Anchor Reinforcement

[EDub24]

Generally when I do a structural design with MEP equipment, I require the Contractor to design the anchorage and provide the calculations for review. I usually have a note that stipulates the equipment pad sizes need to be coordinated with the anchorage calcs regarding thickness and edge distance requirements. Most of the time there's no problem with this approach however a few times the anchorage calcs show that anchor reinforcement is needed (either for tension or shear). My position is that the reinforcement is needed by the anchors and not because the concrete foundation/equipment pad is inadequate structurally. Therefore, it should be designed by the Engineer providing the anchorage calculations. However, I've gotten into countless arguments with Contractors and their Engineers who feel the reinforcement should be designed by the Engineer doing the foundation/equipment pad design. Does anyone have any thoughts on this or can shed light on what they consider is the responsibility of the anchorage designer vs the foundation designer? If I know that reinforcement will likely be required I make that note in the drawings but most of the problems come from smaller equipment that I didn't expect anchor reinforcement to be needed. I posted this question in the ACI (code) issues section but am posting here as well. Thanks!

 

[WARose]

However, I've gotten into countless arguments with Contractors and their Engineers who feel the reinforcement should be designed by the Engineer doing the foundation/equipment pad design. Does anyone have any thoughts on this or can shed light on what they consider is the responsibility of the anchorage designer vs the foundation designer?

I don't see how the anchorage reinforcement (or the anchorage for that matter) could be anyone's responsibility but the guy doing the foundation. (Especially if it is post-installed.) In fact, I'm not sure if I've ever left the anchorage design (with or without reinforcement) to a vendor/contractor.

 

[RPMG]

I would expect the foundation engineer to provide reinforcement. I wouldn't want some intern with Hilti Profis output adding rebars to my foundation.

 

[Celt83]

I am of the opposite opinion as RPMG and WARose.

The equipment manufacture is responsible for their attachment to the base structure if thru the course of their calculations they find they need anchor reinforcement by nature of the name they should be designing it, if their anchor reinforcement design needs to rely on development with the in place bars then that should be clearly noted in the shop drawings and reviewed by the base building design engineer. They should really be providing the connection loads as well for base building engineer to review the adequacy of the structure as more often than not we're working off of a stock spec sheet from very early in the design life of the building.

 

[EDub24]

During design our MEP guys will usually give us the cutsheets of the different manufacturers they are looking at and we will design the foundation for the worst case. Because we don't know which manufacturer the Contractor will choose we push the anchorage calcs on them. We do verify the foundation is adequate based on the submitted/approved equipment. It's a bit of a gray area regarding the anchor reinforcement. In my opinion because the anchorage needs that reinforcement(for breakout or whatever) it should be designed by the anchorage designer. The foundation alone is adequate structurally if they provided higher edge distance or whatever. They say they aren't designing the foundation and aren't responsible for the anchorage reinforcement. I'm tempted to just do the design to get them off my back but was interested in other people's opinion.

 

[Celt83]

EDub24:
Been in your situation before and more often then not the person on the manufacturers end didn't know how to design anchorage reinforcement and was simply putting numbers into Hilti Profis and it not working unless he/she checked the "reinforcement" box in the program. Took a week of back and forth with for them to admit that. Usually ends with us up-sizing the pad by a couple inches to get an edge distance to work because the unit size wasn't really going to change.

 

[canwesteng]

IMO, the only thing that should be on the anchor manufacturer is sizing the anchors and providing loads. Are you expecting the contractor to spec concrete strength as well?

 

[TLHS]

I take responsibility for everything below the baseplate. I'm going to have to check the design anyway, if it's vendor supplied, and I suspect I've done this more than they have. So why not just do it and save everyone the time and multiple revisions.

 

[WARose]

[blue](EDub24) [/blue]

During design our MEP guys will usually give us the cutsheets of the different manufacturers they are looking at and we will design the foundation for the worst case. Because we don't know which manufacturer the Contractor will choose we push the anchorage calcs on them.

I'm from a different world. In the design I do, we design everything based on the certified equipment drawings (from a vendor that has been selected). In fact, we use to do it based on as-builts....but those days are long gone.

I'm not sure I understand how your process is working anyway......how do you provide reinforcement for a already poured foundation? It sounds to me like this is a post-installed anchor situation. I can see providing reinforcement all over the place in a worst case design approach you are describing.....but that would be highly wasteful in most foundation designs.

 

[DETstru]

I always defer MEP anchorage. We often have CD's nearly complete before MEP even starts design so there's no way to design anchorage.
Sometimes they come back and hire us to do the design.

Regardless, I've never needed, or have been asked for anchor reinforcement. Having never fielded that question, I would probably just tell them to provide an anchor that doesn't need it or tell me what they need and I'll draw it with some sort of CYA note about "design by others".

 

[JStephen]

If we furnish the anchor bolts, I assume that steel strength and pull-out design are my responsibility, design for concrete breakout, side-face blowout, and shear and bending in the foundation due to the anchor bolts are all part of the foundation design. Part of the logic there is those latter failure modes aren't a failure of the anchor bolt, they're a failure of the foundation itself. Part of the logic is that the reinforcing used for anchors may be steel that's incidentally there in the foundation anyway, so you can't necessarily separate those two aspects of design. Also, when you add reinforcing for the anchor load, you're converting that anchor load into a general punching shear in the concrete, which can't be treated independently of other loads.

If anchor bolts are furnished by the general contractor or the owner, we specify bolt size, extension, loads, and everything below the face of the concrete is designed by others.

My bigger concern with stuff like this is not so much arguing about who designs it, but failing to have that discussion and both parties assume the other party did it.

 

[EDub24]

Been in your situation before and more often then not the person on the manufacturers end didn't know how to design anchorage reinforcement and was simply putting numbers into Hilti Profis and it not working unless he/she checked the "reinforcement" box in the program. Took a week of back and forth with for them to admit that. Usually ends with us up-sizing the pad by a couple inches to get an edge distance to work because the unit size wasn't really going to change.

Usually the Contractor hires a 3rd party engineer to provide the design but I agree, it's likely they don't know how to provide the design and start pushing back.

I'm not sure I understand how your process is working anyway......how do you provide reinforcement for a already poured foundation? It sounds to me like this is a post-installed anchor situation. I can see providing reinforcement all over the place in a worst case design approach you are describing.....but that would be highly wasteful in most foundation designs.

Typically these are for new construction only where the foundation hasn't been poured yet so reinforcement can be added and/or the foundation modified.


Right now I'm to the point where I will provide the design just to avoid any further delays (and potential claims from the Contractor). I'll likely need to word my response in a way that clarifies I'm doing this at the request of the Anchor designer so the Contractor can't come back with a change order.