Further Investigation Into a Novel Concept for a Deformable Joint in Offshore Structures

Abstract

A new general semi-rigid beam-to-column connection for skeletal structures, also applicable to offshore platforms, was devised. In a previous paper (OMAE02-28264), the general features of this joint together with some proposed details for its use in fabricating new platforms, as well as retrofitting and repair of existing platforms, were introduced. Moreover, the results of some quasi-static tests on the ‘original’ version of the connection, in which the energy-dissipating elements (tubes) of the connection are laid in a parallel relation to the axis of bending, were reported. Here, in this paper, the results of recent experimental work on the ‘alternate’ version of the connection, in which the energy-dissipating sacrificial elements (tubes) are laid in a perpendicular relation to the axis of bending, are reported. The main differences between the behaviour of the two versions are the ‘rigidity,’ as well as the ‘strength’ of the tested specimens. However, the large ‘rotational capacity’ of the specimens is not jeopardized by the configuration of the connection, i.e. the relation between the axes of the tubes and that of bending. It is decided by the geometric parameters (sizes) of the connection. This can be designed independently of the joint strength and stiffness. The advantages of the joint, already observed in tests on the horizontally-laid-tubes version specimens (including the ability to contain damage, the ability to absorb and dissipate high amounts of energy, and the ability to deliver very large rotations), were also observed during the tests on the specimens of the vertically-laid-tubes version. Moreover, the fact that this version is also fabricated as a ‘separate entity,’ and thus can be easily subjected to the desired thermal cycle to remove the adverse effects of welding (in particular, embrittlement), makes it a suitable candidate for being used in ‘retrofitting’ and ‘repair’ of offshore platforms, where fatigue and the induced fracture are crucial factors.