troubles with steel01

[yairbcn]

Dear all,

I am modeling with steel01, and I have noticed that depending on the value I give to the parameter b, I obtain two changes of slope in the graphic force-deflection instead of 1. That happens if b is bigger than 0.025 approximately.

Can somebody explain me why? or if there is some problem with the code or something?

Here is my code, if you plot reaction you will see that there are two changes of slope.


Thank you all so so much!



# SET UP --------------------------------------------------------------------------------------

wipe;
model basic -ndm 2 -ndf 3;
file mkdir Data;

# DEFINE GEOMETRY-------------------------------------------------------------------------------

set L 160.; # Lenght of the column

node 1 0 0;
node 2 0 $L;

# BOUNDARY CONDITIONS---------------------------------------------------------------------------

fix 1 1 1 1;

# MATERIAL PROPERTIES---------------------------------------------------------------------------

set A 4.06;
set Iz 5.14;
set E 29000000.;
set b 0.04;
set Fy 65000.;
set Vy 65000.;
set My 12500.;


uniaxialMaterial Steel01 1 $Fy [expr $A*$E] $b
uniaxialMaterial Steel01 2 $My [expr $E*$Iz] $b
uniaxialMaterial Steel01 3 $Vy [expr $E*$Iz] $b


# NODAL MASSES---------------------------------------------------------------------------

set WCol [expr $L * 119.6];

mass 1 [expr $WCol/2] 0. 0.
mass 2 [expr $WCol/2] 0. 0.


# DEFINE ELEMENTS---------------------------------------------------------------------------

set transfTag 1;
geomTransf Linear $transfTag;

# CONECTIVITY---------------------------------------------------------------------------

# Define section

set secTag 1;
section Aggregator $secTag 1 P 2 Vy 3 Mz;

# Define elements

set numIntgrPts 5;
element nonlinearBeamColumn 1 1 2 $numIntgrPts $secTag $transfTag;


# DEFINE RECORDERS------------------------------------------------------------------------------------

recorder Node -file Data/RBase1.out -time -node 1 -dof 1 2 3 reaction;
recorder Node -file Data/Disp13.out -time -node 2 -dof 1 2 3 disp;


# DEFINE GRAVITY------------------------------------------------------------------------------------

pattern Plain 1 Linear {

load 2 0. 2000. 0.
}

constraints Plain;
numberer Plain;
system BandGeneral;
test NormDispIncr 1.0e-8 6;
algorithm Newton;
integrator LoadControl 0.1;
analysis Static;
analyze 10;
loadConst -time 0.0;


pattern Plain 2 Linear {

load 2 1. 0. 0.
}

integrator DisplacementControl 2 1 0.01;
analyze 1000;

puts "Done!"

[vesna]

In general your model is good and the response you are getting makes sense. The only thing I would not agree with is that the shear stiffness is EI. It is rather proportional to AG.

For your definition of moment-curvature and shear force-deformation relationships there will be two points of slope change: one that comes from moment-curvature relationship and another that comes from shear force-deformation relationship. If you push your column up to a larger displacement but for the smaller "b" you will also see another change of slope. Change b to 0.01 and increase number of steps of analysis to 2000 and you will see two slopes as well.

[yairbcn]

Thanks so much, but I am not very sure how to avoid it then.

[vesna]

Why do you want to avoid it? If your shear force deformation is realistic that is how your element is going to behave.

[borjiajia]

vesna wrote:
> In general your model is good and the response you are getting makes sense. The only
> thing I would not agree with is that the shear stiffness is EI. It is rather proportional
> to AG.
>
> For your definition of moment-curvature and shear force-deformation relationships
> there will be two points of slope change: one that comes from moment-curvature relationship
> and another that comes from shear force-deformation relationship. If you push your
> column up to a larger displacement but for the smaller "b" you will also see another
> change of slope. Change b to 0.01 and increase number of steps of analysis to 2000
> and you will see two slopes as well.

----------------------
What do you mean by"The only thing I would not agree with is that the shear stiffness is EI. It is rather proportional to AG."? If not, how to define the Vy

[vesna]

shear stiffness is proportional to AG, not to EI as he modeled.