Reinforcement Cages

[Kiri Robbie]

Can Justin elaborate on the modelling of reinforcement cage such as connection between bars?  Is any collapse of reinforcement cage due to its flexiblity?

[Justin Smith]

Reo cages are truly horrible to model. 

The number one thing is to model the bars off set from each other or your model will develop too much stiffness. Also model the wire ties as pins. I also carry out tests of the wire tie connections for the particular steel fixer where possible so that some sort of number can be assigned to the ties. You cannot rely on the wire ties for direct structural reliability, but you cannot ignore them either - or you will end up with a very impractical design. 

I never worry about the displacement as long as the bars remain elastic. It is amazing how large the displacement can get before you start to yield the bars. I highly recommend going to site and watching a reo lift. It will show you what you can get away with in term of deflection and how accurate your modelling is. 

The big killer for reo cages is the joint strength. Failures on site that I have observed have been distortion/yielding of the 'church' bars (top lifters) owing to inadequate bracing and bar capacity and the welds/wire ties snapping owing to lifting chains binding and applying massive shear loads that were not allowed for. 

Good luck with reo cage lift design - do not under estimate it!