Leg supported offshore structure with jacking apparatus

Abstract

In offshore platforms and the like of the type comprising a structure, such as a hull, and a plurality of upright legs for supporting the structure on the floor of a body of water, the invention provides an improved rack-and-pinion type jacking apparatus for connecting the structure to the legs in vertically adjustable fashion. For each leg, at least one dual rack bar is employed, the rack bar having two opposed sets of rack teeth each extending along a different one of the two edges of the bar. A jacking unit is mounted on the structure adjacent each rack bar and includes at least one pair of drive pinions with the pinions of the pair each meshed with a different one of the two sets of rack teeth, so that the two pinions are opposed across the rack bar. When the legs each comprise a number of tubular column members, one of the dual rack bars is provided for each of a plurality of the column members of each leg. Alternatively, when the legs are made up of a single tubular member, one or more of the dual rack bars are secured to the single tubular member of each leg.

What is claimed is: 
     
       1. In an offshore installation of the type comprising a structure to be supported and a plurality of legs for supporting the structure, the combination of a plurality of elongated .Iadd.rigid .Iaddend.rack means each having two parallel opposite sides,   each of said opposite sides of said rack means having a set of rack teeth extending therealong with the two sets of rack teeth of each rack means facing away from each other,   each of said rack means being secured to one of the legs in such fashion that both sets of teeth of the rack means are located outwardly . .from.!. .Iadd.of .Iaddend.the leg; . .and.!. a plurality of jacking units . .mounted on the structure to be supported and.!. each cooperating with a different one of said rack means, each of said jacking units comprising     rigid frame means, two pinions each mounted on said frame means for rotation about a fixed axis, each of said pinions being operatively meshed with a different one of said two sets of rack teeth of the corresponding one of said rack means, . .such meshed relation to said pinions with said teeth of said rack means, and the fact that said axes are fixed rigidly on said frame means, causing any force tending to disengage either of said pinions by movement away from the corresponding set of rack teeth to be opposed by reason of engagement of the other of said pinions with its corresponding set of rack teeth,.!.   rotary power means, and   gearing carried by said frame means and operatively connecting said power means to drive said pinions . ...!..Iadd.; and   mounting means mounting said jacking units of the structure to be supported;   the meshed relation of said pinions with said teeth of said rack means, the rigidity of said frame means, and the fact that said axes are fixed rigidly on said frame means causing any force tending to disengage either of said pinions by movement away from the corresponding set of said rack teeth to be opposed by reason of engagement of the other of said pinions with its corresponding set of rack teeth, such opposition being effective via said rigid frame means and independent of said mounting means. .Iaddend.   
     
     
       2. The combination defined in claim 1 and wherein the offshore installation is of the type where each of the legs comprises a plurality of rigidly interconnected mutually parallel column members,   each of said rack means being rigidly secured to a different one of the column members and each of the legs being equipped with a plurality of said rack means.   
     
     
       3. The combination defined in claim 2, wherein each of the column members is tubular and the wall thereof extends for less than 360°, whereby the column member has two longitudinally extending free edges,   each of said rack means being an integral member and being welded to said free edges of the corresponding column member.   
     
     
       4. The combination defined in claim 2, wherein each of the column members is a double webbed H-beam and each of said rack means comprises a member which constitutes one side of the corresponding one of said H-beams.   
     
     
       5. The combination defined in claim 2, wherein each of said rack means comprises a metal member having two integrally formed, longitudinally extending mutually parallel ridges, said ridges being located on different sides of the longitudinal center line of said metal member, the column members of the legs of the offshore structure being tubular and of curvilinear transverse cross-section, and   said metal members are each secured to the corresponding column members by having said ridges welded thereto.   
     
     
       6. The combination defined in claim 2, wherein the column members of the legs of the offshore structure are each made up of a plurality of elongated flat plates secured together to form an elongated hollow structure of which the plates constitute the wall and the wall has a longitudinally extending gap defined by edges of two of said plates,   said rack means each is an integral dual rack member, the root-to-root width of each of said dual rack members is greater than the width of the gap in the corresponding one of the column members, and   each of said rack members is secured to a different one of the column members by welds between said edges and the body of the rack member.   
     
     
       7. The combination defined in claim 6, wherein each of the column members comprises three elongated flat plates so arranged that two of the plates converge away from the other, said two plates having their edges which are distant from said other plate spaced apart to provide said longitudinally extending gap.   
     
     
       8. The combination defined in claim 7, wherein each of the column members is additionally provided with a plurality of flat flange plates welded to the side of said other plate which faces away from the rack member, said flange plates lying in planes which are transverse to the column member,   each leg of the offshore structure including horizontal brace members having their ends secured respectively to said flange plates.  . .9. The combination defined in claim 1, and wherein   the offshore structure is of the type wherein each leg is in the form of a single tubular member,   there being a plurality of rack means for each leg,   each of said rack means being secured to the respective one of the legs in such fashion that the opposed sets of teeth of the rack means lie in a plane which is parallel to the longitudinal axis of the single tubular member of the leg but spaced laterally from the outer surface of the   
     
     
        tubular member..!. 10. The combination defined in claim . .9.!. .Iadd.1.Iaddend. , wherein .Iadd. the offshore structure is of the type wherein each leg is in the form of a single tubular member, there being a plurality of rack means of each leg,   each of said rack means being secured to the respective one of the legs in such fashion that the opposed sets of teeth of the rack means lie in a plane which is parallel to the longitudinal axis of the single tubular member of the leg but spaced laterally from the outer surface of the tubular member, .Iaddend.   an elongated longitudinally extending metal strip . .is.!. .Iadd.being .Iaddend.interposed between each of said rack means and the tubular member making up the corresponding leg, said strip having one of its longitudinal edges welded to the rack means and the other of its longitudinal edges welded to the tubular member, the width of said strip extending radially   
     
     
        with respect to the tubular member. 11. The combination defined in claim 1, wherein each of said rack members has a central body portion having a longitudinally extending face which is directed away from the leg to which the rack member is secured,   the combination further comprising a plurality of guide shoes mounted on the structure to be supported, each of said guide shoes slidably engaging said longitudinally extending face of a different one of said rack   
     
     
        members. 12. The combination defined in claim 11, wherein each of said guide shoes is of generally U-shaped plan configuration, and   each of said rack members is embraced by the corresponding one of said   
     
     
        guide shoes. 13. The combination defined in claim 1, wherein each of said jacking units comprises two additional pinions each mounted on said frame means for rotation about a rigidly fixed axis,   the axis of rotation of each of said additional pinions being aligned below the axis of rotation of a different one of said first-mentioned pinions.   
     
     
          . The combination defined in claim 13, wherein said power means includes a separate motor for each of said pinion, said   
     
     
        motors being mounted on said frame means. 15. In a jacking unit for supporting a structure such as a hull on a plurality of legs in such fashion that the structure can be adjusted vertically, the combination of a rigid frame adapted to be mounted on the structure to be supported;   a plurality of shafts;   means mounting said shafts on said frame each for rotation about a rigidly fixed axis with said shafts arranged in pairs,   the pairs of said shafts being spaced apart vertically and the shafts of each pair being spaced apart horizontally, the respective shafts of each pair lying in the same vertical plane as the corresponding shafts of the next adjacent pair;   a plurality of pinions each carried by a different one of said shafts,   said pinions lying in a common vertical plane extending transversely of said shafts;   a plurality of rotary power devices mounted on said frame; and   gearing carried by said frame and connecting each of said power devices to   
     
     
        drive a different one of said shafts. 16. The combination defined in claim 1, wherein the offshore installation is of the type wherein each of the legs comprises a plurality of rigidly interconnected elongated mutually parallel hollow column members each having a curvilinear transverse cross-section,   each of said means is rigidly carried by a different one of said column members and each of the legs is equipped with a plurality of said rack means, and   said sets of rack teeth of each of said rack means lie in a common plane parallel to and spaced from the longitudinal axis of the column member which carries the rack means.