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Newly Constructed Gym Has Roof Collapse in New Mexico
12

Newly Constructed Gym Has Roof Collapse in New Mexico

Newly Constructed Gym Has Roof Collapse in New Mexico

(OP)
https://www.kob.com/new-mexico/gym-roof-collapses-...



Quote:

ALBUQUERQUE, N.M. — In-person classes have been canceled at a local charter school for the rest of the week after the roof of its new gym collapsed.

School officials say the new gym at the Explore Academy middle and high school campus was basically complete. They were even planning on hosting a ribbon cutting Wednesday, but that’s been canceled, as well as all in-person classes.

Parents learned about the collapse through an email from the school Sunday night.

“The students are out the whole week now,” a parent told KOB 4 anonymously. “Because they have to get inspectors to gather and, at the request of the inspectors in particular, for students to stay away until they can just look the whole thing over.”

The parent said the incident has raised many more concerns about sending her child back to school.

“Students were going to be in that building in two days, and I think one of the big questions I personally have is, did it pass the inspection already?” the parent asked.

The answer is no. KOB 4 spoke with a rep from Albuquerque’s Planning Department. They said the construction company, AIC General Contractors, failed a building frame inspection on March 6. Inspectors found the trusses bowing or bending.

The city’s Planning Department didn’t know the roof had caved in until KOB 4 called Monday afternoon.

Explore Academy leaders say, as of now, it’s just the new gym that seems to be impacted, but they aren’t taking any chances.

“They discovered the damage and evaluated the situation and decided that we would go ahead and go to asynchronous learning until we have a sign off that the entire building and structure is, in fact, safe for students to enter,” said Katia Pride, Explore Academy’s director of outreach.

Pride said there was no obvious damage to nearby classrooms. The school will also have to bring in an engineering company to create a repair plan.

The city’s Planning Department will be sending a building complaints investigator to figure out what went wrong.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

The low bidder wins again.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

An interesting looking truss. How bad does your design have to be to mess that one up? It looks like a rather basic clear span done every day. I guess we can estimate the span off Google Earth.

Edit: Maybe not a basic design. Two girders carrying the trusses and ne of the girders collapsed. Possibly the bearing surface of the support column was inadequate.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Wow! Brand new, no snow/ice/rain load. Someone messed up big time. Maybe overlooked a critical buckling mode.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

From the video, it looks like the trusses weren't even attached to the girder.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

(OP)
It says they failed inspection on March 6th. So over 6 weeks later with no special loading the whole thing comes crashing down.

And they were expecting kids to be using the place in 2 days. So they were presumably going to get an inspection in the next couple of days or open without approval.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

A failed structural inspection would require remediation before roofing and interior finishes commenced. There is a disconnect in here somewhere. Perhaps if the trusses were seen bowing after the roofing was installed, circumstances once again point to field staff or higher lacking appreciation for ramifications of the issue.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Well at least some of the roof stayed up.
I'm a glass half-full kind of guy.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Half full of what and what happened to the other half?

There's a missing web element in the girder.




Edit: re-centered, white balance and brightness enhanced

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

From in-progress, 2:15 in news video:

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Indeed, that missing diagonal could be a cause.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

The truss could have easily been designed for not having that diagonal for mechanical reasons, or whatever. There does not appear to be any distress in the area of the missing diagonal.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I cannot determine the type of framing. Was it long span trusses? with smaller short span trusses framing between. It appears the long span trusses have steel columns at the ends for supports. It appears to be a failure of the support attachment... but just a WAG.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (Hi! Im a ingeneer and this is my compooter!)


I remember designing those things by sliderule, and graphical methods.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Maybe the bending and bowing was in plane bending?

Wouldn't take much to get it to drop out of the rather small end connections onto the walls.

But is that cause or effect?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I'm not so sure about "easily", would proly need a "puter, otherwise maybe. I haven't looked at the design implications. I was just spewing. Not enough information yet.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Just a first blush impression - the large truss bearing failed and dropped one end of the truss. Pulling the adjacent bays on either side down with it.
The other large truss bearing didn't fail and thus the 1/3 of the roof stayed put.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

It's pretty easy to speculate that the as-built connections between truss and column were different from the as-imagined connection the engineer calculated.

Pretty impossible for all of the trusses to be exactly the right length and each of the column pairs to be exactly the right distance apart.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

On the "missing" diagonal- both trusses, both ends are like that, so looks pretty intentional.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Ok, not my field, but you don't need both chords of that style of truss to be separately supported, do you? A diagonal member from the unsupported chord to the supported chord serves the same purpose, doesn't it? The floor trusses for the original WTC 1 & 2 were only connected on the top chord, for load bearing purposes (there was a damper to the bottom chord), similar to the trusses seen here.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Those missing diagonals probably converted the girders from structures into mechanisms. If they'd have put them in the middle where the shear is lowest, they probably would have gotten away with it.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Gotten away with what? Saving a few bucks? What purpose was served, other than cost saving, to not including the additional diagonal braces?

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:

The secret of life is not finding someone to live with
It's finding someone you can't live without

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

If you're interested in the full constructon time lapse see here https://www.facebook.com/100063532571876/videos/29...

There looks to be quite a lot of spare room as they swing the main truss in place sitting on some rather thin looking CMU inner columns

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

They had to jamb the first end deep into the wall pocket to get swing clearance for the opposite end. Video doesn't show them pulling the first end back out after setting the second end. So it's possible the second end had inadequate bearing length.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (hpaircraft )

Those missing diagonals probably converted the girders from structures into mechanisms. If they'd have put them in the middle where the shear is lowest, they probably would have gotten away with it.
A Howe truss is made of triangles, the the members have no bending loads, and the member ends can be approximated as pins in calculations.
The windows put a Vierendeel truss section into a Howe truss. All of the load in the Vierendeel section creates moment loads in the connections, and bending loads in the beam which are not present in the Howe truss section.
It is possible to design this so it will work, but it is a lot more than just removing the diagonal. As all of the members appear to be rectangular structural tube it is possible these considerations were made, we will need to wait for more news.
The beam seats do look a bit sketchy. Is there a steel post hiding in the masonry? If so it must be close to Euler's slenderness limit.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

There doesn't appear to be a steel post in the CMU.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

No need for a steel "post" in a masonry pilaster, but there is need for adequate bearing length as bones mentions.

Not an ICC tornado shelter, that's for sure. Can't even hold up sunlight.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

As many has observed the loss of end bearing seems the final trigger of collapse, but the question then arises what caused this and why. At first I believed the missing diagonals were a red herring and a distraction. But a brief analysis suggests otherwise

The missing diagonal could be critical but not for the obvious reasons. The obvious reason being the large loss of strength when fully restrained. (Approximately a 1/3.) The non obvious reason is that they increase the buckling likelihood of the truss by approximately 40x at ULS! (presuming the bottom chord is unrestrained)

When the bottom chord is under tension it has no obvious desire to buckle. However as soon as you remove one diagonal the chords are now subject to significant bending moments and entire truss is subject to lateral torsional buckling. Furthermore my brief analysis suggests this behaviour is quite non-linear.


My analysis is superficial and brief.

However I will go out on a limb and suggest this was a case of lateral torsional buckling of the truss due to an unrestrained bottom flange. This buckling caused distortion that ultimate loss of bearing. The final trusses mostly look in good condition because the LTB stayed within the elastic zone.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I do love to see a spacegass model. Probably my favourite software, always so intuitive and clean looking

----------------------------------------------------------------------

Why yes, I do in fact have no idea what I'm talking about

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (JohnRBaker)

Gotten away with what? Saving a few bucks? What purpose was served, other than cost saving, to not including the additional diagonal braces?

Yeah, good question. My suspicion is that they wanted those clear spaces for services like HVAC ducting. And again, if they'd run them through the inboard two bays of the truss where the shear is negligible, the bending stiffness of the chords alone probably would have reacted what little shear was applied by the lateral trusses across their tops. Instead, they eliminated the diagonals from bays near the support ends, so in those areas the chords alone have to react the accumulated shear loads of all the lateral trusses inboard of them.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

2
I agree. The diagonal braces were cleared for HVAC ducting. And despite the poor choice of location, I'm currently giving the engineers enough credit that they did for SOME of the effects of removing those diagonals. The obvious effects are the chord and strut bending of the vierendeel truss action.

The less obvious effects is changes to the global buckling behaviour of the truss. (Which to be honest I don't fully grasp myself. Except that my brief analysis shows that the truss is quite sensitive to it. (Also there often exists the notion that a tension chord/flange doesn't need to be braced to prevent LTB. This is mostly the case, but not always.

Tension buckling exists! As does LTB with unrestrained tension members. **

**Though you could just as easily claim this is simply sway of the struts under compression with limited rotational restraint on the top chord and not lateral restrain on the bottom. In reality though buckling is often a SYSTEM phenomenon. A tendency for the system to more to a lower energy state. In this case I'd describe it a LTB of the truss.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Just one correction to the terminology: these are not Howe trusses, but rather Pratt. At least for gravity loading, for net uplift they would be Howe. Pedantic, but after all, this is an engineering website.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Human909 your analysis appears to be a bit off. According to the photos, the omitted diagonal is in the second fully rectangular bay from each end, not in the third as your diagram shows. So you have underestimated the shear in the bay with the omitted diagonal.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

My first thought about the missing diagonals was also that they provided space for HVAC ducts.

However, there is no duct wreckage in the post collapse images. Maybe they were going to open the guy without the ducts, and put them in later. Wouldn't be the first time that a building opened before it was finished.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

The inspection timeline is as follows:



March 6 - structural inspection fails citing dip in truss
- interior work allowed to proceed

March 25 - followup inspection fails citing further dip in truss
- interior work suspended
- third party evaluation required

April 7 - roof collapse

April 8 - news contacts city for comments only to find city unaware of the collapse

April 10 - planned ribbon cutting cancelled

Quote (https://citydesk.org/2024/charter-school-roof-coll...)

“Students were NOT going to be actively using the building this week regardless of the ribbon cutting,” Kolander wrote. “We needed the gas lines to be activated, the flooring to finish being installed, final inspections to be done, etc. I know it was made to seem that kids were days away from using the building, but that is not accurate on anyone’s timeline.”


I'm not familiar with roof space details in hot climates. There appears to be a deep section of unfinished space beneath the roof surface layer and interior space beneath. There appears to be a great deal of material (see my 3d photo posted above) in the debris pile that may be insulation material. Also, in the photo below, embedded rebar at the interior finish level seems to have concrete adhering to it?



Nonetheless, the omitted diagonals in the girder truss would create significant moments at the four corners of the bay. Where the web elements are slender HSS and the chords are broad HSS, this becomes a particularly challenging connection to detail and if not adequately fabricated provides a mechanism for the truss to sag. Additionally, it isn't beyond reason to believe that the sagging truss tore out the bearing connection at the nearest wall contact.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

OK Prat trusses with the ends inverted,

It seems the point I was trying to make is finding some consensus IE the Vierendeel truss stuck into a truss built with two force members is a significant design challenge, with a bunch of potential pitfalls.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Yes, of course it is difficult, if not impractical. There is always some moment transfer even when trusses are triangulated throughout, but the ductility of steel means the hinged assumption works, conservatively. No so much with concrete structures like the FIU pedestrian bridge.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (hpaircraft)

Human909 your analysis appears to be a bit off. According to the photos, the omitted diagonal is in the second fully rectangular bay from each end, not in the third as your diagram shows. So you have underestimated the shear in the bay with the omitted diagonal.
True. But I don't think this affect the conclusions. I don't believe this failure was caused by member failure due to the missing diagonal brace. The loads here were well below ULS loads. I think the more likely conclusion is LATERAL TORSIONAL BUCKLING resulting in the truss pulling away from its support.

Quote (hokie66)

Yes, of course it is difficult, if not impractical. There is always some moment transfer even when trusses are triangulated throughout, but the ductility of steel means the hinged assumption works, conservatively. No so much with concrete structures like the FIU pedestrian bridge.
Agreed. In fact when I design HSS trusses I model it with rigid connected ends and there is non negligible moment transferred. Why? Because that is the reality of most welded truss HSS construction. Those ends are moment connected not pinned.

In a normal truss with full diagonals throughout then that moment transfer plays a minor role and there is no great difference between pinned and rigid connection. But given we now have plenty of computational power at our disposal, it would seem amiss not to consider it.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Human909,

Unless I've misunderstood your diagram, you seem to have looked at a triangular section truss?

It's very clear this is only one plane.

The inspection report seems to indicate a gradual yielding or creep of the truss or its supports.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

No. There is only one truss modelled. What you are seeing is the truss and the deflected shape of the first buckling mode. I tried to view it from an angle that made that more clear, but it wasn't perfect.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

There are some more photos on the GC’s Facebook page showing the installed hollowcore plank roof. I don’t have a Facebook account so it won’t let me share the link.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Would not the tension in the bottom chord tend to direct the bottom chord to move upward from any deflected condition, but that upward movement being restricted, kicks it out laterally instead? Especially in a Pratt configuration. The bottom chord does not appear to be braced against any sideway. Additional shear deflection of the panel with the missing diagonal might have contributed to the possibility of a greater sideways tendency.

It does seem rather odd that there are a diagonals vacant for no yet apparent reason. What's up with that?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Grabbed this from the GC's facebook page. You can see duct piled up on the floor.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Is there a date associated with the photo or posting?



Aside from showing the viewpoint of the Facebook photo, the two a/c units supplying the gym are seen at the window elevation astride the two girder trusses. This would mean that at least some duct work is exposed beneath the ceiling though it could be turned up immediately inside the gym.

I see now - Hollow Core Concrete Panels atop the truss with insulation above.


Enhanced photo from Facebook - AIC General Contractor, Inc. (Photos were posted January 12, 2024)

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

This photo seems odd as there are no supports for the A/C units nor openings for ducting.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (where the shear is negligible,)


Try not to use the term 'negligible' in a report. Maybe, where shear is greatly reduced...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (This photo seems odd as there are no supports for the A/C units nor openings for ducting.)


I'm not sure what you mean. HC projects often have mech units and the precaster accommodates the weight of these in his HC design. The same thing is done for any openings in the HC slab for mech units/access.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

dik, it just seems odd to me that you would cut in HVAC openings rather than block them out or place HVAC units directly on the roofing membrane rather than provide raised supports.

Below is a 2D analysis of a simple pin connected truss showing distribution of tensile and compressive forces. I included the two omitted elements, 60 and 61, to model inadequate moment connections (61) by reducing the modulus of elasticity, and adequate moment connections (60) by using full strength material. Note the diagonals are in tension, I believe a defining element of Pratt trusses.

If this is the type of deformation that was noticed prior to collapse, or even lateral deflection, it is puzzling that over a month of analysis would be required to study the situation. There is a disconnect in the ability of our design and construction personnel to recognize vulnerable structures or to react appropriately. As I stated in a previous thread, I'm quite sure that if a 2x4 could have been used to prop this thing up while they thought about it, they would have done it. However, since temporary support would require more dollars, they just commissioned a study.

If the moment connections were deformed, ....?



Edit: I misdirected references to elements 60 and 61. They are now corrected. (Still getting my ship* together)

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (Sym P. le)

...if a 2x4 could have been used to prop this thing up while they thought about it...

Just eyeballing it, I bet 4x4 fence posts with double-beveled ends, two each wedged into the open bays, would have had enough column strength to keep that mess in the air while they got their shit together.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

LOL(as in yes)


With 4x4 supports/wedgies

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (HVAC openings rather than block them out or place HVAC units directly on the roofing membrane rather than provide raised supports.)


I'm not sure I understand the question. With HC slabs, you don't 'block out' openings. The HC slabs are extruded and the openings are placed in the plant.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (Below is a 2D analysis of a simple pin connected truss showing distribution of tensile and compressive forces. I included the two omitted elements, 60 and 61,)


You design for the missing web diagonals; I've done this numerous times. It's easy to do. You do not have to accommodate it for erection purposes. It becomes part of the design.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I see nothing wrong with the openings for the ventilation. No reason to suspect an "inadequate moment connection"...the top and bottom chord are continuous. Assuming pin connections and short segments is great for a freshman college course or reviewing a 150 year old bridge design, but it's not very useful for analysis of a modern building structure. With steel mills running continuous casting, the only real limit on length of members is the ability to ship them. We don't cut them up and spend money on more labor to make weaker structures. So unless your 2x4 or fence post is 28 feet tall with some amazing ability to be braced along its length, it's not going to do anything to help with propping anything up here.

Based on the negligible information available (a very rough, long distance shot from a circling helicopter), it would appear that there's not much of a positive connection between the hollow core and the truss. If there were, I'd think the truss would be a bit more deformed. If that's the case, then it could well have been an LTB type failure or a buckling failure of the top chord. Looking at the weather, looks like winds were fairly calm leading up to that weekend, and then they jumped up above 20mph. A localized gust or downburst could have been enough to trigger it in that case as it would only take a limited amount of time to start the deformation and second order effects would carry it the rest of the way.

Inadequate bearing could also be a/the cause as increased wind would cause more movement in the walls. Not a lot at that wind strength, but it if that bearing were deficient it may not take much to shift it off or tear the bearing plate out. The lack of damage to the outer walls makes me wonder how well the roof was tied in there, too. So if the truss to wall connection was the stiffest thing out there, it may have taken a much higher out of plane load than the designer might have normally assumed.

Be interesting to see more details if/when they come out. It happened 3 weeks ago, so there may not be...

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

The wall opening for the HVAC duct is what I was referring to and vibrating units can wear the membrane which is why I thought raised supports would be used as they are for the roof hatch and skylights.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

phamENG, ... except for the anecdotal report that there was a dip in the truss. It sounds like a distinctly odd description.

dik, ... it has to be accomodated in the design and is every day. I don't doubt that. Without more info, we are left speculating about possible causes and we may as well itemize a few, no?

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

It does sound odd. But a 'dip in a truss' is sufficiently vague as to be nearly worthless. We know that it had changed its shape - but how? Vertically? Laterally? The top chord only? The bottom chord only? At one end? At the middle? Without a report with accurate descriptions and/or measurements, it's hard to know exactly what that means.

I do agree that a Vierendeel "truss" is less stiff than a more traditional Howe or Pratt if all else is equal, but the timing makes no sense. And why only one? The next one over is just as heavily loaded - why was only one "dipping"? Could be a flaw in the fabrication of one of the trusses. I think the strength of the design is unlikely to be a concern here - stability of the truss, on the other hand, is suspect.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Yes, nothing in any of the imagery says the hollow core elements were well attached to the girder.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Less load towards the center. Why did they need any diagonals at all then?
If you can cut them out of the end panels, you can do the same for the central ones.
I think it transfers a lot of deflection towards the ends, right where too much curvature is not what you need.
My money's on those open panels.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

It appears to me to be a bearing issue caused by the dip in the truss. I suspect the truss may have been inadequate or was designed allowing for too much deflection which occurred causing the end to rotate and slip out of the pocket, so in essence providing inadequate bearing length. The questions I have are how much bearing was required versus provided to allow the truss to be post installed after the walls and how much deflection would it take to start slipping off the bearing plate and/or potentially bowing the wall just enough to allow the truss to slip out? How were the trusses secured? I assume slip connections may have been used. Was the out of plane attachment properly secured to the hollowcore plank roof to help prevent wall rotation/movement? Were the trusses even designed for the weight of hollowcore roofing? We would need much more information to have a more definite answer, but I believe most here are probably on the right track.

As for the missing diagonals, this is quite common to allow large mechanical to pass through trusses. Could have resulted in an improper design, but I would like to think something like this was modeled/designed properly, so without more information, hard to say.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Looks interesting, but beyond my processing capability.
https://www.istructe.org/IStructE/media/Public/TSE...

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Maybe the truss designer didn't know about the heavy hollocore and used typical metal deck/membrane loads. Hollocore will triple your design loads.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

It won't be the first time someone changed a critical component without realising the impact on the design of the roof.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I can’t envision a scenario where the EOR was unaware of a switch from metal deck to hollowcore plank. That would have required a deletion of all the roof purlins as well. A contractor isn’t going to make that many changes on their own.

As others have mentioned, the truss end bearing looked odd - can’t really see a base plate for positive anchorage, doesn’t look like any welding was going on in that video either. Similarly, no indication in the photos of a positive connection between the truss top chord and plank. The top chord bracing would be limited to a friction force between plank and chord. It seems likely the vierendeel panels could have exacerbated things if the truss was near its ultimate capacity.

Could be an accumulation of multiple factors, as is often the case.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

The big question here isn't whether they could successfully use a Vierendeel moment frame for one of the bays. Clearly they could, if they used enough steel to react the vastly increased bending moments in the chords and also keep deflection to an acceptable degree. And I don't think at this point that there is much doubt that they omitted the two diagonals so that they could run HVAC ducts through the clear bays. It seems logical that for a gymnasium you'd want to keep the HVAC as close to the ceiling as possible, above the flight path of basketballs and other sportsing projectilia.

But some of the big unanswered questions here are:

* Why didn't they use multiple smaller HVAC ducts that would fit through the truss triangles?

* Why didn't they web or gusset in the corners of the open bays to reduce the bending moments there?

* Why didn't they just place the open bays at the middle of the truss, where the shear is lowest?

It seems to me like they used a crap ton of extra steel here, and still had more deflection than a much lighter conventional truss would have had, just to save a little trouble with their sheetmetal. And in the end, it couldn't even hold itself up, let alone the two or three feet of snow that Albuquerque occasionally gets.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Man those bearing conditions look really sketchy. The trusses even look small considering the weight they needed carry.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Just watched that truss setting video again. It looks like the truss was spliced with welds right at the mid span, based on the removed paint in the chords and web member.

The two construction workers were also standing directly under the truss the entire time... not where you want to be

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

The splice is visible in the Facebook image I enhanced and posted earlier, the dark portion of the truss on the right edge of the photo. I was wondering why it was discolored.

I don't think it was a factor in the collapse since the buckling is well off to the side.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (hpaircraft)

But some of the big unanswered questions here are:

* Why didn't they use multiple smaller HVAC ducts that would fit through the truss triangles?

* Why didn't they web or gusset in the corners of the open bays to reduce the bending moments there?

* Why didn't they just place the open bays at the middle of the truss, where the shear is lowest?

It seems to me like they used a crap ton of extra steel here, and still had more deflection than a much lighter conventional truss would have had, just to save a little trouble with their sheetmetal. And in the end, it couldn't even hold itself up, let alone the two or three feet of snow that Albuquerque occasionally gets.

I'm guessing you don't work with architects very often...? There's no doubt the structural design would have just been standard (but long-span) joist girders, bar joists, steel deck if that were an option. No structural engineer is going to go out of their way to come up with a fancy custom truss design if they don't have to. In my perfect world, every building would be a solid square concrete box with steel framed flat roof. Sadly we do not live in my perfect world.

In jerseyshore's very first aerial photo it looks like the truss may have buckled right around the area of the Vierendeel panel?

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (Why didn't they use multiple smaller HVAC ducts that would fit through the truss triangles?

Why didn't they web or gusset in the corners of the open bays to reduce the bending moments there?)


It's not difficult design and is often done. I don't know why it failed. Maybe we'll find out. On a level of difficulty with 0 being easy and 10 being difficult, this would likely rate a 2 or maybe 3.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Anyone see any remnants of ductwork going thru those bays in the trusses? I don't. Maybe not yet installed? Or maybe using that inflatable fabric ductwork that was easily ripped down with the roof.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

If that roof is cast concrete hollow slab, I doubt that any duct work would withstand the impact and will be under the rubble and the remains of the roof membrane.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Are ideas (speculation) as to how/why the roof panels failed in a nice straight line, a line that is not at the unfailed girder? Seems odd.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I'm rather impressed that there seems to be zero information released since April 9th. It's an obvious place to use an FPV drone to get more detailed images of the scene, but nothing from news agencies. That leads me to think there are political shenanigans to cover up some decision.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Political shenanigans? In NM? Nah, never happens.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

SWComposites - The panels fell off the truss, the membrane tore at a lap joint.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

2
Roof failure brought down the truss?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote:

And I don't think at this point that there is much doubt that they omitted the two diagonals so that they could run HVAC ducts through the clear bays.

Well, the HVAC units are installed so the ducts would be parallel to the trusses so this reason for the missing diagonals is highly doubtful at this point.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Those gaps in the truss are clearly intentional. Maybe they were going to string up a walkway there to use lights or hang things from the roof - who knnows?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I'll add something for the benefit of those who may not be familiar. With hollowcore plank roofs, sometimes a 2-3" concrete topping slab is added to provide sloping to drains and to reduce the amount of tapered insulation. Hollowcore planks also have an upward camber, which has to be taken into account by the contractor installing the topping slab. There is always potential for the ponding effect, where the structure deflects during concrete placement, and more concrete is added to compensate, which further increases deflection, and so on.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico



For those who don't know, and are speculating.

Large Supply and Return Trunk Duct could have been run thru the two openings in the roof trusses. Supply Trunk on one side and return trunk on other side to create distributed air flow. Registers could be on supply trunk or some branch supply ducts could have been run from trunk, parallel to roof trusses for better distribution of supply.

Duct layout all depends on where HVAC unit is located, and whether one or more units are chosen to meet requirements.

The image posted above, shows two package units mounted on roof at end of gym wall, one on each side. So that would confirm that one unit supply trunk runs length of gym on one side, and other unit on other side of gym doing same thing. Returns for both units would be in between the two units on same end of gym as package units. Thus supply is distributed and flows back to central return ducts. Therefore, clearly the truss openings were for HVAC duct work.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

One of the most common problems for a failure like this a construction error. We can order OWSJ with mechanical blockouts exactly as pictured. This detail is not all that unusual. In my experience this is for the main supply duct. The duct piled up in the picture would seem to be feeder ducts given the small size. Those would be parallel to joists in the joist depth. To get sufficient air flow for a facility like this I would expect some rather large mains that our artistic friends prefer hidden as much as possible.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Seems like that if the roof broke on the straight line, it would get pulled into that position by the time it hit the ground and wind up just like that. The roof moved laterally right while the truss mostly just moved down. The straight seam looks like it moved south as far as a line between the two windows. During that process, the truss was shaken off it's support bearing. Then the roof broke at the other seam. That side doesn't look like it moved laterally very much. It doesn't look like it hardly reached the edge of the first window. That half of the roof went almost straight down. And it did not make that "V" formation like the other side did. Its almost a uniform slope.
Did not the left roof panel cracked in the center then went down, pulling it off the left truss and , the edge landing quite far to the right, as it orbited downward from a radius at the top of the still intact right hand truss, which finally gives way, going straight down. Yeah. Crack initiated at the left roof center span seems to fit the end pattern. The damaged truss moved laterally left, look at the bearing point left of the wall pilaster. Why would it go left like that, if the left panel didn't go down first, pulling it in that direction?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I don't know why the east end of the south girder moved north as it fell down off its support. Sometimes we get too comfortable using our words and loose our bearings. smile

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Like Air Alaska... don't you hate it when they don't put the bolts in?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

The north edge of the fallen concrete panels probably landed on a man lift.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Maybe. Looks like there could be a hump there. Regardless, it still looks to me like the direction arrows point to a center of collapse at the left roof.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (Sym P Ie)

Below is a 2D analysis of a simple pin connected truss showing distribution of tensile and compressive forces.

I may be misinterpreting your output, however it appears you have a pin support at both ends of the truss, with the truss acting as a stiff rope? Both top and bottom chords in tension, near the supports?

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

An interesting observation. Perhaps if I introduce a slight camber it would generate compresion across the top.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

No, make one end a roller.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

A normal instsllation would be welded at both ends?

Edit: Using a roller at 17 generates compression across the top and makes the structure more resilient. That is I have to use a lower modulus of elasticity for 61 to elicit the dip.




With 4x4 support wedgies

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

If the excess deflection was sag and if, as above, a concrete layer is used to control drainage, then that would make for something of a race condition. More concrete is needed to take out the sag and produce correct drainage than expected. The weight of the additional concrete causes more sag. More concrete is used. Someone says "Enough, we've spent more than expected on concrete. Leave it." and thus leaving a very noticeable sag in the main beams.

Since the hollow rectangular roof beams should be supported at each end, that would also add a sag in the gym long direction which would tend to cause the main beams to deflect to the side and make for a non-uniform loading on the pads.

Anyway, any articles after April 9? I suspect a number of people are crowding the exits and trying to reach the lifeboats before this ship sinks.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Using a north facing image of the larger building along with Google Earth, I estimate the gym clear span to be 80 feet. That makes the 16 panels 5 feet wide each and of similar height. A further approximation using the north facing image leads me to believe the top chord buckled at node 4.

Is it possible the vertical compression element coupled with the moment at the lower chord deformed the top face of the lower chord (node 20) and similarly at node 3?

3DDave - if they used topping, you'd be onto something. Since they were only placing insulation on the concrete panels, I don't know if topping was required.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

That is ignoring the lack of shear transfer across the open panels.
A lot of the vertical deflection will happen in that open pannel.
It will not look like a rope in tension, but more like a stair step.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

3D dave - Looks like complete radio silence. A google search with dates other than 9th April just find this site!

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I would be curious to see the connection between the top chord and the hollow cores. I do not see any studs on the top chord, but the pictures are not great for those details. It seems likely this would be an untopped diaphragm.

The analyses being done are not going to tell us much. There is no question the Vierendeel regions will affect deflections. The question is, does the design work. To answer that would require actual sizes and many other details we do not have access too. The welded joints and sizes would be critical for it to work, but it has been done successfully in endless cases. The stiffened joint pictured previously would rarely be used. They would upsize the vertical many sizes before going that route to save fabrication costs.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (Oops409)

Therefore, clearly the truss openings were for HVAC duct work.

The units are on the same wall as the ends of the trusses, so the main ducts would run PARALLEL to the trusses across the roof of this gym, not not through the trusses.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (I would be curious to see the connection between the top chord and the hollow cores.)


I've seen it done with BAR 3/8x4 welded to the truss with #4 rebar between the HC slabs @ 4'0" o/c. I've also seen it done with discreet BAR stock at 4'-0 o/c with a hole drilled through it for the rebar to fit through. I likely would not use headed studs.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

(OP)
Some info from the email that the principal sent:

Quote:

There were aspects of various news reports that were disheartening as they didn't quite get all the facts right, nor were they complete in their information. We wanted to clarify and explain a few details with all of you and provide an update of next steps.
1) The March 6th inspection indicated there was a dipping of the truss that was noted, but the City approved the work to continue - which is why it did. The dip in the truss was still within the expected guidelines. What stopped the interior work was on the 25th of March when the truss had continued to dip. The City required us to hire a 3rd party inspector to check that step of the building plan. That inspection had been ordered but was still pending when the damage started Sunday night.
2) We rely on the inspectors to provide details about the safety of the building. Since we had not had that next inspection, the ribbon cutting was planned to either be moved outside OR postponed, but everything happened on the weekend so we had not sent that communication out yet.
3) The ribbon cutting ceremony is just that - ceremonial to mark the completion of major construction. The work was not yet finished as we needed the gas lines to be activated, the flooring to finish being installed, final inspections to be done, etc. In other words, students were NOT going to be actively using the building this week regardless of the ribbon cutting. The tentative plan was to have them start using the facility until we held the certificate of occupancy. I know it was made to seem that kids were days away from using the building, but that is not accurate on anyone's timeline.
4) On the subject of timelines, on Sunday, at 9:30 PM, I was notified of the damage to the roof. I sent an email to parents by around 10:35 PM, and then someone had notified KOB who then reached out to me at 4:06 AM. I'm sure they were anxious to dig into the story, so yes, they contacted the city quickly after. Communication with the city is something not traditionally done by the school site until we have the certificate of occupancy.
5) Our priority was to ensure the facility is safe for kids. We took our time to do the investigation that needed to be done, so we delayed sharing information until that happened Monday afternoon. We hired an independent engineering firm to inspect the building, and we have contracted with them to remain with the school through the extended completion of construction. This is not typical for these projects, but we wanted to have our own team of engineers hired to oversee the work of the new team of engineers that will be continuing on the building moving forward.
6) To reiterate, there is no apparent damage to the new classrooms, the new theater, new restrooms, or the current building. There also appears to be no structural damage to the gym walls. As stated above, however, we rely on the experts to look into that, and we are unanimous that we need the inspections to be completed on the current building and the remaining new construction before we approve it for kids to return. This will take some time, but we anticipate students returning to the building on Monday.
7)The next steps are for them to inspect where the facilities "neighbor" each other. The new construction is a separate, divorced structure with space between the older facility and the new facility. They want to inspect what connects the building from the top and to ensure no damage was sustained to the structural integrity of the walls in the new building. They are working on that today. Following that, there will be a plan to shore up existing walls in the new building before we move kids into the old one. This will ensure students are safe to return.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

(OP)
And some notes from their Zoom meeting. Seems like they aren't revealing much. Need someone in NM to pull a public records request for us to get the plans.

Quote:

School Leader Report (Jake Kolander)
David Shaffer - AIC General Contractor
Doug Majewski and Wendy Caruso, Design Group NM
Facility/Construction
Gym roof
Mr. Kolander thanked the parents who have reached out. He explained what occurred on Sunday evening, which was triggered by an alarm. School administrators, ELS team members, and Mr. Shafer reported on site immediately to see the damage. The team is waiting for details before putting out information to the community to ensure accuracy. He further noted that the facility was not complete and was not ready for occupancy. Final inspections had not been done and no students would have been in the gym until final review and the certificate of eOccupancy was issued.

Depending on third-party inspections, the main building is expected to be open for students on Monday. This does not include the classrooms and gym in the new addition. If official written assurance of safety is not received, the building will not re-open.


Mr. Shaffer expressed agreement with Mr. Kolander’s comments; he complimented Justin Baiardo for quickly arranging a third-party inspector on behalf of the school. He confirmed that the life support systems are separated from the main building.


Mr. Majewski also agreed and advised that the team is awaiting results of the inspections and investigation and will take the appropriate steps to complete the project.


Ms. Caruso expressed that we are working as a team and that there will be no rush as safety is a priority.

Quote:

PUBLIC COMMENT regarding items not on the agenda
The floor was opened for public comment.
Steve Rowan commented that he will gladly provide guidance about the expected weight load for the black box theater ceiling.
Joe Graziano commented that “the roof is a spring cable suspension system with concrete beams and poured concrete as the material over styrofoam. There is no way the cable system failed. Those walls are under tension right now and are dangerous to be near. I just need assurances that the state inspectors are on the case but the building needs to be removed and rebuilt. The school appears to be ambitious with returning. Thanks.”

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

It is poured concrete over the concrete beams.

This is very like the New York bridge with the unbraced kink in the upper flange; I bet someone thought this job was too simple to bother to analyze because "just look at how big those girders are."

That no one said, let's get some shoring until we can figure out why it is sagging, is a head scratcher.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I should have noticed it had a topping slab earlier, my bad.

Dik, every steel bridge with precast slabs I have seen uses studs. I would use them in a heartbeat. With todays modern technology it is not difficult to accommodate them in the design. This connection is super critical to the truss performance as you know.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I would guess that in all common sense they didn't pour the topping knowing there was a dip in the girder. There is evidence of the topping layer and some cables in the imagery. In any event, the insulation and membrane have to be held down either mechanically, glue or ballast. Does anyone know how this membrane is secured? Also, what is a spring tension system for the topping? Is that just supposed to relieve the weight of the topping? How much tension can be loaded into the parapet? Many questions from the uninitiated. I didn't see anything on Google.

To be clear, we are talking about a topping layer above the insulation not as part of the hollow core base?

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (Dik, every steel bridge with precast slabs I have seen uses studs.)


Different details of construction; when was the last time you saw HC slabs used for a bridge?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Regarding the truss ending up North of the support column. I suspect when the truss lost its bearing, the roof and truss assembly likely pivoted northward around the intact truss, due to the northern end of the failed roof still being connected there.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Yes, Dik, bridges do not use hollow cores, but we can use the same concept with this. Regardless, we are going off topic.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

As previously posted, torsional buckling of top chord makes a lot of sense to move top chord laterally off floating bearing surface, and perhaps the asymmetrically draping and break up of the roof deck provide some more clues?

As far as duct layout, I have not seen any evidence to support how the duct was actually routed inside the gym, once it entered WEST outside wall.

Perhaps an L-shaped supply trunk ducts were used on supply to condition east wall between two roof trusses?

Perhaps return duct used the other Vierendeel truss openings to route return duct at end wall or perhaps only openings at one end of truss were to be used for duct?

Was duct hung off threaded rod, drilled into cores of hollow core deck? Better yet, since we know building was not finished, was interior duct even installed at this point?

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Except it may be the bottom chord. The top chord is more likely to be laterally supported by the roof deck, while I have not seen any evidence of lateral support of the bottom chord.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Yes. My bet is still on the movement of the bottom chord as the primary trigger to the column being pulled off its support. AKA LTB of the member The reports of inspectors seeing the truss "dipping" is on piece of early evidence. The fact it occurred at such a low load is another along with the truss seemingly mostly intact.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I suspect it simply fell off or slipped off the seat, perhaps due to a bearing failure or similar, as opposed to it buckling off the seat. We’ll find out soon enough once we get more pictures and details.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

We still don't know how, or even if, the truss was secured at it's bearing.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

There was a problem, before:

"For this gymnasium roof project, they failed a building frame inspection on March 6, and the Building Inspector required corrections related to the building’s safety. Our Building Inspectors revisited the site on the 15th to inspect progress on the corrections. While some of the construction was sufficient, our Building Inspector once again flagged a deficiency in the construction. The Building Inspector then required a secondary engineering firm to submit calculations, called a peer review, to support the building construction plans. The Building Safety Division never received such secondary engineering calculations."

https://www.koat.com/article/roof-collapse-happens...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (from jerseyshore's comment)

Joe Graziano commented that “the roof is a spring cable suspension system with concrete beams and poured concrete as the material over styrofoam. There is no way the cable system failed. Those walls are under tension right now and are dangerous to be near.

I have no idea what a "spring cable suspension system" is, or why any of the walls would be "under tension"...? Maybe he's referring to the remaining portion of the roof/diaphragm being under tension since there's tons of concrete just hanging out in the air?

Either way, it sounds like (based on this rather confused sounding description) it was perhaps an untopped hollowcore roof with polyiso foam insulation which was then topped with lightweight concrete. That is usually done for acoustic reasons. More so to keep sound in the building.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico



How 'did' they transport the large metal truss from fabrication to job site?

I have seen how they transport wood trusses to job sites, and they are laterally bent in all directions during transportation to job site.

How was truss stored at job site?

So could you bore-sight align truss before and after erection?

Some random options from Google images:





RE: Newly Constructed Gym Has Roof Collapse in New Mexico

When they built our church 15 years ago, in addition to being on the building committee, I documented the construction for our parish records, going over to the job site every couple of days or when anything significant was taking place, such as the day they delivered the 80-foot long main truss for the building, as seen below:


January 2009 (Sony A100, 18-70mm)


January 2009 (Sony A100, 18-70mm)

And I was back the day they placed it in the superstructure of the building:


January 2009 (Sony A100, 18-70mm)

And when the basic steel superstructure was completed:


January 2009 (Sony A100, 18-70mm)

And when they had installed the wooden cross trusses, which was the main support for the roof:


May 2009 (Sony A100, 18-70mm)

And as you can see were exposed to the congregation (this picture was taken the day the building was dedicated):


January 2010 (Sony A100, 18-70mm)

And here is what the building looks like on the outside:


March 2010 (Sony A100, 10-24mm)

Note that this building is located in Southern California and therefore had to be built to strict earthquake codes.

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:

The secret of life is not finding someone to live with
It's finding someone you can't live without

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Actually, are we missing something here concentrating on the truss.

What actually connects the concrete slabs to the wall and what connects them to each other resting on not a large bearing surface on the trusses.

There are some photos on this, but I can't see how the concrete panels are supported onto the CMU wall.

Did the blocks fall / fail first and then dragged the truss off its support or vice versa?

Maybe we'll never know as there isn't any public ally available CCTV footage.

Could wind load have lifted the roof through the open windows and displaced it?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

The panels sit on the block wall and the parapet is built up on top, at least on the ends. Rebar and concrete plugs are used to secure them, visible in the damaged remains.


Facebook

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Hmmmm,

In the faceboook photos, the roof panels look about three blocks wide. Yet on the external shot of the same location all you see three block up from the top of the window frame is blocks.

So what are they actually sitting on? Half a block?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Yes, they generally hold them back a few inches. That lets them a) hide it in the block coursing on the exterior by placing just a face shell along the edge and b) allows them to grout the wall and the ends of the hollow core together. There will typically be a bond beam for them to rest on with bars coming up, and hooks going into the hollow core and turned into the plane of the wall. So when the grout it, the grout flows into the hollow core (the "concrete plugs" mentioned above) and engages the bars coming out of the wall, too. It works well under design loading, but it isn't designed to hang the planks from the wall so the plugs pulled out when they dropped.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Some still of the bearing seat area.


RE: Newly Constructed Gym Has Roof Collapse in New Mexico

You can see in GreenLama's post above, that the bearing pocket appears to be enlarged to the left during erection, to swing truss into pocket. Looking close at the later image shows the pocket was enlarged more. Pay attention to above rebar relationship to the extended pocket area.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Is that a masonry pilaster in the wall for the column to sit on? or, is it masonry cover over a steel column behind. What is the truss support?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Based on the pictures way up above, it's a pilaster.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

There’s a grey chunk at the top of the pilaster, at the otherwise white walls. So it could be a simple bearing failure of the pilaster.

With those trusses having to fit between the walls, the bearing length is only so much, presumably.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

A few more comments.

1) It is unlikely that any lateral restraint of the truss chord existed within the bearing area.
2) From the aerial images, it doesn't appear that any studs were added to the top chord to tie the truss to the roof sections. I'm guessing the red that we see is simply the unpainted truss. It looks like after installation the truss was painted grey.

So a question I have is, Aren't the roof panels supposed to span (in the N-S direction from above) between the concrete block wall and the truss, and then between the trusses? If so, why do we not see in the failed image the truss that remained in place? It appears that there is an overhang. Is this just an optical illusion? You would expect that the roof would fail/crack along the center line of intact truss. From the image below it appears that some portion of the full roof panel is visible to the S of the truss. For reference I drew a line between the corners of the windows.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Some of the design is looking weak.

The block wall seem to be 10" block. I doubt there is a steel column inside the pilasters.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

TheGreenLama - the planks failed with the truss, but there's probably a seam in the roofing material where it separated that doesn't line up with the structure. I'd guess the structure fell away but the roofing is still clinging together in those shots.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

It does appear as tomh has pointed out, that the top inner portion of the pilaster has failed.

If the dip reported is deflection of truss, it appears that would lessen effective top cord bearing surface area, and thus put increased bearing pressure at the inner edge of pilaster.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Half finished 600mm span



--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote:

You would expect that the roof would fail/crack along the center line of intact truss ... For reference I drew a line between the corners of the windows.

You can see a break line on the roof where the intensity goes from bright white to duller white near the edge of remaining roof portion on the left. The intact truss is at the intensity transition, which is consistent with the 3 windows being bracketed by the pilasters holding up the trusses.

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RE: Newly Constructed Gym Has Roof Collapse in New Mexico

phamENG - I suspect you are correct. As mentioned above, on top pf the precast panels there could have been additional insulation, a topping layer, and a membrane. Maybe what we see are a straight line seam in the membrane, with pieces of insulation hanging down. Not parts of the precast panel.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (Greenlama)

You would expect that the roof would fail/crack along the center line of intact truss.

The planks did.

What you see is remnant roof sheeting and insulation. Hence the kink along the truss line.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

There is a V kink in the truss/roof membrane, creating a saddle. The vertex of the saddle appears to be approximately in line with the square station (i.e., the segment lacking a diagonal). There appears to be gross deflection of the truss with the flexure point at this location. Under what circumstance would this disfigurement occur?

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I suspect the fold in the roof sheeting is simply the cantilevering sheeting sagging over the truss line; The fold disappears near the ends of the truss because the sheeting is being held up by the walls here. The sheeting cannot fold down like it does at the middle of the truss.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico



A typical detail option for the welded end of a steel joist, bearing on a masonry block wall. This concept design detail indicates that steel joist should have not been in direct contact with block pilaster (especially the masonry edge of pilaster block). All bearing area should be located on the poured bond beam.

Masonry pilaster damage could have happened as joist deflected, and pulled joist downward and away from bond beam bearing area, and as joist dropped to lower energy state.

Was the suggested 10" block wall too small in depth for required minimum bearing area of large long span steel truss? Thus pilaster added to increase bearing area, and perhaps placed some bearing area all the way to edge of block? Perhaps a Value Engineering offering from Builder to save money on 12" block without pilaster? This also places horizontal rebar further away form edge of block wall bond beam.

Similar could HVAC units have been located on ground running thru steel truss openings, and GC offered Value Engineering approach to change that after steel truss ordered?

I know customers make a lot of demands after project bids are over budget, to bring them back into budget..and of course for other hard to understand reasons....

Duct work running with hollow concrete planks, concentrates all that load on one or two planks, whereas crossing perpendicular to run of planks spreads large mechanical loads across many planks. Probably not enough load to matter, but those large toggle bolt looking holes in the threaded rod picture bones posted sure looks like an incorrect anchor for hollow core planks, according to a quick look on Hilti's hollow core anchor site.



RE: Newly Constructed Gym Has Roof Collapse in New Mexico

(OP)
Still wild to see a pretty-much-finished building have a sudden collapse on a regular night with no live loads. I always say "buildings just don't fall down", but I might have to add the caveat "except when they do".

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Agree, however I imagine thermal changes in roof materials vary a lot in Albuquerque from Hot Clear Days, to dry cool nights. So thermal could be a factor in timing of drop.

In the pictures posted, it appears the sides of hollow core panels fit tightly against the inside face of block wall. No ledge to sit on.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

It was gremlins....had to be.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (Oops409)

that steel joist should have not been in direct contact with block pilaster (especially the masonry edge of pilaster block). All bearing area should be located on the poured bond beam.

I don't understand is comment. The pilaster is exactly where the truss should bear.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I guessed at the block size. It could be 12". Again, need plans.

Pilasters are used exactly for this reason all the time. The truss reaction is in the realm of 140kip or more. That is not the type of load you put on a simple block wall in most cases given the wall height.

I don't think the wall is the problem here. From the newer pictures it seems they managed to get the trusses where they were supposed to be. The question is why did the trusses fall off? Unless there are some very good connections our internet sleuths have not found, I would lean towards a LTB failure.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

JLNJ, Steel Truss should bear on embedded steel plate that is on top of horizontally reinforced concrete/grouted bond beam, and not lintel block outer edge. Drawing above shows this clearly. Joist is resting on reinforced grouted portion of lintel.

Brad, I realize you are guess at block size of wall, and from images it appears that pilaster is about 2" deeper than wall. 10" and 12" blocks would fit that scenario....

It appears Hollow Core Planks only require 3" of bearing depth, so my question is how much bearing depth does a very large steel truss point load require and well as width? Even when blocking mobile homes, aka trailers, in my teens, we never bottle jacked directly on a the concrete block..... We always spread that load with at least a 2x8/10/12 depending on block depth.


Perhaps adding a blue pilaster line and extended rebars would explain why tension horizontal rebar is not directly under extended grouted area of pilaster, whereas if full 12" deep wall, rebar locations would be in better location to assist in spreading bearing load evenly.




RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Just because you found a detail online that shows a truss supported a certain way doesn't mean that is the only way trusses are allowed to be supported...

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Never said it did, but it is hard to explain the top of block pilaster been destroyed if the metal plate extended out over block edge. The whole concrete block pilaster design looks like a very poor design choice...

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (Oops)

so my question is how much bearing depth does a very large steel truss point load require and well as width?

As you’re seeing here, it is a subject of some disagreement. The bottom line is that it needs enough effective bearing area to prevent bearing failure.

You can get wildly different answers depending on your bearing assumptions. The actual concrete bearing stresses depend heavily on eccentricity and assumed contact area.

As you note, steel bearing plates are common, to assure a certain bearing area. It’s not essential, but can be a good idea. There are many corbels and seats out there where the front edge is starting to crumble off due to concentrated bearing at the outer edge.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

So it is clear, below is what a pilaster typically looks like. All you are showing in your wall section can be done at the head of the pilaster. Pilasters generally serve two purposes. The first is to support large point loads, and second is to allow for a thinner wall section or less solids in that wall section. I think the scale of the images makes it difficult to discern dimensions.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Tom and Brad,

I appreciate your input, and Tom you confirm my thoughts about outer edge bearing problems.

Brad in your typically concrete block pilaster cross section, how do you put the rebar stirrup wraps in a masonry pilaster wall that just adds another equal width block adjacent to wall, where you have a point load?

I can see cutting out sides of block between wall and pilaster at stirrup locations, perhaps that is solution?

Also now way can I see more than 2-4" protrusion from wall of pilaster, from the low resolution images, rather than another 8 or 10" block pilaster. Looking at construction sequence on KOB, it appears they are stuffing more steel in block cores about every 4' of height, with more in area of point truss loads.

Can't tell what is going on with pilaster, but it appears it is being laid at same time as wall. From images it appeared to be they just laid in deep block at pilaster area, then filled cores.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

That image was from a tech journal I found. Many professors are not great at the building. Below is an example of a pilaster shape you can buy. There are other ways to make them to. The primary goal is a reinforced concrete column of known higher strength.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Still from one of the construction reels which appears to show U-shaped blocks.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

The wall appears to be constructed using 8" units...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

If the pilaster were masonry, most engineers would design the bearing with the support centre of the large truss falling on the centerline of the pilaster or on the centroid of the composite wall-pilaster section. They would avoid eccentricities for the large truss load. There would be a steel bearing plate of sufficient area to accommodate the bearing with headed studs or welded rebar going into the pilaster. Depending on the code, the composite section would be determined by the pilaster width + 12 x the thickness of the wall or the height of the wall / 12 + pilaster width, whichever is less. Strength would be determined on this... This composite section should easily be capable of supporting roof loads (I'm not so sure for HC slabs which weigh more than 2x a regular roof. This is based on experience with regular roof loads for a building of similar geometry. Pilasters designed properly can easily work for normal roofs.). The pilaster would be designed as a regular masonry column with windload plus a nominal eccentricity from the truss... that's the way I would have designed it (we don't have significant seismic loadings in this area). No rocket science and design level of difficulty out of 10 would be about 3.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (dik)

The wall appears to be constructed using 8" units...

That makes sense. And if so, the pilasters appears to be less than 8"?.



The actual load is around 600kN based on scaling off google maps, and assuming 200 planks and normal topping. (someone else also estimated 140kips above)

That's a lot of load on a small pilaster, assuming it wasn't armored with bearing plates as you discussed above.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I'll see if I can dig up my SMath program...

Do you have the span of the truss and spacing? Do you have the roof construction, HC slabs (55psf in these environs) cementitious topping? lightweight? insulation thickness? type? and roofing membrane. M & E loads? 3 or 4 psf?

Else I'll mod the program to put in different values.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Based off Google maps the truss span is ~25m and spacing ~10m

I don’t know the construction details. I assumed 200mm planks plus 50mm topping.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Looking at a the window jamb picture closer again, it could be 8". I sketched my guess below.

Assuming the window sizes shown in the image below is the same along the side in question, I estimated they are 80" wide. I do not see any better pictures to estimate the space between windows, so I scaled the image. Given the perspective, this could be wrong. I estimated the space between trusses is 30'-4", which is close to Tom's google earth estimate. Counting blocks, the bearing elevation of the truss seems to be approximately 20'-8".

Assuming 8" Hollow Core slabs, their weight is 62psf from Stubbes. The topping thickness seems to be in question given the slopes discussed, but maybe 3" average or 37psf???

A dead load failure suggests a fundamental flaw. Here I suspect the live load is quite low, but I would hope you could load the roof to at least twice the dead loads before you had anything happen like this.







RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Two things:

If the spposition is that the CMU's are 8" deep and your estimation is that there is a 6" reveal at the exterior of the window frame, that leaves 2" for the frame depth, which is rather shallow.

If you are using the wood window opening liner as a frame of reference and assuming double 2" standard lumber sizes, in other words a 3" liner, that is consistent with your previous estimation.

My guess is that the liner is actually augmented with a layer of 3/4" plywood (see image above, particularly along lower sill). Proportinately, the window frame depth is closer to 4" and thus, the CMU's are 10" deep.

Further, the reveal of the pilasters is quite shallow so it would be reasonable to believe them to be 12" deep and provide a 5 or 5 1/2" seat on either end for the girder.

Even further, it appears that the seat plate protrudes from the pilaster maybe 1/2" providing ample protection for the CMU lip.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

The window frames look like 4" aluminum frames I see all the time. I suspect the wood fill is 2"x4" material. The main reason I posted the info was to entice Dik to run thru an analysis to show that the pilaster is feasible as many of us think.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Do you agree that the likely block depth is 10" with a pilaster depth of 12"?

RE: Newly Constructed Gym Has Roof Collapse in New Mexico



A masonry reinforced concrete pilaster similar to below above, at correct size for 30' tall column, with bearing capacity to support very large point load, should work fine....Lost my bearings again!

BUT, that does not 'appear' to be the design we are seeing in the limited images and videos we have available to evaluate....

I wish I could find an image of what it appears to be in my head......


OK, image below is NOT totally accurate, but it conveys concept of just inserting 12" block in 10" block wall to add bearing area for point load. Then capping it all with U-Block Bond Beam. Trouble is you end up with eccentric load at 'Bumped Out' pilaster appearance area...... and continuous wall bond beam reinforcing is not concentric with point load bearing area.





RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I tend to think it could be 10", but I am not sure there is much reason to delve too much into that detail. Dik mentioned a SMath sheet he has. Once he enters a few values he can change variables and determine what might have worked based on our estimates. I don't think the pilaster was the problem. I have not worked with masonry in a long time since we do not have many trades doing the work. Plus, it has lost popularity due to the energy code in Canada in my area.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Thanks for the dimension information...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I also don't think the pilaster was the problem. However, the depth of the block/pilaster affects the available bearing surface and degree of eccentricity. Given the construction method, the bearing surface is limited to less than half the pilaster depth.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (Brad)

OK, image below is NOT totally accurate,

That image whilst maybe not 100% accurate makes more sense than a separate block.

If it was like what you have shown, the failure makes more sense - The outer wall of the block could have broken off, leaving little support.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

(OP)
Did anyone submit a public records request yet for the plans with the City of Albuquerque? This thread is going to re-engineer this whole structure 10x over before we get any new info I bet.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Permit plans would be nice, however no guarantee they match as built. We also need approved shop drawings for the truss.

They are keeping quiet on this whole thing, which smells like all parties involved are concerned about their role in this.

Everybody hunkering down in preparation for litigation. Without whistle blower we may not get any more information for a long time.



RE: Newly Constructed Gym Has Roof Collapse in New Mexico



What is this? Someone above mentioned the roof panels may have fallen on a construction lift. Could it be something else? From another angle this (steel) piece is inclined at a large angle from the vertical, so it wouldn't have been a vertical brace. Could it have been a steel beam, added later when unusual deflections were noticed, connecting the bottom chords of the trusses together to provide lateral support? The location looks to be exactly at midspan.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

A spring tension system? Same as this?

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

From a construction/build standpoint alone, I don't see how you can set the hollow core concrete roof planks without some temporary lateral bracing for the two long span trusses. You would have to set them in the correct install pattern sequence, to avoid 'tipping' the truss. Once truss is tipped out of plane, oh no!

So if lateral bracing likely required for installation, and hollow core deck ends, which appear to be a friction float on the top chord of truss, would 'tip' with any load differential between opposing ends of hollow core planks.

It appears GreenLama is onto something, and a lateral mid-span brace may have been added for construction or resolution attempt after failed framing inspection?

The two steel cables showing thru windows on parapet wall is odd as well?

Classic Example of where a Good System Engineer Construction Manager working solely for the Customer paying the bills is employed to catch the disconnects between design throwing it over wall to GC, and GC then has to figure out how to actually assemble the design safely, and in proper order.

A Great System Engineer/Construction Manager, is money well spent. Now choosing poorly can also WRECK a project. I have personal knowledge of Practicing PE Structural Engineer Construction Manager, that saved his customer lots of $$$ over catching costly design flaws and build-ability issues of design. And this was huge Manufacturing Campus from ground up.

Edit: The kicker is he makes more money as CM than he does doing design work for himself. Now he is unusual person that has design expertise and vast Project Management Field Experience. So not every DEI hire has this level of talent, skills and experience.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

SymPIe, I'm not saying this would have been a good idea. The slenderness ratio would have been huge. And, since both trusses are identical, have identical loads, and identical boundary conditions, if the primary buckling mode pushes center span point out, you would just get both trusses to buckle simultaneously.

The report you noted above says they noted a dipping of the truss. No mention of a horizontal component. But that doesn't mean there wasn't any.

If this is a retrofit, it reminds me of the FIU bridge collapse. They have a nearly completed structure that suddenly shows signs of unusual movements. So, to try and salvage it, and keep to construction schedule, they go in and start trying things, without fully understanding the issues. All this does is put construction workers lives at risk.

There's a lot of speculating here. The way the roof panels fell it just appears that they break across the midspan, implying something substantial running beneath. You can envision a case where the two trusses start moving towards each other at the midpoint, and someone says, Hey, all we have to do is block them somehow.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Based on the assembly video, it's not clear if the bearing engagement on each protruding pilaster was equal, and this may have influenced the failure mode. After engaging the left support, the free end of the truss sweeps just inboard of the other, protruding pilaster. The truss must then be moved longitudinally to engage that bearing surface.

I believe this questionable truss support is the one that lost engagement at the time of the collapse, while the other end was still supported. Check out time interval from 0.20 to 0.25s

https://www.facebook.com/watch/?v=2900271060136528

I don't think this illustration of a truss end support can be relied on, as the actual one is a proper, protruding pilaster.

https://res.cloudinary.com/engineering-com/image/u...




Kevin Kelleher, P.E. (retired)
Internal Mechanical Eng'g Consultant
DuPont ESD Specialists

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (KevinK2)

Based on the assembly video, it's not clear if the bearing engagement on each protruding pilaster was equal, and this may have influenced the failure mode. After engaging the left support, the free end of the truss sweeps just inboard of the other, protruding pilaster. The truss must then be moved longitudinally to engage that bearing surface.

Agreed. The long truss was swung in horizontally, between the walls, leaving marginal support at the edge of the pilaster.

Thermal movement could also potentially have pulled/torn the flimsy edge.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Flimsy. The word I was looking for. Then they piled a lot of precast concrete and other stuff on top.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Yeah, but the FEM showed positive margins.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

In addition to video not showing adjusting bearing depth on last end of truss, how much of the bearing margin depth was lost by swinging trusses into pockets with parapet wall already built, versus dropping trusses in from above before parapet wall built on top of bond beam?

Pocket had unused bearing depth closer to centroid than swinging technique allows utilization of.

Pockets are common on tilt-up reinforced concrete wall panels, however those walls are stronger and more durable than spliced rebar stuffed into grout filled cinder block cores. Especially outer face of cinder block.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (LittleInch)

If you're interested in the full constructon time lapse see here
https://www.facebook.com/watch/?v=2900271060136528

Is there a real time video available? May provide more details of what appears to be steel lined openings for the pilasters, and how the workers were using fasteners? to secure the end of the truss.

Kevin Kelleher, P.E. (retired)
Internal Mechanical Eng'g Consultant
DuPont ESD Specialists

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I have seen the full 31 second video on Facebook, and my eyes don't see a steel lining on pocket, and I offer up the fact that they enlarged the pockets during erection. Those images were posted above and I will post my adding arrow to one of those pictures below, showing they chiseled out the side of pocket to enlarge it so truss would swing into place. Later images show the pocket growing even more than what is pictured here..... They did not chisel thru steel, IMHO.





RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Does it require a steel pocket or just a steel bearing plate?

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I wonder if the original design featured the truss top chord extending into the wall, which might have been shortened later for constructability reasons. It's hard to imagine a designer intentionally allowing the truss to bear only on the outer edge. It's plausible that the designer might have assumed the trusses would be set into pockets, without realising that the builder was going to construct the walls in one go, preventing full length trusses from being dropped in.

We've definitely encountered scenarios where the shop drawings include subtle modifications for easier construction - things shorted a little, etc - and these changes go unnoticed by those reviewing and approving the shop drawings. Then you arrive on site and realise there's a potential problem. Sometimes, these changes are significant and aren't caught by anyone (eg Hyatt walkway collapse)

Of course, this is just speculation, but it's a scenario I've seen play out based on my experience.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

My thinking is steel trusses were very long lead item, and the GC did not want to have to pay mason to re-mobilize for parapet wall as separate step, and did exactly what you have seen, and school was pressing to compress schedule so they bought in on what may have been a read bad decision?

Bearing plate should be sufficient, IMHO.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (Tomfh)

I wonder if the original design featured the truss top chord extending into the wall, which might have been shortened later for constructability reasons.

It does seem like the top cord was initially too long to fit into the original pockets, based on the left pocket apparently being manually deepened. This allowed the right end to swing inboard of the protruding, original pocket/pilaster. It may appear that opening was also widened, perhaps for installer satisfaction vs true function. The installation video shows this was not necessary.

The left pocket on the other previously installed truss appears to have also been deepended (but not widened).

Q: Why didn't they lift the truss, with both ends on the other side of the pilasters? Then the far chord could have been slid horizontally into the open end of the pocket, vs outside of it.

Quote:

It's hard to imagine a designer intentionally allowing the truss to bear only on the outer edge.

Q: By outer edge, does this imply line contact across the width of the cord, at the outer edge of the bearing surface? Hard to control where line contact will occur, based on camber at cord end and plane of the bearing support.


Kevin Kelleher, P.E. (retired)
Internal Mechanical Eng'g Consultant
DuPont ESD Specialists

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

On the pilaster opposite of which has been posted a few times,you can see what appears to be two studs protruding up through the bearing plate, as well as what appears to only be 3" to 4" of bearing area as they sat it down. Without any room to get in from behind, I cannot see how any bolted attachment of the truss to pads could exist. If it was a welded joint, would Aprox 4" of weld per side actually suffice here? Could 2 studs holding the plate down be enough to prevent tilting?

The whole arrangement to me looks like once they got it in there, they assumed it would stay once they blocked it back in.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Zero discussion about investigating the roof collapse during the NM Public Education Commission public meeting that was held April 19th, eleven days after the event. Collapse was only mentioned in passing.
Link

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

The link doesn't work.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

Quote (DirteJoe)

On the pilaster opposite of which has been posted a few times,you can see what appears to be two studs protruding up through the bearing plate, as well as what appears to only be 3" to 4" of bearing area as they sat it down.

Those 2 "bolts" act more like pins spaced wider than the cord. The video shows the top cord being slid sideways into the pocket above those pins, then being dropped down between them.

The installers appear to be working at both cord-pocket connections, but it's not clear what they did to secure them during 2 trips up the sissors platforms.

As others suggested, I believe the root-cause of the failure had to do with the installation of the roof, but with a likely flaw in the truss. In the post failure video, the truss appeared to remain straight, but folded at a hinge zone at about 1/4 to 1/3 of the span away from the right side pilastra.

The longer truss span stayed attached at the left pilastra, and the right cord end appeared to have crushed the outer edge of the supporting concrete as it was pullled out of the pocket during the collapse. As the truss began to hinge at that zone, it also pulled the right cord from it's pocket. This hinge deformation ended when the support on the right side ended, and the net shortened length of the truss span explains why there were no vertical scars on that painted wall on the right side.

It's possible the hinge was really buckling at the open truss square, or the diagonal in the next one away from the wall.

This slow creep-like failure theory is consistent with the measured, gradual bowing/bending of the lower truss reported on March 6 during an inspection. It was noted but still within installed tolerance then, but another check ~2wks? later showed more bowing/bending beyond tolerance, and construction was stopped.

Kevin Kelleher, P.E. (retired)
Internal Mechanical Eng'g Consultant
DuPont ESD Specialists

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

I do not think getting round back to the open truss panels is a coincidence.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

If the design of the trusses assumed the unsupported length of the top chord equals the panel width, and the actual unsupported length is more like 1/2 the truss length, the capacity of the top chord will drop to collapse levels. The pictures do not indicated a lot of top chord bracing other than friction so far and that would support the conclusion the top chord is lacking lateral support. We investigated a collapse in the 90's where the top chord of a bowstring truss was not supported correctly. In that case it took almost 30years for the wood chord to creep, and ultimately collapse, but the dead loads were more like 15% of the design load. Here I suspect the dead load would be more like 80% of the design load. It is not hard to understand the failure speed if any of that is true.

The normal companies that built this type of truss know how to do this, and that is all they do. If they elected for a custom fab shop, then who knows. Another factor I would be curious to know is the amount of design delegation. In this case we have a truss supplier, and hollow core supplier. Things falling thru the cracks is not unheard of.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

My first time here, but have there not been any posts since May 10? Previously there were posts almost daily. I think the possible causes have been well detailed, and it appears to me the failure was a combination of factors - Lateral Torsional Buckling, missing diagonals in high shear bays at either end, lack of adequate bearing due to construction sequencing, possible compression failure at edge of pilaster due to top chord bending, lack of anchoring of top chord to roof, very heavy concrete roof, lack of lateral bracing. It is my understanding that a local structural engineering firm has been tasked with the investigation. It is hard to understand how it could take so long unless legal implications have complicated releasing a report.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

No.

Yes.

A reasonable summation.

Do tell!

Material testing, collecting relevant documents and communications, theoretical analysis to name a few other possible complications.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

They'll be a year at it.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

In the tea leaves: This failure is from something fundamentally stupid, so fundamentally stupid that the person/organization responsible will settle with no public record of the reason for the settlement so as to avoid future clients from tying this disaster directly to them. Even if it is a one-off brain fart and they do excellent work elsewhere and anyone hiring them in the future would be fortunate to get them, the stigma would call into question those who let such a contract.

I think it is reasonable to expect the person/company to change names and maybe address as well; if a person they will get a new LLC.

This will get buried like the New York trail bridge that had the misfortune of no one making a bending moment diagram and looking at the section properties everywhere along that diagram.

No one died, no one was injured. It's a tax dollar problem and money hides money.

Or so the tea leaves suggest.

RE: Newly Constructed Gym Has Roof Collapse in New Mexico

JJohns,

Not only that but if you go gooogling, the only things that pop up after the first day or two is this site!

This has gone into the weeds, I think in part due to lack of available information or drawings, no video of the collapse released to the public and no one got injured or killed. Basically no one wants to actually work out what happened in public so as to avoid all the issues 3DD aludes to is my opinion.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

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