D1.L.4.1.5 Combined Interaction Check

Members subjected to both axial compression and bending stresses are proportioned to satisfy

\frac{f_{a}}{F_{a}} + \frac{C_{m z} f_{b z}}{(1 - f_{a} / {F'}_{e x}) F_{b x}} + \frac{C_{m y} f_{b y}}{(1 - f_{a} / {F'}_{e y}) F_{b y}} \leq 1.0

and

\frac{f_{a}}{0.60 F_{y}} + \frac{f_{b z}}{F_{b z}} + \frac{f_{b y}}{F_{b y}} \leq 1.0

when f_a/F_a > 0.15, otherwise

\frac{f_{a}}{F_{a}} + \frac{f_{b z}}{F_{b z}} + \frac{f_{b y}}{F_{b y}} \leq 1.0

It should be noted that during code checking or member selection, if f_a/F_a exceeds unity, the program does not compute the second and third part of the formula, because this would result in a misleadingly liberal ratio. The value of the coefficient Cm is taken as 0.85 for side-sway and 0.6 - 0.4·(M1/M2), but not less than 0.4 for no side-sway.

Members subjected to both axial tension and bending stress are proportioned to satisfy

\frac{f_{a}}{0.60 F_{y}} + \frac{f_{b z}}{F_{b z}} + \frac{f_{b y}}{F_{b y}} \leq 1.0