According to application notes by AISC, for Direct Analysis Method the UNREDUCED STIFFNESS shall be used for service checks.
Now, due to limitations by Staad for DAM (for instance, not TENSION MEMBER available), I proceed to:
1. Reduce module of elasticity E to 0.8E
2. Apply Notional Loads.
3. Load combinations are Load cases with repeat load.
4. Pdelta analysis.
But this means that the result shown for deflections are calculated on reduced stiffness. After analysis I can change the module of elasticity back but I have to run the analysis again, and with repeat loads the model takes too long. So I decided to use the CHANGE command after Strength load cases like this:
...LOAD 645 1.2(D) + 1.0(W) + 1.0(RL) + 0.5(RLR) + 1.0(CR4) Z-REFERENCE LOADR1 1.2 R9 1.0 R3 1.0 R5 0.5 R304 1.0 NOTIONAL LOADR1 Z -0.0036 R3 Z -0.003 R5 Z -0.0015 R304 Z -0.003 ********************************************************************************PRIMER ANÁLISIS*******************************************************************************PDELTA ANALYSISCHANGE*CONSTANTSMATERIAL STEEL ALL********************************************************************************COMBINACIONES DE SERVICIO*******************************************************************************LOAD 1000 1.0(D)REFERENCE LOADR1 1.0...
But in analysis, I get a warning indicating that CONSTANTS should not be after an analyisis command. And after analysis or edit, the portion CONSTANTS / MATERIAL input after CHANGE, just disappear.
Is there any syntax missing here?