A problem with verification for Forcebased Element

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Posts: 1
Joined: Tue Jan 28, 2020 9:17 pm

A problem with verification for Forcebased Element

Post by BijanSeif » Sun Mar 28, 2021 10:11 am


As shown in below simple code, we have defined a cantilever column with rectangular section with plastic moment capacity 300000 and base shear capacity equal to 1000. But when we run for a range Base shear more than the defined capacity, we didn't encounter with any error and Opensees will run the code and present a wrong Displacement-BaseShear diagram for the range above the shear capacity.

Where is the problem? Why Opensees solve this and do not give any error message/s?

Click below link to see the the result (Base shear - Displacement curve):
https://drive.google.com/file/d/1MITUkJ ... sp=sharing

Code: Select all

model BasicBuilder -ndm 2

node	1	0.0	0.0
node	2	0.0	300.0

fix 1 1 1 1

set steel 1
set Fy 2400.0
set E0 2000000.0
set b 0.00
uniaxialMaterial Steel01 $steel $Fy $E0 $b

set secTag 1
set numSubdivY 10
set numSubdivZ 10
set yI -5.0
set zI -2.5
set yJ 5.0
set zJ 2.5
section Fiber $secTag {
patch rect $steel $numSubdivY $numSubdivZ $yI $zI $yJ $zJ

set transfTag 1
geomTransf Linear $transfTag

set eleTag 1
set iNode 1
set jNode 2
set numIntgrPts 10
element forceBeamColumn $eleTag $iNode $jNode $numIntgrPts $secTag $transfTag -integration Trapezoidal

set tsTag 1
timeSeries Linear $tsTag

set patternTag 1
pattern Plain $patternTag $tsTag {
        load $jNode 1000.0 0.0 0.0

recorder Node -file Node2Disp.txt -node 2 -dof 1 disp
recorder Node -file Node1react.txt -node 1 -dof 1 reaction

constraints Plain
numberer Plain
system BandGeneral

set tol 0.001
set iter 100
test NormDispIncr $tol $iter
algorithm Newton

set dof 1
set incr 0.01
set lambda 0.01
integrator LoadControl $lambda

analysis Static
set numIncr 220
analyze $numIncr

print -ele 1
print -node 1

Posts: 879
Joined: Mon Sep 09, 2013 8:50 pm
Location: University of California, Berkeley

Re: A problem with verification for Forcebased Element

Post by selimgunay » Wed Mar 31, 2021 9:50 am

You are conducting the analysis with load control and using a large tolerance for the displacement convergence test. From your plot, it is obvious that the solution is not correct and there are errors in the convergence, but the analysis continues probably due to the large norm. I would recommend running it with a displacement control and reduce the convergence tolerance.

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