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Modelling stresses in anchor screws (cantilever beam and bolt pretension)

• Saketh Bharadwaj Kopparthy
Subscriber

Goal: I am trying to model stresses in screws, concrete block and deformation in rectangular pipe as shown in below image.

Geometry:
A concrete block with dimensions 400mm*400mm*150mm is the base. On the top of this concrete block, hardened foam of 30mm thickness is placed. On top of this foam, a steel flange of thickness 20mm is placed. A rectangular pipe is placed on top of the steel flange. The steel flange and foam are attached to concrete block using M12 Anchor screws.

Contacts:
1. Frictional contact between concrete and foam
2. Frictional contact between foam and steel flange
3. Frcitional contact between steel flange and bottom face of screw head
4. No contact between screw shank and steel flange or foam since the hole diameter is atleast 1mm bigger than the shank diameter
5. Below is the image of anchor screw. In real time, only the black part is in contact. So the surface of screw shank was split and the bottom 10mm was assigned as bonded contact (i.e., a simplified model)

6. Remaining screw shank inside the concrete block can be frictionless contact or frictional contact with small friction coefficient of 0.1.
7. Bonded contact between steel flange and rectangular pipe.

Boundary conditions:
1. Bottom most surface of concrete block is fixed support
2. Sides of concrete block are frictionless support to arrest movement of these surfaces in normal direction
3. Bolt pretension of 5kN on each bolt
4. A force of 18.75kN is applied on a surface as shown in the picture.

Application of bolt pretension boundary condition:
For each screw, a new coordinate system was created just for the screw shank part that goes through foam and steel flange. Now the complete screw body was selected in Geometry selection and the new co-ordinate system was assigned for each screw respectively.

The execution was performed in 2 steps. In first step, the screw loaded with 5kN and the force of 18.75kN is absent. In the second step, bolt pretension is locked and 18.75kN force was applied. This model ran for more than 4 hours on my laptop(8GB RAM, i5-4th Gen processor) and finally gave me a convergence error. Do you know how to fix this problem? What could be the problem in my model. A similar model without foam in between concrete and steel flange was modelled exactly same way and I got the result in expected range.

• Aniket
Ansys Employee

what are the errors that you got in the solver output? can you post images of convergence plots?

Please try searching for the convergence error and see if you find anything useful on the forum, if you don't you can paste the error here.

From description of the model it seems like foam material is too soft to bear the loads of bolt pretension, you can test the capacity of material in a single element model to see how much load that model can bear.

-Aniket

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