General Mechanical

General Mechanical

How to model a piled raft foundation in ansys workbench

    • manuksajan
      Subscriber

      I have tried to model a pile raft system using Ansys workbench. while doing transient structural analysis, I was unable to get correct results. Could you please give some suggestions on how to model, boundary conditions and do transient analysis under earthquake loading on soil domain.

    • 1shan
      Ansys Employee
      Please insert inline images describing your geometry, BC's and loading so that we can better understand the issue. Also add result images and tell us why you think its incorrect.
      Regards Ishan.
    • manuksajan
      Subscriber
      Dear Ishan Thankyou for a quick response. I will detail the issues i faced along with the images as attached.

      I have modelled a cuboid soil domain of dimension 28m x28mx16m, which has a raft foundation with four pile footings attached to it placed at the top center of the domain. All the materials was modelled as linear elastic material. Then, I assigned contact between pile head and raft bottom as frictionless. Further, a bonded contact between soil and pile lateral surface was provided.
      The soil cuboid bottom was kept fixed and all the lateral faces were assigned elastic supports (a foundation stiffness parameter was needed here, which was calculated as Youngs Modulus/Depth of soil).
      Then a sinusoidal acceleration of 1m/s2 with 1Hz frquency was applied on lateral left side in the x direction.
      Gravitational load was also considered.
      While running the solver Iam gettting an error as shown in the picture. However, the solution is obtained, but the acceleration values are not accurate. I am getting very low values than the input motion, where infact there should be an amplification when the wave travels through soil domain.
      I think the following reasons might have caused this issue The boundary conditions need to be designed as absorbing type boundaries so that they will not reflect the input waves and cause error in reading. I am not sure which type of boundary has to be assigned to get this.
      The type of contact that should be provided between the soil and pile I assigned may not be accurate.
      I was not able to assign the ground motion in the bottom face , because when I try to select the bottom face, i was only able to apply force in Z direction, but it should be assigned in X direction.

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