Determine the moment of resistance of the flitched beam:

A flitched beam consists of a wooden beam of width 120 mm & depth 250 mm & mild steel plates of thickness 10 mm & width 120 mm one on each of side of the wooden beam. The maximum bending stress in wood is equal to7 N/mm² and the modular ratio between steel & wood is 20. Determine the moment of resistance of the flitched beam section.

Solution

Moment of resistance of the wooden beam =  (1/6) σ _w bd ²

                             =  (1/6) × 7 × 120 × (250)²

                             = 8759 × 10³ N-mm = 8750 Nm

Moment of resistance of the steel plates is following,

                                  = 29167 Nm

Moment of resistance of flitched beam = Moment of resistance of wooden beam + Moment of resistance of steel plates.

                                                                         = 8750 + 29167

                                                                         = 37917 Nm