Contents
Theoretical an practical examples for loads on our rails
This month you will ask yourself why I do bother you with food that is so hard to digest? Easy enough: I am planning to do some load tests on our rails. It would be interesting to see how big the gap bvetween theory and practice really is. I do not set my hopes too high, but if our calculations do coreespond to some extent with the test results we could revert them to other loading examples. We will see!
A trip into theory
We will start with an easy case in order to avoid calculations that would take up a few pages.

Force "F" is putting pressure onto the centre of the rail. At this very point the bend "f" is being calculated. The rail length is measured in "l"

Please see above an example which is commonly used in mechanical engineering. The related formula is:

This formula is used to calculate the bend at any part of the rail. We, however, are only interested in the bending at the centre of the rail. This slightly simplifies the the formula as follows:

We could get started if we only know the meaning of "E" and "ly".

"E" stands for the so-called modulus of elasticity. As this is a material constant and we know the material (aluminium), we also know "E".

The "E" of aluminium is 70,000 N/mm2.

And then we have "ly", the so-called moment of inertia which is entirely depending on the cross-section. As we do know our profiles (surprise,surprise), we also know "ly".

A practical example
As I have been talking more or less on general terms so far, I would like to present a practical example with profile 353.

We do know the value of "ly" is 420,895 mm4 for the rail 353.

If we now insert the known figures into the formula, it will lose some of its horror:


After we have added some calculation and cosmetics it will look like this:

The only unknown figures are therefore "l" and "F". This was our goal and we are now in a position to measure, individually for each type of rail, the bend under a certain load.

We want to verify the formula with the following example: We take a rail 353 with a length of 2m and center-load it with 50kg:

We may expect as a result that the 353 rail will bend by 2.8mm with a center-load of 500N (aro.50kg).
What will happen in practice?
I will have to put you on hold just a little bit until one of the next editions of aluNEWS, where I will present you a few practical tests.

Then we will know if theory will prove itself in real life or not.