Second-Order Analysis

The criteria selections by the engineer regarding 2^nd order analysis are reported in this section. This includes the options to perform a P-Delta analysis based on the Geometric Stiffness method and to apply the B₁ and B₂ factors.

Setting	Description
B1 Factors	The worst B₁ ratio for any member for any combination is calculated and reported, and the necessity of including P-d in the analysis or not is indicated according to C2.1(2)(b) of AISC 360-16 or AISC 360-10 or Eq. (A-7-1) of AISC 360-05 (i.e., αPr < 0.15P_eL). The member number and load combination corresponding to the worst ratio is printed. Note that the program searches all load combinations for member’s major and minor axis (except members with pinned ends), and then it reports the worst ratio among all members. The report also shows the number of elements where αPr exceeds 0.15P_eL.
B2 Factors	In this section, information regarding B₂ and its parameters (i.e., R_Mx and R_My) is printed. If B2 factors are applied, the maximum values of B2x and B2y on any diaphragm on any level for any combination is determined and reported. This can be used to determine if the notional loads need be applied to all combinations or to only the gravity combinations. If both B₂ and the current P-delta option are chosen, the engineer is notified that both options are not needed in order to include 2^nd order effects.

Setting

Description

B1 Factors

The worst B₁ ratio for any member for any combination is calculated and reported, and the necessity of including P-d in the analysis or not is indicated according to C2.1(2)(b) of AISC 360-16 or AISC 360-10 or Eq. (A-7-1) of AISC 360-05 (i.e., αPr < 0.15P_eL). The member number and load combination corresponding to the worst ratio is printed. Note that the program searches all load combinations for member’s major and minor axis (except members with pinned ends), and then it reports the worst ratio among all members. The report also shows the number of elements where αPr exceeds 0.15P_eL.

B2 Factors

In this section, information regarding B₂ and its parameters (i.e., R_Mx and R_My) is printed. If B2 factors are applied, the maximum values of B2x and B2y on any diaphragm on any level for any combination is determined and reported. This can be used to determine if the notional loads need be applied to all combinations or to only the gravity combinations. If both B₂ and the current P-delta option are chosen, the engineer is notified that both options are not needed in order to include 2^nd order effects.