Beam me up Scottie - I or H?
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Beam me up Scottie - I or H?
I always wondered this, but never asked anyone. I get that the names come from the sectional shape but what are the actual differences between an I beam and a H beam rod? Why would you want one over the other?
It's to do with maximum bending stress. To get the same strength at a lighter weight you have to satisfy a certain equation (I'll dig it out later). The key to the whole lot is the maximum distance from the neutral axis (I'll explain later) known as the I or Y value (depending on circumstance).
It all adds up that material can be removed from certain areas as long as you maintain the same second moment of area (Ixx, or radius of gyration, J, in a circluar type thing).
It's the same thing for why a hollow pipe used for a propshaft is as strong a solid bar at a smaller diameter and lighter too. In this case we take torsional stress and the radius of gyration, but it's the same basic equation.... :-s
No, that doesn't make much sense does it?
Well you did ask, now I have realised I forgot all that stuff and I'm going to have to go away and study it again so I can do all the calcs for the suspenion force path analysis
It all adds up that material can be removed from certain areas as long as you maintain the same second moment of area (Ixx, or radius of gyration, J, in a circluar type thing).
It's the same thing for why a hollow pipe used for a propshaft is as strong a solid bar at a smaller diameter and lighter too. In this case we take torsional stress and the radius of gyration, but it's the same basic equation.... :-s
No, that doesn't make much sense does it?

Well you did ask, now I have realised I forgot all that stuff and I'm going to have to go away and study it again so I can do all the calcs for the suspenion force path analysis

The extra expense might be to do with the manufacturing process? I beams can have a pretty simple die, but H-beams couldn't be extracted from a simple die due to their shape. They probably need either a multi-piece die with sliders etc, or maybe they do a lot of machining instead - either way it's more cost.
dunno, just a thought
I got H beams!
dunno, just a thought
I got H beams!
Gavin Chisholm - 414ci W2 Stroker SmallBlock Panther Pink '71 Challenger convertible - in bits
Car progress can be viewed here
Car progress can be viewed here
On second thoughts I won't be busting out the max bending stress equation....
I just got another bit of coursework which involves some truly filthy maths! Anyone know how to apply a second order differential equation to an indeterminant bending force?
Why couldn't I have done sport science?!? It's them that get this famous student lifestyle, not us poor engineering types.
I just got another bit of coursework which involves some truly filthy maths! Anyone know how to apply a second order differential equation to an indeterminant bending force?

Why couldn't I have done sport science?!? It's them that get this famous student lifestyle, not us poor engineering types.
Firstly; indeterminant is spelt indeterminate.
If I'm not mistaken I'd say it's a fairly simple case of involving the unknown function y, its derivatives y' and y'', and the variable x. Then use the "guessing" method, which will, of course, only work under the following conditions;
Condition 1: the associated homogeneous equations has constant coefficients;
Condition 2: the nonhomogeneous term g(x) is a special form.
Sorted, Down the pub!
If I'm not mistaken I'd say it's a fairly simple case of involving the unknown function y, its derivatives y' and y'', and the variable x. Then use the "guessing" method, which will, of course, only work under the following conditions;
Condition 1: the associated homogeneous equations has constant coefficients;
Condition 2: the nonhomogeneous term g(x) is a special form.
Sorted, Down the pub!
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The name is Kev, nowadays known as Kevvy or Pommie C***!</center>
The name is Kev, nowadays known as Kevvy or Pommie C***!</center>