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Tilt-up concrete panel cracks at connections

Tilt-up concrete panel cracks at connections

Tilt-up concrete panel cracks at connections

(OP)
A client asked me to look at a building that another engineer designed for him.  The building is a pre-engineered metal building with a concrete tilt-up wall panel facade.  The typical concrete panels are 25' wide (one bay width) and approximately 25' tall.  The panels have embedded (8"x8"x3/8") steel plates with 4 studs embedded in the concrete.  These plates are spaced vertically about 6' from the bottom of the panel and 6' from the top of the panel and are used to connect the panels to the pre-engineered metal building rigid frame.

The issue is a crack has appeared during construction at embedded plates welded to the pre-engineered metal building columns.  The contractors initial thought was the cold concrete (30-40 degrees when erected) cracked due to the heat caused by welding on the embedded plate.

I do not think this is the cause, but would like a second, third and fourth opinion on the matter to see what others think.  The locations of the cracked panels are random throughout the building.  They occur in panels with openings and without openings.  The attached photo of the worst crack is at an opening for an overhead door.  I will attach a close-up in a follow-on post.

At first, it almost appears that the concrete panels shrunk compared to the metal building columns and cracked due to the restrained connection at the columns.  The worst case crack happens to be on the first panels poured, so they cured the longest.  All panels were erected within 2 days.

Any thoughts?  Are repairs required or are the embedded studded anchor rods sufficiently bonded and the crack superficial?  The connection just prevents hurricane force (120-mph) winds from pulling the concrete panels off the building.  The majority of the cracks appear too small to epoxy inject, however this crack is wide enough to inject.

Thanks in advance for your insight.

RE: Tilt-up concrete panel cracks at connections

The connection is much too rigid for the concrete to tolerate.  Concrete shrinks, and steel buildings, particularly the skinny PEMB ones, move all over the place.  Bolted/clamped connections should be used.

RE: Tilt-up concrete panel cracks at connections

I would agree that concrete shrinkage is a good possibilibly.  But that is one heck of a lot of welding and the crack occurred on an END panel where there was no restraint from the opposite end.  There could be restraint from the bottom of the panel.

 

RE: Tilt-up concrete panel cracks at connections

The welds need to be on flexible elements, like the opposing edges of angles.  That is a lot of weld and since there is probably another on the opposite edge of the flange, they are acting against each other.  Because of the size and weight of the panels, I doubt there has to be any other significant restraint.

We see this all the time where two tilt wall panels are welded rigidly together.  If the cracks are tight and there is reinforcement spanning the cracks, you can probably inject epoxy into the cracks and move along.

You say that these panels have to resist hurricane winds.  I wonder if the columns were designed to take that kind of lateral point loading.

RE: Tilt-up concrete panel cracks at connections

Agree with all the comments thus far....combination of issues, most prominently drying shrinkage, restraint and strain incompatibility between the structural components.

That's a lot of weld for the connection.  Looks like a large gap between the panel embed and the column.  Are the panels bowed?

Considering that this crack is vertical, there is no restraint beyond the crack, I would lean toward drying shrinkage of the panel section, pulling in toward the center point between the two columns (assuming your columns are spaced at 20'), and restrained at the columns (obviously) by the welds.

RE: Tilt-up concrete panel cracks at connections

Definately a restraint issue this.

This is a classic example of a rigid connection where a flexible one is required. Not sure why they couldnt use a simple panel clip.

RE: Tilt-up concrete panel cracks at connections

(OP)
@ JAE - This is not an end panel.  The free end you see is the edge of an overhead door opening.  The photo was taken in the middle of a 200' long building.  The bottom of the panel is restrained.  There are 3-4 embedded angles in the bottom of the wall panel which are welded to embedded angles in the foundation.

@ TXStructural & Ron - The panels are not bowed.  They were designed to have a 1/2" gap between the column flange and the wall panel.  There is a 1" diameter rod behind all that weld so that the panels is welded to the rod and the rod is welded to the column flange.

With the cracks being so tight in most cases, I am assuming that the connection is still good with the headed studs and additional edge reinforcement in the panels and that epoxy injection would not be required.  Perhaps they could install a panel clip after the fact in addition to the rigid connections as extra insurance.  Thoughts???

RE: Tilt-up concrete panel cracks at connections

What sort of deformation allowances are there for the PEMB?  I once had a significant extra for a horizontal girt that was supporting the top of a masonry wall... The PEMB people had designed it for a deflection of L/90...

Dik

RE: Tilt-up concrete panel cracks at connections

Looks like a fairly wide crack to me. What is the reinforcement in the panel at the joints? How far is the edge of the panel from the column?  

RE: Tilt-up concrete panel cracks at connections

Agree with Ron and Texas et al, textbook restraint crack at a tilt panel connection. Saved to my "DON'T DO THIS" library, appreciate the contribution. I'll send you a nickel everytime I look at it :)

Grind the weld and set this connection free!

RE: Tilt-up concrete panel cracks at connections

(OP)
@ron9876 - The reinforcement at the panel edge consists of 2 - #5 bars.  The embedded plates are 8"x8" and are aligned on one edge with the panel edge.  The centerline of the column is the edge of the panel.

RE: Tilt-up concrete panel cracks at connections

The cracks will just get worse with time, and the ones that haven't cracked yet, will.  Why are the panels connected to the columns?  Do the panels span horizontally or vertically?  If they span vertically to an eaves strut, then the connections are not required for the panels, but may be required to brace the steel.

I think you need to cut out the welds and provide a cee shaped fabrication which is then welded to the plate and slips on the column flange.

RE: Tilt-up concrete panel cracks at connections

(OP)
The panels span horizontally.  They are connected to the foundation also, but not to the roof via an eave strut or any other way.  They were not supposed to be used to brace the steel, but duing my inspection I did observe that there was no wind bracing or moment frames for lateral loads.

hokie66 - I don't follow how your cee shaped fabrication would work.  Could you give me a quick sketch to explain it?  It would need a double lip to prevent movement inwards and outwards.  Also, since it appears there is no other wind bracing except for the panels, would that still work?

RE: Tilt-up concrete panel cracks at connections

You've got the idea about the cee.  Yes, plates in front of and behind the flange to allow the panel to shrink, but still provide support normal to the wall.  But with no wind bracing, you are in trouble.  The whole design needs a rethink.

RE: Tilt-up concrete panel cracks at connections

As a professional courtesy, if you have not already done so, you should advise the original engineer of your involvement.  It has the trappings of a potential lawsuit.

I agree with those who have said that the connection is far too rigid.  Shrinkage may have been the primary cause, but temperature fluctuations are likely to make matters worse over time.

Your latest observations about the lack of wind bracing adds a new dimension to the problem.  As hokie says, the whole design needs a rethink.

BA

RE: Tilt-up concrete panel cracks at connections

(OP)
@ BARetired - The real problem is that there is no true Engineer Of Record for this building.  The PEMB engineer and the foundation engineer (who also designed the tilt-up panels) most likely never talked or coordinated anything, but left the coordination up to the contractor which hired each of them separately.

I plan to ask for a copy of the PEMB drawings and the foundation/tilt-up wall panel drawings so I can check the question of wind bracing and see if anyone accounted for it or not.  Once I check that out, I will contact both engineers and the contractor if indeed there was no bracing provided in the PEMB design and the tilt-up panel engineer did not design the panels for bracing.

Thanks for all the insight.

RE: Tilt-up concrete panel cracks at connections

If there is no separate structural engineering firm, the PEMB engineer is the engineer of record.  That's not an issue.  Correction of the deficient design is an issue.

RE: Tilt-up concrete panel cracks at connections

Ron, why would you pick the PEMB engineer as the EOR rather than the footing and wall designer?  Whichever is the EOR, I think the one who designed the wall panels and their connections has the case to answer.  The PEMB designer will slither away.   

RE: Tilt-up concrete panel cracks at connections

I've never heard of a PEMB not being designed to independently resist lateral loads, no matter what the cladding (metal panels, CMU dressing, tilt...)

However, depending on the size and dimensions of the building, I would think unless you have horizontal slip connections the tilt panels are so stiff that they will be attracting the majority of the lateral load as shear walls...

Agree with others that this thing is sounding messy with nobody being the boss.

Ron, in the PEMB projects I have been involved with I am usually the EOR. I design the foundations, the connections to the foundations, and many times many other miscellaneous portions of the building outside the scope of the PEMB. I also dictate the loading and if necessary the drift criteria. But on this one I am not sure how the PEMB engineer could say they weren't responsible for laterally bracing their own building unless they made the huge assumption that the engineer designing the foundations and tilt panels was "taking care of that".

Todh- I think I would do a preliminary report of your findings and instruct your client that the foundation and tilt engineer and the PEMB engineer need to explain their design assumptions in writing so you can review all of the information. If they are local a face to face meeting between you and them may help a lot. I am not sure if getting everyone together in the same room would be a good idea or not...

RE: Tilt-up concrete panel cracks at connections

Yes, a meeting of the minds must take place...and soon.

BA

RE: Tilt-up concrete panel cracks at connections

Regarding the PEMB wall design issue.  Where I am, the lateral forces imarted from the walls to the mainframes and endwalls are always the responsibility of the PEMB engineer, as they affect the design of the mainframes, particularly in the case of concrete tilt-up cladding, governed mostlikely by seismic in my area at least.

There is a line of responsibility drawn here, one EOR for the building itself, including the lateral force from the walls to the mainframes and any associated wind beams, and one EOR for the foundation and the tilt-up wall design.  As for the connection of the tilt-up wall to the mainframe, that's relegated to the wall designer, with HEAVY coordination with the PEMB designer.  Just the way it has worked for me over the years  

I have to admit it is a different arrangement though and that good coordination is essential.   

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

RE: Tilt-up concrete panel cracks at connections

(OP)
I reviewed the metal building and wall drawings.  I see no indication that there was any allowance for the panels to take the lateral loads for wind bracing.  However, I may simply be overlooking something obvious so I am attaching a redacted version of the drawings in question.

RE: Tilt-up concrete panel cracks at connections

On the first sheet, the thing that strikes me is no mention of any seismic coefficients, only wind and snow.  Where is this building?

I did not see any wind beams or any seismic loads from either the mezzanine structure or the walls.  Is the mezzanine separated from the mainframes?  If so, then the mezzanine would have to be designed as self-supporting laterally.

I realize that wind usually constrols PEMB designs, but throw out this generalization with tilt-up walls and mezzanine dead loads.

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

RE: Tilt-up concrete panel cracks at connections

Mike, page 12 indicates Seismic Zone 0.

BA

RE: Tilt-up concrete panel cracks at connections

The connection in question is shown as Detail 2, page 17.

BA

RE: Tilt-up concrete panel cracks at connections

(OP)
The building is in the Texas Gulf Coast, so no seismic, only hurricane force winds (120-mph).  The mezzanine is supported on the exterior by the PEMB rigid frames, so it is all tied together.  You are right that there is no independent bracing for the mezzanine.

The connection is detail 2 on sheet 17.  Sheet 18 shows panel P-05 which is the panel in question in the original photos.  Most of the panels in the area without the mezzanine have this issue, but it also appears within the mezzanine area.

I am used to seeing tilt-up wall panels span vertically, but in this case it appears that the panel should have been designed as pinned on the bottom and two sides with the top free.  In which case, the fact that the panels are cracking at the column connections means that the only connection holding the panels up is compromised.  My inclination is to have wind bracing installed by the metal building manufacturer and release the rigid connections at the panels and provide a fabricated cee shape to resist panel loads out-of-plane.

RE: Tilt-up concrete panel cracks at connections

todh,

The General Notes on sheet 12 (Dwg. S0.0) indicates clearly who is the EOR.  I'm not sure I understand your idea of the cee shape, but wouldn't it be better to let the EOR review the situation with you and discuss the best remedy?

BA

RE: Tilt-up concrete panel cracks at connections

(OP)
BAretired,

The contractor is scheduling a meeting between the PEMB engineer, the tilt-up wall panel engineer and myself.  I envision myself more as an mediator that will make sure the two other engineers have thought of these issues and not assumed that each other was handling it when in fact they were not.  I am trying to not recommend a solution myself as it is not "my" building.

What in the general notes on sheet 12 tells you who the EOR is?  Is it something different than on the general nots on sheet 1?

Thanks for all the food for thought!

RE: Tilt-up concrete panel cracks at connections

I want to comment about msquared48's assertion that there are two EORs. I guess maybe laws can vary from state to state, or country to country, but I've never heard of such a thing. By definition, there can be only one EOR for each discipline. The laws here in Florida are very specific. The PEMB engineer is a "Delegated Engineer" only. Somebody else, the foundation and tilt-up engineer in this case, IS the EOR (whether he knows it or not).

It's the same thing with a joist design for a building: the joist designer is a Delegated Engineer for only that portion of the design. The person that designs the overall building is the EOR, and is responsible for all structural aspects of the design, including all of the structure's systems & components. The EOR must provide written design requirements ( his construction documents) to the Delegated Engineer and shall review the engineering documents of the Delegated Engineer for conformance with the design requirements.

RE: Tilt-up concrete panel cracks at connections

I believe your approach as a mediator is the correct one.

Drawings with prefix 'S' are normally considered to be structural drawings.  If he was only responsible for foundation and tilt-up walls, he would not have included a Structural Steel section in Drawing S0.0.  Note 1. under Structural Steel refers to certain items being rejected if not in compliance.  In several places he refers to approval of steel members by the "engineer", meaning himself.

General Notes and drawings by the supplier address only components of the steel structure.  Drawings with prefix 'E' are normally considered Erection Drawings.

That says to me that the guy who prepared the 'S' drawings is the EOR.

BA

RE: Tilt-up concrete panel cracks at connections

spats- "Somebody else, the foundation and tilt-up engineer in this case, IS the EOR (whether he knows it or not)."

I'd hate to wake up one day and find out that I was the EOR on a project!

Well put and agreed. You guys are all correct I believe in your chain of command and in many ways there is no difference between trusses, roof joists, or a PEMB. The big difference, and probably to most people, is the PEMB is the main lateral system, when most delegated portions of a structure are components. But I have had PEMB where we were doing maybe a third of the building as the EOR: CMU bearing walls, lt gage exterior walls, second floor steel composite floors, retaining walls, and of course foundations...

PEMB have come a long way since being just for rural areas and industrial applications, but in many ways the industry and perhaps building departments have not kept pace with the complexities that may be required on these types of projects. I would not be surprised if these types of authority, delegation, and communication issues don't arise more often. This subject would make a great magazine or journal article...

Great thread and subject!

RE: Tilt-up concrete panel cracks at connections

I would likely attend this type of meeting as an Observer, not a mediator.  The issue could be serious enough that I'd like to 'kick it around a bit'...

Dik

RE: Tilt-up concrete panel cracks at connections

I maybe a Johnny come lately, however all the talk so far has been about the column restraint, what about the foundation restraint. Sure you can use some idea to reduce the restraint provided by the columns, but I would like to know about the footing restraint. I assume this is what caused the crack in the middle of the panel. Sorry don't have the time to review the drawings spent too long on the photos, but I am assuming that the panels are heavily restrained at the base.
A few more questions,

1.    Are the joints leaking?
2.    Are the joints in anyway impairing the use of the building?

(again you may have answered this already, but I must admit I was speed reading)
   

ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION."
 

RE: Tilt-up concrete panel cracks at connections

RE,
You read so speedily, you found a crack which we hadn't talked about.  It's probably there, though.

RE: Tilt-up concrete panel cracks at connections

The panels are restained at the bottom by embedded angles welded to similar angles in the foundation.   If the connections to the columns were a bit more flexible, the panels could still function as shearwalls but shrinkage and temperature strains could be accommodated.

BA

RE: Tilt-up concrete panel cracks at connections

I think I need to get my eyes checked,I thought the reflection from the casting was a crack.

ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION."
 

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