Method of reinforcing a structure
Patent Information
- Authority / Receiving Office
- US · United States
- Patent Type
- Applications(United States)
- Current Assignee / Owner
- Filing Date
- 2024-04-04
- Publication Date
- 2026-08-13
Smart Images
Figure US20260234949A1-D00000_ABST
Abstract
Description
[0001] The present invention relates to methods of reinforcing structures, in particular by forming a core between an existing structure and a structural overlay.
[0002] Structural composites based on a sandwich plate system are known in the art. Such structural composites have metal outer layers bonded together by an intermediate core, such as of unfoamed polyurethane elastomer. These structural composites may be used in many forms of construction to replace stiffened steel plates, formed steel plates, reinforced concrete or composite steel-concrete structures. Structural composites may greatly simplify the resultant structures, and improve strength and structural performance (such as stiffness, damping characteristics) while saving weight.
[0003] Offshore structures such as platforms and vessels are exposed to harsh environmental conditions, such that corrosion of structural elements, particularly rusting of steel structural elements, is a common problem. Corrosion of structural elements of offshore structures can lead to equipment failure and on-site accidents. Rusted or corroded structures may need to be repaired or replaced to restore their structural capacity. Replacing structural elements is expensive and time-consuming and may require shutting down part of an offshore operation while the replacement is carried out.
[0004] It is therefore desirable to use structural composites to repair or reinforce existing structures, particularly offshore structures.
[0005] However, known structural composites may rely on welding to seal the metal outer layers so as to form a closed cavity into which a core material may be injected. In offshore contexts, hot work (such as welding) is often not permitted, due to risk of explosion.
[0006] Therefore, it is desirable to provide a method of reinforcing a structure, using a structural composite, without requiring welding or other forms of hot work on site.
[0007] It is an aim of the present invention to at least partially address the aforementioned problems.
[0008] According to the invention, there is provided a method of reinforcing an existing structure, the method comprising: arranging a structural overlay over part of an existing structure to define a cavity between the structural overlay and the existing structure; securing the structural overlay to the existing structure using a structural adhesive, the structural adhesive forming a seal between an edge portion of the structural overlay and the existing structure; injecting a core material into the cavity; and allowing the core material to cure to form a solid core between the existing structure and the structural overlay, wherein the core bonds to the existing structure and the structural overlay with sufficient strength to transmit shear forces therebetween.
[0009] The core bonded to the existing structure and the structural overlay may reinstate the existing structure to beyond its original structural strength. By using a structural adhesive to form a seal around the space between the structural overlay and the existing structure, it is possible to provide a leak-proof seal suitable for containing a curable core material, without requiring welding. Therefore, the method may be used in applications where hot work (such as welding) is restricted or not permitted, such as in potentially explosive environments.
[0010] Optionally, the structural overlay comprises one or more surface members configured to cover an area of the existing structure, and one or more perimeter members configured to surround the area covered by the one or more surface members and be positioned between the existing structure and the one or more surface members, and securing the structural overlay to the existing structure comprises securing the one or more perimeter members to the existing structure using the structural adhesive, such that the structural adhesive forms a seal between the one or more perimeter members and the existing structure.
[0011] Constructing the structural overlay from one or more surface members and one or more perimeter members provides flexibility in installation of the structural overlay, by allowing these parts to be installed separately. This is convenient especially when large areas of an existing structure are to be reinstated. Perimeter members positioned between the existing structure and one or more surface members define a space between the existing structure and one or more surface members which can be filled with a core material.
[0012] Optionally, the one or more surface members are one or more plates and the one or more perimeter members are one or more bars. Plates (surface plates) and bars (perimeter bars) are convenient and cost effective.
[0013] Optionally, the method further comprises securing the one or more surface members to the one or more perimeter members by bolting the one or more surface members to the one or more perimeter members, after securing the one or more perimeter members to the existing structure. Bolting provides a method of securing the one more surface members to the one or more perimeter members without requiring welding.
[0014] Optionally, the method further comprises securing the one or more surface members to the one or more perimeter members using the structural adhesive, after securing the one or more perimeter members to the existing structure. The surface members may be secured to the perimeter members using structural adhesive so as to not require welding.
[0015] Optionally, the method further comprises providing a structural overlay comprising one or more surface members and one or more perimeter members that have been previously secured to one another, prior to arranging the structural overlay over part of the existing structure. Prefabricating a structural overlay (or parts of a structural overlay) before transporting the structural overlay to the site of the existing structure allows for more flexibility in fabricating the structural overlay. This may reduce the amount of assembly work required on site.
[0016] Optionally, the one or more surface members and one or more perimeter members have been previously secured to one another by welding at a location remote to the existing structure. Where the structural overlay is prefabricated at a location remote to the existing structure, it is possible to fabricate the structural overlay using welding. This may be advantageous when the perimeter members and surface members have complex shapes, that are more easily secured to one another by welding.
[0017] Optionally, the method further comprises: securing one or more attachment members to the existing structure using a fast-curing structural adhesive, prior to arranging and securing the structural overlay, wherein the one or more attachment members are configured to fix the position of at least a structure-facing part of the structural overlay relative to the existing structure while the structural adhesive cures, the structure-facing part of the structural overlay is a part which is to be secured to the existing structure using the structural adhesive, and the fast-curing structural adhesive is configured to cure more quickly than the structural adhesive used to secure the structure-facing part to the existing structure.
[0018] This method of securing a structural overlay to an existing structure ensures that structural components which are secured to the existing structure (such as perimeter members) do not move or slide out of place while the structural adhesive cures.
[0019] Optionally, at least one of the attachment members comprises a first engagement portion, the structure-facing part of the structural overlay comprises one or more second engagement portions, wherein the first engagement portion is a protruding portion and the second engagement portion is a hole, or the first engagement portion is a hole and the second engagement portion is a protruding portion, each protruding portion is configured to extend into a corresponding hole to fix the position of the structure-facing part relative to the existing structure, and securing the structural overlay to the existing structure comprises securing the structure-facing part to the existing structure using the structural adhesive with each protruding portion extending through the corresponding hole.
[0020] Engagement between a protruding portion and a hole can fix the position of the structure-facing part of the structural overlay without requiring attachment members located outside the structure facing part, and thus taking up more space on the original structure. Moreover, there may not exist additional space for attachment members to be positioned outside of the structure-facing part.
[0021] Optionally, the structure-facing part comprises the one or more holes and the one or more holes are through holes, each attachment member comprises the protruding portion, and the one or more protruding portions are threaded, and securing the structural overlay to the existing structure comprises securing the structure-facing part to the one or more attachment members by tightening a nut over each protruding portion to clamp the structure-facing part to the existing structure.
[0022] Tightening a nut over each protruding portion provides a clamping force which clamps the structure-facing part to the existing structure, while the structural adhesive cures. This may improve bonding between the structural adhesive and the structure-facing part and existing structure, respectively. Using a nut to clamp the structure-facing part to the existing structure also enables the structure-facing part to be attached to a surface of the existing structure which is vertical or overhead, for example.
[0023] Optionally, each attachment member is a stud comprising the protruding portion and a base portion configured to be secured to the existing structure by the fast-curing structural adhesive. Adhesively secured studs are convenient and cost effective.
[0024] Optionally, there are provided at least two protruding portions and at least two corresponding holes. By providing at least two protruding portions and at least two corresponding holes, the position of a structure-facing part can be reliably fixed, with rotation of the structure-facing part prevented.
[0025] Optionally, the fast-curing structural adhesive has a working time of less than 10 minutes. A fast-curing structural adhesive with a working time of less than 10 minutes allows the positions of the one or more attachment members to be reliably determined, because the attachment members are unlikely to move, or can be prevented from moving, while the fast-curing structural adhesive cures.
[0026] Optionally, the fast-curing structural adhesive is a methacrylate adhesive. However, other types of fast-curing structural adhesive may be used, such as an acrylic structural adhesive. A fast-curing methacrylate adhesive is advantageous, because such adhesives may be high-strength, high-viscosity, and do not allow the attachment member to slide. Any fast-curing structural adhesive which does not allow the attachment member to slide may be used. Preferably, the fast-curing structural adhesive is also high-strength and / or high-viscosity.
[0027] Optionally, the structural adhesive has a working time of at least 20 minutes. Structural components that are to be secured to the existing structure (structure-facing parts) using the structural adhesive are often large and take time to get into position. Also, the structural adhesive may need to be applied to a large area in its uncured state. Therefore, a structural adhesive with a working time of at least 20 minutes allows time for application of the structural adhesive and for structure-facing parts to be arranged into their correct positions.
[0028] Optionally, the structural adhesive is a methacrylate adhesive. However, other types of structural adhesive may be used, such as an acrylic structural adhesive.
[0029] Methacrylate structural adhesives have many properties that are preferable in maritime and offshore applications. In particular, methacrylate adhesives may have a long working time, good gap fill, good resistance to hydrocarbons, water and solvents, and are easy to dispense. Any structural adhesive that has one or more of these properties, or any combination thereof, may be used.
[0030] Optionally, the existing structure is an off-shore structure or vessel. The methods disclosed herein are particularly advantageous when used on off-shore structures or vessels.
[0031] Optionally, the structural overlay is secured to the existing structure without welding at the site of the existing structure. The methods disclosed herein allow the structural overlay to be reliably secured to an existing structure, without requiring welding at the site of the existing structure. Therefore, the method may be advantageously used in environments where there is a risk of explosion.
[0032] Optionally, the structural overlay is formed from steel and the core material is an elastomer. A structural overlay formed from steel and a core material formed from an elastomer have been found to provide excellent strength characteristics of the resulting reinforced structure.
[0033] There is also provided a reinforced structure comprising: an existing structure; a structural overlay arranged over part of the existing structure to define a cavity between the structural overlay and the existing structure; and a core between the existing structure and the structural overlay, wherein the structural overlay is secured to the existing structure using a structural adhesive, the structural adhesive forming a seal between an edge portion of the structural overlay and the existing structure and the core is bonded to the existing structure and the structural overlay with sufficient strength to transmit shear forces therebetween.
[0034] A structure which has been reinforced using the methods disclosed herein may have an extended lifetime compared with non-reinforced structures, and may have improved strength relative to the structure's original operating capacity.
[0035] Embodiments of the invention will be described in detail with reference to the drawings, in which:
[0036] FIG. 1 is a cross-sectional schematic illustration of an existing structure reinforced with a structural composite.
[0037] FIG. 2 is another cross-sectional schematic illustration of an existing structure reinforced by a structural composite.
[0038] FIG. 3 is a plan view schematic illustration of an existing structure reinforced by a structural composite.
[0039] FIG. 4 is a partial cut-away perspective view of an existing structure reinforced by a structural composite, with a structural overlay including a plurality of surface plates and perimeter bars.
[0040] FIG. 5 shows a cut-away perspective view (left), and a cross-sectional view (right) of an existing structure reinforced by a structural composite, wherein the structural overlay includes surface plates secured to perimeter bars by bolts.
[0041] FIG. 6 is a cross-sectional schematic illustration of an existing structure reinforced by a structural composite, including a surface member secured to perimeter members by structural adhesive.
[0042] FIG. 7 is a plan view of a prefabricated part of a structural overlay including a surface plate and a plurality of perimeter bars.
[0043] FIGS. 8 and 9 are cross-sectional schematic illustrations of an existing structure reinforced by a structural composite, wherein the structural overlay includes a surface plate which has been pre-welded to a perimeter bar.
[0044] FIG. 10 is a cross-sectional schematic illustration of a perimeter member secured to an existing structure using a structural adhesive and attachment members secured to the existing structure using a fast-curing structural adhesive.
[0045] FIG. 11 is a cross-sectional schematic illustration of a perimeter member secured to an existing structure by a structural adhesive, and an attachment member secured to the existing structure by a fast-curing structural adhesive, wherein the perimeter member and attachment member are engaged with one another by a respective protrusion and hole.
[0046] FIG. 12 is a perspective view of attachment members being secured to an existing structure by a fast-curing structural adhesive, perimeter members being mounted to the existing structure by a structural adhesive, and the perimeter members being secured to the attachment members by tightening a nut over the protruding portion of each attachment member.
[0047] FIG. 13 is a cross-sectional view through a portion of a perimeter member through which there is provided an attachment member.
[0048] In the various drawings, like parts are denoted by like references. The drawings are not necessarily produced to scale. In particular, the size of various elements may be exaggerated for clarity.
[0049] Disclosed herein are methods of reinforcing an existing structure. Reinforcement as defined herein includes repair of a damaged structure. The existing structure can be any industrial or building structure or vessel. The methods disclosed herein can be used to reinforce offshore structures including vessels such as tankers. The methods disclosed herein can be used to reinforce parts of an existing structure (or structural elements), such as decks, tanks, bulkheads, helidecks, side shells, and pipes.
[0050] The methods disclosed herein can generally be used to reinforce any structural element having an accessible surface to which the overlay of the invention may be applied. The surface of the existing structure to which the overlay is applied is not limited to a flat surface, and may be a curved surface (for example of a pipe) and may be a multifaceted surface, for example extending around a three dimensional structure. It should be noted that the methods disclosed herein are not limited to reinforcing horizontal surfaces from above. The method may be used to reinforce vertical surfaces, overhead surfaces, and sloped surfaces.
[0051] Structural elements to be reinforced by the methods disclosed herein are usually made of metal, for example steel, optionally structural steel, although the invention is not limited in this respect. The material of the part of the existing structure to be reinforced by the overlay can be made of any material that is susceptible to bonding with the core material such that the core bonds to the existing structure with sufficient strength, as will be discussed later.
[0052] A method of reinforcing an existing structure will now be described with reference to FIGS. 1 to 3. The method includes arranging a structural overlay over part of the existing structure to define a cavity between the structural overlay and the existing structure.
[0053] A structural overlay is a structural element, or several structural elements rigidly secured to one another, that is designed to cover a surface of the part of the existing structure that is to be reinforced. The structural overlay is a rigid body with sufficient strength and rigidity for reinforcing the existing structure. The shape of the structural overlay is determined so as to cover a surface of the part of the existing structure to be reinforced. The shape of the structural overlay may substantially replicate the shape of the underlying surface of the existing structure. When the structural overlay is arranged over the part of the existing structure to be reinforced, the shape of the structural overlay is designed so as to provide a cavity between the structural overlay and the surface of the existing structure over which the structural overlay is arranged. The shape of the structural overlay is also configured to contain a liquid, uncured core material, in the space between the structural overlay and the existing structure, when the structural overlay is arranged relative to the existing structure. A thickness of the part of the structural overlay which spans an area of the existing structure, and which is located on the opposite side of the cavity to the existing structure (for example a surface member, which will be described later), may be in the range of 0.5 to 50 mm, preferably 0.5 to 40 mm, more preferably 0.5 to 20 mm.
[0054] The structural overlay, or at least the surfaces of the structural overlay which will contact the core material when in situ, is made of a material that is susceptible to bonding with the core material with bonds of sufficient strength, as will be described later. The structural overlay is preferably made of metal. The structural overlay may be made of steel, optionally structural steel. However, the structural overlay may be made of aluminium, stainless steel or other structural alloys, depending on the environment in which the overlay is to be used or other desired properties of the overlay.
[0055] An example of a part of an existing structure 1 over which a structural overlay 2 is arranged, so as to define a cavity 3 therebetween, is shown in FIG. 1. FIG. 1 is a cross sectional view showing the inside of the cavity 3. Both the existing structure 1 and the structural overlay 2 extend in the directions perpendicular to the plane of the page, to ends at which the cavity 3 is closed (similarly to how the cavity 3 is closed on either side of FIG. 1 by the edge portions 21 of the structural overlay 2). FIG. 2 shows another example of a structural overlay 2 applied to an existing structure 1 to define a cavity 3 therebetween. As shown in FIGS. 1 and 2, the shape of the structural overlay 2 can be designed according to the shape of the surface to which the structural overlay is to be attached.
[0056] The method also involves securing the structural overlay to the existing structure using a structural adhesive, such that the structural adhesive forms a seal between an edge portion of the structural overlay and the existing structure. FIGS. 1 and 2 show an edge portion 21 secured to the existing structure 1 by structural adhesive 4. FIG. 3 shows a plan view of part of an existing structure 1 to which structural overlay 2 has been secured using structural adhesive 4 (not shown).
[0057] When the structural overlay 2 is secured to the existing structure 1, the cavity 3 is sufficiently closed such that uncured core material cannot escape the cavity 3. In particular, uncured core material cannot escape the cavity 3 by passing between the edge portion 21 of the structural overlay 2 and the part of the existing structure 1 to which the edge portion 21 is secured. The edge portion 21 of the structural overlay completely surrounds the area of the surface of the existing structure 1 to which the structural overlay 2 is applied, as shown in FIG. 3. The cavity 3 is of course not entirely closed, before the core material has cured to form a solid core, so as to allow the uncured core material to be injected into the cavity 3, as will be described later.
[0058] It is only necessary to provide the structural adhesive 4 between an edge portion 21 of the structural overlay and the part of the surface of the existing structure 1 which the edge portion 21 faces. The dotted line in FIG. 3 shows the part of the structural overlay 2 occupied by the edge portion 21. The edge portion 21 is a border, or a frame, completely surrounding the area of the structural overlay so as to contain the core.
[0059] The structural adhesive 4 may be applied to the edge portion 21 of the structural overlay, or to a corresponding portion of the existing structure 1 which will face the edge portion 21 of the structural overlay, when it is installed. The structural adhesive 4 may be applied in an uncured form. The uncured structural adhesive 4 may be applied before the structural overlay 2 is arranged over the existing structure 1. After the structural overlay 4 is arranged over the existing structure 1, with the uncured structural adhesive therebetween, the structural adhesive is allowed to cure.
[0060] The structural overlay, or at least a part of the structural overlay to be secured to the existing structure by the structural adhesive 4, may be clamped, braced, or weighted against the existing structure 1 during curing of the structural adhesive 4, to aid the structural adhesive in bonding to surfaces of existing structure and the structural overlay.
[0061] By using a structural adhesive 4 to attach the edge portion 21 of the structural overlay to the existing structure, a seal is formed between the edge portion 21 and the existing structure 1 which is suitable for containing the uncured core material. It is not essential that the structural adhesive 4 alone provides a leak proof seal. If any gaps remain, then sealant may be applied to make the seal leak proof. The seal which is formed may be air tight and / or water tight. This allows the uncured core material to be contained within the cavity during injection and until it has completely cured.
[0062] By using structural adhesive instead of welding, the method avoids the need for hot work in order to form a suitable seal. In this way, the method allows for reinforcement of structures in areas in which hot work (such as welding) is restricted or not permitted.
[0063] Before arranging the structural overlay over the existing structure and securing the structural overlay to the existing structure using a structural adhesive, the surface(s) of the existing structure and / or the structural overlay, which are to be joined by the structural adhesive, may be prepared. For example, materials, obstructions, residue and water may be removed from the surface. The surface of the existing structure may be grit blasted to remove any existing paint, coatings or surface rust, to provide a clean rough surface for adhesion by the structural adhesive. Any incidental holes or cracks may be repaired by fitting a steel reinforcement plate using structural adhesive. Preparation of the existing surface can be performed according to the particular structural adhesive being used.
[0064] Alternatively or additionally, the inner surfaces of the cavity 3 may be prepared so that they are rust free, degreased, dry, solvent free, and free from dust, dirt and grit. This assists with adhesion of the core material to the inner surfaces of the cavity 3, namely surfaces of the existing structure and of the structural overlay which are to be connected by the core material.
[0065] After the structural overlay has been secured to the existing structure using the structural adhesive, such that the cavity may contain the uncured core material during injection, the uncured core material is injected into the cavity. After the cavity 3 has been closed (with the exception of injection and vent ports), but before injecting the core material, the cavity 3 may be tested for leaks, by injecting air into the cavity 3.
[0066] The structural overlay may include one or more injection ports through which the uncured core material is injected. The injection ports may be located anywhere on the structural overlay 2, except for the edge portion 21 which is occupied by the structural adhesive 4. It may be preferable to provide an injection port at a part of the structural overlay 2 which is at a lowest position (in the direction of gravity) when the structural overlay is installed in situ. Vent ports may also be provided in the structural overlay 2, at any location other than the edge portion 21 which is occupied by the structural adhesive 4. Vent ports may be provided in any corner areas and anywhere where there may be potential air traps during injection of the uncured core material.
[0067] After the uncured core material has been injected into the cavity 2, with the uncured core material filling the cavity 2 so as to extend continuously between the inner surfaces of the cavity 2, the core material is allowed to cure to form a solid core 31 between the structural overlay 2 and the existing structure 1. The structural overlay 2 may be clamped, weighted, or braced against the existing structure 1 while the core material cures, to aid bonding between the core material and the inner surfaces of the cavity 3. Preferably the core material is injected as a two component mixture that reacts to form an intermediate layer without requiring additional action. Curing the core material may therefore amount to allowing the core material to cure itself.
[0068] After the core material has cured to form a solid core 31, any injection and / or vent ports may be plugged with plugs, such as with BSPT (British standard pipe thread) plugs. The resultant solid core bonded to a structural overlay may together be referred to as an “overlay”. The resultant structure comprising a layer of the original structure, a layer of structural overlay, and an intermediate layer or core therebetween may be referred to as a “structural composite”.
[0069] The core 31 fills the cavity 3 between the existing structure 1 and the structural overlay 2. The core 31 may also be referred to as an intermediate layer. The core 31 is bonded to inner surfaces of the cavity 3 with sufficient strength to transmit shear forces between the existing structure 1 and the structural overlay 2. The core 31 may be bonded to surfaces of the existing structure 1 and the structural overlay 2 with sufficient strength and have sufficient mechanical properties to transfer shear forces expected in use.
[0070] The core 31 may take various different forms but its major structural component is a main core layer of plastics or polymer material. The core 31 material may be an elastomer. Preferably the core 31 comprises or consists essentially of a thermoset, compact (unfoamed) elastomer such as polyurethane. Suitable materials to form the core are disclosed in WO 2019 / 149634, for example. It should be noted that, in addition to the plastics or polymer material which is the major structural component of the core, and which has the physical properties described below, the core may additionally comprise fillers or hollow forms to reduce the overall weight.
[0071] The bond strength between the core and the surfaces of the existing structure 1 and the structural overlay 2 to which the core 31 is bonded should be greater than 3 MPa, preferably greater than 6 MPa, over the entire operating range. This is preferably achieved by the inherent adhesiveness of the elastomer to steel but additional adhesives may be provided.
[0072] The modulus of elasticity of the material of the core 31 is preferably greater than 200 MPa, preferably greater than 250 MPa. Preferably, the modulus of elasticity of the core 31 is at least 200 MPa, preferably greater than 250 MPa, at the maximum expected operating temperature, which may be 100° C. Desirably, the core 31 is not too stiff so that the modulus of elasticity should be less than 2,500 MPa at the lowest expected operating temperature, which may be −40 to −45° C.
[0073] The tear, compression and tensile strengths as well as the elongation are desirably maximised to enable the structural composite to absorb energy in unusual load events, such as impacts. In particular, the compressive and tensile strengths of the core 31 should be at least 20, and preferably 40, MPa. The compressive strengths can, of course, be considerably greater than these minima.
[0074] The ductility of the core 31 at the lowest operating temperature is desirably greater than that of metal layers (of the existing structure and the structural overlay) which is about 20%. A preferred value for the ductility of the core 31 at lowest operating temperature is 50%. The thermal expansion coefficient of the core 31 is desirably sufficiently close to that of the outer layers of the composite (of the existing structure and the structural overlay) so that temperature variation across the expected operating range does not cause delamination. The extent by which the thermal expansion coefficients of the two materials can differ will depend in part on the elasticity of the core 31 material but it is believed that the thermal expansion coefficient of the core 31 material may be about 10 times that of the metal layers. The coefficient of thermal expansion may be controlled by the addition of fillers to an elastomer used as the core material.
[0075] A thickness of the core 31 is defined between the existing structure 1 and the structural overlay 2, by taking a shortest distance between the surface of the structural overlay which faces the surface of the surface of the existing structure. A thickness of the core may be between 10 mm and 100 mm. The core thickness may be in a range of 10 mm to 40 mm. However, the core thickness may be as low as or even under 10 mm. The core thickness may be up to and even over 200 mm. The core thickness can vary at different locations. The maximal core thickness may be up to double the minimal core thickness. However, in some arrangements, the maximal core thickness may be up to or even over three times the minimal core thickness. A ratio of a total thickness of the outer layers (of the existing structure 1 and the structural overlay 2) to a thickness of the core 31, may be in the range of 0.1 to 2.5.
[0076] Methods of reinforcing a structure using a structural overlay comprising one or more surface members and perimeter members will now be described with reference to FIGS. 4 to 9.
[0077] As noted above, the structural overlay can consist of a single structural member. However, more commonly, the structural overlay comprises a plurality of structural members or elements. In particular, a plurality of members may be required so as to cover a large area of an existing structure, for example as shown in FIG. 4. Even in the case of a small area of an existing structure to be reinforced, the structural overlay preferably comprises a plurality of structural elements or members.
[0078] The structural overlay may comprise one or more surface members and one or more perimeter members. The surface members are configured to cover an area of the existing structure to be reinforced. The one or more perimeter members are configured to surround the area covered by the one or more surface members, and be positioned between the existing structure and the one or more surface members. The one or more perimeter members may entirely surround the area covered by the one or more surface members so as to enclose the cavity. The one or more perimeter members are configured to be positioned between the existing structures and the one or more surface members, such that the one or more perimeter members define the depth of the cavity and thus the thickness of the core.
[0079] When the structural overlay comprises one or more surface members and perimeter members, the perimeter members may be secured to the existing structure using the structural adhesive, such that the structural adhesive forms a seal between the one or more perimeter members and the existing structure. That is, the one or more perimeter members may comprise the edge portion of the structural overlay. The provision of separate perimeter members and surface members provides flexibility of installation, allowing for the perimeter members and surface members to be installed separately. Surface members and perimeter members may also be more cost effective than providing a single member shaped so as to form a three-dimensional cavity having a depth, for example by bending a plate.
[0080] FIG. 4 shows a partial cutaway perspective view of an existing structure 1 which has been reinforced with structural overlay 2, with core 31 therebetween. As shown in FIG. 4, the structural overlay 2 comprises surface members 22 and perimeter members 23. Surface members may comprise plates (surface plates) and perimeter members may comprise bars (perimeter bars), as shown in FIG. 4. In any of the methods described herein, the surface member(s) may be plate(s) and the perimeter member(s) may be bar(s).
[0081] In the arrangement of FIG. 4, the entire area covered by the structural overlay (by the surface members 22) is surrounded completely by perimeter bars 23. In addition, further perimeter bars may be provided between adjacent surface plates, with these perimeter bars being secured to the existing structure and the surface plates by any of the methods described herein for securing perimeter members to the existing structure and surface members. The perimeter members provided between the adjacent surface members may also be connected to the existing structure and the adjacent surface members by methods other than those described for securing the perimeter members. As shown in FIG. 4, where the structural overlay comprises a plurality of surface members, the core 3 may be divided into a plurality of core compartments, each core compartment corresponding to a surface member.
[0082] As noted above, an advantage of using separate perimeter members and surface members is that the one or more perimeter members and one or more surface members may be separately installed. In particular, the one or more perimeter members may be firstly secured to the existing structure, with the one or more surface members being subsequently secured to the one or more perimeter members.
[0083] For example, after securing the one or more perimeter members to the existing structure by the structural adhesive, the one or more surface members may be secured to the one or more perimeter members by bolting. This is shown in FIG. 5. In the example of FIG. 5, a common perimeter member 23 is provided between (and overlapping) two surface members 22. The perimeter member 23 is secured to the existing structure 1 by structural adhesive 4. Each surface member 22 is secured to the perimeter member 23 by bolts 8. Preferably, the bolts 8 are high-strength pre-tensioned bolts.
[0084] In environments where hot work is allowed, the joints between adjacent surface members could be made by means of full penetration welding to the common perimeter member. The key purpose of bolted connections of two adjacent surface plates to a perimeter bar, as illustrated in FIG. 5, is to ensure that the loads (transferred from the existing structure into the new surface member via core bond and shear) are transferred across the joints between these adjacent surface plates by connections made with high-strength pre-tensioned bolts and a common perimeter bar. This achieves the full capacity of the top plate and structural continuity of the whole overlay. This is advantageous if the overlay is required to contribute to the global strength of a vessel or offshore structure, which is usually the case for large repairs. Another advantage of bolting the one or more surface members to one or more perimeter members, as opposed to using structural adhesive for example, is that it is not necessary to wait for the structural adhesive to cure.
[0085] In order to seal the cavity 3, a gasket 9 is provided between each of the perimeter members and respective one or more surface members, which are secured to one another by bolting. In applications where hot work (such as cutting, drilling and welding) is not permitted, it is advantageous to pre-drill all bolting holes in the one or more perimeter members, and one or more surface members, at a location remote to the existing structure. It is also advantageous to countersink the bolts so as to provide a flush surface of the structural overlay.
[0086] Alternatively or additionally, one or more surface members may be secured to one or more perimeter members using structural adhesive, after the one or more perimeters members have been secured to the existing structure by the structural adhesive. An advantage of this method is that the perimeter members and surface members may require less prefabrication because bolt holes are not required.
[0087] An example of an existing structure reinforced in this way is shown in FIG. 6. FIG. 6 shows surface member 22 secured to perimeter members 23 by structural adhesive 4. The perimeter members 23 themselves are also secured to the existing structure 1 using the structural adhesive 4. In this method, the uncured structural adhesive may be applied to the part of the surface of the existing structure 1 which faces the perimeter members 23 when the perimeter members are installed. Alternatively, the uncured structural adhesive may be applied to the perimeter members 23 themselves.
[0088] After the structural adhesive 4 between the one or more perimeter members 23 and the existing structure 1 has cured, structural adhesive 4 may be applied to the surface of the one or more perimeter members 23 which is to face the one or more surface members 22. Then, the one or more surface members 22 are arranged adjacent the one or more perimeter members 23, while the second layer of structural adhesive 4 (between the perimeter member(s) and the surface member(s)) is allowed to cure.
[0089] Rather than separately installing the perimeter member(s) and surface member(s) to the existing structure on site, the surface member(s) and perimeter member(s) may be secured to one another prior to securing any part of the structural overlay to the existing structure. This enables the perimeter member(s) and surface member(s) to be secured to one another at a remote location, which means less assembly work is required on site.
[0090] The prefabricated structural overlay may be provided in multiple parts, each part comprising one or more surface members and one or more perimeter members that have been previously secured to one another.
[0091] An example of a prefabricated part of a structural overlay is shown in FIG. 7. The part of the structural overlay 2 in FIG. 7 comprises a single surface member 22 to which three perimeter bars 23 have been secured. One side (at the bottom of FIG. 7) of the surface member 22 does not have a perimeter bar. This side of the surface member 22 is configured to be attached to a side of another surface member, so as to form a structural overlay comprising multiple surface members.
[0092] An advantage of assembling a structural overlay, or multiple parts of a structural overlay, before any part of the structural overlay is secured to the original structure, is that the surface member(s) and perimeter member(s) may be secured to one another by welding at a location remote to the existing structure. This may be particularly advantageous when the structural overlay is required to have a complex shape such that the perimeter member(s) and surface member(s) are more readily secured to one another by welding.
[0093] Examples of surface members 22 which have been secured to perimeter members 23 by welding, prior to installing the structural overlay relative to the existing structure 1, are shown in FIGS. 8 and 9. As shown in FIGS. 8 and 9, a side edge of a surface plate may be welded to an outer surface (i.e. not facing the existing structure 1) of a perimeter bar.
[0094] In the above described methods, at least a part of the structural overlay (such as one or more perimeter members) is secured to the surface of the existing structure using a structural adhesive. This is because structural adhesive avoids the need to perform hot work, such as welding or drilling of bolt holes, at the site of the existing structure. Because the part or parts of the structural overlay to be secured to the existing structure by the structural adhesive are often large, preferably a structural adhesive with a long working time is used. For example, the structural adhesive may have a cure time of 24 hours (to reach full strength). A long working time means that an installer of the overlay has sufficient time to apply the structural adhesive and arrange the one or more parts of the structural overlay relative to the existing structure, without the structural adhesive curing in the meantime.
[0095] However, because the structural adhesive has a long cure time, there may be a risk that the part or parts of the structural overlay, to be secured to the existing structure by the structural adhesive, move or slide relative to the existing structure, whilst the structural adhesive is curing.
[0096] Therefore, any of the methods disclosed herein may further comprise securing one or more attachment members to the existing structure to fix the position of at least a structure-facing part of the structural overlay relative to the existing structure, while the structural adhesive cures. Such methods will now be described with reference to FIGS. 10 to 13.
[0097] The structure-facing part of the structural overlay is defined as any part of the structural overlay which is to be directly secured to the existing structure using the structural adhesive, for example one or more perimeter members. By fixing the position of the structure-facing part of the structural overlay, while the structural adhesive cures, the structure-facing part is prevented from moving and sliding.
[0098] The one or more attachment members may be secured to the existing structure using a fast-curing structural adhesive, prior to arranging and securing the structural overlay relative to the existing structure. By using a fast-curing structural adhesive, the one or more attachment members can be fixed in position relative to the existing structure, without risk of the attachment members themselves moving or sliding while the fast-curing structural adhesive cures. Then, the one or more attachment members, which are fixed in position, may be used to mechanically fix the position of the structure-facing part relative to the attachment member(s) and thus the existing structure.
[0099] The fast-curing structural adhesive is configured to cure more quickly than the structural adhesive used to secure the structure-facing part to the existing structure. It will be appreciated that the rate at which an adhesive reaches a certain bond strength with respect to time may not be linear. The fast-curing structural adhesive is required to cure more quickly than the structural adhesive, to the extent that the attachment member(s) do not move or slide while the fast-curing structural adhesive is curing. The attachment member(s) typically have a relatively small surface area to be adhered to the existing structure, such that the fast-curing adhesive can be applied quickly.
[0100] An example of attachment members 5 secured to the original structure 1 by a fast-curing adhesive 41 is shown in FIG. 10. FIG. 10 is a cross-sectional view of an edge portion 21 of the structural overlay. In FIG. 10, attachment members 5 are configured to abut sides of a perimeter member 23, which is a structure-facing part 24 of the structural overlay 2. The perimeter member 23 extends in both directions perpendicular to the plane of the page. The attachment members 5, on the other hand, may be much smaller than the perimeter member 23, so that the attachment members 5 may readily be secured to the existing structure 1 using a fast-curing adhesive 41.
[0101] At least one attachment member 5 may comprise a first engagement portion, with the structure-facing part 24 comprising one or more second engagement portions. The first and second engagement portions may provide the engagement between the attachment member(s) and the structure-facing part so as to secure the position of the structure-facing part relative to the attachment member(s) and thus the existing structure.
[0102] The first engagement portion may be a hole, and the second engagement portion may be a protruding portion. Such an arrangement is illustrated in FIG. 11. As shown in FIG. 11, the perimeter member 23 comprises protruding portion 7 which protrudes into hole 6 provided on attachment member 5. Attachment member 5 is secured to the original structure 1 by fast curing structural adhesive 41. After the attachment member 5 has been secured to the original structure, then the perimeter member 23 is secured to the original structure 1 using the (not fast-curing) structural adhesive 4, whilst the protruding portion 7 protrudes into the hole 6. In this way, the position of the perimeter member 23 relative to both the attachment member 5 and the existing structure 1 is fixed, while the (not fast-curing) structural adhesive 4 cures. Subsequently, surface member 22 may be secured to perimeter member 23 by any of the methods described herein.
[0103] A protruding portion may extend in a direction perpendicular to the surface of the existing structure to which the (not fast-curing) structural adhesive 4 is to be applied in the vicinity of the attachment member having the protruding portion or the corresponding hole. The corresponding hole may also have an axis extending in the same direction as the protruding portion.
[0104] Preferably, the structure facing part (such as one or more perimeter members) comprises the one or more holes, and each attachment member comprises a protruding portion. Preferably, the one or more holes provided in the structure-facing part are through holes. Preferably, the structure-facing part may be secured to the attachment member(s), and thus to the existing structure, by tightening a nut over each protruding portion.
[0105] This method of attaching perimeter members 23 to attachment members 5 is illustrated in FIG. 12. In FIG. 12 the structure-facing part 24 comprises a plurality of perimeter members 23. The perimeter members 23 are to be secured to the existing structure by (not fast-curing) structural adhesive 4. In this example, the structural adhesive 4 is applied to the surfaces of the perimeter members 23 which face the existing structure 1. After the attachment members 5, comprising the protruding portions, have been secured to the existing structure 1 using the fast-curing adhesive 41, the perimeter members 23, to which the (not fast-curing) structural adhesive 4 has been applied, are arranged over the attachment members 5, with the protruding portion of each attachment member extending through a corresponding hole in the perimeter members 23. Then, nuts 54 are tightened over the protruding portions of the attachment members 5, so as to clamp the perimeter members 23 to the existing structure.
[0106] This method is advantageous because the clamping of the perimeter members to the existing structure may facilitate the forming of strong bonds between the (not fast-curing) structural adhesive 4 and the perimeter members 23 and existing structure 1, respectively. Furthermore, this method of mounting perimeter members to an existing structure enables the perimeter members to be secured to a non-horizontal surface, or to the underside of a horizontal surface, by virtue of the clamping force provided by the attachment members 5 and nuts 54. Thus, this method enables the reinforcement method of the present disclosure to be applied to a wider range of surfaces.
[0107] As shown in FIG. 12, each attachment member may be a stud 51 comprising a base portion 53 and a threaded protruding portion 52. The base portion 53 provides a surface area for reliable adhesion of the attachment member 5 to the existing structure. The threaded portion 52 permits securing of the perimeter member 23 to the attachment member 5 by nut 54, as previously described.
[0108] FIG. 13 shows a cross-sectional view of a perimeter member 23 and attachment member 5, as shown in FIG. 12. As shown in FIG. 13, the base portion 53 of the attachment member 5 is secured to the existing structure 1 by fast-curing adhesive 41. The (not fast-curing) structural adhesive 4, which is applied to the structure-facing surface of the perimeter member 23, covers both an area of the existing structure 1 and a surface of the base portion 53 which faces the perimeter member 23.
[0109] In the example of FIGS. 12 and 13, the surface member 22 is attached to the perimeter member 23 by bolting. However, the surface member 22 may be attached to the perimeter member 23 by any of the methods disclosed herein. When the surface member 22 is to be attached to the perimeter member 23 by bolting, bolt holes may be provided along the length of a perimeter member at locations other than holes provided for the attachment studs 51.
[0110] The structure-facing part, in this example perimeter member 23, may include recesses surrounding the holes 6, to provide space for the nuts 54. In this way, the surface member 22 and gasket 9 can fit over the surface of the perimeter member 23 without obstruction by nuts 54. FIG. 13 also shows optional use of sealant 42 to further seal boundaries between structural elements so as to secure the cavity 3 from leaks.
[0111] Preferably, there are provided at least two protruding portions and at least two corresponding holes. Such an arrangement is illustrated in FIG. 12. By providing two protruding portions and a respective hole for each of the protruding portions, the position of a structure-facing part may be fixed so as to prevent rotation of the structure-facing part. However, this is not essential, because the shape of the protruding portion may be designed to engage with the shape of a corresponding hole so as to prevent rotation about the axis of the protruding portion.
[0112] Preferably, the fast-curing structural adhesive has a working time of less than 10 minutes. More preferably, the fast curing structural adhesive has a working time of about 5 minutes. Working time is defined as the time from when the adhesive is first dispensed during which the adhesive is in a state to allow arranging of parts to be secured by the adhesive, such that the adhesive will bond to the parts to be adhered (if a time longer than the working time is taken, then the adhesive is not guaranteed to bond). Such a short working time allows the attachment members 5 to be quickly secured to the existing structure, without risking the attachment members themselves moving or sliding while the fast-curing adhesive cures.
[0113] Optionally, the fast-curing structural adhesive is a fast-curing methacrylate adhesive. Optionally, the fast-curing structural adhesive is an acrylic structural adhesive. Such adhesives may be high-strength, high-viscosity, and / or may sufficiently secure the attachment member such that is does not slide. However, other fast-curing structural adhesives may be used. Preferably, the fast-curing structural adhesive is high-strength and / or high-viscosity. Any fast-curing structural adhesive may be used, which sufficiently secures the attachment member such that is does not slide.
[0114] Preferably, the (not fast-curing) structural adhesive 4 which is used to attach the structure-facing part to the existing structure has a working time of at least 20 minutes, more preferably of at least 30 minutes. A structural adhesive having a working time of at least 20 minutes provides sufficient time for an installer to apply the adhesive and arrange the structure-facing part relative to the existing structure before the structural adhesive cures.
[0115] Optionally, the (not fast-curing) structural adhesive 4 is a methacrylate adhesive. Methacrylate adhesives provide high strength (tensile, shear and peel) and resistance to shock, stress and impact across a wide range of operating temperatures (typically −40° C. to 120° C.). Methacrylate adhesives also provide a long working time, good gap fill, and resistance to hydrocarbons, water and solvents. Methacrylate adhesives are also easily dispensed, which makes them particularly suitable for application on site. Methacrylate adhesives can also withstand severe environmental conditions that may be found on offshore structures or vessels. However, any other structural adhesive having one or more of these properties, or any combination thereof, may be used.
[0116] Example technical characteristics and mechanical properties of suitable (not fast-curing) structural adhesives are shown in Table 1. Any structural adhesive, optionally methacrylate adhesive, having any of the characteristics noted in Table 1 within the ranges shown in Table 1 may be used. However, structural adhesives having different properties than those tabulated in Table 1 may also be used. The particular properties of the structural adhesive may be selected based on a given application.TABLE 1CharacteristicsPlexus MA425Purok VX61-90Working time30-35 minutes30-35 minutesFixture time80-90 minutes80-90 minutesGap fill1 mm-10 mm1 mm-10 mmOperating temperature−55° C.-121° C.−40° C. to 120° C.Strain to failure120-140%115-130%Tensile strength (ASTM D638)13.7-17.2 MPa21-23 MPaLap shear strength (ASTM D10.3-12.4 MPa21.7 MPa1002)Chemical ResistanceHydrocarbons, acidsand bases (3-10 pH),salt solutions
[0117] Any of the methods described herein may be used to reinforce or repair part of an existing structure that is an offshore structure or vessel. In particular, the methods described herein can be performed without welding at the site of the existing structure, as facilitated by the use of structural adhesive.
[0118] The methods described herein result in a reinforced structure comprising an existing structure, a structural overlay arranged over part of the existing structure to define a cavity between the structural overlay and the existing structure and a core between the existing structure and the structural overlay. The structural overlay is secured to the existing structure using a structural adhesive which forms a seal between an edge portion of the structural overlay and the existing structure. The core is bonded to the existing structure and the structural overlay with sufficient strength to transmit shear forces therebetween. Such a reinforced structure may improve the strength of the existing structure beyond its original strength.
[0119] Having described exemplary embodiments of the invention, it will be appreciated that modifications and variations of the described embodiments can be made. The invention is not to be limited by the foregoing description but only by the appended claims.
Claims
1. A method of reinforcing an existing structure, the method comprising:arranging a structural overlay over part of an existing structure to define a cavity between the structural overlay and the existing structure;securing the structural overlay to the existing structure using a structural adhesive, the structural adhesive forming a seal between an edge portion of the structural overlay and the existing structure;injecting a core material into the cavity; andallowing the core material to cure to form a solid core between the existing structure and the structural overlay,wherein the core bonds to the existing structure and the structural overlay with sufficient strength to transmit shear forces therebetween.
2. The method of claim 1, whereinthe structural overlay comprises one or more surface members configured to cover an area of the existing structure, and one or more perimeter members configured to surround the area covered by the one or more surface members and be positioned between the existing structure and the one or more surface members,and securing the structural overlay to the existing structure comprises securing the one or more perimeter members to the existing structure using the structural adhesive, such that the structural adhesive forms a seal between the one or more perimeter members and the existing structure.
3. The method of claim 2, wherein the one or more surface members are one or more plates and the one or more perimeter members are one or more bars.
4. The method of claim 2, further comprising:securing the one or more surface members to the one or more perimeter members by bolting the one or more surface members to the one or more perimeter members, after securing the one or more perimeter members to the existing structure.
5. The method of claim 2, further comprising:securing the one or more surface members to the one or more perimeter members using the structural adhesive, after securing the one or more perimeter members to the existing structure.
6. The method of claim 2, further comprisingproviding a structural overlay comprising one or more surface members and one or more perimeter members that have been previously secured to one another, prior to arranging the structural overlay over part of the existing structure.
7. The method of claim 6, wherein the one or more surface members and one or more perimeter members have been previously secured to one another by welding at a location remote to the existing structure.
8. The method of claim 1, further comprising:securing one or more attachment members to the existing structure using a fast-curing structural adhesive, prior to arranging and securing the structural overlay,wherein the one or more attachment members are configured to fix the position of at least a structure-facing part of the structural overlay relative to the existing structure while the structural adhesive cures,the structure-facing part of the structural overlay is a part which is to be secured to the existing structure using the structural adhesive,and the fast-curing structural adhesive is configured to cure more quickly than the structural adhesive used to secure the structure-facing part to the existing structure.
9. The method of claim 8, whereinat least one of the attachment members comprises a first engagement portion, the structure-facing part of the structural overlay comprises one or more second engagement portions,wherein the first engagement portion is a protruding portion and the second engagement portion is a hole, or the first engagement portion is a hole and the second engagement portion is a protruding portion,each protruding portion is configured to extend into a corresponding hole to fix the position of the structure-facing part relative to the existing structure,and securing the structural overlay to the existing structure comprises securing the structure-facing part to the existing structure using the structural adhesive with each protruding portion extending through the corresponding hole.
10. The method of claim 9 whereinthe structure-facing part comprises the one or more holes and the one or more holes are through holes,each attachment member comprises the protruding portion, and the one or more protruding portions are threaded,and securing the structural overlay to the existing structure comprises securing the structure-facing part to the one or more attachment members by tightening a nut over each protruding portion to clamp the structure-facing part to the existing structure.
11. The method of claim 9, whereineach attachment member is a stud comprising the protruding portion and a base portion configured to be secured to the existing structure by the fast-curing structural adhesive.
12. The method of claim 9, wherein there are provided at least two protruding portions and at least two corresponding holes.
13. The method of claim 8, wherein the fast-curing structural adhesive has a working time of less than 10 minutes.
14. The method of claim 1, wherein the structural adhesive has a working time of at least 20 minutes.
15. The method of claim 1, wherein the existing structure is an off-shore structure or vessel.
16. The method of claim 1, wherein the structural overlay is secured to the existing structure without welding at the site of the existing structure.
17. The method of claim 1, wherein the structural overlay is formed from steel and the core material is an elastomer.
18. A reinforced structure comprising:an existing structure;a structural overlay arranged over part of the existing structure to define a cavity between the structural overlay and the existing structure; anda core between the existing structure and the structural overlay,wherein the structural overlay is secured to the existing structure using a structural adhesive, the structural adhesive forming a seal between an edge portion of the structural overlay and the existing structure,and the core is bonded to the existing structure and the structural overlay with sufficient strength to transmit shear forces therebetween.