A nonlinear finite element model with discrete joint modelling capability is developed. A semi-empirical equation introduced for determining the maximum deflections of clamped and vertically jointed roof beam is verified using a nonlinear finite element model. The mechanism of stability is also investigated numerically and concluded that the formation of Voussoir arch (Parobolic compressive zone) plays a major role in the overall stability of beam roofs over underground openings. Approximate linear equations are obtained for three joint spacings of 800, 400 and 200 mm, relating the maximum deflection of the beam and joint width for a given joint spacing.