Equipment Vendor Signed Structural Calculations 6

[rharting]

I'm working on a project where I received structural calculations for a piece of equipment which is around 10'x12'x35' tall and weighs approximately 100K. We are responsible for the base plate design (a bit unusual), anchorage and foundation. After reviewing the calculations, I discovered that the design included a total of 3 load combinations. While they were called Dead Load, Wind Load, and Seismic Load, I discovered that they were really DL, DL + W, and DL + EQ. Their single wind load was a wind load in the X-Z plane (y being vertical)... essentially acting on the diagonal.

They reported that the moment due to wind was around 300K-ft (on the equipment drawings and in their calculations). After digging a bit, I found that the moment due to wind was actually around 700K-ft but they subtracted the resisting moment (~100K*10'... the dead load times the distance from the centroid to the furthest anchor point) from the wind moment. Yes, they took Mwind-Mres as their wind moment even though the resisting moment was larger than their wind moment.

I discussed over the phone with him my questions and he got rather defensive. I asked whether he included the 0.7 factor on his seismic loads to move it from an ultimate load to a service level load to which he replied 'I'm not sure what you mean by ultimate load.' His PE status indicates that he is a mechanical engineer.

My biggest request was to include wind loads in the X and the Z plane as I believe this is normal practice and can produce more realistic/governing designs for all of the base plates and anchorage. His response was that he believes that this is an additional service and will charge our client to perform this task.

Any suggestions on how to proceed? As a structural engineer, I believe there is enough conservatism in some of the loading and can back out some information that is required, however i will be forced to make a lot of assumptions in order to get what i feel is a comprehensive design completed.

 

[TehMightyEngineer]

I guess the big question is how much do you want to work with this other engineer/client again? Regardless, I'd make 100% sure your numbers are correct before you go pointing fingers.

From your description it sounds like he's practicing outside of his engineering experience. At the very least I'd be documenting everything and be prepared to have to go to your engineering board as required by engineering ethics.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[Guastavino]

I had a similar recent experience with an equipment supplier, albeit on a smaller piece of equipment. I got calcs back for a 6-column setup. It didn't take me long to determine that the calculations were faulty, as they assumed the same load to all columns, even though the middle columns clearly took more. Also, the wind and seismic calculations didn't seem to make sense. Turns out, after a closer look, they didn't make sense either. I had to call the engineer and supplier (and had them both on the phone at the SAME TIME which was key) and graciously explained why it didn't SEEM to make sense, but the spirit of it was in asking questions like, "I was anticipating that the loads to the middle columns would be higher, did I miss something?", and not with a smug "got ya" attitude (no need to overplay your hand, you want to look like the reasonable person that you are regardless of your justifiable frustration). In my case, the engineer agreed and resubmitted.

My advice in list form:
1. Make 100% sure your numbers are accurate.
2. Mention specific code requirements they left unchecked and ASK them why they chose not to check them (they may claim engineering judgment, in which case you can claim, well I need those numbers too for the foundation design).
3. Ultimately, I think you can confront the situation by asking questions that expose the issues with the design, as opposed to accusing. It will be obvious to your client who is right and who is wrong (but again, key that you have your client and this engineer on the phone at the same time so that your client knows what's going on).
4. Keep your questions short. Such as, "the code requires checking these other load cases. Is there a reason you didn't provide those numbers as well in this set?"
5. Expect their engineer to get defensive when you begin to ask questions they can't answer. Expect it so that you can stay calm and collected. Your client should be able to tell what's going on.

Ultimately, it's not a fun situation, but stick to your guns.

 

[TLHS]

This happens a worrying amount with equipment. They usually have a mechanical engineer on staff and figure he can do that minor structural stuff. This is likely the case in a lot of situations, but on occasion it's awful.

My favourite was last year when I was getting weird anchorage loads from a vendor. I sent them my rough calcs and asked the to explain why I wasn't getting their numbers. They didn't look at my numbers and sent their calcs to me. It was software output from a vessel design suite that was butchering seismics, plus they had misused the local input values I had provided them and had picked an anchor rod material that you can't get anchor rods in. I wrote a several page document with references explaining what my issues were. They received it and basically said they just use the program and couldn't address my concerns. Eventually I ended up designing anchorage and the equipment was otherwise hilariously over designed.

 

[JStephen]

Ask for the numbers you need, ask for the definitions you need, ask about the basis of the numbers if necessary.

How all this works is that you have a structural engineer on the overall project. He sees the equipment, says "I don't know nothin' bout birthin' no equipments!" and so he puts a note on the equipment saying "Equipment design by equipment designer/manufacturer". So in the equipment-manufacturing-world, that piece of equipment is designed by the equipment designer. And that is likely to be one person, not a team, and that is not likely to be a structural engineer. So you wind up with people doing incidental work outside of their regular fields, which falls into a gray area in many cases.

This is compounded in that the equipment design likely falls under multiple conflicting standards. And in the case of the building codes (including ASCE 7), these tend to be very poorly written for non-building structures, and poorly coordinated with the other standards, even the standards they reference. So, for example, you'll have absolutely critical loads that aren't even included in the load combinations in the building codes, and loads in the building code that may not be included in the equipment-design standard.

This is further compounded by a lack of clarity in the definition of the fields. So, for example, if you look on the forums here, you'll find a "Storage Tank Engineering", and it's under "Mechanical Engineering". You'll find a "Boiler and Pressure Vessel Engineering" and that's also under "Mechanical Engineering". You'll find a "Pipelines, Piping and Fluid Mechanics" forum, which is also in ME. Meanwhile, in Structural Engineering, a "Structure" is "That which is built", if I remember the building code usage, so tanks, boilers, vessels, and piping all fit that definition, as do automobiles, yoyos, cell phones and most other man-made objects. So, you get a certain amount of confusion in the process. In some states, a very clear delineation is made between structural and other work; in many states, that's not the case.

For the ideal case, that original overall Structural engineer would get the geometry, weights, center of gravity, etc., from the equipment supplier and take it from there. In reality, usually some of that design work gets put back on the equipment supplier; in a some cases, ALL of it does.

 

[TLHS]

The problem is that a bunch of that stuff needs to be done by the equipment manufacturer anyway. You can't have things like pressure design for a vertical vessel be done independently of seismic or wind. So equipment engineers that do large scale work need to become familiar with environmental loading and research the legal basis for interpreting those things.

I can do support frames, anchorage, foundations, and all that fun stuff. I can also check that they're in the right ballpark for their stress analysis including environmental loading, but there's no way they could really just delegate all of their 'structural' engineering back to the EOR because large scale equipment is fundamentally similar to a structure and the engineer designing that part of it needs to understand its behaviour.

 

[JStephen]

Well, in our case, the large-scale structures are "not similar to buildings", as the building code says it. But that's beside the issue.

 

[TLHS]

I didn't really mean it in the building code sense anyway, but rather in the sense that they hold up their own weight in conjunction with environmental loads and other external forces.

 

[LSPSCAT]

Great post from JStephen and I do not want to completely hijack the thread but I have been meaning to post about this topic for a long time. I agree that there is a huge gap in large equipment and fabrication design between equipment/mechanical design codes and structural design codes. My personal experience is that I have tried to bridge this gap to the best of my ability, I am a Mech P.E., with a BSME and MSCE with a concentration in structural so at least I have been exposed to the various codes and have some appreciation, however, it is not always easy to come up with load cases that satisfy each code requirements without bending the rules a little on each side. In the background you have a management team that has no appreciation for any of this and has provided for 8 hours engineering, because it is a standard product!


"....likely to be one person, not a team..."

You have a razor thing workforce that needs to integrate various mechanical design specifications that are all written based on allowable stress design and then you need to integrate that with all your civil codes. I do not think everyone understands how thin most equipment manufactures are setup. There are still some large, well run and organized companies but at many places the lone mechanical engineer provides quote assistance to sales, responsible for all project engineering duties, including setting the order in ERP systems, verifying scope and quantities, soup to nuts design, all modeling and drafting, submittals and correspondence, finding vendors and parts suppliers, setting up work orders in ERP systems to actually get the stuff built, setting up QA and maybe being QA, supporting manufacturing because someone cannot find a DXF to cut the part, and coordinating shipping/finding the bolts in the shop that did not get shipped. So.....yeah there are going to be mistakes and I have seen some ugly and costly ones in the last 10 years.

I do not know how we change the attitudes in the corporations but that is how things are being done. By the way..that project was given to a new engineer without any training !! So if you think that an Engineer can keep up to date with the latest SolidWorks version, ASME codes, the latest AWS codes, the latest ASCE codes, and interpret all the loading cases between mechanical engineering codes that are typically based on allowable stress design and the civil codes which are LRFD; it is not going to happen. I am not defending it; it is a incredibly sad to witness and watch going on but that is what I am seeing.

I was recently looking back at many old training documents from the 60's and 70's at an equipment supplier and it must have been paradise. Neatly written training materials, clearly spelling out design methodology and the various steps, decisions, and calculations that needed to be done...look how far we have come.

 

[delagina]

If you are doing the foundation, you are responsible for the foundation and you are stamping it with your PE. So if the equipment vendor, specially a large equipment, is giving you wrong loadings because they don't have competent structural engineer in their company, that is frustrating. Vendor should be reported to the client.

I've designed foundations for large equipments. I knew right away that the loadings I got from the vendor drawing was completely wrong (specially the wind load). I had to call their "structural engineer" and work with him how to correct their loads so I can design my foundation properly.

 

[EngineeringEric]

I am sorry that it is complicated and hard to determine all the loading for a mechanical piece of equipment, maybe it should be someone's job to look at loads and design based on dozens of codes... this amount of experience would require compensation, maybe on the level of a white collar engineer, and then we need to limit those who can do this.... perhaps with a professional license?

If i don't understand all the ins and outs of plumbing i am not going to seal plumbing design, even it is a simple SW drain pipe. I will not seal mechanical loading or design even if it is a simple exchange of air calculation. I am an engineer, it is my job to know what i don't know better than what i do and to not cross that line. The ME should design/detail all their fancy interior super complicated design put it in a box and then hire a SE to tell them what that box is going to do... but nobody wants to hire the SE for anything more than 8 anchor bolts in a slab of concrete because the ME can do it all.


**Sorry for the rant***

 

[LSPSCAT]

EngineeringEric,

It is not to say its too complicated or anything else. This is a fundamental issue that is present in the companies that are doing this work. Its a lack of appreciation from top to bottom. The organizations have been stripped bare over the last X number of years and this is what we now have. My point is that it needs to be brought to light. I know and we all know that 1 person cannot possible design all this "stuff". But the options for the engineer at these companies are either "A" - do it the best they can and hope for the best or "B" quit. Explaining the requirements, showing a manager requirements for licensure, or any other tactic based on reason is going to get one nowhere.

Personally, I left and started my own consulting business exactly because of this. I now usually work on one major project at a time, hire a structural engineer to either peer review or complete calculations when required and am compensated accordingly. However, this took me 10 years in industry to get frustrated and develop enough contacts that appreciated things done right to do this. No field issues, things fit, electrical components sized correctly, etc..etc...

I am not saying to rant or complain. But this is a problem and needs to be brought to light.

 

[Teguci]

Here I am thinking, "Wow, you get equipment drawings that are stamped!"

Of course the work I do involves smaller devices (xrays, lights, medical booms...), but even small items need to be anchored properly to something. Even among structural engineers, this transition of information needs to be reviewed and, even better, typified. Not sure how though. But, most importantly, when someone calls the vendor asking structural questions, do not transfer that call to a sales person.

 

[JStephen]

A couple of other items to add here.
One, I wasn't trying to defend the original engineer's actions- he should be doing differently.

On this item: "The ME should design/detail all their ...design put it in a box and then hire a SE to tell them what that box is going to do..." That's great, if it can be done. Only if it can be done like that, there's not any reason for the manufacturer to round up an extra SE when there's already one working on the job. If that original item is just a big ol' cube of known weight and geometry, there's really not any reason to be getting seismic loads from the manufacturer. But where this falls down is the item also noted above, "You can't have things like pressure design for a vertical vessel be done independently of seismic or wind." So either the person doing the equipment design gets involved in the wind/seismic/gravity/etc loading, or an SE gets involved in the equipment design. Either can be done, either has been done, either will be done in the future. I can't speak for the original poster's equipment. But I will point out that I have a BSME and an MSME and in all that education learned diddly squat about pressure vessel design. So it's not necessarily the case that the ME involved knows some deep dark secret that SE's all missed out on. Any of you could do my job, it'd all work out fine, EXCEPT- you'd wind up stamping a bunch of "mechanical" drawings with an SE or CE stamp. Which, contrary to what you might think, is not necessarily improper, as the PE boards have their own ideas on these things.

Now, back to the original post, let me point out some of the things we run into. I design a lot of tanks per API-650. That design includes sizing of anchor bolts for internal pressure, wind, seismic, combinations thereof, etc. When you go through that sizing, you have 8 different load combinations to consider, and size using the worst case. The catch is that none of those 8 combinations match the load combinations used for ACI 318 concrete design, or the load combinations used in ASCE 7. So I can give you 8 different values of U, the design load for anchor bolts, and you still won't know the loads you need to apply ACI-318 App. D. Now, if you'd like dead load broken out specifically, I can do that, but that's not a required quantity anywhere in the tank design. And that doesn't represent any deficiency in the tank design, either. That may or may not be the kind of issue the original poster is running into. But that was why I advised, "Ask for the numbers you need, ask for the definitions you need, ask about the basis of the numbers if necessary."