problem in BRB frames

[shahroozbral]

Dear sirs,
wishing you a good day.

My thesis is about optimizing BRB steel frames and modeled frames with Opensees and optimized with PSO algorithm via Matlab.
After optimizing some frames, their sections was so big and after rechecking the results of opensees, I found out that there is a problem in modeling the frame in opensees.
All of frame connections are pinned. Just Middle bay has BRBs with inverted V-chevron formation. Lateral loads are forced with a pushover procedure.
The problem is that the beams in bays without BRB must have just local forces by gravity loads but after every step of pushover, they are increased and none of sections can resist them.


I have attached a frame opensees files which it has 3-bay , 3 stories , length of bay are 3 m , and 3-meter load width.
The units are kgf , m
I would be thankful if you check my opensees files and let me know what the problem is.
Your faithfully,
Shahrooz Bral

node 11 0.000000 0.000000
node 12 3.000000 0.000000
node 13 6.000000 0.000000
node 14 9.000000 0.000000
node 21 0.000000 3.200000
node 22 3.000000 3.200000
node 23 6.000000 3.200000
node 24 9.000000 3.200000
node 31 0.000000 6.400000
node 32 3.000000 6.400000
node 33 6.000000 6.400000
node 34 9.000000 6.400000
node 41 0.000000 9.600000
node 42 3.000000 9.600000
node 43 6.000000 9.600000
node 44 9.000000 9.600000
node 121 0.000000 3.200000
node 122 3.000000 3.200000
node 123 6.000000 3.200000
node 124 9.000000 3.200000
node 131 0.000000 6.400000
node 132 3.000000 6.400000
node 133 6.000000 6.400000
node 134 9.000000 6.400000
node 141 0.000000 9.600000
node 142 3.000000 9.600000
node 143 6.000000 9.600000
node 144 9.000000 9.600000
node 212 4.500000 3.200000
node 222 4.500000 6.400000
node 232 4.500000 9.600000

fix 11 1 2
fix 12 1 2
fix 13 1 2
fix 14 1 2

equalDOF 21 22 1
equalDOF 21 23 1
equalDOF 21 24 1
equalDOF 31 32 1
equalDOF 31 33 1
equalDOF 31 34 1
equalDOF 41 42 1
equalDOF 41 43 1
equalDOF 41 44 1
equalDOF 21 121 1 2
equalDOF 22 122 1 2
equalDOF 23 123 1 2
equalDOF 24 124 1 2
equalDOF 31 131 1 2
equalDOF 32 132 1 2
equalDOF 33 133 1 2
equalDOF 34 134 1 2
equalDOF 41 141 1 2
equalDOF 42 142 1 2
equalDOF 43 143 1 2
equalDOF 44 144 1 2
equalDOF 21 212 1
equalDOF 31 222 1
equalDOF 41 232 1

mass 11 68.160000 2.220446e-16 2.220446e-16
mass 12 419.200000 2.220446e-16 2.220446e-16
mass 13 419.200000 2.220446e-16 2.220446e-16
mass 14 68.160000 2.220446e-16 2.220446e-16
mass 21 1418.820000 2.220446e-16 2.220446e-16
mass 22 3403.400000 2.220446e-16 2.220446e-16
mass 23 3403.400000 2.220446e-16 2.220446e-16
mass 24 1418.820000 2.220446e-16 2.220446e-16
mass 31 1418.820000 2.220446e-16 2.220446e-16
mass 32 3403.400000 2.220446e-16 2.220446e-16
mass 33 3403.400000 2.220446e-16 2.220446e-16
mass 34 1418.820000 2.220446e-16 2.220446e-16
mass 41 1170.660000 2.220446e-16 2.220446e-16
mass 42 2624.200000 2.220446e-16 2.220446e-16
mass 43 2624.200000 2.220446e-16 2.220446e-16
mass 44 1170.660000 2.220446e-16 2.220446e-16

#Beams
element nonlinearBeamColumn 2121 122 212 6 105 2
element nonlinearBeamColumn 2122 212 123 6 105 2
element nonlinearBeamColumn 2221 132 222 6 105 2
element nonlinearBeamColumn 2222 222 133 6 105 2
element nonlinearBeamColumn 2321 142 232 6 105 2
element nonlinearBeamColumn 2322 232 143 6 105 2
element nonlinearBeamColumn 2113 121 122 6 105 2
element nonlinearBeamColumn 2213 131 132 6 105 2
element nonlinearBeamColumn 2313 141 142 6 105 2
element nonlinearBeamColumn 2133 123 124 6 105 2
element nonlinearBeamColumn 2233 133 134 6 105 2
element nonlinearBeamColumn 2333 143 144 6 105 2
#Columns
element nonlinearBeamColumn 111 11 21 6 204 1
element nonlinearBeamColumn 121 21 31 6 204 1
element nonlinearBeamColumn 131 31 41 6 204 1
element nonlinearBeamColumn 112 12 22 6 222 1
element nonlinearBeamColumn 122 22 32 6 222 1
element nonlinearBeamColumn 132 32 42 6 222 1
element nonlinearBeamColumn 113 13 23 6 222 1
element nonlinearBeamColumn 123 23 33 6 222 1
element nonlinearBeamColumn 133 33 43 6 222 1
element nonlinearBeamColumn 114 14 24 6 204 1
element nonlinearBeamColumn 124 24 34 6 204 1
element nonlinearBeamColumn 134 34 44 6 204 1

#BRBs
element corotTruss 3121 12 212 387
element corotTruss 3122 212 13 387
element corotTruss 3221 122 222 387
element corotTruss 3222 222 123 387
element corotTruss 3321 132 232 387
element corotTruss 3322 232 133 387

#gravity load
pattern Plain 1 Linear {
eleLoad -ele 2121 -type -beamUniform -957.000000
eleLoad -ele 2122 -type -beamUniform -957.000000
eleLoad -ele 2221 -type -beamUniform -957.000000
eleLoad -ele 2222 -type -beamUniform -957.000000
eleLoad -ele 2321 -type -beamUniform -820.875000
eleLoad -ele 2322 -type -beamUniform -820.875000
eleLoad -ele 2113 -type -beamUniform -957.000000
eleLoad -ele 2213 -type -beamUniform -957.000000
eleLoad -ele 2313 -type -beamUniform -820.875000
eleLoad -ele 2133 -type -beamUniform -957.000000
eleLoad -ele 2233 -type -beamUniform -957.000000
eleLoad -ele 2333 -type -beamUniform -820.875000
}
constraints Plain
numberer RCM
system BandGeneral
test NormDispIncr 1.e-4 10
algorithm Newton
integrator LoadControl 0.1
analysis Static
set ok [analyze 10]
loadConst -time 0.0

[fmk]

if they are moment connections they will increase .. if the lateral system is now the braced frame are they supposed to be moment connections!

[shahroozbral]

all of beam to column connections are pinned . so the moment , axial and shear force of beams which are not located in BRB bays must not change after gravity load but they changed.
what should i do to stop the changes in pushover procedure for beams which aren't located in BRB bays ?

[fmk]

try usig dispBeamColumn elements instead of the forceBeamColumn elements for the beams. large axial loads could be popping up just due to your rigid floor diaphragm constraints in the forceBeamColumn elements.

[baikunthasilwal]

Dear Shahroozbral,

Did you solve the BRB frame with acceptable results? If you solve the modeling issues, please share your findings to improve the BRB model.