Dear, I hope someone could help me

I’m modeling a 144 in OD tower of 1.14 in thickness as a pipe, carbon steel, with 35 mts height and an anchor at botton base. I don’t understand why in sustained and Hydrostatic cases the displacements in all levels are negative like if the pipe were shrinking, some suggestion to avoid this effect?. I wouldn't like to model the tower as a rigid in order to have a better visual presentation of the model. We use Caesar II version 5.2

Thanks in advance

What would you expect to happen ?

Although the column is steel, it's still elastic and presumably the 'shrinking' is the effect of gravity on the weight per unit length. Where contents weight is included (like hydrotest and in your case the water weight would be about 4x the metal), you need to be careful since contents weight is not really a unit weight active uniformly along the column, rather it all acts at the base. A similar problem arises with contents weight on vertical lines off pumps .... the contents weight in that case does not act on the pump flange and needs to be excluded from allowable load comparisons and spring designs.

If you set the Bourdon effect to 1 and include a pressure load, you may find a net upward movement due to pressure elongation.

Simple tension/compression calc on a straight "bar":

delta = PL/AE.

It is good practice to go back to basic "first principles" and perform a simplified comparison.

Thanks for the clarification