Wood Floor Truss Plates - Failing 2

[OHIOMatt]

These are images wood floor trusses, taken from the floor looking up. The building is used as an assisted living facility. I cannot see how the floor would have been overloaded given the use of the facility.

Any thoughts on what could be going on? The facility was constructed in 1996. The floor live load for this area was listed at 100 psf.

I am making an additional visit to the site tomorrow to see if I can figure out what is happening. Apparently as the contractor doing cosmetic renovations removes areas of ceilings, he is finding this condition frequently.

Thanks in advance for any insight.

 

[BAretired]

We are finding the problem extensively throughout the building. While we still don't know what caused it, we have been able to rule out the following:

Over Loading
Mishandling during erection
improper pressing of the plates
Non-approved fabricator

That doesn't leave many options. If the problem is extensive, and the cause is unknown, it may be prudent to avoid ruling anything out.

BA

 

[Ron247]

I agree with BA, not much left if you rule out those 4. I assume overloading would include incorrect design.

Do not rule all of those out except fabricator. The hardest projects I have ever done did not have a single problem, they appeared to be a combination of the possible problems. As I routinely say, "It can be any of these possibilities or any combination of them".

I am curious, how did you rule out mishandling? Mishandling can be anywhere from right after fabrication to right before it is nailed into place. If I messed this up as a carpenter and did not properly correct my problem then, I am pretty sure when asked several years later about it, my memory would be conveniently fuzzy.

What did you find out about the bottom plate? Was that from original design?

 

[bones206]

LuK13 mentioned moisture as a possible culprit. Plates backing themselves out as the lumber dries seems like a viable possibility in my mind. Especially if the lumber used had a high moisture content when fabricated. It sort of jives with the fact that it is widespread throughout the building. Not a phenomenon I was familiar with before reading this thread, but after researching it a bit it seems to be a real thing.

 

[BAretired]

The orientation of members on this project is not standard practice in the industry. This, combined with square cut ends on diagonal web members, results in less contact area for side plates. Plates attached to the underside of the bottom chord could not have been applied in the usual manner, i.e. with hydraulic pressure. Attachment with a hammer would loosen the grip of the teeth, hence "improper pressing of the plates" is extremely probable and cannot be ruled out.

Mishandling during delivery and erection is also a strong possibility and should not be ruled out.


BA

 

[Brad805]

I think it is important to keep in mind the era the trusses were built. I have a 1970's renovated home that used engineered roof trusses as well. I have been up in the attic many times and the size of the plates are far smaller than modern plates I approve on shop dwgs. The level of automation in 1966 would have been less as well. I expect there was far more manual labor and humans cutting parts instead of accurate automatic machines that are fed gcode. The nailer plates on multiple sides is odd.

Misread yr.

 

[HouseBoy]

OP states the year of construction was 1996. That and the poor characteristics of the cutting (along with other shortcomings) make me wonder about the source of the trusses. As others have observed, they do not look like industry standard trusses.