Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
(OP)
Could anyone direct me to the formula for the calculation of Weff (effective section modulus) for a CHS. I need this and the Aeff (effective area) to perform a verification check for local buckling in accordance with BS EN 1993-1 and BS EN 1995-1. I have the following equations but no idea where they came from:
Aeff = A * [( 80*t / do) * (275N/mm-2 / fy) ]^0.5
Weff = Wel * [( 140*t / do) * (275N/mm-2 / fy) ]^0.25
Where:
A - area
Wel - elastic section modulus
t - thickness
do - outside diameter
fy - steel yield strength
Aeff = A * [( 80*t / do) * (275N/mm-2 / fy) ]^0.5
Weff = Wel * [( 140*t / do) * (275N/mm-2 / fy) ]^0.25
Where:
A - area
Wel - elastic section modulus
t - thickness
do - outside diameter
fy - steel yield strength






RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
Whilst as help to work a practical case of a pipe column under compression and uniaxial bending -biaxial can be vectorially reduced to it- with shear I post a printout of a Mathcad 2000 worksheet dealing with the problem, based in information in Galambos guide V. I may provide as well the zipped worksheet if interested, I lately provide mostly printouts because as pdf people has easier access to the content.
I have also a number of other worksheets dealing with related matters, most in setup closer to the american practice.
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
http://www.google.es/url?sa=t&rct=j&q=dnv-...
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
"sections of class 4 (slender) are those in which local buckling also inhibit the development of their elastic resistance capacity, and the yield strength cannot be reached in the extreme compression fibre."
"hence" use of effective section properties
"For slender sections of class 4, the reduction in their resistance capacity in ultimate limit states, as a result of local buckling, may be estimated using ideal effective sections ..."
(still trying to find the original source)
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
any reference to the formulas (present as you see in the BS 5950-1:2000, see previous image quote) is absent.
As you see, then, for Class 4 section, it refers to EN 1993-1-6, that again fails to quote the formulas.
BS EN 1993-1-1:2005
5.5.2 Classification
"Class 4 cross-sections are those in which local buckling will occur before the attainment of yield stress in
one or more parts of the cross-section.
(2) In Class 4 cross sections effective widths may be used to make the necessary allowances for reductions in resistance due to the effects of local buckling, see EN 1993-1-5, 5.2.2."
So one can argue that is what is made through the formulas, yet EN doesn't give any validation to such formulas, since absent.
In short, the formulas seem to never have been (nor in 2000 since not EN, nor in 2005 by absence of explicit quote in EN) part of the Eurocode specification, and by its use, even if someone can prove technically correct, one can't claim the check to be in accord to Eurocodes. Or, maybe, one can claim, but it can be arguably denied.
To claim that one is forced to follow EN 1993-1-6 (or EN 1993-1-3 if cold formed).
(EN 1993-1-3 is for plated structures and in this irrelevant to the case).
Now we can proceed to identify the origin of the equations, that seem be related to BS 5950 (or you can apport the precise origin of the same). I'll still pursue the matter to where I can.
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
(EN 1993-1-3 is for plated structures and in this irrelevant to the case).
should read
(EN 1993-1-5 is for plated structures and in this irrelevant to the case).
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
"For class 4 slender sections the effective elastic modulus Zeff ..."
so as of now we know your stated formulas were correct in a BS 5950 environment.
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
http://www.istructe.org/technical/files/young/TakM...
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
Some other interesting info
http://www.eagle.org/eagleExternalPortalWEB/ShowPr...
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
It is strange however that the Eurocodes that supersede this standard instruct you to use "effective area" and "effective section modulus" and yet there is no mention of the equations to do so (despite there being several looping references to where you should look - driving you round in circles between 3-5 and 3-1 and 3-1-6)
I have decided to use the BS 5950 equations and will do so until Eurocodes inform me otherwise. The only slight concern is that the equations are not valid for very large, very thin sections (and no alternative is provided, which may imply these sections are totally unsuitable for this use) Additionally, the classification of sections differs slightly between BS 5950 and BS EN 1993 and I am unaware as to whether this renders the equations inaccurate for certain cross sections.
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)
Respect the technical info provided by eurocode and what is expected from the designer, I started a thread in the design according to eurocodes forum. Essentially my position is that the code should only be mandatory for the items a solution is provided therein, which not always is the case; with that understanding and the code not providing, you would be justified enough to use the BS 5959 formulation -that is, if you don't find how to better proceed in EN 1993-1-6, which I doubt is the case, for there different modes of failure are treated and how to be combined them mandated ... eurocode then simply directs you to a more complex check, I think, but stills at least provides a "how to".
RE: Weff Effective Section Modulus for Class 4 CHS (Circular/Tubular Hollow Section) (Eurocodes)