Perform analysis versus P-Delta and Direct Analysis

I'm having issues with the different methods of analysis', I can get results for Perform Analysis but when I try to switch to P-Delta and Direct Analysis I get warnings about instabilities and error codes in the output such as 1.#INF, 1.#IND and 1.#QNAN.  There are both moment connections, pinned connections and pinned connections with springs to overcome tempurature forces.  All load combinations that this effects has to do with the following load cases:

7. TL (temperature load)

10 WL1(+Z)

11. WL1(-Z)

14. WL2(+Z)

15. WL2(-Z)

16. WIL2(+Z)

These load cases appear to be what is giving me trouble.  Any help would be great.

Refinery Upgrade 20180716 RJF FIXED BASE PLATES.stdRefinery Upgrade 20180716 RJF Fixed Base Plates P-Delta.stdRefinery Upgrade 20180716 RJF Fixed Base Plates DAM.std

  • The following releases were causing the issue ( specially I think the KFX ones). I commented those out ( modified file attached).

     

    *159 214 775 776 792 793 841 843 872 TO 874 939 941 1055 1056 1144 TO 1146 -

    *1148 1289 1290 1302 1354 1355 1437 1453 1964 2040 END MY MZ KFX 300

    *39 TO 42 94 TO 97 149 TO 152 204 TO 207 736 738 755 TO 757 854 1298 1301 -

    *1448 START MY MZ KFX 300

     

    The load cases 7,10,11 etc. are all component cases which are not going to act on your structure by themselves without other loads like gravity acting simultaneously. So I would suggest that do not carry out a Direct Analysis for these cases. I added a PREFORM ANALYSIS and CHANGE immediately before the REPEAT LOADs to ensure that only the REPEAT LOAD cases ( real cases ) are analyzed using Direct Analysis. A modified file is attached for your reference.

     

    I commented out the design portion in this file as those were not relevant for the purpose of this troubleshooting exercise. You may want to turn these back on.

    Refinery Upgrade 20180716 RJF Fixed Base Plates DAM_rev.std



    Answer Verified By: Russell Fude 

  • Thank you Sye, I will remember to add the PERFORM ANALYSIS and CHANGE before my REPEAT LOAD cases in the future for the DAM.