Let me start by saying I am new to Robot. I am attempting to reinforce an existing truss, which has been found to fail under new loads. Part of what I would like to do is use steel panels to connect the chords, verticals, and diagonals on the ends of the truss- essentially making the ends a plate girder with the diagonals acting as ribs.
I have drawn up the truss, as it currently exists. I created A36 Steel panels that are defined as the individual spaces between verticals and chords. When I analyze this result, I end up with a huge shear stress acting on the lower chord of my truss. In other words, it doesn's appear to be properly distributing the shear load through the panels and both the top and bottom chord, as it should for a plate girder.
Is there a way to have the shear loads tie all the way through the top to the bottom chord through the panel? I am also see this same issue with the last diagonal that I am tying my panels to.
Solved! Go to Solution.
Solved by Artur.Kosakowski. Go to Solution.
Please attach a model and screen captures/ sketches that show what you get and what you would like to get.
Artur,
Thank you for your response. My Robot file and an image showing my concern are below. The image is showing the results for shear stress. Under these conditions, both the diagonal where the panels end and the bottom chord are failing due to shear. However, I want the panels to run web to web between my chords and diagonals. So, this shear load should be taken from top chord to bottom chord and through the panels (like a plate girder with wide plange beams for flanges)., meaning the shear stress should be greatly reduced through this section. Is there a way to make Robot behave in this manner?
Robot file:
1. I think that you wanted to define ry releases rather than rz (to relase rotations in the plane of the truss). Mind that they are defined in the local coordinates of bars.
2. I have generated coherent meshes instead of using kinematic constrains
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Artur,
Thank you for catching my mistake on the release. It looks like you've fixed the problem I was having with the chord behavior. However, when I look at the verticals, I still see a large shear stress where the panel ends (the -20.2 pictured). I believe these should be acting in the same manner as the chords. Where, although a large shear load goes through this region, it is absorbed by both the web and the panel.
Note, I removed one of the panel sections from the model. So, from the one you linked, it would be the diagonal just beyond the failing vertical that would be of main interest.
Thanks again. I really appreciate your help.
As far as I can see this matches the distribution of stresses in the panels. Perhaps you could consider another way of connecting posts and diagonals with chords (with ry releases).
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