Euler load

[esi_opensees]

i want to get the Euler load (buckling load). the end supports are hinge. the model has imperfection at the center of element, but the deflection is constant. would u please tell me what the problem is? how can i get Euler load


#Units: kg,cm
wipe
model BasicBuilder -ndm 3 -ndf 6
# nodal coordinates:
node 1 0 0 0
node 2 0 0 400
node 3 4 0 200
# ---------------------------------------------
# nodal restraint:
fix 1 1 1 1 0 0 0
fix 2 1 1 0 0 0 0
# ---------------------------------------------
# material:
uniaxialMaterial Steel01 1 2400 2.1E6 0.0
# ---------------------------------------------
geomTransf Corotational 1 1 1 0
# ---------------------------------------------
# Define section:

proc pipe { secID matID d t nfcir nfrad } {
set intRad [expr (0.5*$d-$t)]
set extRad [expr (0.5*$d)]
section Fiber $secID {
patch circ $matID $nfcir $nfrad 0.0 0.0 $intRad $extRad 0.0 360.0
}
}
# tag mat D t nfcir nfrad
pipe 1 1 15.9 2.5 8 3
# Add Torsion property to existing sections:
section Aggregator 2 1 T -section 1
# ---------------------------------------------
# element:
element nonlinearBeamColumn 1 1 3 5 2 1
element nonlinearBeamColumn 2 3 2 5 2 1
#-----------------------------------------------
#load
pattern Plain 1 Linear {

load 1 0 0 -10E6 0 0 0
}
#-----------------------------------------------
recorder Node -file node2_bar.out -node 2 -time -dof 3 disp
#----------------------------------------------------------
constraints Transformation
numberer RCM
system BandGeneral
test NormDispIncr 1.0e-6 30
algorithm Newton
integrator LoadControl 0.01
analysis Static
analyze 1000

[imancivil]

if you want to capture the force-deflection curve, you should use an element suitable for analyzing slender to moderately stubby/thick beam structures. This element should be based on Timoshenko beam theory. Shear deformation effects should be included. use imperfection at the center of element and apply a axial load. if you follow this process, you can capture the buckling load.
But unfortunately i don't know how define it in opensees.

Dear friends, would you please tell me how i can define this element in opensees? could anybody have captured Euler load from opensees?

[esi_opensees]

Dear all,

would u please tell me how i can capture the force-deflection curve for a single element?

what is the problem about my script that attached above?

thank u.

[silvia]

are you applying a load on a constrained dof???

[esi_opensees]

Daer silvia,

in ANSYS to capture the force-deflection curve for a single element it is possible to apply an axial load on a constrained dof. (use BEAM188 element). with doing the nonlinear static analysis the force-deflection curve obtained.
but how can i do it in opensees?

I look forward to hearing from you.

[silvia]

in opensees, you can either impose a displacement or a load constraint.
please review the examples manual for examples.

[susan]

Dear silvia,

i have the same question. would u please tell me how i can define an axial load fore at the end of a column with pinned support at one end and roller support at the other end of element?

[silvia]

Please look at the cantilever example and modify it.

[imancivil]

please use the below script;
but notice that you must use Arc-Length method as an integrator because the arc-length method is suitable for nonlinear static equilibrium solutions of unstable problems. Applications of the arc-length method involves the tracing of a complex path in the load-displacement response into the buckling/post buckling regimes.
your case is an unstable problem, so you should use this method instead of LoadControl integrator. But unfortunately i could not set the parameters $arclength $alpha in opensees. Dear friends, would you please help me to solve this problem?

Thanks!


#Units: kg,cm
wipe
model BasicBuilder -ndm 3 -ndf 6
# nodal coordinates:
node 1 0 0 0
node 2 400 0 0
node 3 200 4 0
# ---------------------------------------------
# nodal restraint:
fix 1 0 0 1 0 0 0
fix 2 1 1 1 0 0 0
# ---------------------------------------------
# material:
uniaxialMaterial Steel01 1 2400 2.1E6 0.0
# ---------------------------------------------
geomTransf Corotational 1 1 1 0
# ---------------------------------------------
# Define section:

proc pipe { secID matID d t nfcir nfrad } {
set intRad [expr (0.5*$d-$t)]
set extRad [expr (0.5*$d)]
section Fiber $secID {
patch circ $matID $nfcir $nfrad 0.0 0.0 $intRad $extRad 0.0 360.0
}
}
# tag mat D t nfcir nfrad
pipe 1 1 15.9 2.5 8 3
# Add Torsion property to existing sections:
section Aggregator 2 1 T -section 1
# ---------------------------------------------
# element:
element nonlinearBeamColumn 1 1 3 5 2 1
element nonlinearBeamColumn 2 3 2 5 2 1
#-----------------------------------------------
#load
pattern Plain 1 Linear {

load 1 10E5 0 0 0 0 0
}
#-----------------------------------------------
recorder Node -file node1_bar4.out -node 1 -time -dof 1 disp
#----------------------------------------------------------
constraints Transformation
numberer RCM
system BandGeneral
test NormDispIncr 1.0e-6 30
algorithm Newton

integrator LoadControl 0.005
#integrator ArcLength 0.004 1

analysis Static
analyze 1000

[esi_opensees]

Dear imancivil

thank you very much. as you mentioned if i use LoadControl integrator, after a few steps analysis fail.

Dear all,

how should i set the $arclength $alpha?


thnx

[silvia]

why not displacement control?
if you have convergence problems, you should see the scripts in the examples manual.
analyze 2000 is not a good way to go!