A new beam-to-column joint with high rotational as well as shear deformation capacity was devised. This high rotational ‘capacity’ is required to fulfill the great ‘demand’ for rotation arising during earthquakes, severe waves and current loads, etc. Due to its ability to contain damage during an overload, it leaves the connected elements intact. This, together with its replaceability can reduce the cost of post-event repair substantially. Its bending as well as shear performance under “monotonic” loading had already been assessed experimentally (OMAE’02-28864, OMAE’03-37292, OMAE’04-51494 & OMAE’05-67361) and proved well superior to that of conventional joints. In order to study its performance under “cyclic” flexural loading experimentally, new bending tests were conducted on mild steel specimens of the connection. These tests clearly showed the ability of the devised joint to withstand adequate number of cycles in bending and dissipate energy through well-shaped hysteresis loops. This would result in large amount of energy being dissipated in each cycle. Such very ductile response of this connection in bending is expected to be exploited in various circumstances in offshore as well as onshore structures to give rise to a ductile overall behavior of the structure. In particular, it can be utilized for the repair and retrofitting of the aging offshore platforms which need to be treated in a non-destructive manner.

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.

A new beam-to-column (horizontal brace-to-leg) and bracing-to-frame (diagonal brace-to-horizontal brace/leg) connection was developed. It is a comprehensive package in which the solution to all of the shortcomings and deficiencies of all conventional and/or commonly used connections is provided. The major deficiency of basically all the existing beam-to-column connections is their inability to deliver large rotations. In this devised connection, it has been solved by using a totally different geometry—a geometry which does not restrict the joint from deforming freely in a smooth, uniform and non-violent manner. Such mode of deformation, if delivered by a ductile material, should lead to a high energy dissipation capacity. Especially, if the ductility of the constituting material of the connection is not degraded as a result of fabrication operations, or if so, it is restored through practicing a suitable heat treatment process, e.g. annealing, the energy dissipation capacity should improve substantially. Moreover, in order to attract the damage and prevent it from spreading through the beam (bracing) and the column (leg), whose replacement is formidable, the connection should work in a ‘sacrificial’ capacity. This, together with making it ‘replaceable,’ will reduce the cost of aftermath repair substantially, while replacing the damaged beam or column, if possible, is very costly. In addition to its high rotational (bending) capacity, at least 6 times those of conventional joints (depending on the connection design), its ‘shear deformation capacity’ is quite considerable, absolutely incomparable with those of its conventional counterparts, which are virtually ‘nil.’ This connection is a ‘self-contained separate entity’ which comprises two parallel attachment plates between which two circular, or else, tubes are laid and fixed through welding, though alternatively the whole combination can be produced by extrusion. In the ‘original version’ of the connection, the two plates are laid in a parallel relation with the axis of bending, whereas in its ‘alternate version,’ they are laid in an orthogonal relation with the axis of bending. Tests carried out on specimens of the two distinct versions of the connection proved all its claimed characteristics, both in shear and bending. In particular, those carried out more recently, not reported in previous papers (OMAE’02-28264 & OMAE’03-37292), were quite revealing with regard to the ‘shear strength’ and the ‘shear deformation capacity’ of the original version (horizontally-laid-tube, HLT, version) of the connection—far beyond what was expected by the authors.