Dual lined shaft with openings

[ElizabethHoney]

Hello, 

I am trying to model a concrete shaft with an internal radius of 4.5m. There are two linings of the shaft - each 250mm thick and constructed of C40 concrete. the linings are designed to work together and give a total thickness of 500mm. there is a 1.7m deep mass concrete base slab.  

The outer lining will be loaded by hydrostatic forces only. 

A circular opening of 2m radius will then be made in the internal lining, just above the base slab. Once this is completed, the opening will be extended through the second lining also. 

I need to be able to compare the stresses in the outer lining at each stage - I.e. with no opening, with an opening in the internal lining and then with an opening through both linings. 

I have attached the model I have constructed so far. the linings are made from a revolved rectangle and the base is a cylinder. When I calculate the model, I am not getting sensible results for the stresses in the outer lining. 

I have tried several ways of constructing the model such as extruding circles and modelling the linings as panels and I have tried different ways of combining the objects, as suggested in other posts, but cannot seem to produce a sensible mesh and set of results. 

Could anyone offer advice on how to make this model work?

Many thanks.

[Artur.Kosakowski · Accepted solution]

The openings are going to be difficult. I would try these steps modelling the linings as shells (panels):

Phase 1:

1. Definition of the circular base of the inner lining with set number of divisions e.g. 36

2. Definition of the circular base of the outer lining with the same number of divisions 

3. Extrusion of both circles with the same number of divisions

4. Meshing

5. Connection of nodes with rigid links (or dummy bars)

Phase 2

1. Deleting elements 'inside' the opening in the internal lining with manual change of positions of nodes so that they match the edge of the opening

Phase 3

1. Deleting elements 'inside' the opening in the external lining with manual change of positions of nodes so that they match the edge of the opening

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[ElizabethHoney]

Thank you Artur,

After calculating my model, the stresses seem slightly higher than expected. 

I have the layer for stresses set to the default setting of middle. 

I need to calculate the hoop stresses in the outer lining and so am using the principle S1 value. is this a correct assumption?

[Artur.Kosakowski]

At first you may want to set the projection as Direction Z (assuming that the shaft is vertical) and check 6yy stresses. The middle layer for the initial check is I think OK as in this way you avoid to have the influence of some local bending.

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