General Mechanical

General Mechanical

Tension and Bending results from Static Structural

    • myvue
      Subscriber

      Hello everyone,


      This is a very basic/embarrassing query, and may also bring my structural mechanics knowledge into question, but here it goes.


      I have performed Static Structural on a concrete structure (which is quite complex). For my solution, I used total deformation and max/min principal stress. Is that correct? Because I read that for a brittle material like unreinforced concrete, Principal Stress failure criterion holds.


      But how do I find the the places and magnitude of tension forces and bending on the structure? Is the positive maximum principal stress equal to the maximum tension (and the negative maximum principal stress equal to compression)? But then, what about the minimum principal stresses (positive and negative)?


      Also, I need to find the places (or magnitude) where the bending takes place. I tried using 'bending stress' component, but for some reason it does not seem to work.


      I know these are very basic question, but your clarification would be extremely appreciated. Thank you. 

    • Wenlong
      Ansys Employee

      Hi myvue,


       


      Let me make sure if I understand correctly:


      1. You want to get the reaction force and moment on the structure. To do this you can do a probe of the boundary condition and find out the values.


      2. You want to know the relationship between principal stress and "tension stress". The principal stress does not have to be one positive(tension) or negative(compression). If you plot the Mohr's circle you will find out. 


      3. For members with bending, you can see a stress variation in the member and you can find high bending members by checking that, for example, the following image shows a contour plot of principal max stress. 




      4. The beam stress is specifically for shell and thin solid: https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v201/en/wb_sim/ds_sh_bend_str.html?q=bending%20stress


       


      Regards,


      Wenlong


       



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    • myvue
      Subscriber

      Hello Wenlong,


      Thank you for the elaborate reply. I appreciate it.


      I modified my analysis, and instead of using solid geometry, I am now using line geometry and therefore beam elements. The 'Direct Stress' result that you get from beam tool, is the positive direct stress = tensile stress (and negative direct stress = compressive stress)?


      Also, there is an option to evaluate axial force, but what about normal force. Can normal force be evaluated?

    • peteroznewman
      Subscriber

      Yes, direct stress is axial in the beam and tensile is positive, negative compressive.


      You can use a Probe > Beam > Axial Force on the results.  You can also probe Shear Force.


      I don't know what you mean by normal force.

    • myvue
      Subscriber

      So if the direct stress values are all negative, does it mean that it is completely under compression? If so, then why do I still get bending stresses throughout the structure (without any tension)?

    • peteroznewman
      Subscriber

      Yes, it is under compression and bending at the same time. Those two stresses are computed independently.  The combined stress from the axial direct stress and the bending stress is unsurprisingly called Combined Stress on the Beam Tool. Refer to the definitions below. Referring to Wenlong's excellent diagram using tension, the Maximum Combined stress will be reported from the top of the beam.



      But if the axial force was changed to compression, then the Minimum combined stress would be on the bottom of the beam.


      Use the ANSYS Help and in the Mechanical User's Guide, you can look up the Beam Tool and find these definitions.




      • Direct Stress: The stress component due to the axial load encountered in a beam element.




      • Minimum Bending Stress: From any bending loads a bending moment in both the local Y and Z directions will arise. This leads to the following four bending stresses: Y bending stress on top/bottom and Z bending stress on top/bottom. Minimum Bending Stress is the minimum of these four bending stresses.




      • Maximum Bending Stress: The maximum of the four bending stresses described under Minimum Bending Stress.




      • Minimum Combined Stress: The linear combination of the Direct Stress and the Minimum Bending Stress.




      • Maximum Combined Stress: The linear combination of the Direct Stress and the Maximum Bending Stress.



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