# D1.L.4.1.5 Combined Interaction Check

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

$f a F a + C m z f b z ( 1 − f a / F ′ e x ) F b x + C m y f b y ( 1 − f a / F ′ e y ) F b y ≤ 1.0$

and

$f a 0.60 F y + f b z F b z + f b y F b y ≤ 1.0$

when fa/Fa > 0.15, otherwise

$f a F a + f b z F b z + f b y F b y ≤ 1.0$

It should be noted that during code checking or member selection, if fa/Fa 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

$f a 0.60 F y + f b z F b z + f b y F b y ≤ 1.0$