjh345]

csd72:

I agree.

We don't know the entire story here, so I should not be judgemental until I've walked a mile in the his/her shoes.

There is probably a good reason things ended up the way they did.

 

[msquared48]

With any remodel/addition with no drawings, assumptions will be made during the design process. The key here is to remain flexible by thinking "What if" the assumptions are not correct here, and having some quick and logical options in your hip pocket. Granted, you cannot think of all the scenarios, but finding joists cut over a wall thought not to be bearing is hardly an infrequent occurrence.

Consequently, it would be very advisable to warn both the Contractor and Architect of the possible scenarios prior to opening anything up that might tend to destabilize the structure. The contractor should include these possibilities in his bid and have options too. This should not have been a surprise.

Mike McCann
McCann Engineering

 

[IceNine]

I agree with jike and others as far as this being a means and methods situation. I don't know the whole story, but I have a feeling that the contractor removed the whole floor before the EOR was notified of any inconsistencies with the drawings.

So, it's possible the contractor got himself into this mess by not calling on the EOR during demo. At that point, I could've provided bracing details prior to the completed demo, and he wouldn't have to redo what he's already done...

 

[DRC1]

Ithink the EOR has the responsibility to show where the existing wall requires bracing, or show the maximum unbracrd length with an estimateof the brace loads. How the contractor achieves this is his means and methods.
As for thecontractor not notifying the EOR during construction, it is the contractor's responibility to notify the EOR once he is aware of the problem. It generally is not his responsibility to confirm the plans are accurate before he starts work. The matter was probably not noticed until after the demolition.

 

[jike]

For this project I would expect that bracing locations and forces should be shown on the contract documents. The means and adequacy of this bracing this is the responsibility of the contractor.