Anchor rods to PEMB buildings - post-installed? 1

[Ingenuity]

Last week Saturday there was a sizeable concrete placement close to a project I am working on - more than 700 cy - and being nosy I decided to swing by and take a look.

RC foundation slab with thickened edge beams for a new industrial warehouse lease complex by a local developer, who has many adjacent buildings of the same type (tin-can framing etc).

Anyway, interesting thing I noticed was that there were no anchor rods/bolts cast into the foundation for the steel frames of the PEMB. I went back on Monday and asked one of the workers why they did not install anchor rods, and he informed me that they 'always drill them after, as the frame columns are installed'.

Is this now the typical procedure for installing anchor rods for PEMB's?

 

[canwesteng]

For light PEMB buildings on slabs, I'd go for epoxy anchors, smaller diameter than requested by PEMB fabricator to make c/c spacings work generally. It is kind of a pain to set anchors in a slab as others noted. For heavy loading, I've always had piers below columns, in which case casting in is easier, and you probably need the capacity.

 

[XR250]

XR-250. You're correct for most anchors but I can assure you that it is not common practice or even feasible to drill through a PEMB baseplate hole. If the PEMB baseplate hole is oversized by 3/16" and the drill bit is oversized by 1/8", you only have 1/32" around the drill bit. Hand drilling in the field isn't that precise so you would end up ruining a bunch of drill bits trying to do one. Hypothetically possible but not done in the real world.

Hmm, interesting. I have drilled thru similar base plates without issue.

 

[RWW0002]

@Sandwich - Good to know. I wish more PEMB companies would be involved in building erection, or at a minimum ensuring that it has been erected at least close to the way they intended it. Seems like PEMB are a "Set Design it and Forget it" kind of thing around here.. I am not sure I could get a PEMB company on a physical job site if I wanted to here..

 

[Ingenuity]

==> UPDATE 09/07/2022:

I dropped by the project site briefly today as they were taking a break from erecting the first few frames.

Looks like they used all-thread rods and cut to length. 4 anchor rods per column base. Looked about 1" diameter. No provision for any grouting under the base plates

I was not there when they were actually erecting the frames, and there was NO CRANE to be seen, just 2 each sky tracks and 2 each boom lifts.

The first two frames were fully installed with the transverse moment end frames (between the main frames) installed before I arrived at site.

Looks like they are doing the following for the remaining frames:

1. setout/markout the column base plate C/L or perimeter on the top of concrete slab, and possibly drill the 4 each anchor hole and install anchor rods.

2. using skytrack, lift 1 x column section into place and secure to anchor rods.

3. install the next adjacent bay column section into place and secure.

4. install eave strut between the 2 column sections installed.

5. repeat for the other side.

6. skytrack (double skytrack pick?) the frame rafter into place and connect to the previously installed column sections.

7. install purlins.

8. rinse and repeat​

I think it was the same crew that did the concrete work of several weeks ago, so the developer appears to be self performing all the work.

 

[phamENG]

Oh dear. That spacing is waaaaaaay too close for any post installed anchors. To get a hole large enough to clean and then correctly apply the adhesive/epoxy anchor...you'd have about a 3/4"-" of concrete left between the anchors!

For really small MBS structures I could see it - but most of mine are a) too large to begin with and b) have too much reinforcing in the vicinity of the anchor bolts (2" edge distance - really guys?) to allow drilling and post installing. The GC usually needs very accurate templates with marked centers and a surveyor to locate the templates prior to pouring.

 

[RWW0002]

At least this one appears to have bypass girts, so edge distance is not quite as big of an issue.. I agree that the anchor spacing appears like it might be too close for most published epoxy anchor capacities.

 

[Envelope3]

I find it somewhat pointless to fret about anchor rods. In over a decade of inspecting dozens of PEMB overload failures, not one of them was of an anchorage failure. All were failure of purlins or the main girts in bending.

 

[JoelTXCive]

What about uplift on partially enclosed structures?

I've only done a few PEMB's but the shop drawings I often receive will have ~4" (or less) spacing on the anchors. When you put that geometry into the Hilti software and apply a tension load, alarm bells go off.

 

[JedClampett]

I find it somewhat pointless to fret about anchor rods. In over a decade of inspecting dozens of PEMB overload failures, not one of them was of an anchorage failure. All were failure of purlins or the main girts in bending.

So now the PEMB manufacturers have something to accomplish. We need more anchor bolt failures at the same time as the rest of the building!

 

[GC_Hopi]

Nothing to see here folks. I had a photo of a PEMB anchor failure due to a tornado but can not find it at the moment.

 

[JoshPlumSE]

No provision for any grouting under the base plates

I've only worked on a couple of projects with PEMBs. This is one of the things that really surprised me as all of my commercial and industrial projects other than PEMB used grouted base plates. But, when in Rome.....

I have done post-installed anchors for new construction column bases before on non PEMB projects though. It was considered a "time saver" on a fast paced project. Concrete has to be done first. So, you might not have finished steel drawings and such by the time the foundation gets poured. We didn't hear about any problems from the field in that project. Though, to be fair, I could have been rotated off that project by the time problems happened. The steel stairwell that I'm thinking of would have been ordered way later than the rest of the steel on the project and any post installed anchor issues would have been pretty late in the construction.

 

[hokie66]

Set out for drilling the anchors is simple, but only if the location of reinforcement has been considered. Then there is the unfortunately prevalent practice of not adequately cleaning the holes. And the perhaps less frequent scam of embedding the bolts only 2” or so.

 

[dik]

That failure was caused by erection issues. Most PEMBs dont develop a moment at the frame support. The moment created, may have failed any number of anchor rods. Small PEMBs use 5/8" anchor rods, too.

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

-Dik

 

[human909]

That failure was caused by erection issues. Most PEMBs dont develop a moment at the frame support. The moment created, may have failed any number of anchor rods. Small PEMBs use 5/8" anchor rods, too.

Good point.

Set out for drilling the anchors is simple, but only if the location of reinforcement has been considered. Then there is the unfortunately prevalent practice of not adequately cleaning the holes.

I believe sample pull testing of chemical anchors is becoming more common. On a recent job the head contractor required pull testing of a percentage of bolts. I was not happy when 2 failed! The sub contractors likely did not clean the holes sufficiently. In this case these weren't really mission critical anchor bolts but in other circumstances such failures under ultimate loads could be disastrous.

 

[ads0221]

We’ve done post cast anchor rods on some smaller PEMB buildings. As others have said it’s not something I would ever want to do on giant clear spans but sometimes the client needs to pour a foundation and you don’t have final building drawings so it’s better for both parties.

 

[XR250]

Seems like it would make more sense to install a big embed plate and then weld the PEMB base plate to that. Would solve many of the issues.

 

[phamENG]

Seems like it would make more sense to install a big embed plate and then weld the PEMB base plate to that. Would solve many of the issues.

Yes and no. Their baseplates tend to be thin, which may or may not cause problems. It's also unlikely that many of the PEMB manufacturers out there would approve that, so if anything ever happened to the building, they'd probably claim their warranty was voided by modifying the structure. (Oh, your roof is leaking, I'm sorry - you welded the baseplates which fundamentally altered the behaviour of the structure and that's why it's leaking. Have a nice life.) Some of the larger and more reputable ones with competent engineers on staff who understand the issues with concrete construction and limitations might go for it, but those seem to be the minority. Had one that had no idea that concrete anchors and to be spaced further apart or with greater edge distance that bolts in steel plates. Quite a disturbing conversation.

 

[XR250]

Based on the number of issues reported here (and in my own experience), seems like a fundamental change in the industry is required.

 

[Brad805]

A weld plate with threaded studs welded in the correct pattern after casting would work, but the PEMB manuf would never get on board with welding their typical thin plate intended to be a pinned connection. The problem with the weld plate is setting it in a flat slab like this so it ends up level. That takes thought, and nowadays that seems too darn diff for some.

 

[XR250]

I'm sure most contractors would be happy to pay a significant premium to the PEMB folks in order to not have to precisely set a bunch of sketchy anchor bolts. There has to be a better way.