Construction tolerance - Definition of "Permitted Deviation"

[castleMadrid]

NSCS Guidance, 10.1 states that the permitted deviation (Δ) are generally twice the deviation, as the values are given as both plus and minus numbers, except where separate plus or minus values are given.

EN 13670, 3.13 deifines permitted deviation (Δ) as the permitted algebraic differences between the limits of size and the corresponding reference size. Adding that it is adapted from ISO 1803:1997, 3.8. Unfortunately, I don't have a copy of this standard.

Do the above statements mean that if permitted deviation, Δ = 50mm,
a) Δ = +25/-25, or +30/-20, or something in that order, or
b) Δ = +50/-50.

Thanks for your valued help.

 

[BigInch]

just reading what you wrote,
NSCS: Some problem there. How can [Δ] = 2 x +[Δ]? What exactly does it say. Please quote it exactly.

How I view this,
NSCS: If tolerance is given +25mm and -25mm +[Δ], it means from a reference size, Reference size being the size noted on the drawing, or the size of an object you are trying to duplicate.

ISO: Means the deviation can be from a reference size noted on a drawing or the size of a reference object, up to, or down to, a number = absolute value of [Δ], simply doing the math algebraically (remembering the sign), up to +[Δ], or down to -[Δ].

The way I see it is that they both mean exactly the same thing.




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

 

[castleMadrid]

Thanks BigInch. Here is what exactly the code says:

NSCS Guidance, 10.1: "the permitted deviation are generally twice the deviation, as the values are given as both plus and minus numbers, except where separate plus or minus values are given"

EN 13670, 3.13: defines permitted deviation as "permitted algebraic differences between the limits of size and the corresponding reference size. This is adapted from ISO 1803:1997, 3.8"

"Algebraic difference" for me means that if Δ = 50mm, then the tolerance must be +25-(-25) = 50. Therefore my view is (a).

also,

EN 13670,3.22 defines tolernace as "difference between upper limit of size and the lower limit size". And again qouting ISO 1803:1997, 3.11 "Tolerance is an absolute value without sign, it is however commonly expressed by "the sum of the ± permitted deviation" so that the value of the tolerance is implicit"

I am just surprised to see another very experienced Structural Engineer saying (b) +50/-50 and it shook by long understanding of tolerance.

 

[BigInch]

I still don't understand why NSCS would say D=2D, but I would still say it means +/- 25mm from the reference size. If a tollerance spec has different lengths to the high and low sides, it is always stated exactly in each direction, such as +10mm, -5mm

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

 

[castleMadrid]

Thanks.
NSCS calls "permitted deviation" = Δ, and so
a) Δ = (Δ/2) + (Δ/2) according to NSCS and Δ = (+Δ/2)-(-Δ/2) accroding to EN 13670 <- correct!
b) Δ ≠ (Δ) + (Δ) <- wrong!