The invention provides a composite material structure comprising a plate (2) having an upper side (2a), an under side (2b) and at least first and second beams (3, 4), each beam having a plurality of faces comprising at least an upper face (3c, 4c) and a base face (3b, 4b) and a pair of spaced apart side faces (3a, 4a) intermediate to and adjoining the upper (3c, 4c) and base (3b, 4b) faces, each beam (3, 4) being attached to the underside of the plate (2) at the upper face (3c, 4c) wherein the first beam (3) has an open ended passage (5) extending between the side faces (3a) and the second beam (4) extends through the open ended passage (5).