Corus blue book
Corus Design of SHS welded Joints
Corus SHS welding guide
I have also located a good source of stress / strain data for various steel, which is useful for enabling non-linear analysis to be carried out on the structure, i.e. crash simulation.
SINTAP report UC/07
Below is the true stress strain curve for S355J2 material as used for Corus Celcius 355 prosducts
True stress strain curve for S355J2 steel
This should allow details analysis to be carried out, (I use Patran/Nastran at work so have can use this for linear, non-linear and other analysis), hopefully there will be some interesting stuff to work out.
There are some more possibilities for sections in the Corus 'Precision tube' range, these are products designed for the automotive industrys which cover a wide range of sections and wall thicknesses. And more importantly come in a range of grades covered in under EN 10025, so S355 J2 should be an option.