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?

 

[JedClampett]

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

Don't hold your breath. It's a great system (for them). They delegate, obfuscate and generally pass off all legal responsibility such that no matter what happens to the building, they're not liable.
I'm not sure how many of the buildings even have an EOR. I've made some long drives through the midwest and there's hundreds of them. When I go to the local fireworks stand and it's a PEMB, I wonder if it had an engineer overseeing the design. I've seen churches, warehouses, outlet malls and barns using PEMB designs.
Additional engineering cuts into the margin. Consolidation (Butler and Varco Pruden are one now) will not help. It's a commodity.

 

[XR250]

This is the main reason I won't design PEMB foundations despite being offered them regularly. I don't want to have to deal with the fallout of them misplacing the anchor bolts.

 

[phamENG]

I wonder if it had an engineer overseeing the design. I've seen churches, warehouses, outlet malls and barns using PEMB designs.

And coming from a good and honest supplier that actually operates by the MBMA guidelines, this is fine. The problem is that most of them don't.

I had a church contact me asking for a foundation design for a PEMB. They sent me their preliminary drawings (drawn by a church member who has a day job as an architectural draftsman doing house designs - they weren't bad for prelims, but they needed plenty of work). They also sent me preliminary PEMB drawings. I sent back a very long list of questions and concerns - PEMB was designed for H/60 (good for a barn, not for a finished building), who was designing all the interior framing supporting the second floor? Who's the architect of record? Is there an EOR? The list kept going. The response was: "Thank you for the review and questions. There's a lot to think about there. The supplier told us the building was good for what we wanted, so it's already in production and can't be changed. It arrives in two months. What's your fee for designing the foundation?" I wished them luck with the project and didn't give them a fee.

 

[Brad805]

The foundation contractor usually is not involved in the building in my experience. I doubt the programs these suppliers use will not have an option for a fixed base connection. We are doing one now where there is a building step. They treat it as two separate building so it can be done in the software. On the line the building steps we will have two parallel frames.

I have never had a problem with the anchor bolts for a PEMB, but we work with only a small number of contractors that pay attention. Most of them are using total stations to set/check the anchor bolts. The problem we have now is getting the suppliers to spit out the final design so the foundation can be built. We never post install anchors, and would require the contractor to figure out an appropriate method to secure the bolts for a flat slab like posted. That said, we are typically supporting our buildings on piles so we have a pile cap that makes setting the bolts child's play.

We do not have a problem with the big name building suppliers as far as quality is concerned either, but you need to pay attention. If they can shave out a pound of steel they do.

 

[RWW0002]

As a bit of an aside,
I can't help but wonder if PEMB performance (along with several other "whittled down" structural systems) may have benefited significantly from conservative wind speeds in a large % of the country (US) with previous code editions.

Wind design for much of the interior of the US has not changed much in a long time (even though the number has changed over the years, the resulting pressures have been pretty similar - 70 mph fastest mile, 90 mph ASD wind, 115 mph Ult. wind etc..) Now that wind speeds have been reduced for much of the interior of the country - a change justified by research to be sure - I wonder if we will see a drop in PEMB performance.

Take, for example, the church that phamENG noted above. Maybe H/60 buildings have performed better than expected in the past due to some conservative wind speeds. But if that same H/60 limit is used with the new reduced wind loads, the building is far more likely to see a wind event in its lifetime that causes some issues with serviceability. PEMB companies allowing some loose design criteria may well see worse performance once we take out the extra factor of safety that we got from the conservative wind speeds of the past..

 

[MotorCity]

My concerns with post installed anchors are not specific to PEMBs, but rather apply to any installation. So, there is always an inherent risk of drilling through rebar. Granted, nicking or even drilling through one bar probably isn't the end of the world, but why risk it? This obviously doesn't happen with CIP anchor rods. Secondly, some anchor rods are super sensitive to installation methods and technique, more so than CIP anchors. For example, there are more restrictive installation and in service temperatures. There is also an influence on how the holes are cleaned....huh?? Despite the requirements for special inspections, observations, etc, I have never seen the hole cleaning documented and reported from a field inspection. Post installed anchors definitely have their place, but if given the choice, I'll take CIP anchors.