Modelling a lamp post in FE, add load on a dummy element to add loads to lamp post.

I have done a FE of a lamp post to assess the secondary stresses at the connection between two of its tubes where there are high local stresses (due compatibility of deformation at the intersection between plates meeting at different angles). 

when I introduce an horizontal Uniform distributed loads on the plates (wind affect), I am able to run, the model and obtained results. However,  I do not manage to get the correct wind load on the cylinders wind front.

Now I wish to introduce the wind load in a different manner for all the  elements attached to the lamp post:  stem tube, signboard, speakers, luminary. 

I was thinking of using a 5 meter long dummy beam (say 10 mm solid cylinder) running he whole height of the FE model of the stem tube, with a dummy material of low E and Density, then apply different load cases on the dummy beam. Question is how to do this, I am getting errors: material does not have correct E, .....

I have attached the beam between two end nodes of the FE model of the stem tube. I have not provided internal restraining nodes for this beam, just only at its ends,,,, can this be improved?.

  • I am not sure if I fully understood the problem statement but seems like you are getting errors related to E values during analysis. Check if the values are consistent with the unit setting or not. May be E is becoming almost zero based on the value you entered and the current unit setting. Also connectivity between finite elements happen at the common nodes only and so if your dummy elements are just connected to the start and end nodes of the tube and are not connected to the intermediate nodes of the plate mesh, there are no connections at these intermediate locations and hence no load transfer.   



  • Sye, 

    Many thanks for the answer.

    Remaining of the Questions are:

    -In a dummy material, can the Density and/or E  be set up = 0, or very close to zero? 

    -Suppose I want to load a cylinder with a wind pressure of  1.0 kN/sqm (acting of the wind facing surface) , so total the load per meter length will be = wind pressure x diameter.I How can I add th wind pressure on the plates the tube so at the end I have an identical wind load per meter|?

    Many Thanks and kind regards

  • Density can be zero but E cannot be zero as that would lead to numerical instability. Try using E of 1/100 or at the most 1/1000 of the E used for the rest of the members.

    When modeling with plates, it is better to apply the pressure load directly on the plates (1 KN/m2). You can apply the pressure along the appropriate global direction.



  •  
    Sye
     
    Many thanks
     
    When applying the pressure, I will apply it to half of the circle, then I will check the reaction value to check wind load has been added adequately.
     
    Many thanks again
     
    Jose.
     
     
  • Dear Sie
     
    Many thanks for your support.

    Your said: “When modeling with plates, it is better to apply the pressure load directly on the plates (1 KN/m2). You can apply the pressure along the appropriate global direction.”

    I would like to report that it appears that there is an error in Staad results when we apply a uniform wind load on a tube on the general axis.

    I have done as follow: apply wind load on the section of the semi-cylinder (half of the cylinder), say 1KN/sqm

    I support tube only  in two nodes for easy addition of the reactions.

    I should be obtaining a load = Height of the cylinder (m) x Diameter (m) x 1.0 kN/sqm  = Hx|D

    Instead I am getting H x D x (Pi/2), which is much lurger. Therefore it seems that staad calculates the wind load as total area of the cell x wind load. Instead of calculating the force as the Projection of the area of the cell perpendicular to the wind x wind load.

    In a cylinder, some cells (plates) will be almost perpendicular to the wind, those will take lots of wind. In the extreme, the cells that are parallel to the wind should not take any wind load.

    Many thanks and kind regards
     
    Jose