wrong Initial stress at top of element quadUP

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jaimercado
Posts: 13
Joined: Sun May 22, 2016 5:57 pm
Location: Universidad Nacional de Colombia

wrong Initial stress at top of element quadUP

Post by jaimercado »

Hi all

Currently, I am working with a Four_Nine_QuadUP element and the Pressure Depend Multi Yield 02 material. While i am doing the gravity analysis of a single quadUp element, the top nodes (i.e., node 3, 4 and 7) have a "effective stress" different to zero, which obviously those nodes should have the stress as zero, and the bottom nodes (i.e., 1, 2 and 5) have a effective stress different to the expected one. Curiosily, if you sum the stress at node 1 and at node 3 up, you came up with the real effective stress that the bottom should have.

Surfing on the web, i found that several examples (http://soilquake.net/opensees/94QuadUP/index.htm) have the same "issue".

Why do you think this is happening?

Thanks in advance...

Jaime M.
:D
jinlu
Posts: 47
Joined: Fri Jul 14, 2006 5:50 pm
Location: UC San Diego

Re: wrong Initial stress at top of element quadUP

Post by jinlu »

The stress is recorded at Gauss integration points, not at nodes. Four_Nine_QuadUP element employs 3x3 Gauss integration scheme. Please check a Finite Element textbook for the Gauss point locations. Also, in Four_Nine_QuadUP element, the order of the Gauss points is not the same as that of element nodes, e.g., Gauss point 2 (or material point 2 in recorder) is not near the corner of node 2. --Jinchi
jaimercado
Posts: 13
Joined: Sun May 22, 2016 5:57 pm
Location: Universidad Nacional de Colombia

Re: wrong Initial stress at top of element quadUP

Post by jaimercado »

Thanks very much! You are right!.
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