Moment of Resistance:
Assume Mf be the moment of resistance of the flitched beam.
Consider Mw and Ms is the moments of resistance of wood & steel, respectively.
M f = M w + M s
= ((1/6) b d 2 × σ w + 2 × ((1/6) t d 2 × σ s )
But σs = m σw, where m is the modular ratio.
∴ M f = (1/6) σ w bd 2 + 2 × (1/6) m σ w td 2
= (1/6) σ w [b + m (2t )] d 2