Simple Structural question, about section properties
Simple Structural question, about section properties
(OP)
Can someone plese tell me whether an angle, i.e. a L shape has a plastic neutral axis. Because I have just used a program which gave ( second moment of areas ) Zpl,x & Zpl,y, as both equal to 0 ?






RE: Simple Structural question, about section properties
This is in metric - but you can search for others:
http://www
RE: Simple Structural question, about section properties
However, you didn't read the question properly.
The question is, do angles have a plastic neutral axis, in addition to an elastic neutral axis ?
RE: Simple Structural question, about section properties
Look in the site below, under Beams -> Cross sections -> Angles : you'll get what you are looking for. However only plastic neutral axes locations along geometrical axes x,y are given.
prex
http://www.xcalcs.com
Online tools for structural design
RE: Simple Structural question, about section properties
I can see that the person that has written that small program has included the plastic nuetral axes.
But this really still doesn't proove that they are permissable for use in angles.
I was really wondering if the codes of practice, in the USA, or Europe, allow angles to have a plastic Z value ?
Thanks again.
RE: Simple Structural question, about section properties
What prex showed in the link is that you would have a geometrical axis (x,y) and AISC also describes principal axis - both of which can be applicable based on the nature of the bending and bracing.
RE: Simple Structural question, about section properties
Check out this link, it was the first site in a Google search...
http
Look toward the bottom.
RE: Simple Structural question, about section properties
Referring to the Australian Code AS4100, the plastic section modulus can only be used if the section is compact (ie. element slenderness limits are not exceeded). There doesn't appear to be any limitation on shape.
I can't speak on other Codes.
RE: Simple Structural question, about section properties
RE: Simple Structural question, about section properties
That is indeed what I am asking !
Any shape can have a plastic neutral axis, and therefore a plastic Z value ( second moment of area ), but the question is, is it valid to use it for the case of angles.
RE: Simple Structural question, about section properties
Most handbooks do not give a Z value for angles because it is not standard practice to design angles and other non-doubly symmetric shapes for plastic moments. It it very difficult to ensure stability though the whole range of plasticity of such a shape.
It's hard enough to get yielding at the extreme fibre (S) for non-symmetric shapes...
By the way, Z is the first moment of area, and I is the second moment of area.
Z = sum [area x (distance of the centroid of this area to PNA)]
The plastic neutral axis is sometimes also called the equal area axis - you have equal cross-sectional area above and below it.
tg
RE: Simple Structural question, about section properties
RE: Simple Structural question, about section properties
Hope this helps.
RE: Simple Structural question, about section properties
thanks for your comments, they were all worthwhile !
I have definately learned something from this thread.
Rob.
RE: Simple Structural question, about section properties