Multiple support conditions within same analysis model

Can I change the support conditions in my model and analyze different loads with different support conditions within a single model?

Yes. One can have different support conditions specified within the same model, each with its own set of load cases followed by PERFORM ANALYSIS and CHANGE commands.

Here are a few simple rules that one should follow for such definitions:

1. Each set of support condition should be followed by corresponding load cases and PERFORM ANALYSIS and CHANGE commands.
2. Supports should be specified in the same order before and after the CHANGE.
3. The number of degrees of freedom in subsequent support specifications should not increase. For example in the example below, if supports 2 TO 5 FIXED BUT FY KFX 10000 needs to be defined after the CHANGE, one needs to specify 2 TO 5 FIXED BUT FX FY FZ MX MY MZ  ( which basically means unrestrained ) before the CHANGE.

Here is an example file with multiple support specifications

STAAD PLANE EXAMPLE FOR MULTIPLE SUPPORTS
START JOB INFORMATION
ENGINEER DATE 28-Oct-14
END JOB INFORMATION
SET NL 2
UNIT FEET KIP
JOINT COORDINATES
1 0 0 0; 2 0 10 0; 3 0 20 0; 4 15 20 0; 5 15 10 0; 6 15 0 0;
MEMBER INCIDENCES
1 1 2; 2 2 3; 3 3 4; 4 4 5; 5 5 6; 6 1 5; 7 2 6; 8 2 4; 9 3 5; 10 2 5;
MEMBER PROPERTY AMERICAN
1 TO 10 TABLE ST W12X26
UNIT INCHES KIP
DEFINE MATERIAL START
ISOTROPIC MATERIAL1
E 29000
POISSON 0.3
END DEFINE MATERIAL
CONSTANTS
MATERIAL MATERIAL1 ALL
SUPPORTS
1 PINNED
6 PINNED
2 TO 5 FIXED BUT FX FY FZ MX MY MZ
LOAD 1
JOINT LOAD
2 FX 15
3 FX 10
PERFORM ANALYSIS
PRINT SUPPORT REACTIONS
CHANGE
*
SUPPORTS
1 PINNED
6 PINNED
2 TO 5 FIXED BUT FY KFX 10000
LOAD 2
JOINT LOAD
4 FX -10
5 FX -15
PERFORM ANALYSIS
CHANGE
PRINT SUPPORT REACTIONS
*
FINISH

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