Responsibility of designing the anchor bolts 7

[Robbiee]

Hi all,
With almost every project that involves a pre-eng steel building, the disagreement on who's responsible for the design of the anchors bolts comes up.
The engineer who designs the pre-eng building decides the number, size and material of the anchor bolts, but leaves the embeddment depth to the engineer designing the foundations.
In my opinion, the design of the connections to the foundations needs to be done by the pre-eng engineer, of course after coordinating it with the foundation engineer and requesting the concrete info.
In some cases, the pre-eng engineer decides the type of anchors to use, such as the common L-shaped anchors, which I might think they are not suitable. What do you typically see and do?

 

[CANPRO]

All great reasons why the PEMB engineer would not design the connection the foundation.

I'll add another reason - over the years I've designed PEMB buildings to attached to: conventional concrete foundations (new construction), existing concrete foundations, large temporary concrete blocks, and temporary steel beams on grade. I'm sure 99% of PEMB buildings are going on newly poured concrete, but I just wanted to emphasize that the PEMB guys really are blind when it comes to foundation details.

Regarding PEMB engineers - I have no resentment towards them. PEMB buildings in general are kind of frustrating for your typical engineer (including myself). Common scenario: owner wants to add 0.01 psf to the roof and local engineer engaged on the work tells owner that extensive reinforcing is required, local engineer can't even make the existing building work for original loads, local engineer looks bad.

This isn't a knock against the PEMB engineer or the local guy - PEMB manufactures/engineers have a very real incentive to get the design to 99.999% capacity, which is a level of refinement that most engineers (including myself) are not accustom to working with - which I believe leads to the scenario described above.

 

[Robbiee]

Very good replies. I think I am not convinced that the PEMB engineer can't specify the embeddment because they don't know the foundation system or the concrete properties. We might be doing it differently though.
We start the design of the foundations based on preliminary pre-eng drawings prepared by one company. The drawings are tendered and the same PEMB company or a different one gets the job. The tender package includes all the details of the foundations. The new PEMB drawings (final ones) are reviewed and any required adjustments for the foundations are made to accommodate differences in the PEMB drawings.

 

[Rabbit12]

CANPRO, isn't that the truth? If I had a nickel every time I've been asked to add load to an existing PEMB I'd be rich. The difficultly making a PEMB work for even small loads can't be underestimated. The conversation with an owner telling them they can't support something off their structure because you can't grandfather the structure per IEBC is equally difficult. They never remember that they made the decision to save a buck during the original construction. The truth is, in an industrial setting there is almost always a need to modify buildings over the life of the structure.

I try to avoid PEMB if at all possible because of the future issues they present.

 

[canwesteng]

I've actually had ok luck re-analyzing PEMB frames of late, manage to get by with a bit of extra bracing and connection beef. Why do you say you can't use IEBC?

 

[Aesur]

We cannot even get reactions in a reasonable format.. do we really want them to attempt concrete anchor design?

To expand on my statement, recently I received PEMB reactions for a small residential structure with moment frames in both directions. I summed up their reactions into combinations assuming where WL1 is listed then WL1 for each member is the same load case. Unfortunately a symmetrical building had different reactions on each and every columns, this made no sense, so I called and talked to the PEMB engineer who told me that their software doesn't always call the WL in each direction by the same nomenclature, when I adjusted per this new information the reactions started to match up on each side of the building and the foundation sizes decreased significantly. If we really want the PEMB engineers/manufacturers to improve something, anything, it should be how they provide their reactions.

Wanted to add that not all PEMB manufacturers/engineers are bad, some give really good reactions, but it should be an industry standard format, not whatever each company wants to do.

 

[Rabbit12]

CanWest, if the load is than allowed by the IEBC is what I mean. 5% gravity sometimes is a small load.

 

[canwesteng]

True, I actually often have bridge cranes in the PEMB I work on so 5% gravity is often enough to hand small things from the frame.