The OpenSees Community

Thank you vesna!
Is there any script available so as to give me any idea of the procedure you are talking about?
Once again, thank you!

Dear all,
does anybody know if I can get an output file with the mass that is activated in each mode in a modal analysis?
Thanks in advance!

Can anybody explain to me what exactly the "corrotational truss" is?
What are the degrees of freedom that this element has?

Thanks!

Does anybody know how I can model rotational springs to the base of a structure?

Thanks a lot!

Vesna, thank you for your quick response.
Now, I'm dealing with another problem.
I want to perform a dynamic, time history analysis by considering the gravity load.
The gravity load is imposed as nodal load with the pattern Plain Linear.
Firstly, I run the gravity analysis. Then, I write on the script:
setTime 0.0
wipeAnalysis
and then I perform the dynamic analysis.
But, I think that the gravity load (which is nodal with the linear plain pattern) is still increasing for as much steps as the time series consist of.
Is there any way to elude that problem?
Thanks in advance.

Dear all,

I have modeled a soil-structure-interaction system and the soil is modeled with quad elements. The applied load is a time series with the following command:

pattern Plain $patternTag $tsTag {
load $nodetag
}

where the $nodetag is a node at the bottom of the soil profile. The command "equal" has been used in order to connect the degrees of freedom of all the nodes that belong to that level.

The time series response (accelerations and displacements) in the top of the structure are expressed in relative or absolute values?
I suppose that they are relative. Otherwise, the top of the structure develops lower acceleration than the interface of the soil-structure (!).

Thanks a lot!

Dear all,

I'm trying to simulate a soil-structure iteration system (ssi) but I have some questions concerning the boundary conditions of that problem.
I simulated the soil system as it is proposed in the site of opensees with the use of the quadrilateral elements and the dashpots.
"http://opensees.berkeley.edu/wiki/index ... nalysis%29"

Does anybody know if I should use other boundary conditions for the gravity analysis (i.e. to fix both the x and y directions of the base soil nodes with no use of dashpot) and other boundary conditions for the dynamic analysis (i.e. to fix only the y direction of the base nodes with the use of dashpot and the necessairy equal DOF for dashpot and base soil nodes) ?

Thanks in advance!

Dear all,

I'm trying to simulate a soil-structure iteration system (ssi) but I have some questions concerning the boundary conditions of that problem.
I simulated the soil system as it is proposed in the site of opensees with the use of the quadrilateral elements and the dashpots.
"http://opensees.berkeley.edu/wiki/index ... nalysis%29"

Does anybody know if I should use other boundary conditions for the gravity analysis (i.e. to fix both the x and y directions of the base soil nodes with no use of dashpot) and other boundary conditions for the dynamic analysis (i.e. to fix only the y direction of the base nodes with the use of dashpot and the necessairy equal DOF for dashpot and base soil nodes) ?

Thanks in advance!

Hi everybody!

In the command manual of Opensees-http://opensees.berkeley.edu/wiki/index ... er_Prager- the example of a brick element with the nDMaterial Drucker Prager gives the following note:
"the element is loaded until failure, at which point the model can no longer converge, as this is a stress-controlled analysis".

The model I use consists of 5000 stdBrick elements with the nDMaterial Drucker Prager subjected to a uniform excitation pattern with the duration of 40sec. But, the analysis can no longer converge at 1.16sec. Does this mean that the analysis fails to converge the moment the first failure of an element happens? And how can I solve that problem? In reality, the fact that one element fails doesn't lead to a structural collapse....

Thanks a lot!

Hello everybody!
I'm dealing with a problem concerning timehistory analysis.
I have used the SSPbrick element, the ElasticIsotropic3D nDMaterial, and the analysis parameters as follows:

constraints Transformation
test NormDispIncr 1e-3 15 1
algorithm Newton
numberer RCM
system ProfileSPD
integrator Newmark $gamma $beta
rayleigh $a0 $a1 0.0 0.0
analysis Transient
analyze $nSteps $dT

In order to check my model, I recorded the acceleration, the velocity and the displacement of a point belonging to the top of the structure. But the results are far from being realistic since neither the acceleration nor the displacement have the form I was expected to.
Is there any problem with the model parameters I've chosen?
If anybody knows, please let me know..!
Thanks.
P.S.I have checked the eigen analysis and is totally correct.

Here is my script with a sample of nodes, elements and fixities used:

# SET UP ----------------------------------------------------------------------------
#units: kN,m,ton
wipe; # clear memory of all past model definitions
model BasicBuilder -ndm 3 -ndf 3; # Define the model builder, ndm=#dimension, ndf=#dofs
set dataDir Data; # set up name for data directory
file mkdir $dataDir/; # create data directory
set GMdir "../GMfiles"; # ground-motion file directory
set motionDT 0.01; # time step in ground motion record
set pi 3.141592653589793
#-----------------------------------------------------------------------------------------
# 1. CREATE STRUCTURAL 3D NODES
#-----------------------------------------------------------------------------------------
# nodal coordinates:
node 1 6.149986303 22.92 2.999999998
node 2 6.15 22.92 3.3419867
node 3 5.137482879 22.92 3.341986699
node 4 7.162489728 22.92 3.341986699
node 5 8.174993152 22.92 3.3419867
node 6 9.187496576 22.92 3.341986699
node 7 4.124979455 22.92 3.341986699
node 8 3.11247603 22.92 3.341986699
node 9 6.14995575 22.92 4.133894602
node 10 5.137493931 22.92 4.133952976
puts "Nodes Defined"

fix 43 1 1 1
fix 45 1 1 1
fix 47 1 1 1
fix 49 1 1 1
fix 61 1 1 1
fix 63 1 1 1

puts "Fixities Defined"
nDMaterial ElasticIsotropic3D 1 1800000 0.25 2.243
nDMaterial ElasticIsotropic3D 2 1800000 0.25 2.535
puts "Material Defined"
element SSPbrick 1 287 483 484 6176 313 312 6188 6189 1 0 0 -22
element SSPbrick 2 175 5927 5757 1 177 176 3 2 1 0 0 -22
element SSPbrick 3 5904 175 1 5735 178 177 2 4 1 0 0 -22
element SSPbrick 4 5902 5904 5735 5733 179 178 4 5 1 0 0 -22
element SSPbrick 5 5900 5902 5733 5731 180 179 5 6 1 0 0 -22
element SSPbrick 6 5543 5900 5731 5400 5544 180 6 5401 1 0 0 -22
element SSPbrick 7 5927 5925 5755 5757 176 181 7 3 1 0 0 -22
element SSPbrick 8 5925 5923 5753 5755 181 182 8 7 1 0 0 -22
element SSPbrick 9 5923 5561 5418 5753 182 5562 5419 8 1 0 0 -22
element SSPbrick 10 177 176 3 2 184 183 10 9 1 0 0 -22

puts "Elements Defined"
#-------------------------------------------------------------------------------------------
# 8. DEFINE TIME SERIES
#-------------------------------------------------------------------------------------------
#---ANALYSIS PARAMETERS
# Newmark parameters
set gamma 0.5
set beta 0.25

# reset time and analysis
setTime 0.0
wipeAnalysis
#-----------------------------------------------------------------------------------------
# 5. RECORDERS
#-----------------------------------------------------------------------------------------

## record nodal displacments, velocities, and accelerations at each time step

recorder Node -file Data/L.top.displ.out -time -node 362 -dof 1 2 3 disp
recorder Node -file Data/L.top.accel.out -time -node 362 -dof 1 2 3 accel
recorder Node -file Data/L.top.vel.out -time -node 362 -dof 1 2 3 vel

recorder Node -file Data/L.bottom.displ.out -time -node 373 -dof 1 2 3 disp
recorder Node -file Data/L.bottom.accel.out -time -node 373 -dof 1 2 3 accel
recorder Node -file Data/L.bottom.vel.out -time -node 373 -dof 1 2 3 vel

recorder Node -file Data/thol.top.displ.out -time -node 1266 -dof 1 2 3 disp
recorder Node -file Data/thol.top.accel.out -time -node 1266 -dof 1 2 3 accel
recorder Node -file Data/thol.top.vel.out -time -node 1266 -dof 1 2 3 vel

# record stress and strain at each gauss point in the soil elements
recorder Element -file Data/Gstress.out -time -ele 154 stress
recorder Element -file Data/Gstrain.out -time -ele 154 strain

puts "Finished creating recorders..."

#-----------------------------------------------------------------------------------------
# 9. DEFINE ANALYSIS PARAMETERS
#-----------------------------------------------------------------------------------------

#---GROUND MOTION PARAMETERS
# time step in ground motion record
set motionDT 0.01
# number of steps in ground motion record
set motionSteps 4000
#---RAYLEIGH DAMPING PARAMETERS
# damping ratio
set damp 0.05
# lower frequency
set omega1 [expr 2*$pi*7.04]
# upper frequency
set omega2 [expr 2*$pi*11.09]
# damping coefficients
set a0 [expr 2*$damp*$omega1*$omega2/($omega1 + $omega2)]
set a1 [expr 2*$damp/($omega1 + $omega2)]
puts "damping coefficients: a_0 = $a0; a_1 = $a1"
#-------------------------------------------------------------------------------------------
# 9. DYNAMIC ANALYSIS
#-------------------------------------------------------------------------------------------
# create load pattern: apply acceleration to all fixed nodes with UniformExcitation
# define constant factor for applied acceleration
model basic -ndm 3 -ndf 3; # 3 spacial dimensions,3 DOF's per node
set cFactor 1
# define acceleration time history file
set accelerationFile 277_H1.col.asci.acc.txt
# timeseries object for applied force history
# command: pattern UniformExcitation $patternID $GMdir -accel $timeSeriesID
set mSeries "Path -dt 0.01 -filePath $accelerationFile -factor $cFactor"
# loading object
pattern UniformExcitation 10 1 -accel $mSeries
puts "Dynamic loading created..."
set nSteps 4000
set dT $motionDT
puts "number of steps in analysis: $nSteps"
puts "analysis time step: $dT"
# analysis objects
constraints Transformation
test NormDispIncr 1e-3 15 1
algorithm Newton
numberer RCM
system ProfileSPD
integrator Newmark $gamma $beta
rayleigh $a0 $a1 0.0 0.0
analysis Transient
analyze $nSteps $dT
puts "Finished with dynamic analysis..."
wipe

Vesna, thank you very much!

Hi!
I'd be grateful if anybody knows how the brick8N can be read by the opensees.
When I write the following script:

wipe;
model BasicBuilder -ndm 3 -ndf 3;

# nodal coordinates:

node 1 1 1 4
node 2 -1 1 4
node 3 -1 -1 4
node 4 1 -1 4
node 5 1 1 2
node 6 -1 1 2
node 7 -1 -1 2
node 8 1 -1 2
node 9 1 1 0
node 10 -1 1 0
node 11 -1 -1 0
node 12 1 -1 0

puts "Nodes Defined"

fix 9 1 1 1
fix 10 1 1 1
fix 11 1 1 1
fix 12 1 1 1

puts "Fixities Defined"

nDMaterial ElasticIsotropic3D 1 1800000 0.25 2.243

puts "Material Defined"

element Brick8N 1 1 2 3 4 5 6 7 8 1 0 0 0 0
element Brick8N 2 5 6 7 8 9 10 11 12 1 0 0 0 0

puts "Elements Defined"

I don't receive the final message "Elements Defined". But when I change the type of the brick element to SSPbrick everything is fine. Why is this happening?
Thanks!

Hi!
I have simulated a structure with brick8N elements by using a model BasicBuilder -ndm 3 -ndf 3. But, when I try to run the script, it posts a warning message: "WARNING NDM=3 and NDF=3 is incompatible with available frame elements". Just to notice that the only type of elements I have used is the one mentioned, the brick8N elements. Does anybody know what the problem is?
The second problem I'm dealing with has to do with the geometric Transformation of these elements. As the x,y,z are global axis, is the definition "geomTransf Linear 1;" sufficient?
Thanks!

I have a structure consisted of brick8N elements and I'm dealing with some problems...
1)Since I have defined the mass density (mass/volume) during the definition of the brick8N element, is it sufficient for the dynamic analysis?
2)Can I apply the gravity loads to these brick8N elements using the command "element surfaceLoad" with the pattern of "eleload"? And how about the self weight? Should I apply it manually, gradually increasing it to the bottom? Or is there any easier way? (my structure consists of 2500 brick8N elements...)
3)Are the axis x,y,z of these brick8N elements the same whether they belong to a "column" or a "beam"?
Thanks a lot!

How can I simulate the nonlinear behavior of an unreinforced masonry structure in a model of shell elements?
Is it adequate if I use the nDMaterial Drucker-Prager or should I use another material in order to take into account the constitutional law?
Is the "template Elasto-Plastic" material more proper?