Meaning of Structural Integrity

".... like personal integrity, in that once it is lost it cannot realistically be reinstated"...

People should value personal integrity more. You can't just use it with wild abandon, with no regard for its conservation! You might need it for something really important one day. You'd better save up!

My initial thought was that this a a specious argument but then I realized that you are not considering a crash, but are thinking of normal operation. In that respect, I would include all parts that were considered to act for structural safety in the designing of the vehicle.

In crashes, some of the members are designed to fold plastically to absorb impact forces and allow the cage itself to stay intact.

You are correct. The question is about a typical used un-crashed vehicle.

The "all members are part of the structure" argument is a fairly obvious one, until you want to encompass the definition in a regulatory situation. So, for example if the rule is, "if a strcutural member has been damaged in a crash it cannot be replaced" the implication being that it can't be replaced properly, then perhaps not being allowed to replace bolted-on parts would be silly. and if bolted-on parts can be replaced, then can a part that is lightly spot-welded on (an inner guard perhaps) be replaced. Before you answer this, balance your rule for structure against common practice. And so the argument goes!

You point about folding plastically is understood completely. The real issue in the question is not the simple engineering stuff, but forming a policy/legal constuct in the middle or all of that which fits the real world. The vehicle has to be safe, standard good practice should be allowed, and the literal meaning of "structural integrity" has to stay within a literal interpretation of those words (which can be as tight as "any defect" or as loose as "does the job").

Having got your head around all of the conflicting possibiltiies (and corrosion is an issue as well as crash damage), what do you tihnk the definition haa to be to make a policy based on structural defintion for pass and fail need to be.

This is one for Justice Potter Stewart's "I know it when I see it".

My experience is with static structures, or, at least, I hope they stay still, and when they are damaged, the damage is reviewed, the new calculations are made to either qualify it or disqualify it. I know of no program that can suggest and test for, every conceivable damage in advance, it is only practical to "test" actual damage. Bridges are a good example, in some the damage is acceptable, in others, repairs are made and some are junked.

Perhaps the car makers should have their computer models and engineers ready to assess on a case by case basis.

The first check point in what you say above is whether you have a definition for "fail" or "pass" based on retaining "structural integrity", and if the form of this definition is like, "any defect......is a fail." or "defects until... structural integrity is impacted is a fail".

How hard the maths is, is another matter, and may or may not become important. No analysis is required with the former form of definition because any defect is ruled as "fail". Some analysis is required if the latter is used. This is the major decision point implicit in my original question. That and how far out the structure of the vehicle is considered to extend.

In the motor vehicle industry, at a practical level, one is likely to be guided by rule/s like X rust/damage here bad, Y rust/damage there OK, or "provide comprehensive calculations in this situation". As before, this assumes that the definition for "structural integrity" allows this to be entertained.

And remember, in my earlier posts there was the question, for example, of whether a damaged door skin (which plays a part in meeting side intrusion rules) was part of the vehicles structure, and then if it was, whether or not any damage to it should be allowed to be repaired (because one view is that any previous structural damage is an absolute fail, and the vehicle is to be refused forever).

I am not going off on some intellectual muse here. This is a real issue.