Experimental Analysis of a Slip-Joint Connection with an Octagonal Tubular Cross-Section

This paper presents an experimental study of a slip-joint connection with an octagonal tubular cross-section. The connection investigated consists of two conical steel tubes joined to each other without additional welding or bolts; the load is transferred through the connection geometry and interfacial friction in the overlap region. Despite its practical use in masts and similar vertical structures, its behaviour is not fully understood, particularly with respect to the shape of the cross-section, the length of the overlap and manufacturing imperfections. Six tests were conducted on three specimen types with different conicities, overlap lengths and surface treatments. The measurements focused on stresses, insertion forces, displacements and the effect of repeated loading. The results showed a consistent overall response pattern across the tests, together with marked differences associated with imperfections. The stresses measured during insertion were substantially higher than those predicted by the simplified analytical relations, which is consistent with assembly-induced prestress. These findings improve understanding of the experimental behaviour of octagonal slipjoint connections and provide a basis for further numerical and analytical studies.