Fiber section and forcebeamcolumn element

[mhan40]

There are several problems when Applying Opensees Navigator:

1. If sections apply fiber section, elements apply forcebeamcolumn element, running program appears the following message:
ForceBeamColumn3d::ForceBeamColumn3d -- no torsion detected in sections, continuing with element torsional stiffness GJ/L = 1e+010

2. If sections apply fiber section, elements apply hingebeamcolumn element, running program appears the following message:
ForceBeamColumn3d::update - failed to get compatible element forces & deformations for element: 39(dW: << 1.05576e-012, dW0: 2.02867e-009)

problem: Whether fiber sections can’t be used in forcebeamcolumn, or the Opensees Navigator has bugs?

3. Considering concrete cracking, the initial stiffness of concrete beam and column needs reduction (EI needing reduction). When applying fiber sections, how to reduce EI in Opensees Navigator? If E is reduced, whether the analyses results will be affect?

Thank you to help solving and replying the problems.

[vesna]

1. When in 3D domain you need to define torsion for your section. As you did not assign any torsion to your section program did it for you.

2. Yes, you can use fiber section with forceBeamColumn element. The message you are getting tells you that the opensees could not find solution for element 39. This is not a bug in the code. There are several reasons for seeing this message. Brows the message board to find ways to fix it.

3. If assigning fiber section to element that accounts for distributed plasticity (e.g., forceBeamColumn), you do not need to reduce I. The element will do it itself.

[mhan40]

For matching the results of different experimental stages, the corresponding initial stiffness need to be reduced. Because the stiffness of different stages are smaller than the total cross section stiffness calcuted theoretically. How to implement stiffness reducation?

[vesna]

What element and section are you using? Different sections and elements will require different measures to achieve the goal.

[mhan40]

I am using Fiber Section and Displacement-Based Beam-Column Element. which measure is appropriate for stiffness reducation?

[mhan40]

how to define the torsion of section in Opensees Navigator? When applying fiber section, and forcebeamcolumn element, running program is always fail.

[vesna]

Displacement-Based Beam-Column Element with a fiber section assigned to it will account for stiffness degradation itself as it belongs to group of elements with distributed plasticity. Make sure to model one element with several DB BCEs. Use 3-5 integration points.

Torsion can be defined using section aggregator.