METHOD FOR MOUNTING OF HEAVY STRUCTURAL PARTS

Abstract: In a method for temporary mounting of heavy structural parts (2) on a load-bearing support structure (1) in the correct position for subsequent permanent assembly, elastic spring elements (4) are used between the structural parts (1, 2), the number of elements being determined by the spring force of the elements and the weight of the structural part. As spring elements (4), elements are used where an elastic spring effect is directed substantially in the vertical direction, the elements' resistance to the influence of force being greater in the horizontal direction than in the vertical direction.

Description: Method for mounting of heavy structural parts The invention concerns a method for mounting of heavy struc¬ tural parts on a load-bearing support structure, where force- absorbing elements are provided between the structural part and the support. When erecting large structures it has become increasingly expedient to construct the structures in separate parts which are later assembled to form the total structure. Particularly in connection with offshore structures, e.g. platform struc¬ tures, the base and the actual platform part have each been constructed separately and put together after the base has been placed in the water. Accommodation units and the like have also been built in segments which are subsequently assembled. The assembly of such large, heavy structures is difficult to perform. There are a number of critical factors which must be taken into account during this operation in order to prevent faults from arising in one of the structural parts. A flexible assembly should preferably be performed and during the assembly it should be possible to make allowance for the fact that those surfaces which are intended to abut on each other may not be identical, so that it must be possible to compensate for irregularities. If the assembly is out of alignment or if irregularities occur between the elements, dangerous stress could arise in the completed structure, possibly leading to critical situations, e.g. in an offshore structure in bad weather. In order to achieve a correct balance it is also important to ensure that loads are distributed evenly over the support. Another feature which should also be considered during the assembly of large or heavy structural parts is that during the assembly operations there can easily arise lateral moments which can result in an incorrect assembly and hence subsequent problems with the actual structure, wiring, etc. Until now the principal means of solving the above-mentioned problems has been the use of plastically deformable distance pieces. An example of the state of the prior art can be found in Norwegian patents no. 140 537 and no. 168 492. In the former Norwegian patent the use is proposed of plasti¬ cally deformable metal pipes as mounting elements between the upper and the lower structural parts. In NO patent 168 492 the use is proposed of mounting elements which are plastically deformable and which are designed in the form of laminated blocks, at least one of which consists of lead or of a metal with corresponding plastic properties. These known plastically deformable mounting elements can only distribute forces and compensate for irregularities. Faults ca still arise if major errors occur during the assembly operatio or if the compression capabilities of the elements are ex¬ ceeded. With the methods used to date, in practice a completel rigid structure will be obtained after the assembly of the structural parts and after they are joined together the ele¬ ments will be welded to one another. A further problem in connection with the erection of large structures which have to be assembled is the mounting of the structural parts during the actual construction. During the actual construction period and the installation of modules, unexpected horizontal forces can arise from, e.g., wind, temperature changes, and earthquakes may also occur during the building of, e.g., a deck construction. Such events can lead t deformations and the formation of scratches on the underside o the structural part, which is not at all easy to inspect durin the construction period. The aim of the invention is to improve the conditions existing during the assembly of large structural parts. Thus it is an object of the invention to provide a method for mounting of heavy structural parts on a load-bearing support structure, whether it be an assembly of two or more elements in a complete structure or mounting on a support of structural parts during construction or transport. It should also be stated that structures have been designed which are intended to absorb both horizontal and vertical forces. However, these structures have become very expensive. A further object of the invention is to provide a method whereby a mounting can be obtained which will counteract or prevent the formation of faults in the structural part and which will be capable of protecting the structural parts against the effect of lateral moments or horizontal forces, thus enabling the best possible conditions to be achieved both during the construction period and for the completed structure. These objects are achieved with a method which is characterized by the features in the claims presented. In the invention a different solution has been chosen from that which has been used previously, with a plastically defor¬ mable mounting. The invention has been based on the recognition of the fact that it will be more practical to obtain an elastic joining by means of spring elements. A number of advantages will thereby be achieved. It will be possible to cushion the structure during assembly and in the case of structures which are lying at the construction site, suddenly occurring, unfor- seen forces such as an earthquake or a sudden storm will be able to be absorbed by the mounting instead of directly affect¬ ing the structure. With an elastic mounting it will also be possible to maintain the even distribution of forces between the structural parts and during an assembly operation it will be possible to absorb temporary lateral forces and place the structural parts in the correct position. Thus by means of the invention it will be possible to achieve a better final struc¬ ture and, even though a final welding is performed, the pos¬ sibility will be provided of performing a final adjustment of the relative positions of the structural parts before the welding is performed. By providing the mounting elements in a pattern according to the invention, there will be a definite centering of the sprin forces, thus enabling the structural parts to be exposed to vertical forces in relation to one another. An active system of this kind is in sharp contrast to the previously known passive mountings. The placing of the elements in a pattern of this kind and the necessity for this will be dependent on the design of the spring elements, since these can be designed wit varying horizontal stiffness. The invention will now be illustrated in more detail by means of the drawing, which illustrates some design alternatives for the method according to the invention. Fig. 1 shows two structural parts and indicates purely schematically where the mounting elements should be placed according to the invention. Figs. 2 & 3 are two examples of how elastic mounting elements can be placed. Fig. 4 is a purely schematic illustration of a mounting element which can be used in the method according to the invention. The drawing only illustrates how the method according to the invention can be implemented. Since a significant difference from the prior art is that in the method an elastic and cush¬ ioning mounting is provided instead of a plastically deformabl mounting, the illustration of the method will only provide a very general impression of its design. Thus fig. 1 shows a lower structural part 1 and an upper structural part 2, where the lower structural part 1 supports the upper part. The lower part 1 can be the leg structure of an offshore platform and in this case instead of having a full upper bearing surface as illustrated, will normally consist of several circular shafts in the form of a circle as illustrated in fig. 3. The lower part 1 can also be a supporting structure which is used in the construction, e.g. of an offshore platform deck 2 and in this case can have a larger flat surface, e.g. of the type illustr¬ ated in fig. 2. In both cases the surface area is indicated by 3. According to the invention, on this surface area 3 there ar provided elastic spring elements which are generally indicated by 4. An advantageous embodiment of such spring elements is described, e.g., in NO patent 159 550. Such elements have the major advantage that they can be designed in such a manner tha they compensate for lateral forces, i.e. the spring elements cannot "collapse", thus allowing lateral forces to be "counter acted" directly by the spring elements. The elements can be designed with a number of spring coils and dimensioned so that they are capable of resisting very great loads without being completely compressed. The number of such elements will also b dependent on the surface load and a calculation of the number of spring elements, the spring force of the spring elements an their position will be a simple task for a person skilled in the art. In figs. 2 and 3 there are illustrated different patterns for the positioning of such spring elements. Of course, these drawings are only meant to indicate positioning possibilities and the number of elements can, of course, often be much greater than that which is illustrated and may amount to several hundred. The essential point which figs. 2 and 3 attempt to illustrate is that the spring elements, which are designed in such a manner that they counteract horizontal forces in their longitudinal direction, are placed at differen angles, thus making the entire mounting of the structural part 2 insensitive to lateral forces or horizontal forces. If the structural part 2 is placed on the elements 4 and for some reason receives a moment in the lateral direction, the spring elements will immediately force the structural part 2 back into the correct position. Should vibrations occur these will be absorbed by the spring elements and should it be necessary to balance the parts in relation to one another it will be possible to do this by exercising a force on one of the sides of the structural part 2, thus enabling the spring elements on that side to be compressed a little more before the parts are welded together. Fig. 4 illustrates the design of a spring element as described in NO patent no. 159 550. It should be obvious from the above that there are many ways i which the invention can be implemented, nor is the invention confined to the use of spring elements of the type illustrated. Within the scope of the invention it will also be possible to use other variations of spring elements and it will also be possible to arrange the elements in other patterns than that which is illustrated. Thus many variations will be possible within the scope of the concept of the invention.

Claims: PATENT CLAIMS 1. A method for temporary mounting of heavy structural parts on a load-bearing support structure, in the correct position for subsequent permanent assembly, where force-absorbing, elastic spring elements are provided between the structural part and the support, the number of elements being determined by the spring force of the elements and the weight of the structural part, characterized in that as spring elements there are used elements wherein the elastic, spring effect is directed substantially in the vertical direction, the resis¬ tance of the elements to the influence of force being preferably greater in the horizontal direction than in the vertical direction, and that elements are used with spring arcs which are preferably provided between two plates. 2. A method according to claim 1, characterized in that the spring elements are provided in a pattern which will cause resistance from the spring elements to lateral forces in all directions. 3. A method according to claim 1, characterized in that the spring arc is provided at an angle to the plates' longitudinal direction. 4. A method according to claim 3, characterized in that spring elements are used of a kind known per se, where the spring part is a curved wire, and where spring arcs are provided in groups, where the arc in each group is placed at an equal angle, but where each spring element con¬ tains several groups at opposite angles. 5. A method according to claim 4, characterized in that elements are used where all spring arcs are defined with the same angle and that these elements are distributed over the joining surface for the structural parts in such a manner that distorting joining forces are counter¬ acted.

Inventors: FURU HARALD, FURU, HARALD
Applicants: FURU HARALD, KVAERNER AS, KVAERNER A.S
Application year: 1993
Main classification: E02B17
IPC codes: E02B17, E02D27, E04H9, F16F3