pushover problem in cantilever column

[alish]

hello everybody!
i am modeling a cantilever column ( with I-shaped shear wall section) with fiber section and dispBeamColumn element.
when i push my model and see it's deformation; it is observed that the model moves upward instead of lateral moving
my model is :


wipe
wipeAnalysis

model BasicBuilder -ndm 2 -ndf 3;
file mkdir data1;

# unit kgf,m,s


# Define node
node 1 0. 0. ;
node 2 0. 5. ;


# assign costraint
fix 1 1 1 1 ;


# assign mass
mass 2 100. 1.e-9 1.e-9 ;


geomTransf Corotational 1;


# Define material
uniaxialMaterial Concrete01 1 -28.e6 -.003 -4.8e6 -.006


#### Section ####
proc Wsection { secID matID d bf tf tw nfdw nftw nfbf nftf } {
# ###################################################################
# Wsection $secID $matID $d $bf $tf $tw $nfdw $nftw $nfbf $nftf
# ###################################################################
# create a standard I-section(shearWall) given the nominal section properties
# written by: Ali Biglari
# date: 1392/11/08
# input parameters
# secID - section ID number
# matID - material ID number
# d = nominal depth
# tw = web thickness
# bf = column width
# tf = column height
# nfdw = number of fibers along web depth
# nftw = number of fibers along web thickness
# nfbf = number of fibers along column width
# nftf = number of fibers along column height

# ^ Z
# |
# |
# |
# |
# |
# |
# --------------- > Y


set dw [expr $d - 2 * $bf]


set z1 [expr -$tf/2]
set z2 [expr -$tw/2]
set z3 [expr $tw/2]
set z4 [expr $tf/2]



set y1 [expr -$d/2]
set y2 [expr -$dw/2]
set y3 [expr $dw/2]
set y4 [expr $d/2]


section fiberSec $secID {
# nfIJ nfJK yI zI yJ zJ yK zK yL zL
patch quad $matID $nfbf $nftf $y1 $z1 $y2 $z1 $y2 $z4 $y1 $z4; # left column
patch quad $matID $nfdw $nftw $y2 $z2 $y3 $z2 $y3 $z3 $y2 $z3; # web
patch quad $matID $nfbf $nftf $y3 $z1 $y4 $z1 $y4 $z4 $y3 $z4; # right column
}
}




Wsection 1 1 5.6 .6 .6 .3 400 10 40 40


# element
element dispBeamColumn 1 1 2 10 1 1


eigen 1 ;
set T1model [expr 2*3.1416/(pow([eigen 1],0.5))]
puts "T1model=[expr $T1model]sec"




recorder Node -file Data1/DFree.out -time -node 2 -dof 1 2 3 disp;
recorder Node -file Data1/DBase.out -time -node 1 -dof 1 2 3 disp;
recorder Node -file Data1/RBase.out -time -node 1 -dof 1 2 3 reaction;
recorder Drift -file Data1/Drift.out -time -iNode 1 -jNode 2 -dof 1 -perpDirn 2 ;
recorder Element -file Data1/FCol.out -time -ele 1 globalForce;


recorder display "Mode Shape 1" 0 0 1000 1000 -wipe
prp 300 300 1; # projection reference point (prp); defines the center of projection (viewer eye)
vup 0 1 0; # view-up vector (vup)
vpn 0 0 1; # view-plane normal (vpn)
viewWindow -20 20 -10 10; # coordiantes of the window relative to prp
display 1 5 200; # the 1st arg. is the tag for display mode (ex. -1 is for the first mode shape)
# the 2nd arg. is magnification factor for nodes(if -1 show node number), the 3rd arg. is magnif. factor of deformed shape
after 1000



## Gravity
pattern Plain 1 Linear {
load 2 0. -1000. 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 ;

#wipeAnalysis


# Pushover analyze
pattern Plain 2 Linear {
load 2 10. 0.0 0.0;
}


constraints Plain ;
numberer Plain ;
system BandGeneral ;
test NormDispIncr 1.0e-8 50 ;
algorithm ModifiedNewton ;
integrator DisplacementControl 2 1 0.00001;
analysis Static
analyze 1000 ;

puts " Done!"


thanks a lot

[alish]

Could you tell me please what the problem might be?

[fmk]

your model comprises a single beam with no shear effect to model a short wall and is probably inappropriate!

anyway, to answer your question: you will understand the reason for the lateral if you look at the stiffness matrix. change the lines of code after the last system call to what is shown below to see the matrix. the rows and col correspond to dX, dY and rZ at node 2. as you will see even if you have a lateral load you will have an axial displacement of about the same order for this model of yours.

here is the matrix at the end:
1.2521e+08 -183036 3.13907e+08
-183036 3.36004e+07 9.32018e+07
3.13907e+08 9.32018e+07 1.04806e+09

and here is the code to generate it.

system FullGeneral ;
test NormDispIncr 1.0e-8 50 ;
algorithm ModifiedNewton ;
integrator DisplacementControl 2 1 0.00001;
analysis Static
analyze 1000 ;

puts " Done!"

printA

[alish]

thanks for your reply prof.