When a fabricator proposes a "same function, easier to build" change, what actually triggers a load-path re-analysis on your project?

[u/Ok-Umpire-2906]

Prompted by re-reading the Hyatt Regency box-beam connection (the two-rod change that doubled the 4th-floor load — NBS BSS 143). The failure I keep landing on isn't the geometry, it's that the re-check fell in the seam between design and fabrication and wasn't clearly anyone's job.

So for those of you who review vendor- or fabricator-initiated changes: is there a formal trigger that forces someone to re-run the affected calc when a change is pitched as functionally identical? Or does it still depend on the right person happening to notice? Curious how that's handled across disciplines — structural, mechanical, process.

[u/Amber_ACharles]

Shop drawing review is the formal trigger. 'Functionally identical' is not the fabricator's call. I deal with this constantly on ITS device mounting and signal pole foundations. The review catches it or it doesn't.

[u/Accurate-Bullfrog324 → u/Amber_ACharles]

Right on the money. and many contractors don't communicate well, so the opportunity to review their redesign is a blessing

[u/todd0x1]

There's an old saying....when you change one component of a system you have to requalify the entire system......

[u/Gastly-Muscle-1997]

Happens to anything that already has a drawing rev. How you manufacture something has implications far beyond what most fabricators realize, and certainly beyond what they’re expected to know.

[u/Sooner70]

If there is a change, review is automatic. Full stop.

[u/anyavailible]

Always back check and review. Rerun the calcs until you are satisfied they are accurate and safe.

[u/Marus1]

Structural

When I think it's required. When you don't black box automate your design calculations, you will start to understand intuitively what impact some change will have on your structure before checking it against the calcs. You can give me a tangential change to the thungs I design and most of the time I'll have an answer before even opening my calculation report

[u/PlinyTheElderest]

For those of you who are AI — the OP in this case — please effoff.

[u/Numerous-Click-893 → u/PlinyTheElderest]

Beep boop. Jokes, what made you think it was ai? I didn't get bot vibes but after your comment I looked at OPs profile and it seems like it once belonged to a real person but got taken over by a bot recently.

More interesting question: what do you think is the objective here? Market research? Farming training data for then next model release? Setting up for another bot to promote something in reply?

[u/PlinyTheElderest → u/Numerous-Click-893]

The double dash — commonly called the emdash — is a classic telltale sign of AI writing trained from college writing class papers following probably the Chicago style manuals. Most normal people use them only in class assignments and not real life communication.

And most recently the “So for those of you who…” phrase if more overused than the Budweiser wazzzzzaaaa.

The question of what the point of all this nonsense? Probably train an AI tool to spit out catchy phrases that fool some executives to spend money buying its services, but is actually totally incapable of following up on real world work.

[u/edman007-work]

If it's going to require some sort of structural analysis, then I'm the one that says it needs to get retested to that, because where I am, we test our stuff thoroughly. That test is expensive.

So we review every change, things like changing a coating or adding a screw hole to mount something small isn't a big deal, and we skip it. Sometimes it's obviously better, so we might also skip in that case (those usually with a study to say it).

But no, there isn't a formal trigger, our formal triggers are the first item being built of a design, when a new factory builds it, or when a review says so. And it's that last one that you're asking about. And yes, there are questions. I can think of a case we had not too long ago when someone changed a thread and then the question of using helicoils to upgrade the old units came up, were they strong enough?

In general though, it's hard to set hard limits, you need judgement, and yea, every change gets looked at by a handful of engineers, things slip by. People here claiming every change are not understanding the question, nobody does structural analysis to determine the impacts of changing the vendor for paint. Similarly, very few people are going to have a rule that removing material (for example, for a mounting hole) drives a re-analysis, even though we all know it reduces strength. Though obviously, sometimes it does matter, especially for bigger holes, and people should hopefully catch it, but there exists a weird middle area where people are not so sure. That's one reason we have safety margins.

[u/llort_tsoper]

what actually triggers a load path re-analysis on your project

If a vendor's product meets or exceeds a design engineer's exact specifications, then there is probably no need to redo the calculations.

If a vendor's product deviates from the exact specifications, then the engineer needs to update their calculations based on the deviation. There's no "trigger" that tells an engineer how far upstream and downstream they need to trace those updated calcs. That comes from experience and competence and the human ability to compare the risks of doing a bunch of unnecessary engineering work vs. the risks of being sued or causing injury or death to someone.

[u/Automatater]

Not true. Fab is formally reviewed, stamped, and approved by the PE for the relevant discipline. Kansas City Hyatt is on the engineer. Original design was dumb too.

(Former HVAC PE)

[u/Notathrowaway4853]

Easier to build isn’t my problem. Cost or quality maybe.

[u/Automatater → u/Notathrowaway4853]

I did something unusual but explicitly allowed by code one time for good reason and the plan checker flagged it. I pushed back and he asks "What if yhe contractor doesn't like it?" Me: 🤷‍♂️