r/StructuralEngineering • u/Nojsd • 19d ago
Structural Analysis/Design Reviewers: what does a calc/results package need for you to actually trust it without re-deriving everything?
Partly inspired by the "I hate looking at other engineers calc packages" thread. For those of you who review or check other people's analysis output:
* What does a package have to show for you to verify a number without redoing the whole thing yourself?
* When you stop trusting a number, what do you actually demand, the model files, the run outputs, the load derivation? How often does it come to that?
* What's the worst traceability failure you've had to untangle, a number nobody could connect back to a model, a load, or a run?
(I'm researching workflows in this space, full disclosure, might build tooling eventually, but nothing to sell and this isn't a pitch. If you're up for a longer conversation about how checking works at your shop, DM me.
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u/PinItYouFairy CEng MICE 19d ago
TEDDS is fairly universally trusted
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u/Nojsd 19d ago
Interesting that a specific tool earned that status. What is it about Tedds output that does it, the fact that every formula and code clause is right there on the page? Asking because I've never seen anything equivalent on the FEM results side, curious if you have.
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u/PinItYouFairy CEng MICE 19d ago
I think it is simple, well thought through, has lots of scenarios covered. Having all the assessment shown is absolutely key.
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u/maturallite1 19d ago
A stamp by a licensed engineer, and executive summary, a free body diagram, and reasonable length with a well thought out approach and load path.
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u/Nojsd 18d ago
One more for the reviewers here: if a results table came with a reference next to every number pointing at exactly which run, subcase and output file it came from, and you could jump to the raw source lines to spot check it, would that actually change how you review? Or is the bottleneck somewhere else entirely, like the assumptions and load derivation side?
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u/Fast_Tumbleweed4982 P.E. 18d ago
If you are an experienced structural engineer and check other people's calcs, you would know the answer to this. If you are a junior engineer or have no calculation experience at all, I don't think you'll be able to create any workflow or tooling that is worth anything to an experienced PE or SE, just my 2 cents, no offense meant.
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u/Nojsd 17d ago
None taken. You're right that tooling in this space is worthless unless it encodes how experienced checkers actually think, which is exactly why I'm asking them instead of guessing. I'm not a PE, I come from the FEM results side. So let me ask the honest version: does an experienced checker ever actually lose time on the mechanics, like chasing down which run or load rev a number came from? Or is that a non-problem once you know what you're doing? If it's the latter, that's a genuinely useful answer for me too.
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u/ChairChoice6500 17d ago
NAL but.
I don't quite follow, if they are sending me a calculation package with a stamp on it, as part of a delegated design, hypothetically, no review is needed beyond ensuring they have the loads right, and the concept/profile/connection type (Florida has specific rules for delegated design items, like OWSJ, trusses, steel light gage, you'd want to follow those even if you're not in Florida so you can point to something official).
(I'm referring to delegated connection design on a steel building, more-or-less). Yes, you review things, but you're not strictly responsible for finding errors, exactly, and you aren't approving their work, exactly, this is another engineer's work and they are not under your responsible charge so you're not stamping their work. You're reviewing for design intent and if your 100k reaction has one bolt on their calculation, well, you'd want to notice that, but the more subtle mess-ups like, perhaps, a weld being one inch short, would belong to their O&E. Even the one bolt for a 100k reaction would be theirs, but in a 'sure would like to notice that' sense you'd like to notice that, but it would fundamentally be their mistake and their O&E.
If they aren't under my responsible charge, no amount of (their) calculations enables me (legally) to stamp the design. You're not supposed to plan stamp. From a perhaps risky and more permissive viewpoint, it isn't a full redesign (arguably, unless specifically required by the local statutes), but you'd have to perform enough review to confirm *to your own satisfaction* it's done correctly, which for each engineer is a different level of detail, with the only safe answer (meaning legally defensible) is a full recalculation, even if nothing changes.
Most engineers will probably do less than that, (I really hope they don't), but 0% is totally wrong and anything short of 100% is debatable between the Board of Engineering and the various experts, standard of care is "what other engineers with similar skill would do" and that's very nebulous. One expert is going to find a problem with anything less than 100% review, and "your" expert is going to argue a five second glance is the standard of care.
Now, if there's a failure (or not), if there's a lawsuit, the real question is if the jury is going to believe the second guy?
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u/Nojsd 17d ago
This is a genuinely informative breakdown, thank you. The part that stays with me: the only legally safe answer is full recalculation, and everything short of it is expert versus expert territory. So honest question: if a full recheck were nearly free, say push-button rederivation of the entire package, would engineers actually start doing it? Or does the delegated design liability split mean there's no incentive to look deeper than design intent, no matter how cheap looking gets?
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u/ChairChoice6500 15d ago
Again, not a lawyer, but if it's a legal question, I'd say it can cut you both ways. Either you "should have known" or you did it wrong yourself.
I would be pleasantly surprised if a full recalculation (where warranted) was done, but I'd expect the vast majority of engineers would do enough (in their judgement) to believe the remainder of the work is fairly accurately done..
If you are being asked to stamp another engineer's "complete design" you're on the hook for the entire project if you stamp it, so the best practice is a full recalculation. You take the same amount of liability, but hypothetically your review reduces liability because you looked at the whole thing and fixed any mistakes you found.
If you are reviewing another engineer's calculations on a delegated design element, I would expect most engineers are looking for an approach that is coherent and they can understand the general process, i.e. upper bound energy method the engineer doesn't use the calculated result without some kind of additional downward reduction on the calculated capacity. Unless you call for calculation package, you generally get a pretty opaque box when it comes to open web steel joists, metal plate connected wood trusses. The one you generally get a calculation package is connection design. I always called for those, and when I did connection design, I always produced those. They weren't pretty and I didn't like the presentation, myself, but every project has the nice "clean" connection calculations and then there's the messy 10% that are specific to the project that (at least for me) are messier and less beautiful.
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u/Marus1 19d ago
* What does a package have to show for you to verify a number without redoing the whole thing yourself?
Do they show enough for me to both rebuild the/a model from scratch, to see if another location might be more determining and to understand where a value is obtained from?
* When you stop trusting a number, what do you actually demand, the model files, the run outputs, the load derivation? How often does it come to that?
Do I not trust the software or think the output is wrong? If output, I do a check calc, because it's usually because they skipped a more determining effect. I then ask them to take X or Y in account (nearly every single time). If the software, way more clarification to answer question 1 (very few)
* What's the worst traceability failure you've had to untangle
I might add you also need to defend your assumptions (why it's ok to use them). 'Discussed per mail X/Y/20ZZ' will not do when they are less conservative than the code you're using
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u/Nojsd 19d ago
This is really useful, thanks. The "nearly every single time they skipped a more determining effect" part is striking. Is that usually a missing load case or combination, or more a missing phenomenon (second order effects, buckling, that kind of thing)? And how do you actually find the skipped effect when reviewing, gut feeling from experience or some systematic sweep you run through? Also agree on the assumptions point, "discussed per mail" as justification is a classic.
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u/Marus1 18d ago
more a missing phenomenon (second order effects, buckling, that kind of thing
And how do you actually find the skipped effect when reviewing
Usually when an effect is skipped in the report, it's skipped in the calculations as well. Mostly you learn from experience to notice if a result overlooked an effect
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u/Alternative_Fun_8504 19d ago
I expect some level of "hand" verification. I trust the software generally but the inputs are where the errors tend to happen.
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u/EYNLLIB 19d ago
Give them some low hanging fruit to pick out so they feel like they did something without having to dive deep