Effect of damaged circular flange-bolted connections on behaviour of tall towers, modelled by multilevel substructuring

• Non-linear FE analysis of circular flange-bolted connection with contact and friction.
• Diagrams of connection rigidities depending on pre-tensioning forces in bolts.
• Bending effect of bolts under axial tension of the flanged connection.
• Influence of single loose bolt on progressive damage of the whole connection.
• Two-level substructuring of telecommunication tower with flanged connections.

The paper deals with non-linear analysis of a telecommunication tower with circular flange-bolted connections (CFBCs). They are composed of two flanges, welded to the structural tubes, and then connected together with pre-tensioned bolts. A rigorous FEM analysis is performed for finding the connection stiffness in two cases. One deals with all bolts undamaged and the second one with one or more bolts broken.The analysis, which includes contact and friction forces, shows that when joints are under tension, the bolts are not only subjected to axial forces, but also to bending moments due the prying effect. The value of stresses caused by bending depends strongly on the bolt pre-tension and flange thickness. Removing one of the six connection bolts significantly increases stresses in the remaining bolts. Knowing the behaviour of the connection, it is possible to study the behaviour of the whole structure. This is achieved by applying the multilevel substructuring approach. The first levels is related to the flanges and bolts, whereby the connection model is simplified, and compared with the rigorous one, the second level is related to the assembly of the whole tower.The paper is illustrated with several examples of connections of different thicknesses, and different bolt pre-tensions. The considered tower comes from a real design.

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