I am doing a Pdelta Analysis using STAAD.Pro. When I double click on a member to see the shear/bending results, I get different answers compared to what is being reported in the Postprocessing tables for the same member. Why is that and which one should I use ?

The member query dialog box uses it’s own algorithm to calculate the bending/shear forces at the beam intermediate section locations and these values are not fetched from the analysis engine. This algorithm cannot fully account for the second order effects and hence when analysis like PDELTA, PDLETA KG, DIRECT ANALYSIS etc. are carried out, the values reported by the member query dialog box may be different than what is reported by the postprocessing tables or Beam > Graphs page in the postprocessing mode. The postprocessing table and beam graphs page values are directly fetched from the analysis engine and hence these are accurate for any analysis including second order.

So to summarize, one can use the results from the member query for a first order analysis ( PERFORM ANALYSIS ). For a second order analysis like PDELTA, PDLETA KG, or DIRECT ANALYSIS one should always use the postprocessing tables or the Beam > Graphs page.