Sectional properties for forceBeamColumn element: Required??

[tguha]

Hello,
I want to use a forceBeamColumn element as a beam through the use of an aggregator section for non-linear (dynamic) time history analysis of a structure. The aggregator section I use in the forceBeamColumn command in turn has six non-linear stress strain material models (Steel02) parametrically defined through Fy, E, b,R0, cR1,cR2,<a1 a2 a3 a4>,<sig0> in each of the six principal directions. However unlike the elasticBeamColumn element which requires us to specify sectional properties namely area (A), the moment of interia (Iy and Iz) as well as the torsional constant (J), these parameters does not seem to be required while defining the forceBeamColumn element [or the aggregator section]. The aggregator section has an optional argument for <-section $sectionTag> to include one previously defined section but as mentioned earlier this is optional. My question is then whether I am missing something or are the sectional properties really not required for defining such elements. Here is the sample code where I have defined two materials (as Steel02 material model), created an aggregator section using these material models in six principal directions and then created a forceBeamColumn element based on the aggregator section. But no where have I provided the sectional properties.

# Material "TorqueTubeSteel": matTag Fy E b R0 cR1 cR2 <a1 a2 a3 a4> <sig0>
uniaxialMaterial Steel02 4 +6.000000E+01 +1.115400E+04 +1.000000E-02 +1.850000E+01 +9.250000E-01 +1.500000E-01 +0.000000E+00 +1.000000E+00 +0.000000E+00 +1.000000E+00 +0.000000E+00

# Material "TorqueTubeSteel2": matTag Fy E b R0 cR1 cR2 <a1 a2 a3 a4> <sig0>
uniaxialMaterial Steel02 5 +6.000000E+01 +2.900000E+04 +5.000000E-02 +1.850000E+01 +9.250000E-01 +1.500000E-01 +0.000000E+00 +1.000000E+00 +0.000000E+00 +1.000000E+00 +0.000000E+00

# Section "TorqueTubeSectionAgg2": secTag matTag string ... -section secTag
section Aggregator 4 5 P 5 Vy 5 Vz 4 T 5 My 5 Mz

# Element "TorqueTubeNL": eleTag NodeI NodeJ NIP secTag geoTranTag <-mass massDens> <-iter maxIters tol>
element forceBeamColumn 741 405 406 10 4 1 -mass +0.000000E+00 -iter 10 +1.000000E-12 -integration Lobatto


Regards
Tushar Guha

[Toutant]

It's been a while since I've used OpenSees but I believe that the section Aggregator command is only used to assign materials to your section. In your case, you haven't defined the section yet. So before you assign materials via section Aggregator command you need to define the section itself. I would suggest you to discretize your section using fiber elements.

You're gonna want to look at these commands first :

-Fiber section command
-Patch command

Hope it helps and good luck.

[selimgunay]

You need to define a fiber section and assign defined materials to your section. Please see examples in this link

http://opensees.berkeley.edu/wiki/index ... er_Section

[parasismique]

Hi everyone,

I would need to confirm a few maybe obvious things about the incorporation of shear effect in existing beamColumn elements of OpenSees.
My question is related to section aggregator. I am modelling RC column using the fiber section. I am using nonlinear beam Column element with zero length element submitted to a effort axial.
I actually trying to use section aggregator is compatible (P, M, V or T)?
And why we used generally only the shear effect?
I would appreciate any help in this. Thanks!