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

    • Saketh Bharadwaj Kopparthy

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

      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.

      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.

    • Ashish Khemka
      Ansys Employee

      Hi Saketh,

      It looks like after introducing foam you are getting convergence issues. Can you please share the snapshot of the solver output? It would be easier for forum members to comment.

      Also, please see if the following post helps you: Overcoming Convergence Difficulties in ANSYS Workbench Mechanical, Part I: Using Newton-Raphson Residual Information - PADT (



      Ashish Khemka

    • Saketh Bharadwaj Kopparthy

      Thanks for the reply @Ashish.

      Yes. I think after introducing the foam with frictional contact, the non-linearity of the model increased. I am attaching the solver output file in this Solver output file link and also a screenshot of the messages multiple errors and warnings.

      I also want to ask you if my approach is correct?



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