GB2475088A - Sandwich panels, and vessel or structure made by combining these using closing plates - Google Patents

Abstract

The sandwich panel is made by combining metal plates 11, 12 and an edge member 13b, to form a cavity which is subsequently filled 14. At least one of the metal plates 12 includes a flange 12c, 12d which projects beyond the edge member 13b. The panel 10m is joined to another structure, preferably a sandwich panel 10n, by welding 18 flanged metal plates 12 together and welding 18 the other metal plates 1 to a closing plate 15. The cavity thus formed is then filled 16. Preferably the plates 11, 12, 15 and edge members 13b are steel, and the cores are filled by injecting thermosetting polyurethane elastomer into them, under vacuum. The panels can be used in girders, bulkheads, beams, deck plates, ships, building floors, bridges, off-shore installations, piers and aerials.

Description

METHOD OF CONSTRUCTION OF A VESSEL OR STRUCTURE

The present invention relates to methods of construction of vessels, such as ships, barges or boats, and structures such as buildings, bridges and off-shore structures.

Structural sandwich plate members are described in US 5,778,813 and US 6,050,208, which documents are hereby incorporated by reference, and comprise outer metal, e.g. steel, plates bonded together with an intermediate elastomer core, e.g. of unfoamed polyurethane.

These sandwich plate systems (SPS) may be used in many forms of construction to replace stiffened steel plates, formed steel plates, reinforced concrete or composite steel-concrete structures and greatly simp1if' the resultant structures, improving strength and strutura1 performance (e.g. stiffness, damping characteristics) while saving weight.

Further developments of these structural sandwich plate members are described in WO 01/32414, also incorporated hereby by reference. As described therein, hollow or solid forms may be incorporated in the core layer to reduce weight and transverse metal shear plates may be added to improve stiffness. Hollow forms generate a greater weight reduction than solid forms and are therefore often advantageous. The forms may be made of lightweight foam material or other materials such as wood or steel boxes, plastic extruded shapes and hollow plastic spheres.

In US 5,778,813 referred to above, construction of a ship from SPS is performed by welding steel plates into a structure so as to form cavities and injecting the core material in the cavities. In other words the structural sandwich plate members are formed in situ.

Prefabricating SPS panels in factory conditions can be desirable to improve dimensional tolerances. However, difficulties can then be encountered in welding the prefabricated panels together or to a framework to form a structure. In particular, it is desirable to avoid excessive welding as the heat generated thereby may damage the cores of the prefabricated panels and/or result in thermal distortion of the faceplates. It can also be difficult to accommodate dimensional tolerances in the construction of a large vessel or structure.

It is an aim of the present invention to provide a method of construction of vessels or structures, in particular that results in a vessel or structure having improved fatigue resistance.

According to the present invention, there is provided a method of constructing a vessel or structure comprising the steps of: providing a sandwich plate member comprising a first metal plate and a second metal plate spaced apart from the first metal plate an edge member connected to the first metal plate and the second metal plate so as to define a cavity, and a core layer filling the cavity and bonded to the first and second metal plates so as to transfer shear forces therebetween, wherein at least a part of the first metal plate projects outwardly of the edge member so as to form a flange; welding the flange to another part of the vessel or structure; welding a closing plate between the other part of the vessel or structure and the second metal plate so as to form a cavity; and filling the cavity with material that cures to form a second core bonding to at least the first metal plate and the closing plate with sufficient strength to transfer shear forces therebetween.

In this way the present invention enables the use of prefabricated SPS panels in the construction of large structures such as ships or buildings whilst ensuring fatigue resistant connections, accommodating dimensional tolerances and avoiding damaging the prefabricated panels.

By welding the metal plates of the SPS panel to another part of the structure and to a closing plate outside the perimeter bar, full thickness welds can be used without an excessive heat load. By using welds directly between the outer metal plates of the sandwich panel and the other part of the structure or the closing plate, the edge member of the sandwich panel does not form part of the load path. This strengthens the ultimate structure and also allows use of a simple U-shaped member as the edge member. The other part of the structure may be a framing member such as a girder or bulk head, a simple metal plate or another sandwich plate member.

The closing plate may be a simple flat metal plate or may include a bend or curved part. In this way, the connection can readily accommodate bends or corners, e.g. a knuckle on the centreline of a vessel deck to provide a camber. The closing plate desirably has a thickness substantially equal to that of the second metal plate and further desirably is made of the same metal as the second metal plate.

The materials, dimensions and general properties of the outer plates of the SPS panels used in the invention may be chosen as desired for the particular use to which they are to be put. Steel or stainless steel may be used in thicknesses of 0.5 to 20mm and aluminium may be used where light weight is desirable. Similarly, the plastics or polymer core may be any suitable material, for example an elastomer such as polyurethane, and is preferably compact, i.e. not a foam. The core is preferably a thermosetting material rather than thermoplastic.

The present invention will be described below with reference to exemplary embodiments and the accompanying drawings, in which: Figure 1 is a schematic cross-section of a prefabricated SPS panel that may be used in an embodiment of the present invention; Figure 2 is a cross-sectional view of a joint between adjacent deck panels in a chemical tanker constructed according to a method of the invention; Figure 3 is a cross-sectional view of a connection between inner bottom panels at centreline in a chemical tanker constructed according to an embodiment of the invention; Figure 4 is a cross-sectional view of various joints between deck panels in a chemical tanker constructed according to a method of the invention; Figure 5 is a cross-sectional view of an alternative connection between inner bottom panels at centreline of a chemical tanker constructed according to an embodiment of the invention; Figure 6 is a cross-sectional view of a connection of bottom plates to the centreline girder of a chemical tanker constructed according to an embodiment of the invention; Figures 7 and 8 are cross-sectional views of connections between a transverse corrugated bulkhead and the deck and inner bottom platings in a chemical tanker constructed according to an embodiment of the invention; Figure 9 is a cross-sectional view of a typical block connection in a chemical tanker according to an embodiment of the invention; and Figure 10 is a cross-sectional view of an alternative connection between adjacent SPS panels formed according to an embodiment of the invention.

In the various drawings, like parts are indicated by like reference numerals.

Figure 1 shows an SPS panel 10 that can be used in embodiments of the invention.

The panel preferably presents generally outer surfaces but the outer surfaces need not be flat and either or both surfaces may be provided with recesses, trenches, grooves and/or fittings if required. The panel as a whole may be curved or otherwise shaped if desired. Injection parts and vent holes may be provided for manufacture but are desirably sealed and/or ground flush after use. In plan the panel is desirably substantially rectangular but panels of other shapes may be used if desired.

The panel 10 shown in Figure 1 is a structural sandwich plate member that comprises upper and lower outer plates (faceplates) 11, 12 which may be of steel or aluminium and have a thickness, for example, in the range of from 3 to 8mm, more preferably 3 to 5mm. Edge members 13 (also referred to as perimeter bars), described further below, are provided between the face plates 11, 12 around their outer peripheries to form a closed cavity. In the cavity between the face plates 11, 12 is a core 14, described further below. This core may have a thickness in the range of from 15 to 200mm. In building applications such as floor panels, 15 to 20mm is preferable but much greater thicknesses may be used if lightweight forms are included, as discussed below. In maritime applications 20mm to 30mm is preferable. The overall dimensions of the panel in plan may be from 1 to 2m width by 2 to 14m length. Panels maybe made in standard sizes or tailor-made to specific shapes and/or dimensions.

The core may take various different forms but its major structural component is a main core layer 14 of plastics or polymer material (preferably comprising or consisting essentially of a thermoset, compact elastomer such as polyurethane as discussed above) which is bonded to the face plates 11, 12 with sufficient strength and has sufficient mechanical properties to transfer shear forces expected in use. The bond strength between the layer 14 and face plates 11, 12 should be greater than 3MPa, preferably greater than 6MPa, and the modulus of elasticity of the core material should be greater than 200MPa, preferably greater than 25OMPa. Alternatively, the core 14 may be a concrete layer. The concrete layer may be normal concrete which typically weighs about 2400 kg/rn3 (e.g. between 2100 and 2700 kg/rn3), but preferably light weight concrete which typically weighs about 1900 kg/rn3 (e.g. between 1200 and 2200 kg/rn3), more preferably ultra light weight concrete that typically weighs about 1200 kg/rn3 or less (e.g. between 500 and 1200 kg/m3). The concrete may be of any type of cementitious material (e.g. cements such as Portland cement, fly ash, ground granulated blast furnaces slags, limestone fines and silica fume).

The core 14 may also include a plurality of hollow box-shaped forms enclosing voids. The size and material of the forms are chosen so that the overall density of the forms is lower than the density of the material of the main core, preferably less than 50% of the density of the material of the core layer 14, or preferably less than 25% and most preferably less than 10%. The purpose of the forms is essentially to take up space within the core and thus reduce the amount of the main core material required whilst maintaining or even increasing the desired spacing between faceplates 11 and 12. This reduces cost both directly as the forms are less expensive by volume than the main core material and secondly because the weight of the panels is reduced. The forms do not need to contribute to the overall structural strength of the floor panel 10 but if the panel 10 is formed by injection of the main core layer 14, the forms must have physical properties sufficient to withstand pressures and temperatures arising during casting and curing of the main core layer 14. The size, shape and distribution of forms 15 within the core is chosen so that a sufficient number of ribs and/or columns of main core layer material extend between and bond to faceplates 11 and 12 at regular intervals across the length and width of the panel 10. The forms do not have to be hollow, e.g. if made of a suitable lightweight material such as a foam, or may be filled with lightweight material, which may be insulating and/or fire resistant. A particularly useful material for the forms is expanded polystyrene, having a density of 20-40g/l, which may be provided, e.g., either as spheres or ribs.

An edge member 13 is provided in at least one, preferably all edges of panel 10.

Edge member 13 is a solid bar of metal having a generally constant cross-section throughout its length. It may therefore be described as prismatic. In an embodiment of the invention, edge member 13 projects outwardly of the faceplates 11, 12 and is shaped to facilitate welding of the panel into a framework.

Embodiments of the invention are described below with reference to specific connection details intended for use in a high performance type C chemical tanker for the Rhine river. It will however be appreciated that these details may be adapted, and other details embodying the invention may be designed, for other freshwater or saltwater vessels as well as civil engineering structures including bridges, buildings, aerials, etc. and off-shore structures such as oil production platforms, artificial islands, piers, etc..

Figure 2 is a cross-sectional view of a joint between adjacent deck panels in way of a longitudinal deck girder. A prefabricated sandwich panel lOa has upper metal plate 11 of thickness 4mm, a solid core 14 of thickness 20mm and a lower metal plate 12 of 4mm thickness. As described above, upper and metal plates 11, 12 may be of steel and core 14 may be of compact thermoset polyurethane elastomer. Edge member 1 3a extends along one edge of sandwich panel lOa and is formed of a U-shaped rolled profile of thickness 3mm.

Since in the finished structure this member does not form an important part of the load bearing structure, for manufacture of the panel 1 Oa it may simply be glued in place or held in place with tack welds. A gasket may be provided between edge member 1 3a and either or both of metal plates 11, 12 to improve sealing during filling and curing of the core 14. Other types of edge member may be provided along the other edges of sandwich panel 1 Oc.

Upper metal plate 11 extends beyond edge member I 3a so as to form large flange ha. This flange may have a width Wi in the range of from about 200mm to 400mm. Width WI is determined so that the distal end of flange ha can be welded to the longitudinal deck girder 30 by a fillet weld 19 without the welding heat load causing unacceptable damage to core 14 or thermal distortion of the sandwich plate panel lOa as a whole.

Lower metal plate 12 also extends outwardly of perimeter member 1 3a so as to form a small flange I 2a. Small flange I 2a may have a width W2 in the range of from about 10mm to about 100mm. At the distal edge of flange 1 2a a backing bar 17 is provided. Backing bar 17 assists in the welding of a closing plate 15 between girder 30 and flange 12a in order to form a closed cavity. In this embodiment, closing plate 15 is substantially coplanar with lower metal plate 12 and once welded in place by full thickness weld 18 essentially forms a continuation of metal plate 12. The cavity is subsequently filled with material that cures to form core 16 that bonds to and transfers shear forces between upper and metal plate 11 a and lower metal plate 12 a and closing plate 15. Core 16 may be formed of the same material as core 14 however a different material and/or different additives more suited to injection and curing in situ may also be used. Filling of the cavity may be performed, for example, by injection (in particular reaction injection moulding) or vacuum filling and appropriate parts and/or vent holes may be provided in the cover plate to facilitate this. The parts and/or vent holes may be filled and/or ground flushed after completion of the filling step.

Figure 3 is a cross-sectional view of a connection between inner bottom panels at centreline. It will be seen that the arrangement is essentially the same as that of Figure 2 but lower metal plate 12 is provided with a large flange I 2b which is welded to girder 30 on the centreline CL. Upper metal plate 11 is provided with a small flange 1 lb having at its distal end backing bar 17. Closing plate 15 is welded between centreline girder 31 and upper metal plate 11. It will also be seen that a backing bar 17 is provided on girder 31 to assist in welding closing plate 15 to girder 31. Otherwise the arrangement shown in Figure 3 is the same as in Figure 2. After the closing plate is welded in place a core 16 is formed as described above in relation to Figure 2.

The choice in a particular joint of positioning the closing plate 15 on the upper or lower side of the connection will depend on factors such as convenience in welding and a desirability of presenting fewer welds in the outer surface of the finished vessel or structure on the inner surface of a chamber or compartment. It is desirable to ensure that as much welding as possible can be performed down hand.

Figure 4 is a cross-sectional view of other forms of joint between deck panels.

Sandwich panel lOc is similar to panel lOb of Figure 3 in that the lower faceplate 12 has a larger flange 12b than flange 1 lb of upper faceplate 11. At the other end of panel lOc a solid (i.e not hollow) prismatic perimeter bar 33 is used. This is shaped to enable welding to longitudinal bulkhead 32 as well as steel side deck 35. This helps maintain continuity and provides a steel-to-steel connection between the deck beams and the side transverses.

Perimeter bar 33 has a reduced thickness part 33a that fits between and supports metal plate II and 12. Metal plates 11 and 12 are welded along their edges to perimeter bar 33.

Sandwich panel I Od likewise has a solid prismatic perimeter bar 34 at one edge. This perimeter bar has two reduced thickness portions 34a, 34b. One reduced thickness portion 34a supports and fits between metal plates 11, 12 of sandwich panel lOd whilst reduced thickness portion 34b fits between flange 1 2a of sandwich panel I Oc and closing plate 15 which joins to and forms a continuation of upper metal plate 11 of sandwich panel 1 Oc.

Prismatic perimeter bar 34 is also welded to longitudinal deck girder 30 by full thickness welds 18.

At the centreline CL, sandwich panel 1 Od is joined to a mirror image panel 1 Oe.

Thus, the projecting flanges 1 2b of lower metal plates 12 of sandwich panels 1 Od and 1 Oe are welded directly together on centreline CL. Backing bar 17 is fixed to one of the flanges 1 2b to assist this operation. Closing plate iSa is welded between the short flanges lib of upper metal plates 11 of sandwich panels 1 Od and I Oe. Closing plate 1 5a is bent along its centreline in order to form a knuckle at the vessel centreline in view of the camber formed on the deck.

Thus each half of closing plate iSa is coplanar with and forms a continuation of upper metal plate 11 of sandwich panels lOd and lOe. After the closing plate is welded in place a core 16 is formed as described above in relation to Figure 2.

Figure 5 is a cross-sectional view of an alternative connection of inner bottom panels and centreline. The overall arrangement is very similar to that of Figure 3, but a prismatic perimeter bar 36 similar to perimeter bar 34 of Figure 4 is used. Prismatic perimeter bar 36 is welded to the top of centreline girder 31 and has reduced thickness portions 36a, 36b either side, each fitting between large flange I 2b of the lower metal plate of a sandwich panel and closing plate 15. After the closing plate is welded in place a core 16 is formed as described above in relation to Figure 2.

Figure 6 is a cross-sectional view of the connection of bottom plates to the centreline girder. This is a critical joint at the centreline of a vessel and it is desirable that the centreline girder 31 is connected to the both faceplates of both sandwich panels I Of, lOg. It will be noted that the lower plates 12 of sandwich panels I Of, I Og are somewhat thicker than the upper plates 11, for example lower plates 12 may be of 6mm and upper plates 11 of 4mm. It can also be seen that the flange I 2c of lower panel 12 of sandwich panel I Og is longer than the flanges of other panels described previously. For example flange I 2c may be between 500mm and 1000mm. The bottom of centreline girder 31 is welded to the upper surface of flange 1 2c near its midline. To the left, as shown in Figure, of the centreline a cavity is formed between flange 12c, short flange ha of upper metal plate 11 and closing plate 15, which is welded between flange 1 lb and centreline girder 31 by full thickness welds 18.

After the closing plate is welded in place a core 16 is formed as described above in relation to Figure 2.

The distal end of flange 12c of sandwich panel lOg is butt welded in-line to flange I 2a, which is a continuation of lower metal plate 12 of sandwich panel I Of. Thus, to the right of the centreline, as illustrated, a cavity is formed between flange 12c of sandwich panel lOg, flange 12a of the sandwich panel lOf, flange lib of sandwich panel lOf and closing plate 15.

After the closing plate is welded in place a core 16 is formed as described above in relation to Figure 2. This arrangement allows easy adjustment for variation of width of panels lOg and I Of and also for inspection of the welds between the centreline girder and flange 1 2c prior to installation of the closing plates 15.

Figures 7 and 8 are cross-sectional views of exemplary joints at top and bottom connection to the corrugated transfers bulkhead 32. To accommodate the corrugation of transverse bulkhead 32, top plate 37 has a large width, e.g. in the range of from 400mm to 600mm. It also has reduced thickness parts 37a to accommodate flanges 12a of sandwich panels lOh and closing plates 15.

Figure 9 is a cross-sectional view of a simple panel-to-panel joint between sandwich panels 1 Oj, 10k. In this arrangement, sandwich panel 10k is provided with a prismatic perimeter bar 30 which has a simple rectangular cross-section. This perimeter bar projects outwardly of metal plates 11, 12 of sandwich panel 10k. Sandwich panel lOj is provided with a U-shaped edge member 13a and has a large flange 12b on its lower plate 12 that is welded directly to lower metal plate 12 of sandwich panel 10k. For this weld, prismatic perimeter bar acts as a backing bar to complete the join. A cavity is formed by welding closing plate 15 between upper metal plates 11 of sandwich panels 10k, 1 Of. For this operation, the prismatic perimeter bar 13 acts as a backing bar for the connection to metal plate II of sandwich panel 10k. Backing bar 17 is provided on flange 11 a of upper metal plate 11 of sandwich panel I Oj to assist in welding closing plate 15 to flange 11 a. After the closing plate is welded in place a core 16 is formed as described above in relation to Figure 2. In Figure 9 the lower metal plates 12 are shown as thicker than upper metal plates 11 because sandwich panels 10k, 1 Oj may form part of the outer bottom hull of the vessel. However, this form of panel-to-panel joint is also applicable with sandwich panels having metal plates of equal thickness.

A simpler version of a panel-to-panel connection is shown in Figure 10, which is a cross-sectional view. For this connection, panel 1 Oa has a said prismatic perimeter bar 1 3b of generally rectangular cross-section. Lower metal plate 12 of sandwich panel lOa projects outwardly of perimeter bar 13b to form a flange 12d. The edge of upper plates 11 runs approximately along the midline of prismatic perimeter bar 13b. Sandwich panel IOn is similar in construction with upper metal plate 11 also ending around the midline of perimeter bar 13c which is similar to perimeter bar 13b. Lower metal plate 12 of sandwich panel IOn likewise extends outwardly of prismatic perimeter bar 13c to form flange 12c. In this embodiment flange I 2d is shown as much shorter than flange I 2c but in other embodiments the width of these flanges may be more similar or equal. To form the joint, flanges 12c and 12d are butt welded together at 18. Then closing plate 15 is welded between upper metal plates 11 of panels I Om, 1 On. Prismatic perimeter bars I 3b act as backing bars for the welding of closing plate 15 to upper metal plates 11. Welding of the closing plate in place forms a cavity into which material is provided to form core 16.

This arrangement is simple yet fatigue resistant and flanges I 2c and/or closing plate can be cut in situ as necessary to accommodate dimensional variations in panels I Om, iOn.

This form of joint can of course be varied according to the exact situation.

A preferred method of constructing a panel to be used in the invention is preferably performed off-site and involves: placing the outer metal layers 11, 12, edge members 13 and any forms or spacers in a mould to define a cavity; injecting liquid plastics or polymer material into the cavity through an injection port; and causing or allowing the plastics or polymer material to cure to form the main core layer 14.

After curing, the injection ports and vent holes are filled, e.g. with threaded plugs, and ground flush with the surface of the outer metal plate. It is to be noted that even if a single continuous cavity is present prior to injection, multiple injection ports and vent holes may be provided to ensure complete filling. As an alternative to injection of the core material, a vacuum fill technique can be used.

If the panel is to be provided with recesses, grooves or other surface features, such as fixing or lifting points, these are preferably formed in or on the outer metal plates prior to formation of the core. Grooves and other indentations can be formed by known techniques such as milling, cutting, bending, rolling and stamping as appropriate to the thickness of the plate and size of feature to be formed. Details can be attached by welding. It is also possible to form such features after curing of the main core layer 14 but in that case measures may need to be taken to ensure that the heat generated by activities such as welding does not deleteriously affect the core 14.

In some circumstances it may be possible to avoid the use of a mould by welding edge plates or perimeter bars to the outer metal plates so that the panel forms its own mould.

Depending on the compressibility and resilience of the inner core, it may be necessary to provide restraints to prevent deformation of the outer metal plates due to the internal pressures experienced during injection and for curing of main core layer 14.

It should be noted that after the core has cured, the faceplates and perimeter bars are bound together by the core 14 SO that in some cases the fixing of the perimeter bars to the face plates need only be sufficient to withstand loads encountered during the injection and/or curing steps, and not necessarily loads encountered during use of the floor panel 10. To improve sealing of the cavity, gaskets or sealing strips can be provided between the edge plates or perimeter bars and faceplates.

It will be appreciated that the above description is not intended to be limiting and that other modifications and variations fall within the scope of the present invention, which is defined by the appended claims. In various drawings, hatching has in some cases been omitted and in other cases different directions of hatching have been used for clarity. This should not be taken as indication that material types are not critical nor that different materials are necessarily used.

Claims (24)

1. CLAIMSI. A method of constructing a vessel or structure, the method comprising the steps of: providing a sandwich panel comprising a first metal plate and a second metal plate spaced apart from the first metal plate; an edge member connected to the first metal plate and the second metal plate so as to define a cavity; and a core filling the cavity and bonded to the first and second metal plates so as to transfer shear forces therebetween, wherein at least a part of the first metal plate projects outwardly of the edge member so as to form a flange; welding the flange to another part of the vessel or structure; welding a closing plate between the other part of the vessel or structure and the second metal plate so as to form a cavity; and filling the cavity with material that cures to form a second core bonding to at least the first metal plate which sufficient strength to transfer shear forces therebetween.
2. 2. A method according to claim 1 wherein the other part of the vessel or structure is another sandwich panel.
3. 3. A method according to claim 1 wherein the other part of the vessel or structure is selected from the group comprising girders, bulkheads, beams and deck plates.
4. 4. A method according to any one of the preceding claims wherein the first metal plate is below the second metal plate in the vessel or structure.
5. 5. A method according to any one of claims 1 to 3 wherein the first metal plate forms an exterior surface of the vessel or structure.
6. 6. A method according to any one of claims 1 to 3 wherein the first metal plate forms an interior surface of a chamber or compartment of the vessel or structure.
7. 7. A method according to any one of the preceding claims wherein a backing bar is provided on the second metal plate to assist in welding the closing plate to the second metal plate. -12-
8. 8. A method according to any one of the preceding claims further comprising the step of inspecting the weld between the first metal plate and the other part of the vessel or structure prior to the step of welding the closing plate to the second metal plate in the other part of the vessel or structure.
9. 9. A method according to any one of the preceding claims wherein the metal plates are of steel and preferably have a thickness in the range of 0.5mm to 20mm.
10. 10. A method according to any one of the preceding claims wherein the first and second cores are formed of an elastomer, preferably a thermosetting elastomer such as polyurethane and further preferably are compact.
11. 11. A method according to any one of the preceding claims wherein the cavity is filled by injection of liquid material.
12. 12. A method according to any one of claims I to Ii wherein the core is filled by a vacuum filling.

    20.
13. 13. A method according to any one of the preceding claims wherein the closing plate includes a bend or curved part.
14. 14. A vessel or structure constructed by a method according to any one of the preceding claims.
15. 15. A sandwich panel comprising: a first metal plate and a second metal plate spaced apart from the first metal plate; an edge member connected to the first metal plate and the second metal plate so as to form a cavity; and a core filling the cavity and bonded to the first and second metal plates so as to transfer shear forces therebetween; wherein at least a part of the first metal plate projects outward of the edge member so as to form a flange.

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16. 16. A sandwich panel according to claim 15 wherein the second metal plate does not project outwardly of the edge member at least in the part opposing the flange.
17. 17. A method according to claim 15 wherein the second metal plate projects outwardly of the edge member in at least the part opposing the flange so as to form a second flange, the second flange not projecting outwardly of the edge member as far as the flange.
18. 18. A sandwich panel according to claim 17 wherein the second flange is provided with a backing bar to assist in welding a plate to the second metal plate.
19. 19. A sandwich panel according to any one of claims 15 to 18 wherein the edge member is a U-shaped rolled steel profile.
20. 20. A sandwich panel according to any one of claims 15 to 18 wherein the edge member is a prismatic perimeter bar.
21. 21. A sandwich panel according to claim 20 wherein the prismatic perimeter bar is substantially rectangular in section.
22. 22. A sandwich panel constructed substantially as described herein with reference to any one of Figures 2 to 10.
23. 23. A sandwich panel according to any one of claims 15 to 22.
24. 24. A method of constructing a vessel or structure substantially as described herein with reference to the accompanying drawings.