Loose roof plywood decking and gang nail plates 4

[SpiderM]

I have an apartment complex that was damaged by a wind storm event. Several trusses were broken and the gang nail plates were pried loose, to varying degrees, from the truss members. The top chords are twisted or rolled which pulled or pried the gang nail plates loose, at this point I assume due to racking of the roof diaphragm. Lastly, the plywood now has a gap between the top chords of the trusses.

My questions...

Because of the varying amounts of prying, how much of the gang nail plate must be in full contact with the wood member? I know the easy answer is 100%, but is there a safety factor or something similar.

The twisted or rolled top chords have created a gap between the plywood deck and the top chord. How tightly does the plywood decking need to be attached to chord? Again the easy 100% number, but what are the limitations.

Lastly, because this is an apartment complex, it was most likely design under a prescriptive method of framing. An analysis of the roof diaphragm could determine how much of the roof plywood is required for the diaphragm, but the major unknown is the nailing size and spacing. Do the IRC currently require that the entire roof be the diaphragm? Or are there variations of the roof.

Basically, the proposed solution is to patch all the damage, but my concern is to insure that the capacity of the building can be confirmed.

I may need to elaborate if the conversation deviates from the course.
I can attach photos if anyone would like.

 

[MiketheEngineer]

You might want to check with a truss engineer for the truss questions. Sounds to me like extensive repair or replacement will be required.

As for plywood - look at the APA wood site. But again, based on your description it sounds like replacement may be required.

IBC does allow some prescriptive methods, but for an apartment building I would always do a complete analysis. As for nailing, the IBC shows both prescriptive and diaphragm nailing call outs.

 

[hawkaz]

If you review truss calculations, you will often find that the press plates have been designed right up to allowable tolerances.

A few years ago, I looked at an apartment complex that was under construction that had similar damage. The whole building racked during an extreme wind event, damaging several components and loosening just about every connection (improper construction shoring- and shear walls not in place yet). Based on the extensive repairs, the insurance company deemed it cheaper to demo and rebuild rather than try to repair. Albeit, this was still under construction, had no finish materials and was not occupied yet.

At a minimum, you will probably need to reposition the truss members back to their correct locations and orientations, fix any broken truss members and add plywood gussets at any damaged press plates. As Mike indicated- I would also do a complete analysis and remove/replace the plywood sheathing as needed. Don’t forget to check all the connection points also. I would suspect that some of them were damaged as well.

 

[Ron]

Unless these are townhouses, they do not come under the IRC...they would be under the IBC. See Section 101.2 of the IBC for applicability.

The loss of truss plate capacity goes up rapidly with lack of embedment or contact. A 1/16" reduction in embedment can reduce the capacity by 30 to 40%.

The fact that you have chord twisting is a good indication of poor sheathing fastening, unless you had full gable racking, in which case the gable bracing was not likely correct.

 

[a2mfk]

When doing renovations and repairs, I take this approach:
Anything I am touching, I have bought. If there are any problems in the immediate area of the building you were involved with, you will be dragged into it later... So I am very conservative in this area. I never would base my repairs on the bare minimum requirements of codes or what may be allowed if it does not feel right. I always do repairs with a nice factor of safety above and beyond new construction, since I don't want any collateral responsibility...

1. Damaged trusses- either replace them outright or you have to design a repair. Usually these can be very conservative repairs since over-sized 2xs and 3/4" sheathing (to replace plates) is not the expensive part of the repair. This is done on a case by case basis, though most engineers develop some pretty standard details over time.
2. Damaged sheathing or withdrawn fasteners- I would have them replace, and nail to highest diaphragm/uplift that is required for that wind speed and design. Over-nailing on a small area is of little cost.
3. Have an architect involved to make sure all the roofing, flashing, misc. waterproofing is done properly.
4. Have a GOOD CONTRACT with the owner limiting your responsibility to specifically described areas of the building. Also CYA notes galore on your drawings doing the same. Only take responsibility in writing and on your drawings for the repaired areas that you could visually inspect, and nothing else.

 

[BAretired]

SpiderM,

I would be interested in seeing your photographs. My first reaction is to replace the damaged members.

BA

 

[dik]

The TPIC requirements (TPI in US likely has similar requirements)for truss plates states that the 'gap' must be less than 1/16" and plates with a gap between 1/32" and 1/16" shall be considered at 60%. And if the truss plate is installed in an area where a previous truss plate was installed it shall be considered at 50% (might consider for a loosened condition). It's a bit of a turkey shoot at best...

There is generally little excess or rserve capacity; the market is so competitive.

It's a matter of doing an evaluation and then a repair procedure if it can be fixed. You may be able to consult the truss manufacturer to get added information and a manner of repair.

Dik

 

[SpiderM]

I truly appreciate everyone’s input. I have been out of the office all day and unable to respond. To elaborate slightly, this is an insurance claim. I was originally asked to look at the foundations for the renewal of the insurance policy. While at the site, I spoke with the public adjuster and noticed that a few of the roof trusses were damaged. So, they asked me to look at the remaining buildings for further damage. The claim went from about $150K to $1.8M. Needless to say the insurance company had a conniption. Their engineers and I had agreed that we needed to replace the entire roof for one building, half of the roof on two other buildings, and spot repairs for the rest of the buildings. We also agreed that the decking needed to be replaced and or reattached for conditions of loose decking or rolled top chords to insure the roof diaphragms.
Now the insurance company is saying that their engineers do not agree with my assessment and that they will provide repairs for all the trusses rather than replace them and no roofs will be replaced. The problem I have is the diaphragm. Certainly you can repair a truss, but if they’re not going to reattach the decking, they must have calculated or assumed that there is enough properly attached decking to establish an adequate roof diaphragm. Although there may be sufficient material for the diaphragm, I have a problem with the assumption of nailing. Some sort of verification is necessary, which, I would presume, requires the removal of shingles to see the nailing.
I really like the reference to the TPI. I don’t know why I haven’t thought of that. Thanks.
As for the IRC reference, it really doesn’t apply, but because I need to support my option with calculations and or reference material, I try to find every counterpoint to my conclusions before I write them. I didn’t want to overlook anything.
I have checked with APA, but I haven’t found anything in regards to poorly attached sheathing, other than “don’t do it.” Any further reference here would be great.
As far as the remaining recommendations, such as; replacements, repairs, reattach, analyses, I would totally agree, but I have to compel the insurance company to follow the recommendations by providing an adequate argument for such actions. Hence, I have to convince the insurance company that the other solutions are not possible because X,Y,Z…

Thanks again;

 

[dik]

If the superstructure's done... it doesn't matter how well you attach the sheathing to it... got to fix it first...

 

[msquared48]

Ask them to provide lateral calculations to you verifying that the roof diaphragms will be adequate when repaired.

Whoever is paying the insurance bill needs to have the buildings returned to their pre-damage condition, which is the ultimate purpose of having and paying for the insurance. This should not be a chewing gum and duct tape quality of a fix. The owner deserves better.

How much power and clout do you have here anyway?

FYI, with the trusses and roof sheathing torn, I would be suspicious of the truss members ability to endure further nail penetrations, depending on the extent of the damage to the wood members.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[SpiderM]

I totally agree that something must be done to insure the adequacy of the diaphragm and the structure. I have advised my client to request calculations to be submitted for the reviewed by his engineer, thus me. I hope that will force the insurance company's engineers to think long and hard about the safety of the building rather than the insurance company's apparent desires.

How would you argue for pre-damage condition as the structural engineer? What I mean is...the structure can be repaired and patched, per say, that will meet structural requirements, but that is not the pre-damaged framing condition. The phrase I am most familiar with is "make the insured whole again."

As for the nail penetrations in the truss framing, only uncovering the top chord would confirm whether additional penetrations could be tolerated. So, how would you successfully persuade the insurance company to allow an evaluation of that framing?

Is your question of "power and clout" rhetorical? As in, you’re a Professional Engineer condemn the buildings and make it happen. Or is it, how much influence do you have with the parties involved?

I’m looking forward to your responses.
Best regards;

 

[Ron]

In cases of damage or failure, the person suffering the damage is rarely "made whole". In almost every case, there will be a need for compromise.

Your task is to determine structural equivalence, not financial equivalence. They can be vastly different. There are many items to consider in financial equivalence such as:

requirement to disclose for real estate transactions
stigma of repairs known to the neighborhood
reduction in value for "repairs" vs. replacement

I'm sure a good real estate attorney could come up with a hundred more.

 

[msquared48]

What I was asking I guess is are you the engineer of record for the fix or not?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[dik]

and remember that every dollar an insurance company pays... comes directly out of profits!

Dik

 

[BAretired]

How about those photographs you promised us, SpiderMan?

BA

 

[dik]

The work is a major undertaking and can be very time consuming.

Find out who manufactured the trusses and confirm that they are a TPI member... See if you can get shop drawings of the roof framing. Assuming the fabricator is a TPI member... The city building department may be able to help with providing information on the contractor and/or truss supplier.

Do up a roof plan showing all the trusses and elevations of the various trusses...

Measure the gaps in the truss plate. Any truss members having a gap greater than 1/16" for the connection plate, remove that member from the model. Also remove that truss from the roof plan.

Any member with 1/32" to 1/16" use 60% of it's ft or fc. If it fails, then remove it from your roof plan... Check to see what your roof framing looks like...

 

[BAretired]

Replace the roof system. It's the only way you can assure the owner he is getting a roof system equivalent to the one he lost. If someone else wants to accept responsibility for repairing the damaged roof, that is his problem, not yours.

BA

 

[dik]

BA... to replace the roof... you have to show the extent of damage... then you can replace it. You have to show that it is damage beyond repair for most insurance work...

I've done reports for some companies that still wouldn't replace damage even if the engineering report recommends it... SF comes to mind as an insurance outfit that maximises profits...

Dik

 

[BAretired]

dik,

Why should the insurance companies dictate terms which the engineering profession must live by? It is patently absurd. If the roof cannot be repaired with complete assurance that it will be equivalent to the damaged material, it must be replaced. Anything less is unacceptable to the owner and, if accepted by the engineer, sets him up for future litigation in the event of another similar incident.

BA

 

[Ron]

BA...I only wish that our profession were such that you were right! Unfortunately it is not.

Insurance companies are usually only contractually obligated to restore function, not to replace to new condition. If Engineer A, through the application of sound engineering judgment and the application of codes and standards, opines that the roof trusses, and thus the sheathing, need to be replaced in order to restore function, the insurance company will find Engineer B who will say that scabbing a few 2x4's on the trusses will suffice. Further, Engineer B will opine that the work can be done without sheathing removal. He will sign and seal his report and the insurance company will "take it to the bank".

Engineer B has just turned engineering judgment into a risk management function, not an engineering endeavor as it should be. He has changed the standard of care. He takes on significant risk, but he knows that he can do that for several reasons. First, the likelihood of the roof ever seeing the design loads is very low. There is certainly a greater likelihood that it will not see such loads. He knows that if his opinion is favorable to his client, he will get more work from them, so he compromises his ethics for gain. Since there is no arbiter of correct and incorrect in engineering practice, he is free to use his judgment, since he knows that he will not likely be reported to his governing engineering board for malpractice...and even if he is reported, he'll find another engineer who will agree with him. And who knows...maybe he's right! It goes on and on without resolution.

Dik is correct. It isn't right, but it is a fact. The best we can do is keep our standard of care high as a group, promote sound engineering practice, and not compromise our ethics....and on each project involving a failure, the insurance company will attempt to break each of those for profit.