Stress Strain Recorder

[eapCLAROS]

Hello!

I am modeling a cantilever circular column using the fiber section approach. The element is being pushed by a horizontal force at its tip, oriented towards X+ direction, and has a constant axial load. The rebar layer is uniformly distributed throughout the perimeter (45 deg angle between rebars), such that one of the rebars coincides with Y+ local axis, and other one coincides with Y- local axis.

I would expect that the rebar located along the Y- axis experience tension (positive stress). However, when I plot the data using the stressStrain recorder I obtained the opposite (negative stress). The sintaxis I am using in the recorder is the following:

recorder Element -file $FileName.out -time -ele 1 -section 1 fiber -3.75 0.0 $matTagReinf stressStrain

Can anybody please help me?

Thank you!

[mhscott]

Do you get tension stress in that fiber when the axial load is zero? The axial load will put all the fibers in compression and the lateral load may not be large enough to put that fiber into tension.

[eapCLAROS]

Hello,

Thank you for your response.

I did a test using 0 axial load and I keep obtaining the same results. I am able to get reasonable results when I invert the orientation of the Y axis (with respect to this scheme for local coordinates https://opensees.berkeley.edu/wiki/inde ... tation.png) meaning that instead of putting the -3.75 coordinate, I put 3.75. I have not changed the positive external force in the X direction at the tip of the cantilever column.

Thank you again!

[mhscott]

Can you give more information about your model?
- 2D or 3D?
- type of element, e.g., forceBeamColumn?
- type of section, e.g., section Fiber or RCCircularSection command
- are you using a section aggregator?

[eapCLAROS]

** It is a 2D model and I am using 10 dispBeamColumn elements.

** I am defining the section as follows:
#Section 1
section fiberSec 1 {;
patch circ $matTagConcCSMA $numSubdivCircCore $numSubdivRadCore 0.0 0.0 0.0 5.0 0.0 360.0;
layer circ $matTagReinf $numBars1 $Asri 0.0 0.0 3.5 45 360
};

** I am not using the section aggregator option, only the fiber approach.

I think that the problem probably is the sign convention of the output. For example when you record a reaction, the output is opposite to the direction of the external force. Could it be the case for the stressStrain output that that is happening as well?

Thank you!

[selimgunay]

You probably solved it by changing the local y axis? What are the values for $vecxzX $vecxzY $vecxzZ when you get the correct sign?

[eapCLAROS]

I am not sure if I understand your question, but I am not changing those parameters. Since it is a 2D model I am defining the coordinate transformation as:

geomTransf Linear 1

[selimgunay]

According to this note, you would get compression at a negative y coordinate when the load is towards +X

NOTE: When in 2D, local x and y axes are in the X-Y plane, where X and Y are global axes. Local x axis is the axis connecting the two element nodes, and local y and z axes follow the right-hand rule (e.g., if the element is aligned with the positive Y axis, the local y axis is aligned with the negative X axis, and if the element is aligned with the positive X axis, the local y axis is aligned with the positive Y axis). Orientation of local y and z axes is important for definition of the fiber section.

[eapCLAROS]

Thank you! That solves my question. I appreciate your help!

[mhscott]

This might help explain local x,y,z for beam elements: https://wp.me/pbejzW-R5

Make z=[0,0,1] for 2D problems.