Hello everyone, I have modeled a two-story structure and realized some irregularities when using the master slave command. When I run the analysis of the structure with the master and slave nodes I have observed the following irregularities in the post processing mode (under the tab Beam - Graphs) :
-The max moment (Mz) experienced by all the columns is the exactly the same, which shouldn't be based on the geometry of the system.
-The max axial load (Fx) on the columns are roughly the same, with some exterior columns having higher axial loads than the interior columns, which is very strange.
-The maximum node displacement is 23.614 mm (more of an observation rather than an irregularity).
When I run the model without the master slave these irregularities do not occur, but the maximum node displacement becomes significantly higher in this model (59.527mm)
Does anyone have an idea as to why these irregularities occur and how can they be fixed.
NB: The Staad editor description is below.
STAAD SPACESTART JOB INFORMATIONENGINEER DATE 14-Sep-15END JOB INFORMATIONINPUT WIDTH 79UNIT METER KNJOINT COORDINATES1 -8.534 0 0; 2 -8.534 0 6.096; 3 -8.534 0 12.192; 5 -8.534 4.831 0;6 -8.534 4.831 6.096; 7 -8.534 4.831 12.192; 9 -8.534 8.5 0;10 -8.534 8.5 6.096; 11 -8.534 8.5 12.192; 12 0 0 0; 13 0 0 6.096;14 0 0 12.192; 16 0 4.831 0; 17 0 4.831 6.096; 18 0 4.831 12.192; 20 0 8.5 0;21 0 8.5 6.096; 22 0 8.5 12.192; 23 7.315 0 0; 24 7.315 0 6.096;25 7.315 0 12.192; 27 7.315 4.831 0; 28 7.315 4.831 6.096;29 7.315 4.831 12.192; 32 7.315 8.5 0; 33 7.315 8.5 6.096; 34 7.315 8.5 12.192;36 14.63 0 0; 37 14.63 0 6.096; 38 14.63 0 12.192; 40 14.63 4.831 0;41 14.63 4.831 6.096; 42 14.63 4.831 12.192; 45 14.63 8.5 0;46 14.63 8.5 6.096; 47 14.63 8.5 12.192; 49 21.945 0 0; 50 21.945 0 6.096;51 21.945 0 12.192; 52 21.945 4.831 0; 53 21.945 4.831 6.096;54 21.945 4.831 12.192; 55 21.945 8.5 0; 56 21.945 8.5 6.096;57 21.945 8.5 12.192; 58 29.26 0 0; 59 29.26 0 6.096; 60 29.26 0 12.192;61 29.26 4.831 0; 62 29.26 4.831 6.096; 63 29.26 4.831 12.192; 64 29.26 8.5 0;65 29.26 8.5 6.096; 66 29.26 8.5 12.192;MEMBER INCIDENCES1 1 5; 2 2 6; 3 3 7; 4 5 6; 5 6 7; 6 5 9; 7 6 10; 8 7 11; 9 9 10; 10 10 11;11 16 5; 12 6 17; 13 7 18; 14 20 9; 15 10 21; 16 11 22; 17 12 16; 18 13 17;19 14 18; 20 17 16; 21 18 17; 22 16 20; 23 17 21; 24 18 22; 25 21 20; 26 22 21;27 16 27; 28 17 28; 29 29 18; 30 20 32; 31 21 33; 33 23 27; 34 24 28; 35 25 29;36 27 28; 37 28 29; 38 27 32; 39 28 33; 40 29 34; 41 32 33; 42 33 34; 43 27 40;44 28 41; 45 42 29; 46 32 45; 47 33 46; 48 47 34; 49 36 40; 50 37 41; 51 38 42;52 40 41; 53 41 42; 54 40 45; 55 41 46; 56 42 47; 57 45 46; 58 46 47; 59 40 52;60 41 53; 61 54 42; 63 46 56; 64 57 47; 65 49 52; 66 50 53; 67 51 54; 68 52 53;69 53 54; 70 52 55; 71 53 56; 72 54 57; 73 55 56; 74 56 57; 75 52 61; 76 53 62;77 63 54; 78 55 64; 79 56 65; 80 66 57; 81 58 61; 82 59 62; 83 60 63; 84 61 62;85 62 63; 86 61 64; 87 62 65; 88 63 66; 89 64 65; 90 65 66;DEFINE MATERIAL STARTISOTROPIC CONCRETEE 2.17185e+007POISSON 0.17DENSITY 23.5616ALPHA 1e-005DAMP 0.05TYPE CONCRETESTRENGTH FCU 27579END DEFINE MATERIALMEMBER PROPERTY AMERICAN1 TO 3 6 TO 8 17 TO 19 22 TO 24 33 TO 35 38 TO 40 49 TO 51 54 TO 56 -65 TO 67 70 TO 72 81 TO 83 86 TO 88 PRIS YD 0.45 ZD 0.454 5 9 TO 16 20 21 25 TO 31 36 37 41 TO 48 52 53 57 TO 61 63 64 68 69 -73 TO 80 84 85 89 90 PRIS YD 0.5 ZD 0.45CONSTANTSMATERIAL CONCRETE ALLMEMBER CRACKED1 TO 3 6 TO 8 17 TO 19 22 TO 24 33 TO 35 38 TO 40 49 TO 51 54 TO 56 -65 TO 67 70 TO 72 81 TO 83 86 TO 87 -88 REDUCTION RAX 0.700000 RIX 0.700000 RIY 0.700000 RIZ 0.7000004 5 9 TO 16 20 21 25 TO 31 36 37 41 TO 48 52 53 57 TO 61 63 64 68 69 -73 TO 80 84 85 89 -90 REDUCTION RAX 0.350000 RIX 0.350000 RIY 0.350000 RIZ 0.350000SUPPORTS1 TO 3 12 TO 14 23 TO 25 36 TO 38 49 TO 51 58 TO 60 FIXEDSLAVE RIGID MASTER 63 JOINT 5 TO 7 16 TO 18 27 TO 29 40 TO 42 52 TO 54 61 62SLAVE RIGID MASTER 66 JOINT 9 TO 11 20 TO 22 32 TO 34 45 TO 47 55 TO 57 64 65DEFINE IBC 2012SS 1.1 S1 0.375 I 1.5 RX 8 RZ 8 SCLASS 4 CT 0.0466 PX 0.2943 PZ 0.2943 TL 12 - FA 1.06 FV 1.65 K 0.9SELFWEIGHT 1 MEMBER WEIGHT4 5 9 10 84 85 89 90 UNI 20.2111 13 14 16 UNI 23.1412 15 UNI 30.1320 25 36 41 53 58 69 74 UNI 23.4444 47 76 79 UNI 27.3427 29 30 61 64 77 80 UNI 21.9243 46 75 78 UNI 25.5245 48 UNI 27.5928 31 60 63 UNI 37.2921 26 37 42 52 57 68 73 UNI 33.3959 UNI 11.99LOAD 1 LOADTYPE Seismic TITLE EQ +XIBC LOAD X 1 DEC 0 ACC 0PDELTA ANALYSIS SMALLDELTA PRINT LOAD DATACHANGELOAD 2 LOADTYPE Seismic TITLE EQ -XIBC LOAD X -1 DEC 0 ACC 0PDELTA ANALYSIS SMALLDELTA PRINT LOAD DATACHANGELOAD 3 LOADTYPE Seismic TITLE EQ +ZIBC LOAD Z 1 DEC 0 ACC 0PDELTA ANALYSIS SMALLDELTA PRINT LOAD DATACHANGELOAD 4 LOADTYPE Seismic TITLE EQ -ZIBC LOAD Z -1 DEC 0 ACC 0PDELTA ANALYSIS SMALLDELTA PRINT LOAD DATACHANGELOAD 5 LOADTYPE Dead TITLE DEAD LOADMEMBER LOAD4 5 9 10 84 85 89 90 UNI GY -20.2111 13 14 16 UNI GY -23.1412 15 UNI GY -30.1320 25 36 41 53 58 69 74 UNI GY -23.4444 47 76 79 UNI GY -27.3427 29 30 61 64 77 80 UNI GY -21.9243 46 75 78 UNI GY -25.5245 48 UNI GY -27.5928 31 60 63 UNI GY -37.2921 26 37 42 52 57 68 73 UNI GY -33.3959 UNI GY -11.99SELFWEIGHT Y -1 PDELTA ANALYSIS SMALLDELTA PRINT LOAD DATACHANGELOAD 6 LOADTYPE Live REDUCIBLE TITLE LIVE LOADMEMBER LOAD4 5 9 10 84 85 89 90 UNI GY -3.6611 13 14 16 UNI GY -7.5112 15 UNI GY -15.0127 29 30 59 61 64 77 80 UNI GY -6.8143 46 75 78 UNI GY -7.6920 21 25 26 36 37 41 42 52 53 57 58 68 69 73 74 UNI GY -7.3228 31 44 47 60 63 76 79 UNI GY -13.6245 48 UNI GY -9.63PDELTA ANALYSIS SMALLDELTA PRINT LOAD DATACHANGELOAD 17 LOADTYPE None TITLE 1.4DLREPEAT LOAD5 1.4 LOAD 18 LOADTYPE None TITLE 1.2DL + 1.6LLREPEAT LOAD5 1.2 6 1.6 LOAD 19 LOADTYPE None TITLE 1.2DL + 0.5LLREPEAT LOAD5 1.2 6 0.5 LOAD 20 LOADTYPE None TITLE 1.2DL + 1EQ+X + 0.5LLREPEAT LOAD5 1.2 6 0.5 1 1.0 LOAD 21 LOADTYPE None TITLE 1.2DL + 1EQ-X + 0.5LLREPEAT LOAD2 1.0 5 1.2 6 0.5 LOAD 22 LOADTYPE None TITLE 1.2DL + 1EQ+Z + 0.5LLREPEAT LOAD3 1.0 5 1.2 6 0.5 LOAD 23 LOADTYPE None TITLE 1.2DL + 1EQ-Z + 0.5LLREPEAT LOAD4 1.0 5 1.2 6 0.5 LOAD 24 LOADTYPE None TITLE 0.9DL + 1EQ+XREPEAT LOAD1 1.0 5 0.9 LOAD 25 LOADTYPE None TITLE 0.9DL + 1EQ-XREPEAT LOAD2 1.0 5 0.9 LOAD 26 LOADTYPE None TITLE 0.9DL + 1EQ+ZREPEAT LOAD3 1.0 5 0.9 LOAD 27 LOADTYPE None TITLE 0.9DL + 1EQ-ZREPEAT LOAD4 1.0 5 0.9 PDELTA 30 ANALYSIS SMALLDELTACHANGEPERFORM ANALYSIS PRINT ALLSTART CONCRETE DESIGNCODE ACIMAXMAIN 25 ALLMINMAIN 25 ALLMINSEC 10 ALLRHOMN 0.01 MEMB 1 TO 3 6 TO 8 17 TO 19 22 TO 24 33 TO 35 38 TO 40 49 TO 51 -54 TO 56 65 TO 67 70 TO 72 81 TO 83 86 TO 88DESIGN BEAM 4 5 9 TO 16 20 21 25 TO 31 36 37 41 TO 48 52 53 57 TO 61 63 64 -68 69 73 TO 80 84 85 89 90DESIGN COLUMN 1 TO 3 6 TO 8 17 TO 19 22 TO 24 33 TO 35 38 TO 40 49 TO 51 54 -55 TO 56 65 TO 67 70 TO 72 81 TO 83 86 TO 88MINMAIN 32 ALLEND CONCRETE DESIGNPRINT STORY DRIFT 0.010000FINISH
I agree with what Amir’s observation. Instead of defining rigid master slave connection, I would suggest you to use the rigid floor diaphragm command to model the diaphragms. This would require small changes to be made to the model but it would help you to correctly account for the lateral stiffness and also account for torsion effects due to the rigid diaphragm. For details on floor diaphragms please refer to the section 5.28.2 of the technical reference manual.
Couple of observations :
You do not need to do a PDLETA analysis for DL or LL or seismic acting by itself. It is only when the vertical and lateral loads act together that you get the pdelta effects. So just do a PDELTA 30 ANALYSIS for the REPEAT LOAD cases. Use PERFORM ANALYSIS for primary cases ( loads 1 to 6 ).
Use a LOAD LIST command before the design to ensure that the design is carried out for these combos only and not for the basic cases.
Since definition of a mass type reference load is required for rigid diaphragm, you can avoid defining the same again as part of the seismic definition. STAAD.Pro will use the mass definition from within the mass reference load for the IBC load generation too.
The PERFORM ANALYSIS after the PDELTA is redundant and can be taken out.
Simply use PDELTA 30 ANALYSIS instead of PDELTA 30 ANALYSIS SMALLDELTA as small delta effect is included in the pdelta analysis by default and you do not need to explicitly mention that.
I have attached a modified file for your reference.
6428.Structure1.std
Thanks, however I'm concerned with regards to the high nodal displacement in the model, which translates to a high story drift (drift limit exceeded in this case). Is there any method for me to control this high node displacement (other than changing member sizes) or are the values obtained for the node displacement in post processing the absolute values (ie. only acceptable values).
The nodal displacements that you see in the postprocessing tables represent the total displacements of these nodes from its original position. For drift computation you would rather want to know the relative displacement of a floor with respect to the floor below. You should refer to the output corresponding to the PRINT STORY DRIFT 0.01 command that you have used in the model. In the analysis output file ( ANL ), STAAD.Pro will report the drift and also report PASS or FAIL depending on the limit ( which is L/100 in your case ). I see all the drift check is passing for all floors even with the factored cases.
Actually you may want to add some unfactored service cases and use a separate LOAD LIST command before the print story drift command so that drifts are reported for the service cases only.