When running my nonlinear analysis in opensees the same beam experiences 1.8 mm deflection at 19.8 kN load. Which is just crazy, even with linear handcalculations u_max = (1/48)*Q*L^3/EI = 2 mm.
Now I have modeled some columns from the peer database before and have had no major problems regarding the results, now however I´m troubled.
This experiment and the uses of opensees is a part of a masters thesis in structural engineering and I would appreciate some comments from all you good people out there
I will include the tcl file for the model wich is very simple and should take anyone with some opensees experience only a few moments to run through.
Much appreciated
and best regards
#the file:
# --------------------------------------------------------------------------------------------------
# fiber section, nonlinearBeamColumn element
#
#
# ^Y
# | set-up
# |
#
# 1------2------3 -->x
# XX 00
# LCol
#
#
# SET UP ----------------------------------------------------------------------------
wipe; # clear memory of all past model definitions
file mkdir Data/1A; # create data directory
model BasicBuilder -ndm 2 -ndf 3; # Define the model builder, ndm=#dimension, ndf=#dofs
# set basic units
set mm 1.0;
set N 1.0;
set pi 3.141593;
set MPa [expr $N/$mm/$mm];
set kN [expr 1000*$N];
#source DisplayModel2D.tcl
# define GEOMETRY -------------------------------------------------------------
set LCol [expr 1150*$mm];
set MCol [expr $LCol/2];
# define section geometry
set HCol [expr 150*$mm]; # Column Depth
set BCol [expr 150*$mm]; # Column Width
# nodal coordinates:
node 1 0 0; # node#, X, Y
node 2 $MCol 0;
node 3 $LCol 0;
# Single point constraints -- Boundary Conditions
fix 1 1 1 0; # node DX DY RZ
fix 3 0 1 0;
# Define ELEMENTS & SECTIONS -------------------------------------------------------------
set ColSecTag 1; # assign a tag number to the column section
# define section geometry
set diaK6 [expr 6*$mm];
set barArea [expr $pi/4*pow($diaK6,2)]; # area of longitudinal-reinforcement bars M30
# MATERIAL parameters -------------------------------------------------------------------
set IDconcU 1; # material ID tag -- unconfined cover concrete
set IDreinf 2; # material ID tag -- reinforcement
# nominal concrete compressive strength
set fc [expr 25*$MPa]; # CONCRETE Compressive Strength (+Tension, -Compression)
# unconfined concrete
set fc1U [expr -$fc]; # UNCONFINED concrete (todeschini parabolic model), maximum stress
set eps1U -0.002; # strain at maximum strength of unconfined concrete
set Ec [expr 5000*pow($fc,0.5)]; # Concrete Elastic Modulus
set fc2U [expr 0.7*$fc1U]; # ultimate stress
set eps2U -0.0035; # strain at ultimate stress
set lambda 0.2; # ratio between unloading slope at $eps2 and initial slope $Ec (not used here)
# tensile-strength properties
set fct [expr 2.6*$MPa]; # EC2
set Ets [expr $fct/0.002]; # tension softening stiffness
set epsT 0.01; # ATH
# Steel properties-----------
set Fy [expr 500*$MPa]; # STEEL yield stress
set Es [expr 200000*$MPa]; # modulus of steel
set Bs 0.001; # strain-hardening ratio
uniaxialMaterial Steel02 $IDreinf $Fy $Es $Bs; # build reinforcement material
uniaxialMaterial Concrete04 $IDconcU $fc1U $eps1U $eps2U $Ec $fct $epsT; # build concrete material
# FIBER SECTION properties -------------------------------------------------------------
# symmetric section
# y
# ^
# |
# ---------------------
# | | |
# | | |
# | | |
# z <--- | + | H
# | | |
# | o o | | -- cover
# --------------------- -- --
# |-------- B --------|
#
# RC section:
set coverY [expr $HCol/2.0]; # The distance from the section z-axis to the edge of the cover concrete -- outer edge of cover concrete
set coverZ [expr $BCol/2.0]; # The distance from the section y-axis to the edge of the cover concrete -- outer edge of cover concrete
set Y1 [expr $HCol/2 -15*$mm]
set Z1 [expr $BCol/2 -15*$mm]
set nfY 20; # number of fibers for concrete in y-direction
set nfZ 20; # number of fibers for concrete in z-direction
section fiberSec $ColSecTag { # Define the fiber section
#patch quad $matTag $numSubdivIJ $numSubdivJK $yI $zI $yJ $zJ $yK $zK $yL $zL
#layer straight $matTag $numBars $areaBar $yStart $zStart $yEnd $zEnd
patch quadr $IDconcU $nfZ $nfY -$coverY $coverZ -$coverY -$coverZ $coverY -$coverZ $coverY $coverZ; # Define the concrete patch
layer straight $IDreinf 2 $barArea -$Y1 $Z1 -$Y1 $Z1; # Define the reinforcement
}; # end of fibersection definition
# define geometric transformation: performs a linear geometric transformation of beam stiffness and resisting force from the basic system to the global-coordinate system
set ColTransfTag 1; # associate a tag to column transformation
geomTransf Linear $ColTransfTag;
# element connectivity:
set numIntgrPts 5; # number of integration points for force-based element
element nonlinearBeamColumn 1 1 2 $numIntgrPts $ColSecTag $ColTransfTag; # self-explanatory when using variables
element nonlinearBeamColumn 2 2 3 $numIntgrPts $ColSecTag $ColTransfTag;
puts "Model Built"
# Define RECORDERS -------------------------------------------------------------
#recorder Element -file ele1sec1StressStrain.out –time -ele 1 section 1 fiber $y $z <$matID> stressStrain
recorder Node -file Data/1A/Dnode2_1A.out -time -node 2 -dof 2 disp; # displacements of free node
recorder Node -file Data/1A/Forcenode2_1A.out -time -node 2 -dof 2 reaction;
recorder Element -file Data/1A/StressStrain_1A_ConcB.out -time -ele 1 section 5 fiber -$coverY 0.0 $IDconcU stressANDstrain; # stress strain in outermost part (bottom) of concrete near node2
recorder Element -file Data/1A/StressStrain_1A_ConcT.out -time -ele 1 section 5 fiber $coverY 0.0 $IDconcU stressANDstrain; # stress strain in outermost part (top) of concrete near node2
recorder Element -file Data/1A/StressStrain_1A_K6.out -time -ele 1 section 5 fiber -$Y1 $Z1 $IDreinf stressANDstrain; # stress strain in M30
# pushover analysis: load controlled static analysis
constraints Plain; # how it handles boundary conditions
numberer Plain; # renumber dof's to minimize band-width (optimization), if you want to
system BandGeneral; # how to store and solve the system of equations in the analysis
test NormDispIncr 1.0e-6 100 0; # determine if convergence has been achieved at the end of an iteration step
algorithm Newton; # use Newton's solution algorithm: updates tangent stiffness at every iteration
integrator LoadControl 0.01;
#integrator DisplacementControl 2 2 0.25; # determine the next time step for an analysis
analysis Static # define type of analysis static or transient
# define LATERAL load -------------------------------------------------------------
set Pu [expr -30*$kN];
# Lateral load pattern
pattern Plain 1 Linear {
load 2 0 $Pu 0; # node#, FX FY MZ -- representative lateral load at middle node
}
analyze 100; # apply 100 steps of pushover analysis to reach 1.0 X applied load
puts "Done!"
print node 2
wipe