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Instability of Joint

 
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karanderohan
SEFI Member
SEFI Member


Joined: 17 Mar 2011
Posts: 6
Location: Mumbai

PostPosted: Tue Aug 30, 2011 3:52 am    Post subject: Instability of Joint Reply with quote

Dear All,

I have modelled the simple module in STAAD-V8i (as attached below).After doing analysis there is warning of instability of joint (Joint No. 6).
I have gone through the previous discussions about this and I have done accordingly ( I have assigned moment release), but still I am getting the same warning.

Please assist me in this.

Thanks and Regards
ROhan

STAAD SPACE
START JOB INFORMATION
ENGINEER DATE 29-Aug-11
END JOB INFORMATION
INPUT WIDTH 79
UNIT METER KN
JOINT COORDINATES
1 0 0 1; 2 0 0 0; 3 1.5 0 0; 4 1.5 0 1; 5 0 1.5 1; 6 0 1.5 0; 7 1.5 1.5 0;
8 1.5 1.5 1; 10 0.75 4 0.5;
MEMBER INCIDENCES
1 1 2; 2 2 3; 3 3 4; 4 4 1; 5 1 5; 6 2 6; 7 3 7; 8 4 8; 9 5 6; 10 6 7; 11 7 8;
12 8 5; 13 6 10; 14 7 10; 15 8 10; 16 5 10; 17 2 5; 18 2 7; 19 3 8; 20 1 8;
DEFINE MATERIAL START
ISOTROPIC STEEL
E 2.05e+008
POISSON 0.3
DENSITY 76.8195
ALPHA 1.2e-005
DAMP 0.03
ISOTROPIC CONCRETE
E 2.17185e+007
POISSON 0.17
DENSITY 23.5616
ALPHA 1e-005
DAMP 0.05
ISOTROPIC MODULE
E 2.5e+008
POISSON 0.3
DENSITY 164.136
ALPHA 1.2e-005
DAMP 0.3
END DEFINE MATERIAL
MEMBER PROPERTY AMERICAN
1 TO 4 9 TO 12 TABLE ST W4X13
17 TO 20 TABLE ST PIPS30
5 TO 8 TABLE ST PIPS40
MEMBER PROPERTY AMERICAN
13 TO 16 PRIS YD 0.05
CONSTANTS
MATERIAL MODULE ALL
SUPPORTS
10 PINNED
MEMBER RELEASE
16 START MX MY MZ
15 START MX MY MZ
14 START MX MY MZ
13 START MX MY MZ
LOAD 1 LOADTYPE None  TITLE DL
SELFWEIGHT Y -1 LIST 1 TO 20
PERFORM ANALYSIS PRINT STATICS LOAD
PARAMETER 1
CODE AISC
FYLD 248213 MEMB 1 TO 4 9 TO 12
FYLD 241290 MEMB 5 TO 8 17 TO 20
CHECK CODE MEMB 1 TO 12 17 TO 20
FINISH
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gpsarathyy
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Joined: 28 Jun 2010
Posts: 484
Location: chennai

PostPosted: Tue Aug 30, 2011 7:49 am    Post subject: Reply with quote

Dear Sefian,

You should not release all three rotations (Mx, My, Mz) for any beams at start or end. Restraint any one moment and check. Then it will be ok.
If you try the same in the GT strudl it will not even analyse. It will give the rotation warning.

_________________
G.PARTHASARATHY M.E. CEng(UK), MICE., MIE.,
CHENNAI
GPSARATHYY@GMAIL.COM
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karanderohan
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Joined: 17 Mar 2011
Posts: 6
Location: Mumbai

PostPosted: Tue Aug 30, 2011 9:12 am    Post subject: Instability of joint Reply with quote

Dear G.PARTHASARATHY

I have tried to release only single moment (either of Mx, Mx or My), but still same warning
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gpsarathyy
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Joined: 28 Jun 2010
Posts: 484
Location: chennai

PostPosted: Tue Aug 30, 2011 1:35 pm    Post subject: Reply with quote

Dear Sefian,

I also checked, it works without any member release only.
Then structural configuration has to be modified to avoid this warning.
Provide additional bracing and check.

_________________
G.PARTHASARATHY M.E. CEng(UK), MICE., MIE.,
CHENNAI
GPSARATHYY@GMAIL.COM
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karanderohan
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Joined: 17 Mar 2011
Posts: 6
Location: Mumbai

PostPosted: Wed Aug 31, 2011 11:12 am    Post subject: Instability of Joint Reply with quote

Dear Sefian,

As it is a sling (the tension member), so all the moments should be released, so as to ascertain that it is an axial member.
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karanderohan
SEFI Member
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Joined: 17 Mar 2011
Posts: 6
Location: Mumbai

PostPosted: Wed Aug 31, 2011 11:22 am    Post subject: Instability of Joint Reply with quote

Dear G.PARTHASARATHY



I have assigned the spring support with specified stiffness, in horizontal plane (X-Z), so as to restrain the horizontal motions that takes place during lifting.



Now I am not getting any instability warnings.



Please check with the attached file herewith.





Thanks and Regards,

Rohan





TAAD SPACE
START JOB INFORMATION
ENGINEER DATE 29-Aug-11
END JOB INFORMATION
INPUT WIDTH 79
UNIT METER KN
JOINT COORDINATES
1 0 0 1; 2 0 0 0; 3 1.5 0 0; 4 1.5 0 1; 5 0 1.5 1; 6 0 1.5 0; 7 1.5 1.5 0;
8 1.5 1.5 1; 10 0.75 4 0.5;
MEMBER INCIDENCES
1 1 2; 2 2 3; 3 3 4; 4 4 1; 5 1 5; 6 2 6; 7 3 7; 8 4 8; 9 5 6; 10 6 7; 11 7 8;
12 8 5; 13 6 10; 14 7 10; 15 8 10; 16 5 10; 17 2 5; 18 2 7; 19 3 8; 20 1 8;
DEFINE MATERIAL START
ISOTROPIC STEEL
E 2.05e+008
POISSON 0.3
DENSITY 76.8195
ALPHA 1.2e-005
DAMP 0.03
ISOTROPIC CONCRETE
E 2.17185e+007
POISSON 0.17
DENSITY 23.5616
ALPHA 1e-005
DAMP 0.05
ISOTROPIC MODULE
E 2.5e+008
POISSON 0.3
DENSITY 447.978
ALPHA 1.2e-005
DAMP 0.3
END DEFINE MATERIAL
MEMBER PROPERTY AMERICAN
13 TO 16 PRIS YD 0.05
9 TABLE ST W4X13
10 TABLE ST W4X13
12 TABLE ST W4X13
20 TABLE ST PIPS30
19 TABLE ST PIPS30
4 TABLE ST W4X13
5 TABLE ST PIPS40
6 TABLE ST PIPS40
17 TABLE ST PIPS30
18 TABLE ST PIPS30
11 TABLE ST W4X13
8 TABLE ST PIPS40
3 TABLE ST W4X13
1 TABLE ST W4X13
2 TABLE ST W4X13
7 TABLE ST PIPS40
CONSTANTS
MATERIAL MODULE MEMB 1 TO 12 17 TO 20
MATERIAL STEEL MEMB 13 TO 16
MEMBER RELEASE
13 START MX MY MZ
16 START MX MY MZ
14 START MX MY MZ
15 START MX MY MZ
SUPPORTS
6 FIXED BUT FY MX MY MZ KFX 5 KFZ 5
10 FIXED
LOAD 1 LOADTYPE None  TITLE DL
SELFWEIGHT Y -1 LIST 1 TO 20
PERFORM ANALYSIS PRINT STATICS LOAD
PARAMETER 1
CODE AISC
FYLD 248213 MEMB 1 TO 4 9 TO 12
FYLD 241290 MEMB 5 TO 8 17 TO 20
CHECK CODE MEMB 1 TO 12 17 TO 20
FINISH
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rahul.leslie
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Joined: 01 Apr 2008
Posts: 493
Location: Trivandrum

PostPosted: Wed Aug 31, 2011 11:26 am    Post subject: Reply with quote

I'm not sure whether this is what you wanted (attached). If it is the case, I shall explain what went wrong.
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karanderohan
SEFI Member
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Joined: 17 Mar 2011
Posts: 6
Location: Mumbai

PostPosted: Wed Aug 31, 2011 12:15 pm    Post subject: Instability of Joint Reply with quote

Dear Rahul,

Please guide me in this case

Thanks and regards,
Rohan
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