Steel Buildings in Europe

Part 5: Detailed Design of Trusses 5 - 45 5 VERIFICATION OF CONNECTIONS 5.1 Characteristics of the truss post connection 5.1.1 General It is essential to connect the truss and post according to the assumptions in the modelling. In particular, the choice between a fixed connection and a pinned connection must be respected. The difference between these two types of connection is that the pinned connection allows a rotation independent deflection of the truss and the post. The outcome in terms of loading is that the hinge does not transmit any bending moment from the truss to the post, whereas a fixed connection does. The rotation at the support of a truss is manifested by a differential horizontal displacement between the original node of the upper chord and the original node of the lower chord. In order to permit global rotation, it is therefore necessary to allow the horizontal displacement of the end of one of the chords in relation to the post: usually, the displacement of the chord which does not receive the diagonal on support is released. A Figure 5.1 Elongated hole on the bottom chord of the truss With such an arrangement, the axial force is zero in the lower chord in the first panel. The lower chord of the first truss node could therefore be stopped short (A in the diagram); nevertheless it is preferable to lengthen the lower chord and to connect it to the post in order to provide lateral stability of the truss at the level of the lower chord. An application of this type of hinge action in the worked example is given in 5.1.2 below. By contrast, in order to carry out a rigid truss-column connection, it is necessary to make a connection without slack from each of the chords of the truss to the column.