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.

 

[3DDave]

Are the outside walls plumb?

 

[dik]

You need an engineer, quickly... could have a catastrophic failure...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[OHIOMatt]

dik, I am an engineer. I am headed to the site first thing in the morning. I understand that this is a serious issue, just looking for insight as to what may cause it. I have never seen anything like this before.

 

[dik]

They could have been mishandled during erection. They may be overstressed... I dunno... looking at the site may give you an idea of the circumstance. Can you obtain shop drawings of the trusses? Check the design loads, that would be my first step.

You also may want to contact the truss supplier and see if they can offer an opinion. Can you obtain drawings for the building? and any inspection reports? Just a lot of stuff to do initially to get a handle on the problem... also take a bunch of photos? You should also assess how safe it is? Can you erect some scaffolding so the place can be occupied.

Who was the engineer that did the initial design and drawings? You should contact him to inform him of the issue. Inform him as a professional courtesy; I don't rely on engineering association ethics. It's just the proper thing to do.

Find out the loading circumstances... was the area just hit by a tornado/hurricane?

I'm pretty laid back, for the most part, but when things are serious, I act decisively and quickly... as my initial response... I also don't panic... Ron's likely got some 'kind' words, too.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

I've sent it on to my wood guy for comments...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[OHIOMatt]

Dik, to answer some of your questions,

The original, 1996 documents were sealed by an architect, who is no longer practicing.

I have the original drawings, but shop drawings are likely not to be found. We have been to the site for some other, non-related issues looking through the owner's archives, and those were not there.

I am not sure who supplied the trusses, I am hoping to find a make or part number on a plate today, so that I can at least start down that path.

The area directly above these trusses is a communal use area. It has been closed due to COVID protocols, which I am thankful for at the moment.

I have seen truss plates fail before, just not in this manner. What I have seen in the past is shear teeth and or drag marks on the wood. I cannot wrap my head around how this could behave this way. I thought perhaps it was getting axially load as some type of accidental drag strut, but the building geometry does not lend itself to that.

I am not sure what you mean about Ron and his "Kind" words. Almost as if you are accusing me of something. If you think I am handling this incorrectly, tell me! I am not sure what the expectation is. I was sent photos yesterday afternoon and today I am making the three hour trip to the site for a morning meeting.

 

[MotorCity]

The gap between the members looks too large to me. Perhaps the gap forced the truss plate to go into bending, which they are not designed for. It also looks like the truss plate was removed and reinstalled (perhaps in the field?) since you can see teeth marks from a previous installation. I would guess the truss was damaged during erection and someone tried to fix it on their own.

 

[Ron247]

The teeth look straight rather than bent. This tends to indicate the plate pulled directly away from the wood rather than laterally pulled loose.

I would think tension on the chord would have bent the teeth some as it pulled them loose. For this reason, I tend to agree with MotorCity and dik. I would more think mishandling than overloading.

I would look very close at all plates to see if I could determine how they pulled loose. Also, do I think all plates were original. I have never seen a bottom chord with a plate across the bottom. I have seen both sides plated, but not the bottom. This may be because I have never had a highly stressed one.

 

[dik]

Is this condition for one truss? or for a bunch?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[3DDave]

To pull the teeth straight out the plates would have to resist a load normal to their surface, but I'm at a loss as to how one would do that without also bending them in the direction the teeth are pointing.

If a pry-bar was used it should have bent the plates into a curve as the plates don't appear stiff enough to remain fully elastic; in fact they are bent - they yielded.

If the rest of the structure isn't pulling these apart, then I suspect another contractor getting clever when the beams were too short and "fixed" them. Depending on the blocking between the beams they may have arranged for some composite load path rather than allowing all the gaps to line up.

 

[GC_Hopi]

Probably a combination of issues but I would also think they were mishandled or "fixed" as being too short per Dave's comment. However the splice looks like it is midspan which seems odd so maybe there is something else going on behind the insulation

 

[LuK13]

3DDave

Cyclical wetting and drying of the truss can cause the plates to back out as the wood swells and then shrinks. I've seen it in a number of attics with poor ventilation and widespread biological growth issues. However, in these cases the plates back straight out, the bend at the gap in the photos is closer to the "peeling" you see from being overloaded.

OHIOMatt

That being said, Ron has a point. Those teeth are in better shape than I would expect for a plate that peeled away due to an overload. The teeth tend to look like that when the plate backs out.

Since half the visual evidence is in favor of moisture, and half is in favor of overload, I'm going to also vote some sort of manufacturing defect or mishandling during shipping/installation. Hopefully your time on site yields some additional information.

 

[3DDave]

Were it not that all the teeth are straight I would think overload at some time, but there's a straight tooth extending into the gap.

Perhaps the maker built them with a gap and that allowed abnormal bending?

 

[hokie66]

It does look very strange to see very little distortion of either the plate teeth or the holes in the wood. Are those plates indicative of a manufacturer, or are they generic?

 

[BAretired]

Truss plates occur on both sides and bottom of the bottom chord. The side plates may have been pressed on using a hydraulic press, but perhaps the bottom plate was hammered in place. If so, it would not have achieved a firm grip on the chord.



BA

 

[OHIOMatt]

Well, I am back from my site visit. The following is what I have been able to ascertain, some of this may be duplicate information

Span: 25'
Depth: 20" (nominal, but actual depth varies from 19 1/4" to 20")
Bottom Chord: Select Structural SYP
Top Chord:#2 SYP
Webs: #2 SYP
Connector Plates: Mitek (M-20)
All members are 2x4

I was not able to find any evidence of water damage or exposure to moisture. The trusses are in a continually conditioned space, so very little temperature change during the life of the structure.

The area that these trusses support is residential in nature with a design live load of 40 psf.

There are numerous trusses exhibiting this failure mechanism, in addition, there are signs that some of the damage is recent.

The following photo shows the panel point of the truss. Please note that the web members have square cut ends, resulting in a gap in the joint. In looking at the standards of today, this does not appear acceptable, but I have not found any standards from 1996.

Could the nature of the joint allow excessive deflection that would work the teeth loose?

 

[jayrod12]

Oh that's terrible jointing. That forces the plates to act in compression which I don't believe they're designed to do. I wonder if the truss plant that fabricated these are still around, hopefully not.

I'd be having a conversation with one of the local truss plants regarding some of these issues. Hopefully they've got someone on staff that's been around since the time of this construction that can speak to the normal methods of the day.

I'd say this is a huge issue, and if widespread like you seem to indicate has the potential for a massive issue if they were to all finally let go at the same time.

I'm generally not one to instantly say get people off of the floor, but in this instance if this is a widespread issue and all trusses were fabricated the same then I would be concerned about the ability of the floor to support the design loads.

 

[bones206]

The area directly above these trusses is a communal use area. It has been closed due to COVID protocols, which I am thankful for at the moment.

The area that these trusses support is residential in nature with a design live load of 40 psf.

I would expect a communal use area to have a higher live load than 40 psf. Could be a contributing factor. To me it looks like there was an overloading event (Saturday night hoedown?), then the trusses returned to their original dead load deflected shape, but the plates remained bent as a record of the live load deflection that was experienced.

 

[WARose]

All sorts of things can happen with wood. As others have suggested: could be loads normal to the plane......and sometimes wood just plain warps under the right environmental conditions.

To tell you the truth, I've never gotten how those truss manufacturers justify using those plates. After a inspection once, I ran those plates as per NDS and I couldn't get it to work (for one thing, the spikes didn't have min. penetration). I guess it's just a product they have confidence in. Whenever I have been asked to fix stuff like that.....I've just wound up getting them to add framing nails (12d, 16d, etc). Those slots you see on the plates are typically wide enough for that.

[red]EDIT[/red]: A footnote on that....some years ago (about 25 to be exact) I bought the Truss Plate Institute's manual on designing those plates.....and (IIRC) even that did not address these types of plates. (Just figuring stuff like required plate area under different loads and so forth.)