Best element to model viscous damper

[rmandok]

I want to model a brace like viscous damper and As i read other posts it is said that best materials to model this kind is to use truss or zerolength element. I have couple of question about this:

1-I want to model viscous damper with K=1.9e6 (N/m) and Cd=4.0e5 (N.s/m) and alpha=0.6 . I used both truss and zerolength element but since an area should be defined for truss element, the results are quite different. In this case what should I do?
2- since I defined brace like damper from bottom of left column to top of right column, is it necessary to define orientation for zerolength element?

[sgjsgj]

hi

for viscous damper. try viscous materials
uniaxialMaterial Viscous $matTag $C $alpha
$matTag integer tag identifying material
$C damping coeficient
$alpha power factor (=1 means linear damping)

link: http://opensees.berkeley.edu/wiki/index ... s_Material

i guess you should assign it to a truss element. or assign it to a zero length element on a two duplicate nodes on truss or beamcolumn elements.


but if you want to model viscoelastic damper. using k and c. parallel viscous and elastic materials.

regards

[vesna]

The easiest way to do what you want is to use zeroLength element (orientation needs to be defined for your case) and assign to it Maxwell material.

[rmandok]

Dear Vesna, How should the orientation define in my case? can I have an example?

[vesna]

Here you can find an example:http://opensees.berkeley.edu/wiki/index ... th_Element

[rmandok]

Dear Vesna, I can't imagine how silly I am right now but can you please make me an example rather than 45 degrees?

[vesna]

Given the span of the bay of 360 and height of the frame of 240, the orient vector for the brace going from lower-left corner to the top-right corner is going to be:
-orient 360 240 0 -240 360 0

I hope this helps.

[Basa]

Dear Vesna,
I am trying to model 1 storey 1 bay steel braced frame with viscoelastic dampers, which will be connected between the node of the bracings and the middle node of the beam. Since, I have already read most of the topics regarding the implementation of the dampers I think the most suitable method is to use truss or nonlinear beam column elements for bracings and zerolength element at their ends to model the damper. When I use non linear beam column elements the results are fine and coincide with the ones from SAP2000. However when I use truss elements I can't even get natural frequencies. I would appreciate it if you could have a look to my code.
#2D ELASTIC ANALYSIS OF A 1 STOREY 1 BAY STEEL FRAME GRAVITY ANALYSIS
#---------------------------------------------------------------------------------------------------
#---------------------------------------------------------------------------------------------------
#SI Units: m,sec,Kg,N
wipe all; # clear opensees model
model basic -ndm 2 -ndf 3; # 2 dimensions, 3 dof per node
file mkdir Output; # create data directory

set L 6; #Length of frame
set H 3.5; #Height of frame
puts "L=$L H=$H"
# Nodes
node 1 0. 0.;
node 2 $L 0.;
node 3 0. $H;
node 4 $L $H;
node 5 [expr $L/2] $H;
node 55 [expr $L/2] $H;
equalDOF 3 5 1
equalDOF 3 4 1

#Constraints
#-------------
fix 1 1 1 1; # node DX DY RZ
fix 2 1 1 1; # node DX DY RZ

# nodal masses
#---------------
set mass_x 3058; # mass at x direction = 3058kg
set mass_y 1.0e-06; # mass at y direction approximately 0
set mass_z 1.0e-06; # mass at z direction approximately 0
mass 3 $mass_x $mass_y $mass_z
mass 4 $mass_x $mass_y $mass_z
set g 9.81;

#MATERIAL
#--------------------------
#--------------------------
set matID 1;
set Fy 2.75e08; #Yielding force in N/m2
set Es 210e09; #Elastic Modulus of Steel
set ratio 0; #Strain-hardening ratio
#uniaxialMaterial Steel01 $matTag $Fy $E0 $b
uniaxialMaterial Steel01 $matID $Fy $Es $ratio

#Material for Viscoelastic damper
uniaxialMaterial ViscousDamper 2 30000 28000 0.60


#ELEMENTS
#-------------
# calculated geometry parameters
#Column Section: HEM550, Beam Section: IPE550
set ACol 0.0354;
set ABeam 0.0134;
set ABracings 0.1;
set IzCol 1.98e-03;
set IzBeam 6.71e-04;
set Es 210e09;
set ColTransfTag 1;
set BeamTransfTag 2;
geomTransf Linear $ColTransfTag ;
geomTransf Linear $BeamTransfTag ;

# element elasticBeamColumn $eleTag $iNode $jNode $A $E $Iz $transfTag
element elasticBeamColumn 1 1 3 $ACol $Es $IzCol $ColTransfTag
element elasticBeamColumn 2 2 4 $ACol $Es $IzCol $ColTransfTag
element elasticBeamColumn 3 3 5 $ABeam $Es $IzBeam $BeamTransfTag
element elasticBeamColumn 4 5 4 $ABeam $Es $IzBeam $BeamTransfTag

#Bracings
#element truss $eleTag $iNode $jNode $A $matTag
element truss 5 1 55 $ABracings 1
element truss 6 55 2 $ABracings 1

#element zeroLength $eleTag $iNode $jNode -mat $matTag1 -dir $dir1 $dir2
element zeroLength 7 55 5 -mat 1 -dir 1 ; #Zerolength Element for Damper


#EIGEN ANALYSIS
#---------------------
set numModes 2
set lamda [eigen $numModes];
set omega {}
set f {}
set T {}
foreach lam $lamda {
lappend omega [expr sqrt($lam)]
lappend f [expr sqrt($lam)/(2*3.14)]
lappend T [expr (2*3.14)/sqrt($lam)]
}
set omega1 [lindex $omega [expr $numModes-2]]
set omega2 [lindex $omega [expr $numModes-1]]
puts "omega1 = $omega1"
puts "omega2 = $omega2"
puts "Natural Periods are $T"

#RECORDERS
#----------------
recorder Node -file Output/DFree.out -time -node 3 4 -dof 1 2 3 disp; # displacements of free nodes
recorder Node -file Output/DBase.out -time -node 1 2 -dof 1 2 3 disp; # displacements of support nodes
recorder Node -file Output/RBase.out -time -node 1 2 -dof 1 2 3 reaction; # support reaction
recorder Element -file Output/FCol.out -time -ele 1 2 globalForce; # element forces -- column
recorder Element -file Output/FBracingsGlobal.out -time -ele 5 6 localForce; # Bracings Local Forces Fx Fy Mz
recorder Element -file Output/FBracingsLocal.out -time -ele 5 6 globalForce; # Bracings Global Forces FX FY MZ
recorder Element -file Output/FBracingsAxial.out -time -ele 5 6 axialForce; # Bracings Forces
recorder Element -file Output/FBracingsDeformations.out -time -ele 4 5 deformations; # Bracings Deformations
recorder Element -file Output/FBeam.out -time -ele 3 4 globalForce; # element forces -- beam

#GRAVITY LOADS
#-------------
timeSeries Linear 1
set LateralForce 10000; #10kN
pattern Plain 1 1 {
load 3 $LateralForce 0 0
}
set Tol 1.0e-8
constraints Plain;
numberer Plain;
system BandGeneral;
test NormDispIncr $Tol 6 ;
algorithm Linear;
integrator LoadControl 0.1;
analysis Static;
analyze 10;
loadConst -time 0.0;
puts "Model Built"
wipe