Maximum bending moment in simply supported beam under offset point load.
Bending moment
$$ M_{B_{p_{max}}} = {{( P \cdot a \cdot b ) \over \left({ a + b }\right)}} $$
Calculate minimum diameter of shaft subject to bending by point load using AS1403 formula 1 (no tension & no torsion).
This is based on AS 1403, Table 2, Formula 1 for manually or power applied condition.
Original formula has been shortened due to Pq = 0 and Tq = 0.
Minimum shaft diameter
$$ D_{shaft_{min_{p_{max}}}} = {\left({ {F_S \over F_Y} \cdot M_{B_{p_{max}}} \cdot 10 ^ 4 }\right) ^ \left({ {1 \over 3} }\right)} $$