Use of the word "conservative"
Use of the word "conservative"
(OP)
I recently had a senior engineer get rather miffed that I had used the word "conservative" on some foundation calcs that I did. He essentially said, "Think about what that word means. You're not being conservative; just say what you really mean."
I think what he's suggesting is that we often use the word conservative to imply that we're assigning values that we know to be too large (or too small, depending on the situation), when in reality we simply don't have an accurate handle on the "real" value. In other words, we're not actually being conservative; we're being purposefully broad to cover our lack of knowledge. Or something like that...
Any thoughts?
I think what he's suggesting is that we often use the word conservative to imply that we're assigning values that we know to be too large (or too small, depending on the situation), when in reality we simply don't have an accurate handle on the "real" value. In other words, we're not actually being conservative; we're being purposefully broad to cover our lack of knowledge. Or something like that...
Any thoughts?





RE: Use of the word "conservative"
What he states is not true all the time. Sometimes we can do an accurate solution, but due to the budget or to save the client money, we just "err" so to say on the "conservative" side. There is nothing wrong with that approach. What matters is knowing you are on the right side of the line.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Use of the word "conservative"
One other consideration is that you don't want to write the word on your calcs. That can have a liability implication. If you ever have a project go bad, your calcs and everything you have in the file will be meticulously mauled over to pick up on the nuances of why you did what you did. That word would stick out, since it really has no business on the page with the calcs. Your assumptions are what they are, right or wrong. Your "conservative" might be considered by someone more persuasive to be "non-conservative"....and they might be right. If so, the credibility of the rest of your calcs goes south.
RE: Use of the word "conservative"
RE: Use of the word "conservative"
As Ron points out, it is perhaps best not to write terms that can be construed by others in a different manner - yet, it is what we all do, isn't it?
Is one being conservative when he/she takes an umbrella out on a dark cloudy day? Mmmm
RE: Use of the word "conservative"
By that you express in qualitative terms what in more rigorous technical terms you would define 'upper bound', 'lower bound', upeer-or lower- fractile, first or third quartile, and so on.
I absolutely agree that we must have a verifiable idea of what is the mean value before saying that our value is conservative, that is erring on the safe side of an unknown amount.
In Eurocode 7 the adjective 'conservative' has been substituted by the adjective 'cautious' like in: ...The characteristic value is a cautious estimate of the value which governs the occurrence of a limit state..."
In litigation the big issue may be how cautious you should be in adopting a cautious value.
I'll stick to the statistical method of defining a cautious or conservative value since I believe it's the only one which is really defensible in court.
RE: Use of the word "conservative"
RE: Use of the word "conservative"
We typically use 'recommended' or 'it is our opinion' or if insufficient testing was undertaken to derive the parameters then we start the sentence as 'Although a limited amount of testing was undertaken...' or something in those lines.
We Geotechs are always conservative, it is the nature of our field/industry. You just need to find another way of expressing your conservative approach.
RE: Use of the word "conservative"
RE: Use of the word "conservative"
As engineers we try not to assume anything, but in reality there are many unknowns, and approximations. While we spent a lot of money/time/effort to reduce the unknowns it is not possible for us to eliminate them all. I think it's important to know what are the truths and what are assumptions in any analysis. Identifying them in the calc's may be okay, if you back it up and explain why it is conservative, or why the actual value is not available.
RE: Use of the word "conservative"
And no matter if you like to use conservative or liberal to show an added safety factor, it means liberal spending once it comes to construction.
RE: Use of the word "conservative"
Looking at the dictionary, one meaning is: 'Tending to give freely', which is not really a property that I like to have in my retaining wall designs :)
RE: Use of the word "conservative"
The smarter some Engineers think they are, the less safety factor (or conservatism?) they think they need.
[I guess we could substitute cheaper or weaker materials etc. in place of "safety factor" and still have the same basic meaning, and I am putting REAL heavy emphasis on the cogitative adjective employed!]
RE: Use of the word "conservative"
RE: Use of the word "conservative"
@reconner - correctomundo! Someday, an engineer (geotechnical, most likely oriented with dams) is going to be so smart, it collapses as he ponders his prowress over a glass of Laurent-Perrier's Brut Millesime champagne!