Shrinkage movements in slab with movement joints (Plate End Release)

Question:

I am trying to model a slab support on pile caps, built in stages. The slab is ~150m long so we are providing two movement joints - via plate edge releases (see boundary groups 'Base EJ GL11' and 'Base EJ GL6'). These are activated in the construction sequence as soon as the plates either side are activated.

This model previously had a lot more elements in - hence the redundant construction stages and load cases.

If you run the model and look at the longitudinal displacement dx you will see the issue - in all stages after the movement joints are activated. The three slab 'parts' separated by the movements joints should shrink individually - effectively towards their own centres of fixity. But instead they move as rigid bodies. The outer parts move over 100mm towards the centre of the model, not towards their own centres of fixity. This cannot be correct.

Could you please review and advise why this is happening, and how to fix it? We are progressing the design of this at the moment so this is very urgent.

Many thanks

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Answer:Hello,

It is preferred to not use plate end releases in such cases, as there is always a discrepancy related to displacement. Now, lets consider a common node between 2 plates at the plate end release location. This node should actually have 2 displacement values based on forces of plates on either side. Now, its not possible to consider this in finite element modelling. So, certain internal adjustments are done in the model so as to accommodate for this and it would seem like the behaviour is inappropriate.
Hence, as a solution, what I generally do is to use the elastic links. I remove the plates over a very small length and add the links with properties as required. Kindly refer the image below.

This is the behaviour as one would expect from such structure. Now, there would be 2 deformations, since there are actually 2 nodes and no internal adjustment or discrepancy. The link properties used in this case, to mimic the plate end releases, are as in the image below.

For plates Fx and My was released. Hence for the link, SDx and SRx are released. If the slab is simply supported, then SRy could be released. The links were added in appropriate construction stages, when the relevant plates were activated.