This paper describes an experimental and analytical study on the states of stresses of a box-type joint and a further application of this type to a column stabilized drilling unit.

The box-type joint has been developed in lieu of the conventional tubular joint. The tubular members can be connected compactly by having them reshaped and formed into the box type section at the area close to the joint.. Regarding the transfer of load and the distribution of stress at joint, we have carried out the structural experiments using the three different types of models and analysis by the finite element method.

The result of the above shows that the distribution of stress at this joint is not so complicated as that at the tubular joint and that the coefficient of stress concentration in the former is less than that in the latter. The configuration of the box-type joint being comparatively simple, the analysis can be easily and accurately made and the flow of stresses can be clearly understood.

We have found that the local bending stress occurring around the area forming the box-type section from that of tubular shape was decreased by adding a suitable ring stiffener to this area and that the buckling strength in this area was sufficient.

It is expected that this type of joint having been already applied to the column stabilized drilling unit under construction at our Hiroshima Shipyard will prove to be perfectly effective and satisfactory.


With the recent ocean development towards deeper and rougher areas of the sea, the column stabilized drilling unit and the drilling platform have come to be required to be larger in size and more reliable than ever before. To these offshore structures are usually applied tubular members to minimize the effects of waves, wind and tidal currents.

As is known, the thin cylindrical shell has such desirable characteristics, from the view point of structural strength, that it has superior properties in elasticity to the other ones. In order to make the best use of these characteristics, strength of the connecting joint between members has to be 'equal to or greater than of the members to be connected. This may well explain that the majority Taking into consideration the course of development of the joints in the offshore structures built for the past ten years, concerning the fixed type of the offshore structure, the gusset system was adopted, as a typical pipe structure for the tanker berth dolphin of the Cook Inlet; the flare joint system was also adopted for the, drilling platform operating in the same place.

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