My question has two parts .
1. When using the command PERFORM DIRECT ANALYSIS is the stiffness of the structural member reduced or does REDUCEEI 1 need to be explicitly mentioned?
2. How can I perform the staad analysis for serviceability design following strength design since stiffness should not be reduced using PERFORM DIRECT ANALYSIS LRFD PDITER 15 REDUCEDEI 1 TBITER?
Please let me know if the following example is correct. If yes, is a CHANGE command required following the PERFORM DIRECT ANALYSIS .. command?
STAAD SPACE...LOAD 1 (DS1) * DEADLOAD_OF_STRUCTURE-SELFWEIGHTSELFWEIGHT Y -1MEMBER LOAD1 CON GY 0 0...LOAD 60 (ECZ) * NONSTRUCTURAL_COMPONENTS_EARTHQUAKE_LOAD_+ZMEMBER LOAD1 CON GY 0 0*PERFORM ANALYSISCHANGE*LOAD 101 *---------|Frame| P1F: 0.9 (Ds + De) + 1.2 Ts + 1.0 W-------* L-101REPEAT LOAD1 0.9 2 0.9 3 0.9 4 0.9 5 0.9 6 0.9 7 0.9 8 0.9 52 1.2 53 1 54 1 -55 1 56 1NOTIONAL LOAD1 X 0.0018 2 X 0.0018 3 X 0.0018 4 X 0.0018 5 X 0.0018 6 X 0.0018 -7 X 0.0018 8 X 0.0018 1 Z 0.0018 2 Z 0.0018 3 Z 0.0018 4 Z 0.0018 -5 Z 0.0018 6 Z 0.0018 7 Z 0.0018 8 Z 0.0018*PERFORM DIRECT ANALYSIS LRFD PDITER 15 REDUCEDEI 1 TBITER*LOAD 201 *---------|Frame| P1F: 0.9 (Ds + De) + 1.2 Ts + 1.0 W-------* L-101REPEAT LOAD1 0.9 2 0.9 3 0.9 4 0.9 5 0.9 6 0.9 7 0.9 8 0.9 52 1.2 53 1 54 1 -55 1 56 1NOTIONAL LOAD1 X 0.0018 2 X 0.0018 3 X 0.0018 4 X 0.0018 5 X 0.0018 6 X 0.0018 -7 X 0.0018 8 X 0.0018 1 Z 0.0018 2 Z 0.0018 3 Z 0.0018 4 Z 0.0018 -5 Z 0.0018 6 Z 0.0018 7 Z 0.0018 8 Z 0.0018*PERFORM PDELTA 15...**++++++++++++++++++++++++++++++ DESIGN CHECK +++++++++++++++++++++++++++++**...*(LY/LZ)...LOAD LIST 101PARAMETER 1CODE AISC UNIFIED 2010CHECK CODE MEMB _STL-ALL*LOAD LIST 201PARAMETER 2CODE BRITISHTRACK 4 MEMB_STL-COLUMNDFF ALLDJ1 1 MEMB 16DJ2 2 MEMB 16CAN 1.0 ALLCHECK CODE MEMB _STL-COLUMN*UNIT INCHES KIPSTEEL TAKE OFF ALLFINISH
The stiffness is automatically reduced. The REDUCED EI option is only to tell the software whether to consider the reduced stiffness for the calculation of intermediate section displacements and moments. By default the reduction is considered for that too.
Your example looks ok. You will need to insert the CHANGE after the DIRECT ANALYSIS. The load 201 would be analyzed with full structural stiffness. Also for the design portion you will need to define serviceability and strength envelopes which is explained in the wiki below
https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/20793/strength-serviceability-check-in-design
Thank you for the explanation. Could you elaborate on the purpose of the CHANGE command?
The CHANGE command is primarily used to reset the stiffness matrix and is used in models having multiple analysis commands. You can find more details related to it's application inside the help documentation (refer to TR.38 Change Specification )