PLATTFORM TIL MONTERING I HAV ELLER ANNEN VANNMASSE, SAMT FREMGANGSMAATE TIL DENS OPPFOERING

摘要

1481960 Offshore platforms; structural joints C G DORIS (COMPAGNIE GENERALE POUR LES DEVELOPPEMENTS OPERATIONNELS DES RICHESSES SOUS-MARINES) 5 Nov 1974 [29 Nov 1973] 47730/74 Headings E1H and E1W A concrete jacket is built from two sections which are constructed separately and then mounted one on top of the other and the two sections comprise a bottom part formed by a base 10 with stiffeners 11, peripheral wall 9, tubular members 8 and hollow columns 3 and a top part formed by a deck 7, hollow legs 6, collars 18 and tubular members 17. The columns 3 are attached integrally to the members 8 and are surrounded by wall 9. Columns 3 and the tubular members 8, 17 are internally divided by bulkheads 14, 16, 17a into buoyancy tanks with associated ballast lines 15, 16 and 19. Fabrication. The deck 7, collars 18, tubular members 17 and the lowermost portions of the legs 6 are built in a dry dock with the bridge 7 above the members 17 and resting on, a sliding formwork which is used to cast the legs 6. After flooding the dock, the partially built and buoyant top section is moved to a sheltered location where erection of the legs 6 is completed afloat, the bridge 7 being simultaneously raised as the legs 6 are formed by a hoist mechanism and finally connected to the legs. Whilst the top section is being completed afloat, the bottom section is partially constructed in the dry dock and the columns 3 are completed with the section afloat at another location. The columns 3 are sealed at their upper ends and are each attached to an auxiliary buoyancy chamber. The bottom section is then towed to a location having a flat water bed where it is sunk by flooding the buoyancy tanks in member 8. The auxiliary buoyancy chambers are removed and the top section is positioned above the sunken bottom section so that the collars 18 are connected to columns 3. After joining the top and bottom sections together, the jacket is partially deballasted, towed to its final location and then sunk to the bottom. Connecting the deck 7 to the legs 6 is performed using openings 23 in the deck 7 in to which are positioned sleeves 27a and steel reinforcement 28a which cooperate with sleeves 27 and fixings 28 located in the concrete of the deck 7 and legs 6 at an earlier building stage. After concrete has been poured and set in the openings 23, prestressing cables 30 are assembled in the sleeves 27, 27a whereafter further concrete is poured into these sleeves. The legs 6 are connected to the columns 3 by prestressing cables 45 anchored at points 45a 45b. This work is undertaken using a panel 41 which is used to seal off the open bottom of a leg 6 which has a male projection 37 cooperating with a female recess in the upper end of the columns 3. Inflatable seals 40 prevent ingress of ambient sea water.