Local responses, forceBeamColumn vs. dispBeamColumn ?

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DKJung
Posts: 4
Joined: Wed Apr 22, 2015 11:13 pm

Local responses, forceBeamColumn vs. dispBeamColumn ?

Post by DKJung »

Hi all,

I am trying to run transient analysis for a RC cantilever column and check the local response (stress & strain) of concrete fibers at the bottom of the column where I can see the highest strain.
Here are some questions regarding it.

1. one forceBeamColumn element vs. several dispBeamColumn elements. Which one gives me more accurate local response (stress & strain)?
Is the recorder command below is the right approach to see the stress & strain of concrete fiber at the bottom of column?

I built the model using either one forceBeamColumn element or ten dispBeamColumn elements.
In terms of global response (Top node displacement), I can see the comparable behavior for both cases.
However, when I check the stress & strain of concrete fiber on section 1 of element 1 (bottom of column) using element recorder below, the responses were quite different depending on the element type I used.
The number of integration points for both cases were 5. I could see higher concrete strain when using forceBeamColumn element.

recorder Element -file Data/SSfib01sec01.out -time -ele 1 section 1 fiber [expr $coverY-$coverCol] 0 $IDconcU stressStrain;


2. The stress & strain of concrete fiber at the bottom of column differ significantly depending on the number of integration points when I used one forceBeamColumn element.
How can I choose the number of integration points to see the accurate local responses if I am using forceBeamColumn element.

Below is the script I used to built model for both cases in case you wondered. (node location & element only)

Thank you!



##### dispBeamColumn #####


# --------------------------------------------------------------------------------------------------
# Example 2. 2D cantilever column, dynamic eq ground motion
# Silvia Mazzoni & Frank McKenna, 2006
#
# ^Y
# |
# 2 __
# | |
# | |
# | |
# (1) LCol
# | |
# | |
# | |
# =1= _|_ -------->X
#

# SET UP ----------------------------------------------------------------------------
# units: kip, inch, sec
wipe; # clear memory of all past model definitions
file mkdir Data; # create data directory
model BasicBuilder -ndm 2 -ndf 3; # Define the model builder, ndm=#dimension, ndf=#dofs


# define GEOMETRY -------------------------------------------------------------
set LCol 432; # column length
set Weight 2000.; # superstructure weight
# define section geometry
set HCol 60; # Column Depth
set BCol 60; # Column Width

# calculated parameters
set PCol $Weight; # nodal dead-load weight per column
set g 386.4; # g.
set Mass [expr $PCol/$g]; # nodal mass


# nodal coordinates:
node 1 0 0; # node#, X, Y
node 2 0 50
node 3 0 100
node 4 0 150
node 5 0 200
node 6 0 250
node 7 0 300
node 8 0 350
node 9 0 400
node 10 0 $LCol

# Single point constraints -- Boundary Conditions
fix 1 1 1 1; # node DX DY RZ

# nodal masses:
mass 10 $Mass 1e-9 0.; # node#, Mx My Mz, Mass=Weight/g, neglect rotational inertia at nodes

# define geometric transformation: performs a linear geometric transformation of beam stiffness and resisting force from the basic system to the global-coordinate system
set ColTransfTag 1; # associate a tag to column transformation
geomTransf Linear $ColTransfTag ;
# geomTransf PDelta $ColTransfTag ;

# element connectivity:
set numIntgrPts 5; # number of integration points for force-based element
element dispBeamColumn 1 1 2 $numIntgrPts $ColSecTag $ColTransfTag; # self-explanatory when using variables
element dispBeamColumn 2 2 3 $numIntgrPts $ColSecTag $ColTransfTag;
element dispBeamColumn 3 3 4 $numIntgrPts $ColSecTag $ColTransfTag;
element dispBeamColumn 4 4 5 $numIntgrPts $ColSecTag $ColTransfTag;
element dispBeamColumn 5 5 6 $numIntgrPts $ColSecTag $ColTransfTag;
element dispBeamColumn 6 6 7 $numIntgrPts $ColSecTag $ColTransfTag;
element dispBeamColumn 7 7 8 $numIntgrPts $ColSecTag $ColTransfTag;
element dispBeamColumn 8 8 9 $numIntgrPts $ColSecTag $ColTransfTag;
element dispBeamColumn 9 9 10 $numIntgrPts $ColSecTag $ColTransfTag;





##### forceBeamColumn #####


# --------------------------------------------------------------------------------------------------
# Example 2. 2D cantilever column, dynamic eq ground motion
# Silvia Mazzoni & Frank McKenna, 2006
#
# ^Y
# |
# 2 __
# | |
# | |
# | |
# (1) LCol
# | |
# | |
# | |
# =1= _|_ -------->X
#

# SET UP ----------------------------------------------------------------------------
# units: kip, inch, sec
wipe; # clear memory of all past model definitions
file mkdir Data; # create data directory
model BasicBuilder -ndm 2 -ndf 3; # Define the model builder, ndm=#dimension, ndf=#dofs


# define GEOMETRY -------------------------------------------------------------
set LCol 432; # column length
set Weight 2000.; # superstructure weight
# define section geometry
set HCol 60; # Column Depth
set BCol 60; # Column Width

# calculated parameters
set PCol $Weight; # nodal dead-load weight per column
set g 386.4; # g.
set Mass [expr $PCol/$g]; # nodal mass

# nodal coordinates:
node 1 0 0; # node#, X, Y
node 2 0 $LCol

# Single point constraints -- Boundary Conditions
fix 1 1 1 1; # node DX DY RZ

# nodal masses:
mass 2 $Mass 1e-9 0.; # node#, Mx My Mz, Mass=Weight/g, neglect rotational inertia at nodes

# define geometric transformation: performs a linear geometric transformation of beam stiffness and resisting force from the basic system to the global-coordinate system
set ColTransfTag 1; # associate a tag to column transformation
geomTransf Linear $ColTransfTag ;

# element connectivity:
set numIntgrPts 5; # number of integration points for force-based element
element forceBeamColumn 1 1 2 $numIntgrPts $ColSecTag $ColTransfTag; # self-explanatory when using variables
fmk
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Re: Local responses, forceBeamColumn vs. dispBeamColumn ?

Post by fmk »

as your model is RC and i presume you have strength degredation probably NEITHER are accurate due to loss of objectivity .. more elements or integration points you throw at it does not improve convergence towards a solution .. look at the beamWithHinges (a force based element with fancy integration is disguise)

http://web.engr.oregonstate.edu/~mhscot ... E_2006.pdf
sghanaatpishe
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Joined: Mon Dec 08, 2014 10:27 pm
Location: university of science and culture

Re: Local responses, forceBeamColumn vs. dispBeamColumn ?

Post by sghanaatpishe »

Hello

i would like to know more about dispBeamColumn and forceBeamColumn and their formulations. could you recommend me some articles about these topics ?
fmk
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Posts: 5884
Joined: Fri Jun 11, 2004 2:33 pm
Location: UC Berkeley
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Re: Local responses, forceBeamColumn vs. dispBeamColumn ?

Post by fmk »

the manual has a lot of references for the force beam column:
http://opensees.berkeley.edu/wiki/index ... mn_Element

the displacement beam column is your standard finite element formulation in which a displacement field assuming linear curvature and constant axial deformation is assumed between the ends, resulting deformations along length can be obtained and using integration the stiffness and resisting force is determined.
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