Time History Earthquake Analysis for a simple Piping System

[rsoni2]

Dear all,

I am trying to solve a simple piping model using both SAP and OpenSees to compare the results and get a better understanding of things in Opensees
My results from SAP and OpenSees do not match and I was trying to understand why ?


Actual Model
/<
/
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^Z /^Y |
| / |^
|/----->X >___________________|




Open Sees Code
# Example Model
wipe; # clear opensees model
model basic -ndm 3 -ndf 6; # 3 dimensions, 6 dof per node

# Units : Kip-in
#define GEOMETRY -------------------------------------------------------------
# nodal coordinates:

# NODES

node 1 0 0 0
node 2 100 0 0
node 3 200 0 0
node 4 288 0 0
node 5 288 0 45
node 6 288 0 100
node 7 288 0 200
node 8 288 0 288
node 9 288 100 288
node 10 288 200 288
node 11 288 288 288

#Constraints

# node dx dy dz th-x th-y th-z
#anchors
fix 1 1 1 1 1 1 1
fix 11 1 1 1 1 1 1

#general constraint
fix 5 1 1 1 0 0 0

set E 29e3;
set A 1.0745;
set G 11153.8461534;
set J 1.3315;
set I 0.6657;

# Define ELEMENTS -------------------------------------------------------------
# define geometric transformation: performs a linear geometric transformation of beam stiffness and resisting force from the basic system to

geomTransf Linear 1 0 0 -1; # associate a tag to transformation
geomTransf Linear 2 0 1 0;

element elasticBeamColumn 1 1 2 $A $E $G [expr 2*$I] $I $I 1
element elasticBeamColumn 2 2 3 $A $E $G [expr 2*$I] $I $I 1
element elasticBeamColumn 3 3 4 $A $E $G [expr 2*$I] $I $I 1
element elasticBeamColumn 4 4 5 $A $E $G [expr 2*$I] $I $I 2
element elasticBeamColumn 5 5 6 $A $E $G [expr 2*$I] $I $I 2
element elasticBeamColumn 6 6 7 $A $E $G [expr 2*$I] $I $I 2
element elasticBeamColumn 7 7 8 $A $E $G [expr 2*$I] $I $I 2
element elasticBeamColumn 8 8 9 $A $E $G [expr 2*$I] $I $I 1
element elasticBeamColumn 9 9 10 $A $E $G [expr 2*$I] $I $I 1
element elasticBeamColumn 10 10 11 $A $E $G [expr 2*$I] $I $I 1


#masses

mass 1 0.015234261 0.015234261 0.015234261 0 0 0
mass 2 0.030468522 0.030468522 0.030468522 0 0 0
mass 3 0.028640411 0.028640411 0.028640411 0 0 0
mass 4 0.020261567 0.020261567 0.020261567 0 0 0
mass 5 0.022089678 0.022089678 0.022089678 0 0 0
mass 6 0.030468522 0.030468522 0.030468522 0 0 0
mass 7 0.028640411 0.028640411 0.028640411 0 0 0
mass 8 0.028640411 0.028640411 0.028640411 0 0 0
mass 9 0.030468522 0.030468522 0.030468522 0 0 0
mass 10 0.028640411 0.028640411 0.028640411 0 0 0
mass 11 0.01340615 0.01340615 0.01340615 0 0 0

# ------------------------- END OF MODEL DEFINITION -------



set xi 0.02

set w1 0.4198876040085013
set w2 198.51340005148268

set a0 [expr 2*$xi*$w1*$w2/($w1+$w2)];
set b0 [expr 2*$xi/($w1+$w2)]

# set damping factors
rayleigh $a0 0. 0. $b0

# - over to the rest of the code

set g 386.4

# DYNAMIC ground-motion analysis -------------------------------------------------------------
# create load pattern
set accelSeries "Series -dt 0.005 -filePath elcentroA6inX.txt -factor $g"; # define acceleration vector from file (dt=0.005 is associated with the input file gm)
pattern UniformExcitation 1 1 -accel $accelSeries; # define where and how (pattern tag, dof) acceleration is applied


# Define Recorder
recorder Element -file EXmodelA6inx.txt -time -ele all globalForce ; # element forces -- beam
# create the analysis
wipeAnalysis; # clear previously-define analysis parameters
constraints Plain; # how it handles boundary conditions
numberer Plain; # renumber dof's to minimize band-width (optimization), if you want to
system BandGeneral; # how to store and solve the system of equations in the analysis
test NormDispIncr 1.0e-8 10; # determine if convergence has been achieved at the end of an iteration step
algorithm Newton; # use Newton's solution algorithm: updates tangent stiffness at every iteration
integrator Newmark 0.5 0.25 ; # determine the next time step for an analysis
analysis Transient; # define type of analysis: time-dependent
analyze 60000 0.0005; # apply 60000 0.0005-sec time steps in analysis

puts "Done!"


I was careful enough in SAP to put the appropriate section properties as well as applying the EQ as acceleration Time history
The results from SAP and OpenSees are off by a considerable amount . I was wondering if there is anything wrong with the code !

I checked the Eq input and the Modal damping with both SAP and Opensees and the values are same .

I was thinking may be my element transformation from local to global might be wrong . But again The orientation of Y and Z axis for a Circular Piping System dont make much difference ( Orientation is not an issue )


As an aside a different question
Is it possible to get the Moments in an element at particular sections ( along the beam ) I know the section command does that but when i was trying to implement that the ouput file was empty . I used the Syntax as mentioned in the Opensees Manual .

Any help would be appreciated !
Regards
Rohit Soni

[billu]

Brother Can i Ask that how u have defined nodal masses??