Unusual behaviour of truss members

We experience this problem when we assign "Truss member" to cross bracing.
The structural behaviour is normal without "Truss member" specs assigned.

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*************STAAD EDITOR**************

STAAD SPACE PH
START JOB INFORMATION
ENGINEER DATE 01-JUL-2021
JOB NAME CONV
JOB PART CONV99
END JOB INFORMATION
***
INPUT WIDTH 79
SET NL 300
*** NODE
UNIT METER KN
JOINT COORDINATES
310001 1.288 3.97127 0; 310002 0.8115 3.97127 0; 310003 0.335 3.97127 0;
310005 -0.335 3.97127 0; 310006 -0.8115 3.97127 0; 310007 -1.288 3.97127 0;
310013 0.335 3.97343 0.04; 310015 -0.335 3.97343 0.04;
310023 0.335 3.97541 0.0765; 310025 -0.335 3.97541 0.0765;
310031 1.288 3.9875 0.299673; 310032 0.8115 3.9875 0.299673;
310033 0.335 3.9875 0.299673; 310035 -0.335 3.9875 0.299673;
310036 -0.8115 3.9875 0.299673; 310037 -1.288 3.9875 0.299673;
310041 1.288 4.00246 0.575939; 310042 0.8115 4.00246 0.575939;
310043 0.335 4.00246 0.575939; 310045 -0.335 4.00246 0.575939;
310046 -0.8115 4.00246 0.575939; 310047 -1.288 4.00246 0.575939;
310051 1.288 4.01742 0.852206; 310052 0.8115 4.01742 0.852206;
310053 0.335 4.01742 0.852206; 310054 0 4.01742 0.852206;
310055 -0.335 4.01742 0.852206; 310056 -0.8115 4.01742 0.852206;
310057 -1.288 4.01742 0.852206; 310061 1.288 4.03238 1.12847;
310062 0.8115 4.03238 1.12847; 310063 0.335 4.03238 1.12847;
310065 -0.335 4.03238 1.12847; 310066 -0.8115 4.03238 1.12847;
310067 -1.288 4.03238 1.12847; 310071 1.288 4.04735 1.40474;
310072 0.8115 4.04735 1.40474; 310073 0.335 4.04735 1.40474;
310075 -0.335 4.04735 1.40474; 310076 -0.8115 4.04735 1.40474;
310077 -1.288 4.04735 1.40474; 310081 1.288 4.06465 1.72427;
310082 0.8115 4.06465 1.72427; 310083 0.335 4.06465 1.72427;
310085 -0.335 4.06465 1.72427; 310086 -0.8115 4.06465 1.72427;
310087 -1.288 4.06465 1.72427; 310091 1.288 4.08196 2.0438;
310092 0.8115 4.08196 2.0438; 310093 0.335 4.08196 2.0438;
310094 0 4.08196 2.0438; 310095 -0.335 4.08196 2.0438;
310096 -0.8115 4.08196 2.0438; 310097 -1.288 4.08196 2.0438;
310101 1.288 4.09926 2.36333; 310102 0.8115 4.09926 2.36333;
310103 0.335 4.09926 2.36333; 310105 -0.335 4.09926 2.36333;
310106 -0.8115 4.09926 2.36333; 310107 -1.288 4.09926 2.36333;
310111 1.288 4.11657 2.68287; 310112 0.8115 4.11657 2.68287;
310113 0.335 4.11657 2.68287; 310115 -0.335 4.11657 2.68287;
310116 -0.8115 4.11657 2.68287; 310117 -1.288 4.11657 2.68287;
310121 1.288 4.13387 3.0024; 310122 0.8115 4.13387 3.0024;
310123 0.335 4.13387 3.0024; 310125 -0.335 4.13387 3.0024;
310126 -0.8115 4.13387 3.0024; 310127 -1.288 4.13387 3.0024;
310131 1.288 4.15118 3.32193; 310132 0.8115 4.15118 3.32193;
310133 0.335 4.15118 3.32193; 310134 0 4.15118 3.32193;
310135 -0.335 4.15118 3.32193; 310136 -0.8115 4.15118 3.32193;
310137 -1.288 4.15118 3.32193; 310141 1.288 4.16848 3.64146;
310142 0.8115 4.16848 3.64146; 310143 0.335 4.16848 3.64146;
310145 -0.335 4.16848 3.64146; 310146 -0.8115 4.16848 3.64146;
310147 -1.288 4.16848 3.64146; 310151 1.288 4.18579 3.96099;
310152 0.8115 4.18579 3.96099; 310153 0.335 4.18579 3.96099;
310155 -0.335 4.18579 3.96099; 310156 -0.8115 4.18579 3.96099;
310157 -1.288 4.18579 3.96099; 310161 1.288 4.20309 4.28052;
310162 0.8115 4.20309 4.28052; 310163 0.335 4.20309 4.28052;
310165 -0.335 4.20309 4.28052; 310166 -0.8115 4.20309 4.28052;
310167 -1.288 4.20309 4.28052; 310171 1.288 4.2204 4.60006;
310172 0.8115 4.2204 4.60006; 310173 0.335 4.2204 4.60006;
310174 0 4.2204 4.60006; 310175 -0.335 4.2204 4.60006;
310176 -0.8115 4.2204 4.60006; 310177 -1.288 4.2204 4.60006;
310181 1.288 4.2377 4.91959; 310182 0.8115 4.2377 4.91959;
310183 0.335 4.2377 4.91959; 310185 -0.335 4.2377 4.91959;
310186 -0.8115 4.2377 4.91959; 310187 -1.288 4.2377 4.91959;
310191 1.288 4.25501 5.23912; 310192 0.8115 4.25501 5.23912;
310193 0.335 4.25501 5.23912; 310195 -0.335 4.25501 5.23912;
310196 -0.8115 4.25501 5.23912; 310197 -1.288 4.25501 5.23912;
310201 1.288 4.27231 5.55865; 310202 0.8115 4.27231 5.55865;
310203 0.335 4.27231 5.55865; 310205 -0.335 4.27231 5.55865;
310206 -0.8115 4.27231 5.55865; 310207 -1.288 4.27231 5.55865;
310211 1.288 4.28962 5.87818; 310212 0.8115 4.28962 5.87818;
310213 0.335 4.28962 5.87818; 310214 0 4.28962 5.87818;
310215 -0.335 4.28962 5.87818; 310216 -0.8115 4.28962 5.87818;
310217 -1.288 4.28962 5.87818; 310221 1.288 4.30692 6.19771;
310222 0.8115 4.30692 6.19771; 310223 0.335 4.30692 6.19771;
310225 -0.335 4.30692 6.19771; 310226 -0.8115 4.30692 6.19771;
310227 -1.288 4.30692 6.19771; 310231 1.288 4.32423 6.51725;
310232 0.8115 4.32423 6.51725; 310233 0.335 4.32423 6.51725;
310235 -0.335 4.32423 6.51725; 310236 -0.8115 4.32423 6.51725;
310237 -1.288 4.32423 6.51725; 310241 1.288 4.34153 6.83678;
310242 0.8115 4.34153 6.83678; 310243 0.335 4.34153 6.83678;
310245 -0.335 4.34153 6.83678; 310246 -0.8115 4.34153 6.83678;
310247 -1.288 4.34153 6.83678; 310251 1.288 4.35884 7.15631;
310252 0.8115 4.35884 7.15631; 310253 0.335 4.35884 7.15631;
310254 0 4.35884 7.15631; 310255 -0.335 4.35884 7.15631;
310256 -0.8115 4.35884 7.15631; 310257 -1.288 4.35884 7.15631;
310261 1.288 4.37615 7.47584; 310262 0.8115 4.37615 7.47584;
310263 0.335 4.37615 7.47584; 310265 -0.335 4.37615 7.47584;
310266 -0.8115 4.37615 7.47584; 310267 -1.288 4.37615 7.47584;
310271 1.288 4.39345 7.79537; 310272 0.8115 4.39345 7.79537;
310273 0.335 4.39345 7.79537; 310275 -0.335 4.39345 7.79537;
310276 -0.8115 4.39345 7.79537; 310277 -1.288 4.39345 7.79537;
310281 1.288 4.40841 8.07164; 310282 0.8115 4.40841 8.07164;
310283 0.335 4.40841 8.07164; 310285 -0.335 4.40841 8.07164;
310286 -0.8115 4.40841 8.07164; 310287 -1.288 4.40841 8.07164;
310291 1.288 4.42337 8.34791; 310292 0.8115 4.42337 8.34791;
310293 0.335 4.42337 8.34791; 310294 0 4.42337 8.34791;
310295 -0.335 4.42337 8.34791; 310296 -0.8115 4.42337 8.34791;
310297 -1.288 4.42337 8.34791; 310301 1.288 4.43834 8.62417;
310302 0.8115 4.43834 8.62417; 310303 0.335 4.43834 8.62417;
310305 -0.335 4.43834 8.62417; 310306 -0.8115 4.43834 8.62417;
310307 -1.288 4.43834 8.62417; 310311 1.288 4.4533 8.90044;
310312 0.8115 4.4533 8.90044; 310313 0.335 4.4533 8.90044;
310315 -0.335 4.4533 8.90044; 310316 -0.8115 4.4533 8.90044;
310317 -1.288 4.4533 8.90044; 310323 0.335 4.46539 9.12361;
310325 -0.335 4.46539 9.12361; 310333 0.335 4.46736 9.16;
310335 -0.335 4.46736 9.16; 310341 1.288 4.46952 9.2;
310342 0.8115 4.46952 9.2; 310343 0.335 4.46952 9.2; 310345 -0.335 4.46952 9.2;
310346 -0.8115 4.46952 9.2; 310347 -1.288 4.46952 9.2;
*** MEMBER
MEMBER INCIDENCES
310001 310003 310013; 310002 310013 310023; 310003 310023 310033;
310004 310033 310043; 310005 310043 310053; 310006 310053 310063;
310007 310063 310073; 310008 310073 310083; 310009 310083 310093;
310010 310093 310103; 310011 310103 310113; 310012 310113 310123;
310013 310123 310133; 310014 310133 310143; 310015 310143 310153;
310016 310153 310163; 310017 310163 310173; 310018 310173 310183;
310019 310183 310193; 310020 310193 310203; 310021 310203 310213;
310022 310213 310223; 310023 310223 310233; 310024 310233 310243;
310025 310243 310253; 310026 310253 310263; 310027 310263 310273;
310028 310273 310283; 310029 310283 310293; 310030 310293 310303;
310031 310303 310313; 310032 310313 310323; 310033 310323 310333;
310034 310333 310343; 310101 310005 310015; 310102 310015 310025;
310103 310025 310035; 310104 310035 310045; 310105 310045 310055;
310106 310055 310065; 310107 310065 310075; 310108 310075 310085;
310109 310085 310095; 310110 310095 310105; 310111 310105 310115;
310112 310115 310125; 310113 310125 310135; 310114 310135 310145;
310115 310145 310155; 310116 310155 310165; 310117 310165 310175;
310118 310175 310185; 310119 310185 310195; 310120 310195 310205;
310121 310205 310215; 310122 310215 310225; 310123 310225 310235;
310124 310235 310245; 310125 310245 310255; 310126 310255 310265;
310127 310265 310275; 310128 310275 310285; 310129 310285 310295;
310130 310295 310305; 310131 310305 310315; 310132 310315 310325;
310133 310325 310335; 310134 310335 310345; 311011 310031 310032;
311012 310032 310033; 311013 310035 310036; 311014 310036 310037;
311021 310071 310072; 311022 310072 310073; 311023 310075 310076;
311024 310076 310077; 311031 310111 310112; 311032 310112 310113;
311033 310115 310116; 311034 310116 310117; 311041 310151 310152;
311042 310152 310153; 311043 310155 310156; 311044 310156 310157;
311051 310191 310192; 311052 310192 310193; 311053 310195 310196;
311054 310196 310197; 311061 310231 310232; 311062 310232 310233;
311063 310235 310236; 311064 310236 310237; 311071 310271 310272;
311072 310272 310273; 311073 310275 310276; 311074 310276 310277;
311081 310311 310312; 311082 310312 310313; 311083 310315 310316;
311084 310316 310317; 312111 310001 310031; 312112 310031 310041;
312113 310041 310051; 312114 310051 310061; 312115 310061 310071;
312116 310071 310081; 312117 310081 310091; 312118 310091 310101;
312119 310101 310111; 312120 310111 310121; 312121 310121 310131;
312122 310131 310141; 312123 310141 310151; 312124 310151 310161;
312125 310161 310171; 312126 310171 310181; 312127 310181 310191;
312128 310191 310201; 312129 310201 310211; 312130 310211 310221;
312131 310221 310231; 312132 310231 310241; 312133 310241 310251;
312134 310251 310261; 312135 310261 310271; 312136 310271 310281;
312137 310281 310291; 312138 310291 310301; 312139 310301 310311;
312140 310311 310341; 312211 310002 310032; 312212 310032 310042;
312213 310042 310052; 312214 310052 310062; 312215 310062 310072;
312216 310072 310082; 312217 310082 310092; 312218 310092 310102;
312219 310102 310112; 312220 310112 310122; 312221 310122 310132;
312222 310132 310142; 312223 310142 310152; 312224 310152 310162;
312225 310162 310172; 312226 310172 310182; 312227 310182 310192;
312228 310192 310202; 312229 310202 310212; 312230 310212 310222;
312231 310222 310232; 312232 310232 310242; 312233 310242 310252;
312234 310252 310262; 312235 310262 310272; 312236 310272 310282;
312237 310282 310292; 312238 310292 310302; 312239 310302 310312;
312240 310312 310342; 312311 310006 310036; 312312 310036 310046;
312313 310046 310056; 312314 310056 310066; 312315 310066 310076;
312316 310076 310086; 312317 310086 310096; 312318 310096 310106;
312319 310106 310116; 312320 310116 310126; 312321 310126 310136;
312322 310136 310146; 312323 310146 310156; 312324 310156 310166;
312325 310166 310176; 312326 310176 310186; 312327 310186 310196;
312328 310196 310206; 312329 310206 310216; 312330 310216 310226;
312331 310226 310236; 312332 310236 310246; 312333 310246 310256;
312334 310256 310266; 312335 310266 310276; 312336 310276 310286;
312337 310286 310296; 312338 310296 310306; 312339 310306 310316;
312340 310316 310346; 312411 310007 310037; 312412 310037 310047;
312413 310047 310057; 312414 310057 310067; 312415 310067 310077;
312416 310077 310087; 312417 310087 310097; 312418 310097 310107;
312419 310107 310117; 312420 310117 310127; 312421 310127 310137;
312422 310137 310147; 312423 310147 310157; 312424 310157 310167;
312425 310167 310177; 312426 310177 310187; 312427 310187 310197;
312428 310197 310207; 312429 310207 310217; 312430 310217 310227;
312431 310227 310237; 312432 310237 310247; 312433 310247 310257;
312434 310257 310267; 312435 310267 310277; 312436 310277 310287;
312437 310287 310297; 312438 310297 310307; 312439 310307 310317;
312440 310317 310347; 313001 310023 310025; 313002 310323 310325;
313101 310001 310002; 313102 310002 310003; 313103 310005 310006;
313104 310006 310007; 313201 310341 310342; 313202 310342 310343;
313203 310345 310346; 313204 310346 310347; 314001 310033 310035;
314002 310073 310075; 314003 310113 310115; 314004 310153 310155;
314005 310193 310195; 314006 310233 310235; 314007 310273 310275;
314008 310313 310315; 314101 310033 310054; 314102 310035 310054;
314103 310054 310075; 314104 310054 310073; 314105 310073 310094;
314106 310075 310094; 314107 310094 310115; 314108 310094 310113;
314109 310113 310134; 314110 310115 310134; 314111 310134 310155;
314112 310134 310153; 314113 310153 310174; 314114 310155 310174;
314115 310174 310195; 314116 310174 310193; 314117 310193 310214;
314118 310195 310214; 314119 310214 310235; 314120 310214 310233;
314121 310233 310254; 314122 310235 310254; 314123 310254 310275;
314124 310254 310273; 314125 310273 310294; 314126 310275 310294;
314127 310294 310315; 314128 310294 310313; 315101 310033 310054;
315102 310035 310054; 315103 310054 310075; 315104 310054 310073;
315105 310073 310094; 315106 310075 310094; 315107 310094 310115;
315108 310094 310113; 315109 310113 310134; 315110 310115 310134;
315111 310134 310155; 315112 310134 310153; 315113 310153 310174;
315114 310155 310174; 315115 310174 310195; 315116 310174 310193;
315117 310193 310214; 315118 310195 310214; 315119 310214 310235;
315120 310214 310233; 315121 310233 310254; 315122 310235 310254;
315123 310254 310275; 315124 310254 310273; 315125 310273 310294;
315126 310275 310294; 315127 310294 310315; 315128 310294 310313;
*** GROUPS
START GROUP DEFINITION
MEMBER
_CNV31_GIR-1 310001 TO 310034 310101 TO 310134
_CNV31_GIR-11 310001 TO 310034
_CNV31_GIR-12 310101 TO 310134
_CNV31_GIR_CRS-1 314001 TO 314008
_CNV31_GIR_CRS-2 313001 313002
_CNV31_CRS_BEAM 311011 TO 311014 311021 TO 311024 311031 TO 311034 311041 -
311042 TO 311044 311051 TO 311054 311061 TO 311064 311071 TO 311074 311081 -
311082 TO 311084
_CNV31_FLR_BEAM-1 312111 TO 312140 312411 TO 312440
_CNV31_FLR_BEAM-11 312111 TO 312140
_CNV31_FLR_BEAM-12 312411 TO 312440
_CNV31_FLR_BEAM-2 312211 TO 312240 312311 TO 312340
_CNV31_FLR_BEAM-21 312211 TO 312240
_CNV31_FLR_BEAM-22 312311 TO 312340
_CNV31_FLR_BEAM_S 312112 312116 312120 312124 312128 312132 312136 312212 -
312216 312220 312224 312228 312232 312236 312312 312316 312320 312324 312328 -
312332 312336 312412 312416 312420 312424 312428 312432 312436
_CNV31_FLR_BEAM_E 312115 312119 312123 312127 312131 312135 312139 312215 -
312219 312223 312227 312231 312235 312239 312315 312319 312323 312327 312331 -
312335 312339 312415 312419 312423 312427 312431 312435 312439
_CNV31_FLR_CRS 313101 TO 313104 313201 TO 313204
_CNV31_FLR_CRS_S 313101 313103 313201 313203
_CNV31_FLR_CRS_E 313102 313104 313202 313204
_CNV31_BRC 314101 TO 314128 315101 TO 315128
_CNV31_BRC-1 314101 TO 314128
_CNV31_BRC-2 315101 TO 315128
_CNV31_BRC-11 314101 314103 314105 314107 314109 314111 314113 314115 314118 -
314120 314122 314124 314126 314128
_CNV31_BRC-12 314102 314104 314106 314108 314110 314112 314114 314116 314117 -
314119 314121 314123 314125 314127
_CNV31_BRC-21 315101 315103 315105 315107 315109 315111 315113 315115 315118 -
315120 315122 315124 315126 315128
_CNV31_BRC-22 315102 315104 315106 315108 315110 315112 315114 315116 315117 -
315119 315121 315123 315125 315127
_CNV31_CHK_MEMB 310001 TO 310034 310101 TO 310134 311011 TO 311014 311021 -
311022 TO 311024 311031 TO 311034 311041 TO 311044 311051 TO 311054 311061 -
311062 TO 311064 311071 TO 311074 311081 TO 311084 312111 TO 312140 312211 -
312212 TO 312240 312311 TO 312340 312411 TO 312440 313001 313002 -
313101 TO 313104 313201 TO 313204 314001 TO 314008 314101 TO 314128 315101 -
315102 TO 315128
_CNV31_STEEL 310001 TO 310034 310101 TO 310134 311011 TO 311014 -
311021 TO 311024 311031 TO 311034 311041 TO 311044 311051 TO 311054 311061 -
311062 TO 311064 311071 TO 311074 311081 TO 311084 312111 TO 312140 312211 -
312212 TO 312240 312311 TO 312340 312411 TO 312440 313001 313002 -
313101 TO 313104 313201 TO 313204 314001 TO 314008 314101 TO 314128 315101 -
315102 TO 315128
_CNV31_HND 312111 TO 312140 312411 TO 312440
JOINT
_CNV31_SPRT 310013 310015 310333 310335
FLOOR
_CNV31_FLR-1 310001 TO 310034 310101 TO 310134 312111 TO 312140 -
312211 TO 312240 312311 TO 312340 312411 TO 312440 313101 TO 313104 313201 -
313202 TO 313204
_CNV31_FLR-11 310001 TO 310034 312111 TO 312140 312211 TO 312240 313101 -
313102 313201 313202
_CNV31_FLR-12 310101 TO 310134 312311 TO 312340 312411 TO 312440 313103 -
313104 313203 313204
END GROUP DEFINITION
DEFINE MATERIAL START
ISOTROPIC STEEL
E 2.05e+08
POISSON 0.3
DENSITY 77
ALPHA 1.2e-05
DAMP 0.03
TYPE STEEL
STRENGTH FY 253200 FU 407800 RY 1.5 RT 1.2
***
ISOTROPIC STEEL-DUMMY
E 2.05e+08
POISSON 0.3
DENSITY 0
ALPHA 1.2e-05
DAMP 0.03
TYPE STEEL
STRENGTH FY 253200 FU 407800 RY 1.5 RT 1.2
END DEFINE MATERIAL
*** MEMBER SECTION
MEMBER PROPERTY AMERICAN
_CNV31_GIR-1 TABLE ST W16X36
_CNV31_GIR_CRS-1 TABLE ST C6X8
_CNV31_GIR_CRS-2 TABLE ST C4X6
_CNV31_CRS_BEAM TABLE T W16X31
_CNV31_FLR_BEAM-1 TABLE ST MC6X151
_CNV31_FLR_BEAM-2 TABLE ST L20203
_CNV31_FLR_CRS TABLE ST L25254
_CNV31_BRC TABLE ST L20205
CONSTANTS
BETA 180 MEMB 312411 TO 312440 313002 314005 TO 314008
BETA 45 MEMB 312311 TO 312340 313101 TO 313104 314101 314103 314105 314107 -
314109 314111 314113 314115 314118 314120 314122 314124 314126 314128
BETA -45 MEMB 312211 TO 312240 313201 TO 313204 314102 314104 314106 314108 -
314110 314112 314114 314116 314117 314119 314121 314123 314125 314127
BETA 135 MEMB 315101 315103 315105 315107 315109 315111 315113 315115 315118 -
315120 315122 315124 315126 315128
BETA 225 MEMB 315102 315104 315106 315108 315110 315112 315114 315116 315117 -
315119 315121 315123 315125 315127
MATERIAL STEEL ALL
***
MEMBER RELEASE
_CNV31_FLR_BEAM_S START MY MZ
_CNV31_FLR_BEAM_E END MY MZ
_CNV31_GIR_CRS-1 START MX MY
_CNV31_GIR_CRS-1 END MX MY
_CNV31_FLR_CRS_S START MX MY MZ
_CNV31_FLR_CRS_E END MX MY MZ

MEMBER OFFSET
_CNV31_BRC-1 START 0 0.175 0
_CNV31_BRC-1 END 0 0.175 0
_CNV31_BRC-2 START 0 -0.175 0
_CNV31_BRC-2 END 0 -0.175 0
MEMBER TRUSS
_CNV31_GIR_CRS-2
MEMBER TRUSS
_CNV31_BRC
***
*** SUPPORT
SUPPORTS
_CNV31_SPRT pinned
****
**** LOADING
LOAD 10 LOADTYPE Dead TITLE DL
SELFWEIGHT Y -1

PERFORM ANALYSIS
CHANGE

FINISH