Dynamic analysis under bidirectional earthquake

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aaataha
Posts: 9
Joined: Sun Oct 13, 2019 1:44 pm

Dynamic analysis under bidirectional earthquake

Post by aaataha » Sat Aug 22, 2020 12:22 pm

Hi,

I am carrying out dynamic analysis on a 3D RC structure with fixed supports using a bidirectional earthquake. When I extract the straining actions of the base columns at the base section, i get no moments about the x and y axes. why is that? All frame elements are modeled using the dispBeamColumn element.

0.01 -911.536 -0.00131958 -0.00140777 0 0 9.01374e-011
0.02 -911.533 0.0122507 0.0126421 0 0 3.09545e-010
0.03 -911.524 0.0807038 0.0822782 0 0 -3.18308e-008
0.04 -911.51 0.230929 0.236235 0 0 5.27547e-007
0.05 -911.484 0.451771 0.469283 0 0 5.57384e-006
0.06 -911.449 0.69925 0.740998 0 0 2.22992e-005
0.07 -911.408 0.922459 0.998208 0 0 4.31111e-005
0.08 -911.359 1.08531 1.19794 0 0 5.99747e-005
0.09 -911.302 1.18016 1.32252 0 0 8.05646e-005
0.1 -911.238 1.23188 1.38825 0 0 9.47996e-005
0.11 -911.169 1.30013 1.45313 0 0 0.000100139
0.12 -911.089 1.47798 1.61717 0 0 0.000122112
0.13 -910.992 1.84486 1.97374 0 0 0.000167999
0.14 -910.863 2.43329 2.57278 0 0 0.00026348
0.15 -910.695 3.2199 3.40495 0 0 0.000683585
0.16 -910.484 4.12743 4.39641 0 0 0.00344265
0.17 -910.218 5.06711 5.43825 0 0 0.00809269

selimgunay
Posts: 808
Joined: Mon Sep 09, 2013 8:50 pm
Location: University of California, Berkeley

Re: Dynamic analysis under bidirectional earthquake

Post by selimgunay » Sat Aug 22, 2020 12:27 pm

This looks like a simply supported boundary condition. I would recommend checking the boundary conditions for the bottom nodes of your columns.

aaataha
Posts: 9
Joined: Sun Oct 13, 2019 1:44 pm

Re: Dynamic analysis under bidirectional earthquake

Post by aaataha » Sat Aug 22, 2020 12:34 pm

selimgunay wrote:
Sat Aug 22, 2020 12:27 pm
This looks like a simply supported boundary condition. I would recommend checking the boundary conditions for the bottom nodes of your columns.
This is the command I used for the boundary conditions

fixY 0.0 1 1 1 1 1 1

aaataha
Posts: 9
Joined: Sun Oct 13, 2019 1:44 pm

Re: Dynamic analysis under bidirectional earthquake

Post by aaataha » Sat Aug 22, 2020 1:00 pm

i figured out the problem. It is because i defined the element recorder like that:
recorder Element -file Results/Force11111.out -time -ele 11111 section 1 force

But once I deleted the "seciton 1" part, the results are reasonable. But I still don't understand what the results at the section mean?! I though the stresses are integrated along the section and the forces are given exactly as when recording the element response without including the section in the recorder!

mhscott
Posts: 444
Joined: Tue Jul 06, 2004 3:38 pm
Location: Corvallis, Oregon USA
Contact:

Re: Dynamic analysis under bidirectional earthquake

Post by mhscott » Sat Aug 22, 2020 2:08 pm

The section force output is P Mz Vy My Vz T
axial force, moment about local z, shear along local y, moment about local y, shear along local z, torsion
Was my answer helpful to you? https://www.buymeacoffee.com/mhscott
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Michael H. Scott, Ph.D.
OpenSees blog: www.portwooddigital.com

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