For combinations that do not contain notional loads the program will determine what gravity load cases and factors are contained and insert appropriate notional load cases. So for example given the following load combination:

1.2DL + 1.2LP + 1.3W1

The program will create the following load combination for the calculation of λ_cr: 1.2ND + 1.2NL, where ND = Notional Dead Load and NL = Notional Live Load.

Note that the original (gravity and lateral) load cases are not considered in the combination used to determine λ_cr but the appropriate load case factors are.

For a gravity only load combinations, notional loads are typically included automatically. For a combination such as:

1.2DL + 1.2ND + 1.6Lp + 1.6NL,

The program will remove the gravity load cases to only consider the notional terms as follows for calculating λ_cr:

1.2ND + 1.6NL

Note that these notional terms are then further expanded as described in the next section to account for the direction that notional loads are required to be acting in.