GB2399540A - A method of reinforcing an existing metal structure - Google Patents

Abstract

To reinforce an existing structure, reinforcing plates 10 with a least one flange 12, 13 depending from an edge of a main part thereof are used. A first reinforcing plate is welded to the existing structure along the free edges of its flanges. Subsequent plates are welded to corners of previously fixed reinforcing plates and via the free edges of their flanges. Plastics or polymer material is injected into the resulting cavities 40.

Description

IMPROVED METHOD FOR REINFORCING

OR REINSTATING EXISTING STRUCTURES

The present invention relates to methods for reinforcing or reinstating existing structures, especially metal panels, whereby the reinforced structure comprises two outer plates and a core of plastics or polymer material bonded to the outer plates with sufficient strength to substantially contribute to the structural strength of the structure.

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 unformed polyurethane. These sandwich plate systems may be used in many forms of construction to replace stiffened steel plates and greatly simplify the resultant structures, improving strength and structural performance (stiffness, damping characteristics) while saving weight. Further developments of these structural sandwich plate members are described in International Patent Application WO 01/32414, also incorporated hereby by reference. As described therein, foam forms may be incorporated in the core layer to reduce weight and transverse metal sheer plates may be added to improve stiffness.

According to the teachings of WO 01/32414 the foam forms can be either hollow or solid. Hollow forms generate a greater weight reduction and are therefore advantageous. The forms described in that document are not confined to being made of light weight foam material and can also be make of other materials such as wood or steel boxes.

International Patent Application WO 02/078948 is a further development of the concept of including hollow forms and describes forms that are easy to manufacture and assemble, in particular hollow elongate forms made from snap together pieces are described.

GB-2,366,543-A discloses a method, referred to as overlay, of reinforcing existing structures so that the reinforced structure effectively incorporates structural sandwich plate members, with a plate or panel of the original structure forming one faceplate of the structural sandwich plate member. In this method, which has been applied to reinforce deck plates of Ro-Ro ferries, flat bars are welded to the existing deck plate and a new top plate welded to the flat bars so that a cavity is formed. The core is then formed by injecting plastics or polymer material which sets and bonds to the existing deck plate and new reinforcing plate.

This method has considerable advantages over conventional repair techniques which generally involve removing the existing plate and replacing it. In particular, the method of GB-2,366,543-A is much quicker, reducing the time that the existing structure is out of service. Nevertheless, further simplification of the overlay technique and/or reduction of the time taken for it would be desirable.

It is an aim of the present invention to provide an improved method of reinforcing existing structures that preferably is simpler and/or quicker.

According to the present invention, there is provided a method of reinforcing or reinstating an existing metal structure comprising the steps of: providing a reinforcing metal layer on said metal structure in spaced apart relation to thereby form at least one cavity between inner surfaces of said metal structure and said reinforcing metal layer; injecting an intermediate layer comprised of an uncured plastics material into said at least one cavity; and curing said plastics material so that it adheres to said inner surfaces of said metal structure and said reinforcing metal layer, wherein: said step of providing a reinforcing metal layer comprises providing a reinforcing plate having at least one flange depending from an edge thereof and welding a free edge of said flange to said metal structure.

The flange or flanges incorporated in the reinforcing plate replace the flat bars used in the prior art and considerably simplify the overlay procedure since only one weld per edge is required, rather than the two of the prior art. Also, the flanges are automatically positioned correctly.

A reinforcing plate adjacent an already installed reinforcing plate may be installed by welding an edge, that does not have a flange, to the corner between the already installed plate and its flange. Thus, the later installed plates need not have flanges on all edges. To cover a rectangular area with rectangular reinforcing plates, an initial reinforcing plate has flanges on all four edges, plates in lines leading from the sides of the initial reinforcing plate have flanges on three edges and the other reinforcing plates have flanges on two edges. Alternatively, by starting centrally with a block of four reinforcing plates and adding further plates around that, an area can be covered using only reinforcing plates with flanges on two adjacent edges.

Where an area to be covered extends to a suitable perpendicular surface, such as a wall or bulkhead, edges of reinforcing plates without flanges may be welded to that surface.

Each reinforcing plate may define a separate cavity to be injected with material to form the core, or cavities may be built up from several reinforcing plates.

The materials, dimensions and general properties of the reinforcing plate may be chosen as desired for the particular use to which the reinforced structure is to be put and in general may be as described in US-5,778,813 and US-6,050,208.

Steel or stainless steel is commonly 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, as described in US-5,778,813 and US-6,050, 208.

Lightweight forms may be included in the core, as described in WO 01/32414 and WO 02/078948. It should be noted that the lightweight forms serve to reduce the mass of the structural sandwich plate member and need not contribute significantly to its structural strength. The principal requirements on the lightweight forms are that they are of lower density than the plastics or polymer material forming the core and have sufficient thermal and mechanical properties to maintain the desired shape during injection and curing of the plastics or polymer core. The layout of the forms within the core may be as described in British patent application 0 212 392.5 filed 29 May 2002. Lightweight forms are placed, and glued if necessary, on the structure to be reinforced before the reinforcing plates are welded in place.

The present invention will be described below with reference to an exemplary embodiment and the accompanying schematic drawings, in which: Figure 1 is a cross-sectional view of a reinforcing plate according to the present mventlon; Figure 2 is an enlarged cross-sectional view of a part of a structure reinforced according to the method of the present invention; Figure 3 is a plan view illustrating an order of placing reinforcing plates in a method of the present invention; and Figure 4 is a plan view illustrating an alternative order of placing reinforcing plates in a method of the present invention.

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

Figure 1 shows a reinforcing plate 10 which may be of steel and have a thickness of e.g. in the range of from 0.5 to 20mm. Flanges 12, 13 depend from two edges of a main part 11 of the reinforcing plate 10. Other flanges also depend from the edges not shown in the view. The flanges have a height so that when their free edges are welded to an existing structure a closed cavity is formed. The flanges may be formed by bending a flat plate at the corners 14, 15.

The cavity is then filled with a core of plastics or polymer material, preferably a polyurethane elastomer. Preferably the core material is injected via injection ports 17 which are ground-off and, along with vent holes 18, sealed after use. The core may have a thickness in the range of from 10 to 200mm. The core is bonded to the reinforcing plate and the existing structure with sufficient strength and has sufficient mechanical properties to transfer shear forces expected in use between the two and ensure that the reinforcing plate and existing structure behave as a unit. The bond strength between the core and plates should be greater than 3MPa, preferably 6MPa, and the modulus of elasticity of the core material should be greater than 250MPa. For low load applications, such as floor panels, where the typical use and occupancy loads are of the order of 1. 4kPa to 7.2kPa, the bond strength may be lower, e.g. approximately lMPa. By virtue of the core layer, the reinforced structure has a strength and load bearing capacity of a stiffened steel plate having a substantially greater plate thickness and significant additional stiffening.

In general, the reinforcement will be applied to a flat surface and will present a parallel flat surface on completion. Thus the flanges will be of equal, constant height. However, where the existing structure is not flat or a surface not parallel to the existing structure is desired, the flanges may differ in height along their length and between each other.

To reduce the weight of the structural sandwich plate member 10, an array of lightweight forms may be provided, occupying a substantial part of the internal volume of the plate member. The lightweight forms do not need to significantly contribute to the structural strength of the plate and they require only to have thermal and mechanical properties sufficient to withstand the pressure of injection of the material to form core 13 and the heat from the exothermic reaction of the core during curing.

Figure 2 shows the reinforcing plate 10 and a further reinforcing plate 20 installed to reinforce an existing structure 30, with cores 40 injected. Reinforcing plate 10 is attached to the existing structure 30 by welds 16 along the free edges of the flanges 12, 13. Reinforcing plate 20 has an edge without a flange and this is welded at 24 to the corner 14 of previously installed reinforcing plate 10. Flange 21 at the opposite edge of reinforcing plate 20 is welded at 23 to the existing structure 30. Corner 22 between the main part of reinforcing plate 20 and flange 21 provides a site for welding the next reinforcing plate (not shown). In this way a large area can be covered with reinforcing plates with a reduced total length of welding and a reduced number of weld operations.

A scheme for placing reinforcing plates to cover an area 31 of an existing structure 30 is shown in Figure 3. First, in one corner of the area to be reinforced, a reinforcing plate 10 with flanges on all four edges is welded to the existing structure 30 by welds around the free edges of its flanges. Next, reinforcing plates 20 with flanges on three edges are welded in lines extending from the initial reinforcing plate 10 along the edges of the area 31 to be covered. The area 31 is then covered using reinforcing plates 50 having flanges on two adjacent edges, starting in the corner next to the initial reinforcing plate 10. In this Figure, the number in each reinforcing plate indicates the number of flanges it has.

An alternative scheme, using only reinforcing plates with flanges on two adjacent edges, is shown in Figure 4. In this figure, the arrows indicate the orientation of the various reinforcing plates 50 and point to the corner between the two flanges of each reinforcing plate. Firstly, four reinforcing plates 51-54 are welded to each other along their flangeless edges and to the existing structure along the edges of their flanges to form a large cavity. The initial group of reinforcing plates 51-54 may be situated anywhere in the middle, edges or corners of the area 31 to be covered. Then, additional reinforcing plates 55 are added around the edges of the initial group as required to cover the area. In some cases, each additional reinforcing plate forms a separate cavity, in others two reinforcing plates together form a cavity to be injected.

It will be appreciated that whilst the reinforcing plates are principally fixed in place via their flanges and the corners of other reinforcing plates, flat bars may be used along some edges, e.g. to avoid the need to produce one-off plates to start an area, where the edge of the area to be reinforced is irregular or where there are details such as pillars, doors or hatches in the area to be reinforced. Also, particularly if the reinforcing plates are large, spacers may be provided to support the middles of the reinforcing plates and prevent sagging prior to injection of the core material.

Manufacture of the reinforcing plates, including bending to form the flanges and the additional of details such as injection ports and vent holes, may be performed in situ, or off-site in factory conditions and the finished plate transported to the installation site.

It will be appreciated that the above description is not intended to be limiting and that other modifications and variations that fall within the scope of the present invention, which is defined by the appended claims are possible.

Claims (13)

1. A method of reinforcing or reinstating an existing metal structure comprising the steps of: providing a reinforcing metal layer on said metal structure in spaced apart relation to thereby form at least one cavity between inner surfaces of said metal structure and said reinforcing metal layer; injecting an intermediate layer comprised of an uncured plastics or polymer material into said at least one cavity; and curing said plastics or polymer material so that it adheres to said inner surfaces of said metal structure and said reinforcing metal layer, wherein: said step of providing a reinforcing metal layer comprises providing a reinforcing plate having at least one flange depending from an edge of a main part thereof and welding a free edge of said flange to said metal structure.

2. A method according to claim 1, comprising the further steps of: providing a further reinforcing plate having a main part having first and second edges and a further flange depending from said second edge; welding said first edge of said further reinforcing plate to an edge of said first-mentioned reinforcing plate and welding a free edge of said further flange to said existing metal structure.

3. A method according to claim 2, wherein said steps of providing reinforcing plates are repeated to cover an area of said existing metal structure, said reinforcing plates are rectangular in plan, the reinforcing plate first provided has flanges depending from each of its four edges, reinforcing plates extending from said reinforcing plate first provided in lines perpendicular to its edges have flanges depending from three edges thereof and other reinforcing plates have flanges depending from two edges thereof.

4. A method according to claim 2 or 3, wherein each reinforcing plate forms a separate cavity.

5. A method according to any one of the preceding claims, wherein said flanges are integral with said reinforcing plates and formed by bending.

5. A method according to any one of the preceding claims, wherein the or each reinforcing plate has a thickness in the range of from 0.5 to 20mm.

6. A method according to any one of the preceding claims, wherein said intermediate layer has a thickness in the range of from 10 to 200mm.

7. A method according to any one of the previous claims, wherein said plastics or polymer material is an elastomer.

8. A method according to any one of claims 1 to 7, wherein said existing metal structure is a metal panel of larger existing structure.

9. A method according to any one of claims 1 to 7, wherein said existing metal structure is an existing metal part of a larger existing structure.

10. A vessel with an existing panel reinforced using the method of any one of the preceding claims.

11. A reinforcing plate for use in a method according to any one of the preceding claims, having at least one flange depending from an edge of a main part thereof, at least one injection port and at least one vent hole.

12. A reinforcing plate according to claim 11 wherein said flange has a height in the range of from 10 to 200mm.

13. A reinforcing plate according to claim 11 or 12 having a thickness in the range of from 0.5 to 20 mm.