Tilt-up concrete panel cracks at connections 1

[todh]

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.

 

[BAretired]

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

BA

 

[msquared48]

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

 

[todh]

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.

 

[msquared48]

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

 

[BAretired]

Mike, page 12 indicates Seismic Zone 0.

BA

 

[BAretired]

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

BA

 

[todh]

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.

 

[BAretired]

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

 

[todh]

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!

 

[spats]

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.

 

[BAretired]

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

 

[a2mfk]

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!

 

[dik]

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

 

[rowingengineer]

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.”

 

[hokie66]

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

 

[BAretired]

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

 

[csd72]

Looks like they probabaly could have done with this book:

http://www.cement.org/bookstore/profile.asp?itemid=EB110

 

[rowingengineer]

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.”