adjacent cassettes by means of self cutting and self tapping screws or possibly rivets fitted vertically through the shelves 6 of the said web and two top sections 9 on the upper or lower side of the shelf 6 when the top section 9 is exposed to tensile stresses at a right angle to the longitudinal direction of the edge beam sections 2 the joint absorbs this stress as a shear stress acting on the fastener this inter alia means that no indentations are formed about the heads in the sheet as a result of the arrangement where the webs 3 and the flanges 9 are facing the same direction room is made for modern assembly tools required to bring about the vertical joints it is advantageous to locate the shelves 6 at as low a level as possible since inter alia projecting parts of the joint actively take part in the co operation between the concrete and the cassettes 1 a disadvantage of having the shelf 6 and the flange 5 facing in the same direction consists in the fact that the web 3 tends to be deflected in that direction and subjected to loading this can be avoided by inclining the web 2 of the cassettes 1 the shelf 6 and flange 5 of which are located uppermost during assembly towards the centre 10 of the cassette so that the web 3 forms an angle of 70 u00b0 89 u00b0 with the bottom 11 of the cassette see left hand illustrations in fig4 when the adjacent webs 3 are joined see right hand illustration in.