An ETABS file of a 40 story tower was shared with the problem. The advance solver cannot run P Delta, the standard solver cannot complete the run for more than 48 hours run time…modal results were not seen…. The engineer tried to run the analysis for more than a week…also tried with only DL run and checked instability but couldn’t find any instability…..He couldn’t find the solution exploring different possibilities… Requested me to review and advise…
Answer from my side and it was correct and worked
Following are the list of observations which will create problem in P Delta Analysis Run.
1.Huge Cantilever beam with span more 5 or 6mt..Or Large span beams whose vertical displacement is huge..
2.Release of Secondary beams in internal floor area as well as releases in Cantilever projection area is very important.
3.Assignment of support
4.Beam properties assignment..Sometimes Heavy beam rested on Dummy or Null Element by mistake..which may create issue in P delta Analysis.
5.If Cantilever projection slabs are assigned as membrane element instead of Shell element..
6.If Membrane slabs are assigned with manual Meshing by mistake..
7.Overlapping of Beams
8.”Check Model” will not captute detached point
9.If Staircase Landing beam is modelled at Landing level and if it is rest at some interal part/distance of Shear wall instead of Outer joint of Shear wall..It will show discontinuty at that joint unless you break
10.Any single node point which is detached to column or beam will also create issues in P Delta Analysis..
One of the best way to resolve this issue is to remove all shell and membrane slabs from Etabs File..Just Run in Dead Load only..We will get easily deflected or Detached Node location.