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• Last Post 16 September 2019
• Topic Is Solved
Ahmad Abubakar posted this 14 March 2019

Hello,

I am analyzing a rectangular hollow steel section. When I draw the load displacement curve, the load keeps increasing always unless the curve becomes smooth and parallel to x-axis rather than the curve going down after reaching ultimate load. What can be the problem?

peteroznewman posted this 14 March 2019

Please insert images of your model, the geometry, the material data, the support, the load and the results graph.

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Ahmad Abubakar posted this 14 March 2019

This is rectangular hollow section model with K joint. All the ends of braces are constrained except one brace loaded axially in compression with displacement loads.

E= 210 GPa

poissions ratio= 0.3

Ahmad Abubakar posted this 15 March 2019

and here is the load-disp curve

mrife posted this 15 March 2019

We will need to know the material model used to properly answer this.  Maybe post the graph of the model data (material) too.

I'm assuming that there is some rate independent plasticity model defined.  Otherwise why would you expect the force-deflection curve to go negative slope?  Buckling?

Mike

Ahmad Abubakar posted this 15 March 2019

Hey Mike,

Here is the material model for steel grade S500M

TB,PLASTIC,1,1,27,MISO
TBTEMP,0.0                       ! Temperatur = 0.0
TBPT,DEFI,0.0000,529
TBPT,DEFI,0.0055,530
TBPT,DEFI,0.0155,534
TBPT,DEFI,0.0255,568
TBPT,DEFI,0.0355,593
TBPT,DEFI,0.0455,614
TBPT,DEFI,0.0555,631
TBPT,DEFI,0.0655,645
TBPT,DEFI,0.0755,657
TBPT,DEFI,0.0855,667
TBPT,DEFI,0.0955,676
TBPT,DEFI,0.1055,685
TBPT,DEFI,0.1155,692
TBPT,DEFI,0.1213,697
TBPT,DEFI,0.1455,721
TBPT,DEFI,0.1705,742
TBPT,DEFI,0.1955,761
TBPT,DEFI,0.2455,794
TBPT,DEFI,0.2955,822
TBPT,DEFI,0.3455,847
TBPT,DEFI,0.3955,868
TBPT,DEFI,0.4955,906
TBPT,DEFI,0.5955,938
TBPT,DEFI,0.6955,966
TBPT,DEFI,0.7955,991
TBPT,DEFI,0.8955,1013
TBPT,DEFI,0.9955,1034

Ahmad Abubakar posted this 15 March 2019

This is the material graph. I want to see the ultimate force experienced and its strange to me how the force isn't reduced and just keep increasing even for large displacement loads.

Vitaliy_Degtyarev posted this 16 March 2019

How do apply the load to your model? Generally, a descending branch can be obtained if the model is loaded by imposed displacements (not forces) applied in small increments. The load-displacement curve becomes the reaction-displacement curve in this case.

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Ahmad Abubakar posted this 16 March 2019

Hello,

Yeah I applied displacement loads but no negative slope experienced.

Vitaliy_Degtyarev posted this 17 March 2019

You may try to add steps/substeps to apply the displacements in smaller increments. If you upload your model I could look into it.

Ahmad Abubakar posted this 17 March 2019

I've tried it with various substeps ranging up to 200 but it doesn't help

Ahmad Abubakar posted this 17 March 2019

Here is the model for circular hollow section.

/clear,start
/filname,Model_1_S500M_CHS,1

!*afun,deg
!/UNITS,SI

!************ Chord parameters(in mm) ******************

H=   840    !height of chord from local coordinate system
Roc= 140    !Outer radius of chord
to=  20
ric= 120    !inner radius of chord
L=   2300    !length of chord

!************ Brace parameters(in mm) ******************

Hob= 590    !inclined height of brace
Rob= 70    !Outer radius of brace
rib= 50    !Inner radius of brace
Lob= 850    !inclined length of brace
Lo=  1248.1    !length of brace from chord origin
g=   85    !gap between the braces

!********** Material parameters ***********
EM=210000
v=0.3

!********** Element definition ***********
/prep7

!et,1,42
et,1,186

Type,all            !Zuweistung zu Elementtyp 1
MPTEMP,1,0                       ! Definiere Temperatur

!********** Base materials **********

MPDATA,EX,1,,EM                  ! Definiere E-Modul
MPDATA,EY,1,,EM                  ! Definiere E-Modul
MPDATA,EZ,1,,EM                  ! Definiere E-Modul
MPDATA,PRXY,1,,v                 ! Definiere Querdehnungszahl
MPDATA,PRYZ,1,,v                 ! Definiere Querdehnungszahl
MPDATA,PRXZ,1,,v

!MPDATA,EX,2,,EM                  ! Definiere E-Modul
!MPDATA,EY,2,,EM                  ! Definiere E-Modul
!MPDATA,EZ,2,,EM                  ! Definiere E-Modul
!MPDATA,PRXY,2,,v                 ! Definiere Querdehnungszahl
!MPDATA,PRYZ,2,,v                 ! Definiere Querdehnungszahl
!MPDATA,PRXZ,2,,v

TB,PLASTIC,1,1,27,MISO            ! Aktiviere TB,PLASTIC Dateneingabe
TBTEMP,0.0                       ! Temperatur = 0.0
TBPT,DEFI,0.0000,529
TBPT,DEFI,0.0055,530
TBPT,DEFI,0.0155,534
TBPT,DEFI,0.0255,568
TBPT,DEFI,0.0355,593
TBPT,DEFI,0.0455,614
TBPT,DEFI,0.0555,631
TBPT,DEFI,0.0655,645
TBPT,DEFI,0.0755,657
TBPT,DEFI,0.0855,667
TBPT,DEFI,0.0955,676
TBPT,DEFI,0.1055,685
TBPT,DEFI,0.1155,692
TBPT,DEFI,0.1213,697
TBPT,DEFI,0.1455,721
TBPT,DEFI,0.1705,742
TBPT,DEFI,0.1955,761
TBPT,DEFI,0.2455,794
TBPT,DEFI,0.2955,822
TBPT,DEFI,0.3455,847
TBPT,DEFI,0.3955,868
TBPT,DEFI,0.4955,906
TBPT,DEFI,0.5955,938
TBPT,DEFI,0.6955,966
TBPT,DEFI,0.7955,991
TBPT,DEFI,0.8955,1013
TBPT,DEFI,0.9955,1034

!********** Chord ***************

cyl4,0,H,Roc,0,ric,180,0
cyl4,0,H,Roc,180,ric,360,0
asel,all
aglue,all
vext,1,3,,,,L

!********** Creating working plane at a new location **********

wpoffs,0,880,200
wprota,0,40,0

!********** 1st brace *************

cyl4,0,Hob,Rob,0,rib,180,0
cyl4,0,Hob,Rob,180,rib,360,0
asel,all
aglue,all

csys,4
vext,11,13,0,,,400

csys,4
allsel
vext,21,0,0,0,0,400
vsba,5,4,,keep,keep
allsel

vdele,7,,,1
vdele,5,,,1

!*** penetrating brace into chord
csys,0
vext,31,,,,-100

vsba,5,4,,keep,keep
vsba,5,6,,keep,keep
vdele,5,,,1
vdele,7,,,1
vdele,8,,,1
allsel
!********** 2nd brace *********

vsel,s,volu,,3
vsel,a,volu,,4
vsel,a,volu,,6
cm,volume,volu

vsymm,z,volume,,0,,0,0
allsel

vsel,s,volu,,5
vsel,a,volu,,7
vsel,a,volu,,8
!vsel,a,volu,,10
cm,vgene,volu

vgen,2,vgene,,,,,1125*2 + g,,0,1

!*** Gluing 2nd brace with chord
vglue,8,1
allsel

!*** Refining chord volu for meshing
agen,2,1,,,,,750,0,0
agen,2,3,,,,,750,0,0

agen,3,43,44,,,,410,410,0,0

!*** Dividing volu into sub-volu
vsel,s,volu,,1
vsel,a,volu,,2
cm,volu-div,volu

asel,s,area,,43,48,1
cm,area-div,area
allsel

vsba,volu-div,area-div,,keep,keep

!*************Keypoints for evaluation of results
!**top part
k,1002,-0.35,979.99,1160        !mid of braces
k,43,-0.58,979.99,1227.39        !toe
k,44,-1.99,979.98,1445.13        !heel
k,41,-0.35,979.99,1570        !near to heel

!******Gluing volume parts together
vglue,17,9,11,15
vglue,17,16,10,12
vglue,15,16
vglue,17,3,4
vglue,6,5,7

!***** Meshing
smrt,5
mshkey,0
mshape,1,3d
vmesh,8

mshkey,1
vsweep,9
vsweep,10
vsweep,15
vsweep,16
vsweep,11
vsweep,12

vsweep,3
vsweep,4
vsweep,5
vsweep,7

!******* Boundary conditions *********

csys,0
nsel,s,loc,z,0        !restraning chord origin
d,all,all,0
allsel

nsel,s,loc,z,L        !restraning chord end
d,all,all,0
allsel

!***1st brace
csys,4
wpoffs,0,500,0
nsel,s,loc,z,1,-1
nsel,r,loc,y,0,200
nmodif,all,,,,,40,,
d,all,all,0
allsel

!***2nd brace
wprota,0,-40,0
wpoffs,0,0,1290
wprota,0,-40,0
wpoffs,0,18,

nsel,s,loc,z,0,50
nsel,r,loc,y,0,190
nmodif,all,,,,,-40,,
d,all,uz,-200
d,all,uy,0
d,all,ux,0
allsel
csys,0

!autots,on
kbc,0
NSUBST,50,300,50

antype,static

/solu
outres,all,all
solve
finish

save

bsista posted this 17 March 2019

When I draw the load displacement curve, the load keeps increasing always unless the curve becomes smooth and parallel to x-axis rather than the curve going down after reaching ultimate load. What can be the problem?

Ahmad, the multilinear plastic model that you defined does not include any information about the ultimate load. Once the total plastic strain in the material goes beyond the max. value defined in the curve, the solver treats the material as perfectly plastic (stress-strain curve parallel to X-axis). If the objective of your simulation is to check at what point does the structure fail, then look for the displacement at which the max. stress in the structure reaches its ultimate strength.

Ahmad Abubakar posted this 17 March 2019

Hey,

But as for the case of tensile test where the curve experiences negative slope when necking occurs, shouldn't there also be a negative slope for my case when the specimen undergoes large deflection when loaded?

bsista posted this 17 March 2019

But the curve that you had input does not contain that portion of the material so the model will not record that response.

A bit of digression but relevant information: when you input the material response note that the deformation should be uniform (same strain throughout the material) which is not the case when necking happens.

Also, you're performing a static analysis in which case a negative slope is considered as instability and you will run into convergence issues. In your case, you're still able to achieve convergence (I'm assuming you do) as your loading is displacement driven.

Vitaliy_Degtyarev posted this 17 March 2019

When I ran your file, I got some errors; and the model looks as shown below, which does not seem to be correct. Could you double check your model?

Thanks,

Vitaliy

Ahmad Abubakar posted this 17 March 2019

Hey,

Thats little strange I just copied the code I posted and by me it runs okay.

Vitaliy_Degtyarev posted this 17 March 2019

Below is the error message I received. Hopefully, ANSYS people on the forum could help us with this.

Internal error in the volume Sweeping.  The VSWE command is ignored.

to your technical support provider, as this will allow ANSYS, Inc to

improve the program.

Ahmad Abubakar posted this 18 March 2019

Hey Vitaliy,

Can you run this code? Its with same material model but with rectangular hollow section and mapped meshing.

finish
/clear,start
/filname,Model_8_S500M_SHS,1

*afun,deg
/UNITS,SI
boptn,keep,no
!********** chord parameters *************
Bo=0.280
Ho=0.280
To=0.012
Len=2.1

!********** brace parameters *************
b1=0.185
h1=0.185
t1=0.0096
lob=0.70    !length of brace
lo=1.47        !location of brace from chord origin
linc=0.8    !inclined length of brace
ro=0.0192
ri=0.0096
gap= 0.085    ! weld gap b/w two braces

!********** Material parameters ***********
EM=210000000000 !(Pa)
v=0.3

!********** Element definition ***********
/prep7
et,1,42
et,2,186

Type,all            !Zuweistung zu Elementtyp 1
MPTEMP,1,0                       ! Definiere Temperatur

!********** Base materials **********

MPDATA,EX,1,,EM                  ! Definiere E-Modul
MPDATA,EY,1,,EM                  ! Definiere E-Modul
MPDATA,EZ,1,,EM                  ! Definiere E-Modul
MPDATA,PRXY,1,,v                 ! Definiere Querdehnungszahl
MPDATA,PRYZ,1,,v                 ! Definiere Querdehnungszahl
MPDATA,PRXZ,1,,v

MPDATA,EX,2,,EM                  ! Definiere E-Modul
MPDATA,EY,2,,EM                  ! Definiere E-Modul
MPDATA,EZ,2,,EM                  ! Definiere E-Modul
MPDATA,PRXY,2,,v                 ! Definiere Querdehnungszahl
MPDATA,PRYZ,2,,v                 ! Definiere Querdehnungszahl
MPDATA,PRXZ,2,,v

TB,PLASTIC,1,1,27,MISO            ! Aktiviere TB,PLASTIC Dateneingabe
TBTEMP,0.0                       ! Temperatur = 0.0
TBPT,DEFI,0.0000,529000000
TBPT,DEFI,0.0055,530000000
TBPT,DEFI,0.0155,534000000
TBPT,DEFI,0.0255,568000000
TBPT,DEFI,0.0355,593000000
TBPT,DEFI,0.0455,614000000
TBPT,DEFI,0.0555,631000000
TBPT,DEFI,0.0655,645000000
TBPT,DEFI,0.0755,657000000
TBPT,DEFI,0.0855,667000000
TBPT,DEFI,0.0955,676000000
TBPT,DEFI,0.1055,685000000
TBPT,DEFI,0.1155,692000000
TBPT,DEFI,0.1213,697000000
TBPT,DEFI,0.1455,721000000
TBPT,DEFI,0.1705,742000000
TBPT,DEFI,0.1955,761000000
TBPT,DEFI,0.2455,794000000
TBPT,DEFI,0.2955,822000000
TBPT,DEFI,0.3455,847000000
TBPT,DEFI,0.3955,868000000
TBPT,DEFI,0.4955,906000000
TBPT,DEFI,0.5955,938000000
TBPT,DEFI,0.6955,966000000
TBPT,DEFI,0.7955,991000000
TBPT,DEFI,0.8955,1013000000
TBPT,DEFI,0.9955,1034000000

!********** chord ***********

asel,s,area,,all

allsel

asel,s,area,,all

allsel

rect,rco,bo-rco,0,to
rect,rco,bo-rco,ho,ho-to
rect,0,to,rco,ho-rco
rect,bo-to,bo,rco,ho-rco

allsel
aglue,all

vext,all,,,0,0,Len

vsel,all
vglue,all

!********** Creating wp at a new location **********
wpoffs,0.04625,Ho,0.7
wprota,0,40,0
wpoffs,0,0,-0.5
csys,4

!********** Brace **********
CYL4,ro,h1-ro,ro,-180,,-270,0
CYL4,ro,ro,ro,-90,,-180,0
CYL4,b1-ro,h1-ro,ro,0,,90,0
CYL4,b1-ro,ro,ro,-90,,0,0

asel,s,area,,41,44,1

allsel

CYL4,ro,h1-ro,ri,-180,,-270,0
CYL4,ro,ro,ri,-90,,-180,0
CYL4,b1-ro,h1-ro,ri,0,,90,0
CYL4,b1-ro,ro,ri,-90,,0

asel,s,area,,45,48,1

allsel

rect,ro,b1-ro,0,t1
rect,ro,b1-ro,h1,h1-t1
rect,0,t1,ro,h1-ro
rect,b1-t1,b1,ro,h1-ro

allsel
aglue,51,42,49,43,50,41,52,44

!*** Extruding 1st brace ****

csys,4
vext,41,48,1,0,0,0.75

wpoffs,0,0,0.5
wprota,0,50,0

vsel,s,volu,,9,16,1
vsbw,all,sepo,delete

vsel,all
vdele,25,32,1,1

wprota,0,-50,0
wpoffs,0,0,-0.5

!******** Generating 2nd brace *******
csys,0
vsymm,z,17,24,1,,0,0
vgen,2,9,16,1,,,1.02*2 + gap,,0,1

vglue,9,10,11,12,13,14,15,16        !gluing brace parts together

vgen,2,9,16,1,,,-0.03219,,0,1
vgen,2,17,24,1,,,0.03219,,0,1

!******** penetrating braces into chord by brace area

vext,90,,,,-to            !from first brace
vext,95,,,,-to
vext,85,,,,-to
vext,100,,,,-to
vext,103,,,,-to
vext,109,,,,-to
vext,106,,,,-to
vext,112,,,,-to

vext,50,,,,-to            !from second brace
vext,56,,,,-to
vext,62,,,,-to
vext,68,,,,-to
vext,74,,,,-to
vext,78,,,,-to
vext,114,,,,-to
vext,118,,,,-to

!***** Refining the geometry for meshing

agen,2,1,8,1,,,0.6935,,0,0
agen,2,1,8,1,,,1.43150,,0,0
agen,2,1,8,1,,,1.06250,,0,0

agen,2,1,,,,,0.763369897476,,0,0
agen,2,3,8,1,,,0.763369897476,,0,0
agen,2,1,,,,,0.991439010493,,0,0
agen,2,3,8,1,,,0.991439010493,,0,0

agen,2,1,,,,,1.13356098951,,0,0
agen,2,3,8,1,,,1.13356098951,,0,0
agen,2,1,,,,,1.36163010252,,0,0
agen,2,3,8,1,,,1.36163010252,,0,0

a,225,78,112,226
a,246,109,79,245
a,265,266,141,93
a,285,286,144,96

a,103,228,227,73
a,102,248,247,76
a,86,138,268,267
a,139,288,287,87

!********* Dividing volumes into sub volumes *********

vsel,s,volu,,1,8,1
cm,first-voludiv,volu

asel,s,area,,49,54,1
asel,a,area,,201,208,1
asel,a,area,,225,231,1
asel,a,area,,232,238,1
asel,a,area,,217,224,1
asel,a,area,,246,252,1
asel,a,area,,239,245,1
asel,a,area,,209,216,1

allsel
allsel

vsel,s,volu,,42
vsel,a,volu,,99
vsel,a,volu,,100
vsel,a,volu,,50
cm,sec-voludiv,volu

asel,a,area,,259,262,1
asel,a,area,,255,258,1

allsel
allsel

lcomb,663,664,no
lcomb,668,667,no

agen,2,292,,,0.04395,,,,0,0
agen,2,290,,,-0.04395,,,,0,0
agen,2,268,,,0.04395,,,,0,0
agen,2,266,,,-0.04395,,,,0,0

a,98,72,52,134        !between braces
a,100,71,55,136

vsel,s,volu,,113
vsel,a,volu,,116
cm,volubw-braces,volu

asel,s,area,,509
asel,a,area,,510
cm,areabw-braces,area

vsba,volubw-braces,areabw-braces,,keep,keep

allsel

a,131,42,294,296    !regularizing braces edges
a,290,129,39,292
a,65,105,299,300
a,107,304,303,66

vsel,s,volu,,50
vsel,a,volu,,42
vsel,a,volu,,114
vsel,a,volu,,115
cm,chord-voludiv,volu

asel,s,area,,505
asel,a,area,,506
asel,a,area,,507
asel,a,area,,508

asel,a,area,,218
asel,a,area,,530
asel,a,area,,531
asel,a,area,,532

allsel
allsel

!******Concatenating areas
accat,525,399
accat,330,544
accat,354,552
accat,520,396
accat,327,540

!****** Adding volumes again to make sure meshing

!****** Gluing volumes together to ensure meshing

vglue,118,40,34,39,36,37,33,38,35
vglue,117,30,28,29,27,31,26,32,25

!******* Meshing *********

mshkey,1

!***Braces

lsel,s,line,,98        !First brace
lsel,a,line,,101
lsel,a,line,,103
lsel,a,line,,100

lsel,a,line,,190    !Second brace
lsel,a,line,,186
lsel,a,line,,178
lsel,a,line,,182
cm,brace-semicircle,line

lsel,s,line,,73        !First brace
lsel,a,line,,81
lsel,a,line,,70
lsel,a,line,,84

lsel,a,line,,96        !Second brace
lsel,a,line,,127
lsel,a,line,,68
lsel,a,line,,113
cm,brace-thickness,line

lsel,s,line,,72        !First brace
lsel,a,line,,79
lsel,a,line,,69
lsel,a,line,,88

lsel,a,line,,114    !Second brace
lsel,a,line,,93
lsel,a,line,,128
lsel,a,line,,71
cm,brace-rect,line

allsel
lesize,brace-semicircle,,,7
lesize,brace-thickness,,,2
lesize,brace-rect,,,6
esize,0,5

vmesh,9,16,1
vmesh,17,24,1
allsel

!***Sweep part
lsel,s,line,,223    !for volu 117
lsel,a,line,,199
lsel,a,line,,205
lsel,a,line,,213

lsel,a,line,,278        !for volu 118
lsel,a,line,,272
lsel,a,line,,288
lsel,a,line,,262
cm,sweep-thickness,line

!lsel,s,line,,664
lsel,s,line,,165
lsel,a,line,,167
lsel,a,line,,164

lsel,a,line,,184
lsel,a,line,,192
lsel,a,line,,188
lsel,a,line,,180
cm,sweep-semicircle,line

lsel,s,line,,160
lsel,a,line,,139
lsel,a,line,,149
lsel,a,line,,135

lsel,a,line,,120
lsel,a,line,,106
lsel,a,line,,170
cm,sweep-rect,line

allsel
lesize,sweep-thickness,,,2
lesize,sweep-semicircle,,,7
lesize,sweep-rect,,,6

vsweep,110
vsweep,109
allsel

!****Brace adjacent side on chord (right and left)
lsel,s,line,,440    !First brace
lsel,a,line,,436
lsel,a,line,,488    !Second brace
lsel,a,line,,484

lsel,s,line,,501    !longitudinal direction
lsel,a,line,,500
lsel,a,line,,492
lsel,a,line,,494

lsel,s,line,,631    !First brace
lsel,a,line,,629
lsel,a,line,,645    !Sec brace
lsel,a,line,,647

allsel

vmesh,107
vmesh,108
vmesh,101
vmesh,105

!****Brace penetration into chord (right and left)
!(lesize cannot be controlled)

vmesh,26,28,2    !first brace
vmesh,35,36,1    !Second brace

!****Brace penetration into chord (front and back)
!(lesize cannot be controlled)

vmesh,25,27,2    !First brace
vmesh,33,34,1    !Second brace

!****Small curved volume edges

vmesh,37,40,1
vmesh,102,103,1
vmesh,104
vmesh,106

!****Brace adjacent sides on chord (front/back)
lsel,s,line,,696    !First brace
lsel,a,line,,687
lsel,a,line,,373    !Second brace
lsel,a,line,,705
cm,rec-long,line
allsel

lesize,rec-long,,,4
allsel

vmesh,119,125,6        !First brace
vmesh,120,126,6        !Second brace

!***** Concatenating/meshing the adjacent curve volu
accat,393,520        !First brace
accat,402,525        !Second brace
accat,548,351

vmesh,122,124,2        !front
vmesh,133,135,2        !back

lsel,s,line,,609,610,1
lsel,a,line,,613,614,1
lesize,all,,,3
allsel

vmesh,121,123,2        !front
vmesh,134,136,2        !back

!******* Chord curves surrounding braces to downwards
!*** Top-side curve
lsel,s,line,,366
lsel,a,line,,342
lsel,a,line,,344
lsel,a,line,,368
cm,chord-curves,line
allsel

lesize,chord-curves,,,3
allsel

vmesh,69,70,1
vmesh,93,94,1
vmesh,82,84,2
vmesh,81,83,2
vmesh,88,89,1
vmesh,62,63,1

!*** Flanges (left/right) beginning from 1st brace
lsel,s,line,,334
lsel,a,line,,332
lsel,a,line,,356
lsel,a,line,,358
lesize,all,,,5

vmesh,58,59,1
vmesh,86,87,1
vmesh,73,75,2
vmesh,74,76,2
vmesh,91,92,1
vmesh,65,66,1

!*** Bottom-side curve
lsel,s,line,,338,340,1
lsel,a,line,,362
lsel,a,line,,364
lesize,all,,,3
allsel

vmesh,60,61,1
vmesh,95,96,1
vmesh,77,80,1
vmesh,97,98,1
vmesh,67,68,1
allsel

!*** Bottom chord-rec
lesize,345,,,6
lesize,321,,,6
vmesh,57
vmesh,85
vmesh,71,72,1
vmesh,90
vmesh,64

!****** Chord remaining geometry
!*** From 1st Brace side***
lesize,526,,,9
lesize,678,,,9
lesize,524,,,9
lesize,527,,,9
lesize,671,,,9
lesize,673,,,9
lesize,527,,,9
lesize,530,,,9
vmesh,132        !top chord-rect
vmesh,127,128,1

vmesh,47,48,1        !top-side curves
vmesh,43,44,1        !flanges
vmesh,45,46,1        !bottom side curves
vmesh,41        !bottom chord-rect

!*** From 2nd brace side ***
vmesh,131        !top chord- rect
vmesh,129,130,1
vmesh,55,56        !top-side curves
vmesh,51,52        !flanges
vmesh,53,54        !bottom side curves
vmesh,49        !bottom chord-rect

!******* Boundary Conditions ********

csys,0
nsel,s,loc,z,0        !chord origin
d,all,all,0
allsel

nsel,s,loc,z,len    !chord end
d,all,all,0
allsel

csys,4
wpoffs,0,0,0.02
nsel,s,loc,z,0,0.01        !displacement at first brace
nsel,r,loc,y,0,0.3
nmodif,all,,,,,40,,
d,all,all,0

wprota,0,-40,0
wpoffs,0,0,1.45
wprota,0,-40,0

nsel,s,loc,z,0,0.03    !displacement at second brace
nsel,r,loc,y,0,0.3
nmodif,all,,,,,-40,,
d,all,uz,-0.3
d,all,uy,0
d,all,ux,0
allsel

!autots,on
kbc,0
NSUBST,30,200,30
outres,all,all

/solu
solve
finish

save

Vitaliy_Degtyarev posted this 19 March 2019

!autots,on
kbc,0
NSUBST,30,200,30
outres,all,all

Please try the following and see if it gives you what you are looking for

!autots,on
kbc,0
AUTOTS,1
NLGEOM,ON
NSUBST,100,1e6,100
outres,all,all

NLGEOM,ON makes a big difference. I checked reaction at one node only (you need to add all reactions at the end of the loaded brace to get the total load). The reaction went up, then down, then again up. I believe that it went up again due to the membrane action of the chord wall. Basically, the chord wall started to work in tension rather than in bending when wall deflections exceeded the wall thickness (please see large-deflection theory of thin plates for more information on this), which resulted in the hardening phase. Nether the reaction reduction nor hardening phase was observed when NLGEOM,ON was not used. AUTOTS,1 (or autots,on as in your file) may not be needed. I have not tried to run the file without it.

You should also check von Mises total mechanical strain and limit your maximum load to the one corresponding to the steel ultimate strain.

Hope this helps,

Vitaliy

• Liked by
Ahmad Abubakar posted this 21 March 2019

Vitaliy,

Thanks a lot for help. It works

leecooper posted this 16 September 2019