For spans greater than 4.8 m, when no intermediate supporting walls are available for purlins, framed structures called trusses are used. Spacing between trusses is guided by roof loads, truss material, spans and location of cross walls
In a king post truss, the central vertical post called as king post provides a support for the tie beam. The inclined members are known as struts and are used to prevent the principal rafters from bending at the centre. A king post truss can be used economically for spans 5–8 m.
The joint between the king post and the tie beam is an ordinary mortise and tenon joint. An iron stirrup is also provided to strengthen the joint further. For joining principal rafters and the king post, a tenon is cut in the principal rafter and the corresponding mortice into the head of the king post. A bridle joint is provided to connect the principal rafter with the tie beam. Joints between the king post and the strut are also mortice and tenon joints.
Leave a Reply