Is it recommended to apply notional load, If the structure is analyzed with p delta analysis, as the effect of secondary moment M=P*Δ already considered??
A notional load is a lateral load (horizontal load) which is derived from an existing vertical load case. The notional load feature was created in STAAD.Pro for use with Direct Analysis in mind (as a code requirement say for example the code AISC 360-05) but it may be used for other scenarios as well (for example PDelta Analysis) that may require applying horizontal loads as a certain percentage of vertical loads in the structure.
Notional Loads are used by some of the building codes for stability design of a structure. They serve as a minimum lateral load, or as an alternative to modelling the actual out-of-plumbness of the structure. Instead of changing the geometry of the structure, an equivalent de-stabilizing load is added to the structure. This is due to fact that there are associated numerical benefits for handling these imperfections and it is quicker to adjust the loading than it is to modify the geometry (stiffness matrix) of the structure. So, the choice of using notional loads or not in a model is actually related to the requirement of applying this de-stabilizing load as a percentage of vertical loads on the structure and whether user wants to consider it. For more details on the feature please see Home > Technical Reference of STAAD Commands > TR.32 Loading Specifications > TR.32.13 Notional Loads