Code is as follows -
STAAD SPACESTART JOB INFORMATIONENGINEER DATE 28-Aug-18END JOB INFORMATIONINPUT WIDTH 79UNIT FEET POUNDJOINT COORDINATES1 -3.375 0 0; 2 -2.958 0 0; 3 -1.125 0 0; 4 -0.875 -1.574 0;5 -0.29167 -1.574 0; 6 0 0 0; 7 1.667 -1.574 0; 8 1.667 0 0; 9 3.334 0 0;10 5.001 -1.574 0; 11 5.001 0 0; 12 6.668 0 0; 13 8.335 -1.574 0; 14 8.335 0 0;15 10.002 0 0; 16 11.669 -1.574 0; 17 11.669 0 0; 18 13.336 0 0;19 15.003 -1.574 0; 20 15.003 0 0; 21 16.67 0 0; 22 18.337 -1.574 0;23 18.337 0 0; 24 20.004 0 0; 25 20.2957 -1.574 0; 26 20.879 -1.574 0;27 21.129 0 0; 28 22.962 0 0; 29 23.046 0 0;MEMBER INCIDENCES1 1 2; 2 2 3; 3 2 5; 4 3 5; 5 4 5; 6 3 6; 7 5 6; 8 5 7; 9 6 7; 10 6 8; 11 7 8;12 7 9; 13 8 9; 14 7 10; 15 9 10; 16 9 11; 17 10 11; 18 10 12; 19 11 12;20 10 13; 21 12 13; 22 12 14; 23 13 14; 24 13 15; 25 14 15; 26 13 16; 27 15 16;28 15 17; 29 16 17; 30 16 18; 31 17 18; 32 16 19; 33 18 19; 34 18 20; 35 19 20;36 19 21; 37 20 21; 38 19 22; 39 21 22; 40 21 23; 41 22 23; 42 22 24; 43 23 24;44 22 25; 45 24 25; 46 24 27; 47 25 26; 48 25 27; 49 25 28; 50 27 28; 51 28 29;DEFINE MATERIAL STARTISOTROPIC STEELE 4.176e+009POISSON 0.3DENSITY 489.024ALPHA 6e-006DAMP 0.03TYPE STEELSTRENGTH FY 7.2e+006 FU 9.36e+006 RY 1.5 RT 1.2G 1.60615e+009END DEFINE MATERIALMEMBER PROPERTY SJIJOIST1 TO 51 TABLE ST 24LH09CONSTANTSMATERIAL STEEL ALLSUPPORTS2 28 FIXED BUT FX MY MZMEMBER TRUSS 3 4 7 9 11 12 15 17 18 21 23 24 27 29 30 33 35 36 39 41 42 45 48 49LOAD 1 LOADTYPE Dead TITLE DEADMEMBER LOAD1 2 6 10 13 16 19 22 25 28 31 34 37 40 43 46 50 51 UNI GY -137.51 2 6 10 13 16 19 22 25 28 31 34 37 40 43 46 50 51 UNI GY -10LOAD 2 LOADTYPE Snow TITLE SNOW BALANCEDMEMBER LOAD1 2 6 10 13 16 19 22 25 28 31 34 37 40 43 46 50 51 UNI GY -137.5LOAD 3 LOADTYPE Snow TITLE SNOW DRIFTMEMBER LOAD22 TRAP GY -8.48224 0 0 0.62419 TRAP GY -31.1423 -8.48224 0 1.66716 TRAP GY -53.8024 -31.1423 0 1.66713 TRAP GY -76.4625 -53.8024 0 1.66710 TRAP GY -99.1225 -76.4625 0 1.6676 TRAP GY -114.415 -99.1225 0 1.1252 TRAP GY -139.332 -114.415 0 1.8331 TRAP GY -145 -139.332 0 0.41751 UNI GY -18550 UNI GY -185 1.75 1.833LOAD COMB 4 D+S1 1.0 2 1.0 3 1.0 PERFORM ANALYSIS*PARAMETER 1*CODE AISC UNIFIED 2010*METHOD ASD*DJ1 4 MEMB 5 8 14 20 26 32 38 44 47*DJ2 26 MEMB 5 8 14 20 26 32 38 44 47*DFF 0.09064 MEMB 5 8 14 20 26 32 38 44 47*DJ1 1 MEMB 1 2 6 10 13 16 19 22 25 28 31 34 37 40 43 46 50 51*DJ2 29 MEMB 1 2 6 10 13 16 19 22 25 28 31 34 37 40 43 46 50 51*DFF 0.11 MEMB 1 2 6 10 13 16 19 22 25 28 31 34 37 40 43 46 50 51FINISH
There are a few issues in your model:
1) You should not be using a Joist properties for this truss. Instead, use some standard section, i.e. channel, angle or any other from which the truss will be made.
2) Do not release FX direction for both supports.
3) Change MEMBER TRUSS specification to Partial Moment release with a factor 0.99 at both ends of the truss members. This will allow the truss member to experience or carry a very little moments even though in usual way we analyze the truss to carry axial force only, but will eliminate instabilities. You should change the input from:
MEMBER TRUSS 3 4 7 9 11 12 15 17 18 21 23 24 27 29 30 33 35 36 39 41 42 45 48 49
to:
MEMBER RELEASE3 4 7 9 11 12 15 17 18 21 23 24 27 29 30 33 35 36 39 41 42 45 48 -49 BOTH MPY 0.99 MPZ 0.99
With these modifications all warnings should disappear.
First and second point is very stupid I did. Thank You. I have changed that. I tried using that third point you have mentioned but then the thing is then every member of the top chord will fail for the defined loading. You can see that in this code I have modified -
STAAD SPACESTART JOB INFORMATIONENGINEER DATE 28-Aug-18END JOB INFORMATIONINPUT WIDTH 79UNIT FEET POUNDJOINT COORDINATES1 -3.375 0 0; 2 -2.958 0 0; 3 -1.125 0 0; 4 -0.875 -1.574 0;5 -0.29167 -1.574 0; 6 0 0 0; 7 1.667 -1.574 0; 8 1.667 0 0; 9 3.334 0 0;10 5.001 -1.574 0; 11 5.001 0 0; 12 6.668 -1.574 0; 13 6.668 0 0;14 8.335 -1.574 0; 15 8.335 0 0; 16 10.002 0 0; 17 11.669 -1.574 0;18 11.669 0 0; 19 13.336 -1.574 0; 20 13.336 0 0; 21 15.003 -1.574 0;22 15.003 0 0; 23 16.67 0 0; 24 18.337 -1.574 0; 25 18.337 0 0; 26 20.004 0 0;27 20.2957 -1.574 0; 28 20.879 -1.574 0; 29 21.129 0 0; 30 22.962 0 0;31 23.046 0 0;MEMBER INCIDENCES1 1 2; 2 2 3; 3 2 5; 4 3 5; 5 4 5; 6 3 6; 7 5 6; 8 5 7; 9 6 7; 10 6 8; 11 7 8;12 7 9; 13 8 9; 14 7 10; 15 9 10; 16 9 11; 17 10 11; 18 10 12; 19 10 13;20 11 13; 21 12 14; 22 13 14; 23 13 15; 24 14 15; 25 14 16; 26 15 16; 27 14 17;28 16 17; 29 16 18; 30 17 18; 31 17 19; 32 17 20; 33 18 20; 34 19 21; 35 20 21;36 20 22; 37 21 22; 38 21 23; 39 22 23; 40 21 24; 41 23 24; 42 23 25; 43 24 25;44 24 26; 45 25 26; 46 24 27; 47 26 27; 48 26 29; 49 27 28; 50 27 29; 51 27 30;52 29 30; 53 30 31;START USER TABLETABLE 1UNIT FEET POUNDGENERALL1X1X0.1090.00142805 0.083 0.083 0.0833 0.083 9.23571e-007 9.32e-007 3.88736e-008 -1.56679e-005 1.57707e-005 0.000627538 0.000630195 3.97331e-005 2.00648e-005 -1.97952e-011 0.083PROFILE_POINTS -0.024203 -0.024053 0.059097 -0.024053 0.059097 -0.01497 -0.01512 -0.01497 -0.01512 0.058947 -0.024203 0.058947L1.5X1.5X0.1380.00274275 0.125 0.125 0.125 0.125 4.0893e-006 4.0893e-006 1.20199e-007 -4.5687e-005 4.5687e-005 0.00119379 0.00119379 0.000115727 5.8267e-005 -1.41145e-010 0.125PROFILE_POINTS -0.0354932 -0.0354932 0.0895068 -0.0354932 0.0895068 -0.0239932 -0.0239932 -0.0239932 -0.0239932 0.0895068 -0.0354932 0.0895068L1.5X1.5X0.1130.0022655 0.125 0.125 0.125 0.125 3.42943e-006 3.42943e-006 6.74622e-008 -3.7993e-005 3.7993e-005 0.000976568 0.000976568 9.63999e-005 4.84214e-005 -7.99326e-011 0.125PROFILE_POINTS -0.0347352 -0.0347352 0.0902648 -0.0347352 0.0902648 -0.0253185 -0.0253185 -0.0253185 -0.0253185 0.0902648 -0.0347352 0.0902648L1.25X1.25X0.1090.00180985 0.104167 0.104167 0.104167 0.104167 1.88205e-006 1.88205e-006 -4.96043e-008 2.51709e-005 2.51709e-005 0.000785407 0.000785407 6.37924e-005 -3.20949e-005 4.06177e-011 0.104167PROFILE_POINTS -0.0293962 -0.0293962 0.0747708 -0.0293962 0.0747708 -0.0203129 -0.0203129 -0.0203129 -0.0203129 0.0747708 -0.0293962 0.07477082L2X2X0.1630.00642248 0.166666 0.166666 0.319749 0.166666 1.38921e-005 3.70354e-005 -3.99687e-007 0.000104535 0.000231653 0.00156886 0.00368668 0.00035424 -0.000184644 8.46334e-010 0.166666PROFILE_POINTS -0.159874 0.0201882 -0.0067915 0.0201882 -0.0067915 -0.132895 0.0067915 -0.132895 0.0067915 0.0201882 0.159874 0.0201882 0.159874 0.0337712 -0.159874 0.03377122L2X2X0.1370.00573063 0.166667 0.166667 0.324083 0.166667 1.32237e-005 3.24129e-005 -2.80594e-007 0.000100615 0.000199918 0.00147354 0.00314488 0.000306415 -0.000176607 6.06695e-010 0.166667PROFILE_POINTS -0.161952 0.0238211 -0.00670238 0.0238211 -0.00670238 -0.131429 0.00637762 -0.131429 0.00637762 0.0238211 0.162131 0.0238211 0.162131 0.0352378 -0.161952 0.0352378ENDDEFINE MATERIAL STARTISOTROPIC STEELE 4.176e+009POISSON 0.3DENSITY 489.024ALPHA 6e-006DAMP 0.03TYPE STEELSTRENGTH FY 7.2e+006 FU 9.36e+006 RY 1.5 RT 1.2G 1.60615e+009END DEFINE MATERIALMEMBER PROPERTY AMERICAN4 11 17 22 24 30 32 37 43 50 UPTABLE 1 L1X1X0.1097 12 41 47 UPTABLE 1 L1.5X1.5X0.1389 44 UPTABLE 1 L1.5X1.5X0.11315 19 25 28 35 38 UPTABLE 1 L1.25X1.25X0.1091 TO 3 6 10 13 16 20 23 26 29 33 36 39 42 45 48 51 TO 53 UPTABLE 1 2L2X2X0.1635 8 14 18 21 27 31 34 40 46 49 UPTABLE 1 2L2X2X0.137CONSTANTSBETA 180 MEMB 5 8 14 18 21 27 31 34 40 46 49MATERIAL STEEL ALLSUPPORTS2 PINNED31 FIXED BUT FX MY MZ12 19 FIXED BUT FX FY MX MY MZMEMBER TRUSS 3 4 7 9 11 12 15 17 19 22 24 25 28 30 32 35 37 38 41 43 44 47 50 51*MEMBER RELEASE*2 6 8 10 13 14 16 18 20 23 26 27 29 31 33 36 39 40 42 45 46 48 49 -*52 START MP 0.99*2 6 8 10 13 14 16 20 21 23 26 27 29 33 34 36 39 40 42 45 46 48 52 END MP 0.99LOAD 1 LOADTYPE Dead TITLE DEADMEMBER LOAD1 2 6 10 13 16 20 23 26 29 33 36 39 42 45 48 52 53 UNI GY -137.51 2 6 10 13 16 20 23 26 29 33 36 39 42 45 48 52 53 UNI GY -10LOAD 2 LOADTYPE Snow TITLE SNOW BALANCEDMEMBER LOAD1 2 6 10 13 16 20 23 26 29 33 36 39 42 45 48 52 53 UNI GY -137.5LOAD 3 LOADTYPE Snow TITLE SNOW DRIFTMEMBER LOAD23 TRAP GY -8.48224 0 0 0.62420 TRAP GY -31.1423 -8.48224 0 1.66716 TRAP GY -53.8024 -31.1423 0 1.66713 TRAP GY -76.4625 -53.8024 0 1.66710 TRAP GY -99.1225 -76.4625 0 1.6676 TRAP GY -114.415 -99.1225 0 1.1252 TRAP GY -139.332 -114.415 0 1.8331 TRAP GY -145 -139.332 0 0.41753 UNI GY -18552 UNI GY -185 1.75 1.833LOAD 5 LOADTYPE Dead TITLE SpecialMEMBER LOAD1 2 6 10 13 16 20 23 26 29 33 36 39 42 45 48 52 53 UNI GY -573LOAD COMB 4 D+S1 1.0 2 1.0 3 1.0 PERFORM ANALYSISPARAMETER 1CODE AISC UNIFIED 2010METHOD ASD**DJ1 4 MEMB 5 8 14 18 21 27 31 34 40 46 49**DJ2 28 MEMB 5 8 14 18 21 27 31 34 40 46 49**DFF 0.09064 MEMB 5 8 14 18 21 27 31 34 40 46 49**DJ1 1 MEMB 1 2 6 10 13 16 20 23 26 29 33 36 39 42 45 48 52 53**DJ2 31 MEMB 1 2 6 10 13 16 20 23 26 29 33 36 39 42 45 48 52 53**DFF 0.11 MEMB 1 2 6 10 13 16 20 23 26 29 33 36 39 42 45 48 52 53CHECK CODE ALLFINISH
It does not matter if you are using MEMBER TRUSS or PARTIAL RELEASE specification - the members in the top chord will be failing in any case. The suggestion to use PARTIAL RELEASE specification was just to get rid off the instability warnings.I see that you are not defining any design parameters for the design. Do you really want to perform the design with the default values of the design parameters? In such case, you probably need to increase the section sizes of the members which are failing.
I will give design values. Skipped it for now as I want to see the behavior of the model. Thanks