Rocking Mechanism for an A-Frame

[songwang]

Hi, everyone

I just learn to use OpenSees and try to model a rocking A-frame (Quincy Ma, 2005), however I encountered some contact problems for the rocking points.

First I used Elastic and Viscous UniMaterials to model the TMD only and it worked successfully. Then I try to model the whole A-frame by adding gap element for the compression-only spring. The script is shown below:

####################################################
model BasicBuilder -ndm 2 -ndf 3

# nodal coordinates:
node 1 0.5 2
node 2 0 0
node 3 0 0
node 4 0 0
node 5 0 0
node 6 0 0
node 7 1 0
node 8 1 0
node 9 1 0
node 10 1 0
node 11 1 0

# boundary conditions:
fix 4 1 0 1
fix 6 0 1 1
fix 9 1 0 1
fix 11 0 1 1

# nodal masses:
mass 1 680156.1 680156.1 0
mass 3 6801.561 0 0
mass 5 0 6801561 0
mass 8 6801.561 0 0
mass 10 0 6801561 0

# transformation
geomTransf Linear 1

#UniaxialMaterial
uniaxialMaterial ElasticPPGap 1 2.685e9 -1e20 0 0 # horizontal
uniaxialMaterial ElasticPPGap 2 1.032e9 -1e20 0 0 # vertical
uniaxialMaterial Elastic 3 1.132e9 0 # horizontal
uniaxialMaterial Elastic 4 9.509e9 0 # vertical
uniaxialMaterial Viscous 5 3.324e8 1 # horizontal
uniaxialMaterial Viscous 6 1.165e8 1 # vertical

# element connectivity
rigidLink beam 1 2 # rigid body
rigidLink beam 1 7 # rigid body
element zeroLength 1 3 2 -mat 1 -dir 1 # horizontal compreesion-only spring (left)
element zeroLength 2 4 3 -mat 3 5 -dir 1 1 # horizontal TMD (left)
element zeroLength 3 5 2 -mat 2 -dir 2 # vertical compreesion-only spring (left)
element zeroLength 4 6 5 -mat 4 6 -dir 2 2 # vertical TMD (left)
element zeroLength 5 8 7 -mat 1 -dir 1 # horizontal compreesion-only spring (right)
element zeroLength 6 9 8 -mat 3 5 -dir 1 1 # horizontal TMD (right)
element zeroLength 7 10 7 -mat 2 -dir 2 # vertical compreesion-only spring (right)
element zeroLength 8 11 10 -mat 4 6 -dir 2 2 # vertical TMD (right)

##########################################################################################
##########################################################################################

Then I try to apply gravity load to top node, apply initial displacement, remove the load and let it free vibrate, basically according to the OpenSees manual example "Simply supported beam modeled with two dimensional solid elements" Gravity Load and Free Vibration command scripts are shown below:

####################GravityLoad######################

# Load Pattern
pattern Plain 1 Linear {
load 1 0 -6665529.78 0
}

constraints Transformation
numberer RCM
system BandGeneral
test NormDispIncr 1.0e-6 6
algorithm Newton
integrator LoadControl 0.1
analysis Static

analyze 10
loadConst -time 0.0

# recorders
recorder Node -file Node1disp.out -time -node 1 -dof 1 disp
recorder Node -file Node1vel.out -time -node 1 -dof 1 vel

################################FreeVibration#################################

# Load Pattern
pattern Plain 2 Linear {
load 1 10 0 0
}

integrator DisplacementControl 1 1 0.1
test NormDispIncr 1.0e-6 6
algorithm Newton
numberer RCM
constraints Plain
system ProfileSPD
analysis Static

analyze 4

# Remove LoadPattern 2
wipeAnalysis
setTime 0.0
remove loadPattern 2

# Free Vibration
test NormDispIncr 1.0e-6 6
algorithm Newton
numberer RCM
constraints Plain
integrator Newmark 0.5 0.25
system BandGeneral
analysis Transient

analyze 500 0.1

###############################################################################
###############################################################################

However, when I run the GravityLoad, OpenSees shows me some errors in solver and iteration. I did encountered this kind of error before, that's due to my boundary condition mistake. But now, no matter how I revised the model, the GravityLoad still cannot run.

In addition, for the FreeVibration, I think there are some problems about nodal constraints with the two contact rocking points. When I run the FreeVibration, OpenSees shows me this:

"......constraint matrix not identity, ignoring constraint for node 2
constraint matrix not identity, ignoring constraint for node 7......."

Node 2 and node 7 are the two contact rocking points.

Does anyone have idea about where the problem is and give me some suggestions. I'd appreciate for your help. Thanks.

Song

[saeedjafari]

Hi
I have modeled a TMD in a 5 story 3D RC structure and I have carried out a Time history analysis of it. But the displacements are the same when there is no TMD. I will write down it's part of my scripts. Please helllllp me. thanks

# 5thstory

node 61 0. 17.5 0.
node 62 4. 17.5 0.
node 63 8. 17.5 0.
node 64 12. 17.5 0.

node 65 0. 17.5 5.
node 66 4. 17.5 5.
node 67 8. 17.5 5.
node 68 12. 17.5 5.

node 69 0. 17.5 10.
node 70 4. 17.5 10.
node 71 8. 17.5 10.
node 72 12. 17.5 10.

# Master nodes for TMD
node 82 4. 17.5 5.
node 83 4. 17.5 5.

equalDOF 66 82 1 2 4 5 6
equalDOF 66 83 2 3 4 5 6

uniaxialMaterial Elastic 4 173672604.0
element zeroLength 405 66 82 -mat 4 -dir 3 3
element zeroLength 406 66 83 -mat 4 -dir 1 1

*******
What is wrong with that????

[fmk]

in answer to the first post .. there are not enough constraints.

in answer to the second post .. can you ask the question again as i do not understand

[saeedjafari]

Dear fmk
When I run the model without TMD I get the results which are as same as the results when I run it without TMD. Do you think I modeled TMD correctly in my transcripts (the second post)?
Kind regards
Saeed

[mkcivilsepehr]

Dear fmk
I have the same problem please help as soon as you have time for that

[mkcivilsepehr]

Dear Saeed
I think you are using a ground motion to do time history analysis, which dose not lead to take your model in nonlinear area.

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