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Responsibility of designing the anchor bolts
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(Structural)
(OP)
6 Apr 20 17:14Hi 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?
Replies continue below
(Structural)
6 Apr 20 17:18Around here, the Pre-Eng designer provides a size and layout based on their design. However the final design of the anchor bolts is by the foundation designer. If the foundation designer determines that the anchor bolts need to be bigger, longer, spaced out further etc. then that gets relayed back to the pre-eng supplier and they update their baseplates accordingly.
2
JAE(Structural)
6 Apr 20 17:22For our projects (in the US):Engineer of Record specifies building layout, general configuration of framing (columns, etc.)Engineer of Record specifies code, standards, applicable loads to use on the building.EOR then delegates the design to the PEMB company.The PEMB company designs their proprietary building system, asking the EOR for various alterations to the original design criteria as needed to meet their system needs.The PEMB company designs the size, number and material of the bolts ... but NOT the embedment depth.The EOR determines the bolt embedment depth based on ACI criteria.The EOR also is responsible to verify that the PEMB company utilized all applicable code, standard, and load criteria specified on the primary contract documents.
(Civil/Environmental)
6 Apr 20 17:25If you want the PEB guy to dictate the type of foundation and member thickness, then you can delegate the responsibility through contract. But it may be unpractical and undesirable, as the building is likely ordered in very early stage of the project, and variables are kicked in during the later design phase that causing changes.
(Structural)
6 Apr 20 17:31Quote (JAE)
The PEMB company designs the size, number and material of the bolts ... but NOT the embedment depth.
This seems completely backwards to me all of those things are directly related to the embedment depth via the various ACI anchorage checks. I'd take the position if they are doing the base plate design and finding the forces in the anchors they should do the complete anchor design and not just pass the buck on the embedment portion. Are they giving you per bolt forces or are you getting base reactions and then trying to replicate their base plate design to then finally do the embedment checks?
My Personal Open Source Structural Applications:
https://github.com/buddyd16/Structural-Engineering
Open Source Structural GitHub Group:
https://github.com/open-struct-engineer
(Civil/Environmental)
6 Apr 20 17:50The size, thickness of plate, and diameter of anchor bolt are independent of type of foundation, except the concrete compressive strength, which would be covered in the purchase order. However, the length of embedment has everything to do with the type of foundation (spread footing, SOG with turn down, grade beam...) and reinforcing, and the type of foundation depends on variables such as subgrade conditions, and other considerations.
The subsequent need to revise the PEMB's original design, after it was received and accepted by the EOR, can be considered a change order that bears monetary consequence.
(Structural)
6 Apr 20 17:56The last thing I'd want is a PEMB designer designing the embedment of the anchor rods. I've never tried to get them to do it, but I think at best it'd be a tough sell and they would likely flat out refuse.
(Structural)
6 Apr 20 17:56I always provide the base plate thickness - anchor bolts dia and locations, and provide the length as well.what i do is check the adequacy against the concrete failures , and if there is a failure i highlight that as a note under my base plate detail asking the concrete designer to add sufficient rebars reinforcement.
ôIf you don't build your dream someone will hire you to help build theirs.ö
Tony A. Gaskins Jr.
(Structural)
(OP)
6 Apr 20 18:01JAE: That is exactly how it is being done here too,(Ontario, CA), but I agree with Celt83 that the complete design should be by them.
Celt83:
What they typically provide are the base reactions; horizontal and vertical forces.
Now what if the EOR doesn't like the L-shaped anchors they are proposing and wants to use a more expensive headed anchors? are they going to come back with a request for extra saying: we accounted for this type of anchors?
(Structural)
6 Apr 20 18:09Can you imagine a PEMB Engineer figuring out ACI Appendix D?
(Civil/Environmental)
6 Apr 20 18:10The PEB designers, I've worked with, usually provide the necessary anchor bolt assembly details such as,
material properties,
diameter, spacings, embedded depth of bolts,
size and thickness of baseplates etc
We are then required to design the pedestals/foundations and perform the anchorage checks for the specified service/ultimate reactions.
(Civil/Environmental)
6 Apr 20 18:14When I first started working after graduation, this was the first task I was asked to perform. It took me close to one week, just to understand the provisions for tension checks only.Quote:
Can you imagine a PEMB Engineer figuring out ACI Appendix D?
Contact us to discuss your requirements of anchor bolt installation. Our experienced sales team can help you identify the options that best suit your needs.
When I first started working after graduation, this was the first task I was asked to perform. It took me close to one week, just to understand the provisions for tension checks only.
(Structural)
6 Apr 20 18:21I don't understand statements like this you just trusted them to design an entire building, they are also PE's why can't they do the anchorage engineering? My, very limited, experience is they are all using in house proprietary software to get their structures to work and designing to the nats ass. This might mean they did a full FEM analysis on the base plate to get it to work, If I just take their reactions and run with a standard rigid plate analysis I'd get different anchor forces than what their model is relying on.Quote:
Can you imagine a PEMB Engineer figuring out ACI Appendix D?
I don't understand statements like this you just trusted them to design an entire building, they are also PE's why can't they do the anchorage engineering? My, very limited, experience is they are all using in house proprietary software to get their structures to work and designing to the nats ass. This might mean they did a full FEM analysis on the base plate to get it to work, If I just take their reactions and run with a standard rigid plate analysis I'd get different anchor forces than what their model is relying on.
My Personal Open Source Structural Applications:
https://github.com/buddyd16/Structural-Engineering
Open Source Structural GitHub Group:
https://github.com/open-struct-engineer
(Structural)
(OP)
6 Apr 20 18:21Buggar,
Here, I think the same Appendix D is called Annex D and it is a pain to navigate and understand.
(Structural)
6 Apr 20 18:31Quote (BUGGAR (Structural))
Can you imagine a PEMB Engineer figuring out ACI Appendix D?
Judging by the number of times I've seen 2" edge distances to bolt centers, no, no I can't.
(Structural)
6 Apr 20 18:43PEMB companies won&#;t design the embedment because:1. They generally don&#;t have any information on the foundation design, concrete strengths, surrounding reinforcement, bolt edge distances, etc to do an embedment design2. They only design in steel, not concrete3. Their liability insurance doesn&#;t cover anything below the base floor elevation4. It is more efficient for the EOR to determine embedment since they have all the immediate knowledge of the items in reason 1 above.
(Structural)
6 Apr 20 18:50I've never had a single one give me flak for asking for larger diameter, or a different layout. If you're getting them to increase their baseplate size significantly, or the thickness significantly, then yes I can see that coming as an extra. But to be honest, I've found that their diameters and layout tend to work from the steel side of things. And the only variable that I need to change to get them to work on the concrete side is embedment depth.
I would not want them designing the foundation elements. And to ask them to design the embedment depth, is in fact asking them to design the foundation. That's not their purview, that's the EOR's (or as I'm starting to see lately a different delegated design engineer).
On a side note, I have no idea how some engineers have sold owners on paying them professional fees, only to have them delegate both the superstructure and the foundation designs to other engineers. What they hell are they providing the owner besides someone to coordinate between two engineers for an exorbitant fee.
(Structural)
6 Apr 20 19:00Embedment depth is now and always shall be, part of the foundation design, amen. I've never had a disagreement on this. As stated above, they can't design embedment without designing the concrete.
[Post Deleted]2
Anonymous_ENG(Structural)
6 Apr 20 19:31Quote:
BUGGAR (Structural)
Can you imagine a PEMB Engineer figuring out ACI Appendix D?
I've posted before in a question about sealed drawings and PEMBs, and I work as a sealing engineer at a major PEMB supplier.Jayrod and JAE have it correct, we check the anchors for the tension and shear requirements of the steel itself, but make no attempt to make any of the concrete checks. We only design the steel, and that is laid out pretty specifically in our contracts. If the EOR desires a different anchor bolt pattern or size, we usually accommodate that for no charge, as long as it doesn't require us to provide a drastically different amount of steel.Most of the more experienced engineers do understand the provisions of Appendix D and Chapter 17 (ACI 318-14 and beyond). Some of the states I seal require an SE license, so I've passed the same 16 hour exam others on this forum have as well.I know PEMB engineers get a bad name for what they do, but to think we're incapable of understanding a different material or the requirements of it is downright insulting.
(Civil/Environmental)
6 Apr 20 20:16I don't think BUGGAR meant insulting, but reflecting the prevalent sentiment of dislike and distrust of the PEMB designers, who provide those details (spacing, edge distance) that are not shown the slight understanding of the concerns/design difficulties of the structural/foundation designers. I have no doubt there are talent/capable persons in the PEMB industry, but to my disappointment, the industry is so rigid, and incapable of change after years of complains gathered from the design engineers.
(Structural)
6 Apr 20 20:28All 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.
(Structural)
(OP)
6 Apr 20 20:55Very 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.
(Structural)
6 Apr 20 20:59CANPRO, 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.
(Structural)
6 Apr 20 23:15I'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?
(Structural)
6 Apr 20 23:33We 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.
(Structural)
7 Apr 20 03:11CanWest, if the load is than allowed by the IEBC is what I mean. 5% gravity sometimes is a small load.
(Structural)
7 Apr 20 17:40True, 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.
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I deal with the BC Building Code. It specifies certain diameters and spacing of anchor bolts but does not specify that they must be cast in place (wet set).
On projects with ICF foundations, or also structural slabs, the contractors like to use wedge anchors or sleeve anchors for ease of installation.
Opinions on these different types of anchor bolts?
Note: I am not in a seismically active zone and our wind loading is low.