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Term to express compliance with code requirements
2

Term to express compliance with code requirements

Term to express compliance with code requirements

(OP)
What term/method do you use to express compliance with code rules?
My company has been reporting results as a "Factor of Safety", which I've been asked to stop doing.

Example:
Allowable deflection is 4mm. Calculated deflection is 3mm, so this requirement is met. Separately, the code also requires a "Factor of Safety" is 1.5 vs yield.
What is a good way to express this deflection compliance mathematically?

4/3 = 1.33 ... What can I call this term? "Factor of Safety" is something else, reviewer gets confused as it is less than the 1.5 he knows he needs.

I ran across "Margin of Safety", which apparently is used in aerospace and nuclear applications, but also apparently has a couple different definitions. I checked with some of my reviewers and they have not come across this term. They also haven't told me what they want...
4/3 -1 = 0.33 "Margin of Safety"?

I don't want to invent a new term ("Margin of Compliance"). Surely there must be a commonly used term? Thanks!!




RE: Term to express compliance with code requirements

"factor of safety = 1.5 vs yield"

so you know the allowable yield stress (tension or compression) ?
you know the maximum stress in your component ?

the factor of safety of your component is maximum stress/yield stress (which should be greater than 1.5 to meet the requirement), needs to be >1 for a safe design

the margin of safety = factor of safety - 1, needs to be +ve (>0) for a safe design.

Quando Omni Flunkus Moritati

RE: Term to express compliance with code requirements

Why do you feel the need to coin a phrase for something that can be expressed clearly and unambiguously in plain language?

Quote:

The calculated deflection is 3 mm. This is less than the allowed maximum of 4 mm. Therefore this is compliant to the code requirement.

RE: Term to express compliance with code requirements

(OP)

Quote (rb1957)


the margin of safety = factor of safety - 1, needs to be +ve (>0) for a safe design.
So you use the term "Margin of Safety" in your work?
See en.wikipedia.org/wiki/Factor_of_safety for the two definitions I came across; yours looks like the first. This isn't exactly what I'm looking for, as it is factor of safety and not the code compliance I want to show. But it would still be better than reusing the "factor of safety" term. Hmm...


Quote (MintJulep)


Why do you feel the need to coin a phrase for something that can be expressed clearly and unambiguously in plain language?
Exactly! I do not want to make a new term. I want to know if the above 1.33 number (or alternative) has a name that people use. A term other than "Factor of Safety", which would be confusing as it also means something else.

RE: Term to express compliance with code requirements

factor of safety shows design compliance. in your case if the factor of safety > 1.5 then compliance is shown, granted FS < 1.5 is non-compliant but not obviously so; you'd need to make that statement after the calc.

the other approach is to factor your allowable ...
allowable material stress = 45ksi
allowable compliance stress (that includes the required FS = 1.5) = 30 ksi (= 2/3 of material allowable)
applied stress = 20ksi
factor of safety (inexcess of required 1.5) = 1.5 (30/20)
margin of safety (over required compliance minimum FS) = 0.5

another is to factor your calculated stress ...
applied stress = 20ksi
include compliance required FS = 1.5, factored applied stress = 30ksi
allowable = 45ksi
factor of safety (in excess of required 1.5) = 1.5
margin of safety (over required compliance minimum FS) = 0.5

it depends on how well readers understand the compliance required 1.5 factor. in my business when we say "ultimate" load, you know it has a 1.5 FS built in. it should? be clear enough if you clearly factor your calculated stresses (or material allowables) to include your compliance FS, calc MS based on these, include a statement that MS calculated include compiance required minimums.

Quando Omni Flunkus Moritati

RE: Term to express compliance with code requirements

Compliance is black and white, yes or no, so in mathematical terms, 1 or 0. The clearest way to present the information is to simply show the minimum required value, then show your calculated value for the design. Percentages, factors, margins, will just confuse the issue. The more familiar someone is with the calculations, the more confusing it will be for them to figure out what you are trying to say. Then when you explain exactly what your factor/%/margin means, people with a less detailed understanding will get confused.

Max allowable deflection: 4mm
Calculated deflection: 3mm

RE: Term to express compliance with code requirements

KISS and less is more.
If you have to ask the question, then there it is open to interpretation. Therefore as 1gibson, Mint and others state, use plain language.

RE: Term to express compliance with code requirements

Also, in the example cited, I don't that that 4/3 = 1.33 has a valid physical interpretation.

RE: Term to express compliance with code requirements

Tolerance?

RE: Term to express compliance with code requirements

Got plenty of fudge factor in their so no worries mate.

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RE: Term to express compliance with code requirements

x% of alllowable limit

RE: Term to express compliance with code requirements

"Allowable deflection is 4mm. Calculated deflection is 3mm, so this requirement is met. Separately, the code also requires a "Factor of Safety" is 1.5 vs yield."

re-reading it sounds like the code is saying "do your analysis with 150% loading" (what we call ultimate loads) so you embed that factor of safety in your analysis. then you do your analysis and calculate the deflection (sounds like it'll be 4.5mm). then you compare with the allowable (the deflection requirement, or yield strength, etc).

Quando Omni Flunkus Moritati

RE: Term to express compliance with code requirements

(OP)
Hey guys, thanks so much for weighing in on this. I really appreciate all the different points of view. Let me see if I can express them in different terms:

1. Such a term that I am looking for is not often used, and has not been an issue for many/most engineers.

2. "Factor of Safety" is the name for a result, allowable stress divided by calculated stress; even if a different factor of safety/safety factor is included in the final result. (My reviewers frown upon this double definition, and are asking me to not do this).

3. "Margin of Safety" is a different way to express Factor of Safety. (While it is a different term, it's definition still uses the term "Factor of Safety", and does not avoid problem in #1)

4. No need to coin a new phrase, as it can be explained in a sentence. (Analogy: This round red fruit is an Apple. We don't have a name for this yellow fruit, so please just call it "yellow moon shaped fruit".)

5. "Margin of Safety" can be defined as in excess of requirements. (This would work, but am hesitant to use due to it having multiple definitions, and "safety" not being inherently very clear)

6. Compliance is black and white, percentages etc are not needed, hence this term is not needed. (This number can be very helpful if you are considering engineering time and build cost. If my part calculates to have a FOS of 4.5, and I need 1.0, I might not need to spend much more time on it. If it is an expensive part then I will want to look closer. I can understand this may be a non-issue for all industries.)

7. FOS/MOS/MOC is not applicable to values other than stress. (Why not stiffness, buckling, weight, etc? This number allows the same advantages as #6. Perhaps poster is only used to the term FOS to mean stress. Which should be absolutely fine, because ideally that term should only mean one thing. This suggests that we need another.)

Maybe I'm just really thick skulled, but I'm starting to think using "Margin of Compliance" might not be a bad idea. My stab at a definition...

"Margin of Compliance": Percentage by which calculated results exceed requirements. Anything 0 or above is acceptable.
MoC = requirement/result-1 (for allowable minimums)
MoC = result/requirement-1 (for allowable maximums)

RE: Term to express compliance with code requirements

So, using your original example: Allowable deflection is 4mm. Calculated deflection is 3mm

and your new definition: MoC = result/requirement-1 (for allowable maximums)

MoC = 3/4 - 1 = -.25

Not a vary satisfying number.

Imagine that you present this calculation and result in a design submittal. The reader's reaction is going to be "What?"

Your submittal is rejected. You need to revise it. Or you need to explain it, then revise it anyway.

How it that better than simply writing "Allowable deflection is 4mm. Calculated deflection is 3mm. We comply."?

No questions, no revisions, no wasted time.

RE: Term to express compliance with code requirements

"2. "Factor of Safety" is the name for a result, allowable stress divided by calculated stress; even if a different factor of safety/safety factor is included in the final result. (My reviewers frown upon this double definition, and are asking me to not do this)."

first, we include the required by our regulations by defining two types of loads, with clearly understood differences.
Limit load is the maximum load expected, calculated.
Ultimate load includes the required FoS of 1.5 = limit load*1.5
so you can include required FoS within the definition of the load.

second, use your calculated load, derive your FoS and compliance is shown if greater than the required FoS. you can state either
calculated FoS exceeds minimum required
or continue the calculation and say the FoS over the required (FoS/1.5) or the margin of safety to the required (FoS = 1.5) as (FoS/1.5 -1)

third, as we'll do when including a factor that may or may not be buried inside the calc. an example for us is the "fitting factor", some fittings need it, some may, some won't; so if it's included in the calc the MS is annotated "FF inc".

personally I'd turn the question back to the reviewers "how do you want me to express this ?" (two reviewers will probably give you three opinions !) or look at reports they've written, or consult your company standard.

Quando Omni Flunkus Moritati

RE: Term to express compliance with code requirements

btw, I've seen FoS calculated for fatigue lives !?
= calculated life / required life ... don't like it myself but I'm not going to fuss it.

Quando Omni Flunkus Moritati

RE: Term to express compliance with code requirements

(OP)
Doh I wrote it backwards, to be recorded as so for eternity. Thanks for pointing that out!

"Margin of Compliance": Percentage by which calculated results exceed requirements. Anything 0 or above is acceptable.
MoC = result/requirement-1 (for allowable minimums)
MoC = requirement/result-1 (for allowable maximums)

Simia purpuram disco fullonibus

RE: Term to express compliance with code requirements

Googling "margin of compliance" yields many results, so you are not coining a new term. The first page has a few links to automotive emission testing information.

RE: Term to express compliance with code requirements

i thought we started with showing compliance is a binary (yes/no) thing ?

another day in paradise, or is paradise one day closer ?

RE: Term to express compliance with code requirements

We use Demand Capacity Ratio (DCR). It is used in any cases requiring comparing a required value and a provided value, e.g., force, stress, deflection, temperature, dimension, and etc. When DCR > 1, the checks indicate non-compliance.

RE: Term to express compliance with code requirements

coefficient of fear

RE: Term to express compliance with code requirements

Don't confuse safety factor with compliance to code, or margin over breaking point.
Safety factor is often understood to be that margin over breaking point, but typically it is not even that. Few things actually break at "allowable stress", which often includes other safety factors in itself, perhaps based on brittleness of the particular material it is composed of.
Some things are not functional, even though design code provisions are exceeded. 4mm deflection may be fine for a bridge beam, but not for a patio deck floorboard. Neither will probably fail, just not comfortable to walk on.

It may be preferable to define the condition as some percentage over or under a design requirement, be that requirement defined by code, or by what you consider as adequate for mission functionality.

you must get smarter than the software you're using.

RE: Term to express compliance with code requirements

The way our company handles this is to analyze loadings and then calculate the minimum material condition that would meet the code requirements along with a simple statement of that requirement.

For example, wellhead equipment designed to API 6A may include:

DESIGN STRESS INTENSITY (Sm) = 32500 PSI
MIN. ALLOWABLE YIELD STRENGTH (Sy) = 48750 PSI (BASED ON Sm ≤ (2/3)Sy PER API 6A)

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