REPAIR OF STRUCTURAL MEMBERS

Abstract: A method of increasing the structural strength of a load bearing member such as a pile (12), particularly for the purpose of reparing a damaged pile, includes the steps of securing a rigid, structural sleeve (17) around the pile (12) and spaced therefrom to form an interspace (18), filling the interspace (18) with an expansive filler (19), and allowing the filler (19) to set and expand in the interspace (18) to impose tensile hoop stresses in the sleeve (17) and corresponding compressive hoop stresses in the pile (12) to enhance the load transfer between the pile (12) and the sleeve (17).

Description: REPAIR OF STRUCTURAL MEMBERS BACKGROUND OF THE INVENTION Field of the Invention This invention relates to the repair of structural members and relates particularly to improved methods and apparatus for effecting repairs of structures such as piles in situ. The invention will be described with particular reference to effecting repairs of structures such as piles, but it will be understood that the invention has wider application to maintenance, protection and repair of a wide range of structural members including steel jacket offshore structures, structural members on bridges or the like, tubular and non-tubular posts of all types, columns, poles and pillars. The invention will also be described particularly with reference to cylindrical metal piles although it will be understood that the invention is applicable to other forms of structures, including concrete piles, timber piles and the like. Description of the Prior Art Piles, such as those used to support jetties, wharves, piers, offshore structures such as steel jacket platforms and similar structures are subject to damage caused by erosion, corrosion and related chemical or electro-chemical erosion, and by impact such as from marine vessels and the like. Piles which are immersed in water, particularly sea water, are generally subject to most corrosion on that area of the pile between tide levels. That portion of the pile is periodically immersed in water and then exposed to atmosphere causing accelerated corrosion as compared to other parts of the pile. As the structural integrity of the jetty, wharf, pier, bridge, offshore structure or the like can be substantially impaired by damage to the piles, it is necessary to repair or replace any piles which suffer substantial damage. Heretofore, the repair of hollow, steel tubular piles has been effected by welding full or part sleeves to the pile so that the sleeves overlie the affected damaged portion. A full sleeve may be formed by welding two half sleeves to the pile along longitudinal and end edges thereof thus effectively adding an outer skin to the damaged pile. However, as most damage to piles occurs in the area between maximum and minimum water levels, and as the repair sleeve or part sleeve must extend substantially beyond the damaged area to provide the necessary strength to effect a proper repair, it is generally necessary to effect the welding of such sleeves in the tidal zone or underwater. Such welding is relatively expensive and time consuming, may require special equipment, and the welds so made, unless carried out with great skill, can be less than perfect, thus, compromising the structural integrity of the repaired pile. Australian Patent Specification No 59285/86 discloses a method of repairing a concrete pile by using a steel sleeve and filling the space between the sleeve with a grout. The method includes removing damaged concrete from the pile before placing the sleeve. The specification discloses the method in relation to a square pile and the sleeve is provided with internal, integral metal spacers formed as part of the sleeve and which bear on the surfaces of the pile. Such sleeves are relatively expensive and need to be custom made for each different type, shape and dimension of pile. United States Patent No 4,306,821 discloses a method for reconditioning structural piles whereby a building filler is placed into a space between a flexible sheet form and the damaged piling. The filler provides a protective and structural coating to the damaged piling. With this method, the strength of the repaired pile is dependent solely on the strength of the filler material, which is preferably an epoxy material and on the adhesive interface with the pile. Therefore, the amount of filler required is that amount necessary to provide the desired strength to the pile. United States Patent No 4,697,649 discloses a method of reinforcing a damaged post in the ground by providing a split casing having helical threads at one end which are driven into the ground by a casing rotary drive mechanism. An annulus between the casing and the post is filled with a suitable filler material. However, this system is designed for above ground posts and not for underwater piles. Further, the driving mechanism is relatively complex and expensive and adds substantially to the repair costs. US Patent No 4,439,070 relates to a method of restoring an underwater pile which uses a flexible jacket placed around the pile and filling the formed annular space between the pile and the jacket with an appropriate epoxy resin compound. Upper and lower seals are provided between the jacket and the pile and the jacket has inlet ports for injection of the epoxy resin and outlet ports for venting water from the annular space. Again, the strength of the repaired pile is dependent on the strength and amount of epoxy resin and on the adhesive interface with the pile, and the system relies on the effective operation of the seals at each end to form the closed annular space. A similar system is shown in Swiss Patent No 573520. Description of the Invention It is therefore desirable to provide an improved method and apparatus which enables a repair of a damaged pile to be efficiently and effectively carried out. It is also desirable to provide a method for effecting the repair of a damaged pile which obviates the need for tidal zone or underwater welding. It is also desirable to provide a method and apparatus for carrying out the repair of a damaged pile which can be used in a wide variety of applications and in respect of a wide variety of piles, columns, posts and the like as referred to above. It is also desirable to provide a method and apparatus for repairing piles which is relatively inexpensive and which enables the repair to be carried out relatively quickly and economically. It is also desirable to provide an improved method and apparatus for carrying out the repair of piles which can be used by relatively unskilled personnel. Summary of the Invention In accordance with one aspect of the invention there is provided a method of increasing the structural strength of a load bearing member, such as a pile, including, inter alia, the steps of fitting a rigid, structural sleeve to the member, the sleeve having internal dimensions greater than the external dimensions of the member to provide an interspace between the member and the sleeve, supporting the sleeve so that it is spaced from the member, and filling the space between the sleeve and the member with an expansive filler, allowing the filler to set, cure and expand to generate compressive forces on the member and tensile forces on the sleeve. The sleeve may be a single piece sleeve for those applications where a single piece sleeve is able to be engaged with the member. Otherwise, the sleeve may be formed of two or more parts which are interconnected, as by welding, bolts or other mechanical connectors, by clipping, by adhesion or chemical bonding, by the use of hinge means or by a combination of these. The sleeve is spaced from the member by the use of spacer means, which may include spacing tabs, indentations or other deformations of the sleeve material or separate spacers including spacers formed of synthetic plastic or rubber materials or the like attached to the inner surfaces of the sleeve. Alternatively, spacer means may be attached to the member prior to engagement of the sleeve thereon or spacer means may be inserted between the member and the sleeve after the engagement of the sleeve on the member. In one arrangement, a seal is provided between the lower edge of the sleeve and the member to seal the interspace between the sleeve and the member at the lower end thereof. A second seal may also be provided spaced from the first seal, and preferably at the upper edge of the sleeve. The seal or seals act to retain the expansive filler within the space between the sleeve and the member before the filler has set and expanded. When the sleeve is composed of two or more parts, seals may also be used between the parts of the sleeve, depending on the means of fixing the sleeve parts together. The expansive filler may comprise a grout, such as a cementitious grout to which an expansive agent is added so that the grout sets and expands on curing. The expansive filler, when cured, induces compressive hoop stresses in the member and tensile hoop stresses in the sleeve so that loading actions on the member are able to be transferred between the member and the sleeve. For a cementitious grout, the expansive filler may be a calcium-sulpho-aluminate or lime based mixture. With the method of the invention, the load transfer between the member and the sleeve is effected primarily by friction across the grout to member interface and across the grout to sleeve interface. The invention also includes the apparatus for repairing a damaged pile or otherwise increasing the strength of a load bearing member comprising a sleeve adapted to surround the member, means to space the sleeve from the member, and an expansive filler adapted to fill the space and to expand on setting and curing to post-tension the sleeve, the filler forming a rigid interface between the sleeve and the member. In one form of the invention, shear keys are provided to positively and rigidly connect the sleeve with the expansive filler and to connect the filler with the member. Where the member is a timber pile, shear keys may be engaged with the pile prior to the engagement of the sleeve. The shear keys may comprise studs, bolts, including coach bolts or the like fastened to the member. The sleeve itself may also have inwardly extending shear keys formed by any suitable means including bolts, punched or pressed deformations of the sleeve, welded pins or the like. The shear keys may be preformed so as to also constitute the or some of the spacer means. According to another aspect of the invention there is provided a method of repairing a substantially tubular, cylindrical structural member, such as a pile, having a damaged area including the steps of securing sleeve means around the member, the sleeve means having an axial length to extend in both directions beyond the area of damage on the member and have an inner diameter greater than the outer diameter of the member, spacer means to space the sleeve means from the member to form a substantially annular space therebetween, filling the annular space with an expansive grout, allowing the grout to set and expand within the space to thereby tension the sleeve and apply compressive forces to the member whereby the set grout facilitates load transfer between the member and the sleeve primarily by friction across the member/grout/sleeve interfaces. In order that the invention may be more readily understood, embodiments thereof will now be described with reference to the accompanying drawings wherein: Fig. 1 is a part sectional view of a jetty pile and an encasing repair sleeve in accordance with the present invention; Fig. 2 is a cross-sectional plan view of a cylindrical, tubular pile and an encasing sleeve in accordance with one embodiment of the invention; Fig. 3 is a part cross-sectional elevational view of a lower end of an encasing sleeve in accordance with a further embodiment of the invention; Fig. 4 is a schematic, perspective view of a further form of sleeve of the invention; Fig. 5 is a view of a part sleeve illustrating a further embodiment of a sleeve seal in accordance with the invention; and Fig. 6 is a cross-sectional plan view of a timber pile and encasing sleeve in accordance with another embodiment of the invention. Referring to the drawings, the embodiments illustrated in Figs. 1 to 5 are designed particularly for the repair of a cylindrical, tubular pile 12 such as those used for jetties and the like. Fig. 1 illustrates a jetty superstructure 14 supported by a pile 12 in a sea water environment. The sea water 15 has, over a period of time, caused corrosive damage 16 to the pile 12 over an area on the pile 12 generally corresponding to the tidal limits. In order to effect a proper repair and reinstate the integrity of the pile 12, and to provide protection against corrosion, it is necessary to secure a sleeve 17 to the pile 12 so that the sleeve can carry at least part of the load on the pile 12. In accordance with the present invention, the repair is effected by locating the sleeve 17 about the pile 12 and spacing the sleeve 17 from the pile to form a substantially annular space 18. The space 18 is then filled with an expansive grout 19 which expands when it sets thereby tensioning the sleeve 17 and forming a substantially firm or rigid interface between the pile 12 and the sleeve 17. In order that the grout is retained in the annular space 18 before setting, a seal 21 is provided at least around the lower edge of the sleeve 17 to extend between the sleeve and the pile 12. The seal shown in Fig. 1 is formed by a flexible, deformable rubber ring separated at a location to allow the separated ends to be spaced to engage the ring or the pile. However, the seal 21 may be formed by any suitable means or material, including synthetic plastic material, mastic or the like. Preferably, a second seal 22 is provided at the upper end of the annular space 18 to maintain the grout within that annular space during the initial setting and expanding period. Such a seal 22 is fitted in place after the grout has been conveyed into the annular space 18 and all water and air expelled, otherwise, provision needs to be made to allow the water and air to escape. It will be appreciated that the sleeve 17, which may be formed of two or more parts, is, when assembled, a load bearing member which is able to carry at least part of the load on the pile. Further, the expansive grout must also be of a material which, on setting, facilitates load transfer between the pile and the sleeve. The preferred grout for use in this invention is a cementitious grout mixture having as an expansive agent a calcium-sulpho-aluminate formulation. Such a formulation has an initial setting period during which the grout hardens. This period is followed by a curing period during which the grout expands and generates radial pre-stress forces resulting in tensile hoop stresses in the sleeve 17 and compressive hoop stresses in the pile 12. A pre-stress of 12 MPa or more is achievable. Further, by roughening the inner surface of the sleeve 17, a greater degree of resistance to slip between the grout and the sleeve is achieved. The surface roughness may be increased by any suitable means including machining, stamping, shot blasting or the like. Referring to Fig. 2, a sleeve 17 is illustrated formed of two parts 17a and 17b which are held together with two axially extending rows of bolts 24 which engage threaded holes 26 or captive nuts in the opposed sleeve half. The sleeve 17 is assembled around the pile 12 and is spaced therefrom by a series of internal deformable rubber spacers 27 which are fixed to the inside surface of each sleeve part 17a and 17b, such as by adhesive or mechanical fastening. The spacers 27 are provided at several locations along the length of the sleeve parts whereby, when the sleeve parts are connected as illustrated, the spacers act to centre the sleeve 17 on the pile 12 so that a substantially annular space 18 exists between the sleeve 17 and the pile 12. This space is then filled with the expansive grout mixture aforesaid which, on setting, expands and produces tensile stresses in the sleeve 17 and compressive stresses in the pile 12, the grout being of a material which facilitates load transfer between the pile and the sleeve. Referring to Fig. 3, there is illustrated an alternate form of spacer 28 which comprises a part cylindrical ring 28 formed of a flexible material, such as a spring steel or the like, and which is able to be clipped around the pile 12. The ring 28 has a number of depending, inwardly extending legs 29 the inner edges of which are adapted to engage the surface of the pile so that the body of the ring 28 is spaced therefrom. The ring 28 engages over the lower end of the sleeve 17 thereby supporting that end such that the sleeve 17 is evenly spaced from the pile 12. Fig. 3 also illustrates a lower seal 21 formed of one or more pockets 31 of a flexible material, such as rubber, synthetic plastic material, fabric or the like. The pockets 31 are open at their upper end and are secured to the lower edge portion of the sleeve 17 by bonding or by any other suitable fastening means. In use, when the expansive grout 19 is introduced into the annular space 18 from the upper end, the grout fills the pockets 31 causing the inner face thereof 32 to engage and seal against the outer surface of the pile 12. The grouted pockets 31 thus form a seal preventing the expansive grout 19 passing downwardly and out of the annular space 18. It will be understood that when the sleeve 17 is formed of two or more interconnected part circular parts such as is shown in Fig. 2, the pockets 31 are provided on each of the individual sleeve parts and end pockets abut each other when the sleeve parts are interconnected. Referring to Fig. 4, a modified form of sleeve 17 is illustrated. The sleeve 17 is formed of two parts 17a and 17b connected together with a continuous hinge 33 which is fixed to the sleeve parts by rivets 34 or welding or other suitable fastening means. The sleeve 17 of this embodiment is able to engage over the pile 12 by opening the sleeve parts about the hinge axis and then closing and securing the parts by means of fastening bolts 24. Appropriate spacers 27 are provided to space the sleeve 17 from the pile 12 and a seal 21 is located at the lower end of the annular space 18 to enable that space to be filled with an expansive filler material, preferably the aforesaid cementitious grout mixture containing an expansive agent which causes the grout to expand on setting. Referring to Fig. 5 there is illustrated a further embodiment of the invention in which the sleeve part 17a is provided with an active seal 21 at its lower end which comprises a bag structure or bladder 36 of substantially toroidal shape attached to the inner surface of the sleeve part 17a by bonding with adhesive, or by fastening means 37. The bag structure or bladder 36 is flexible and is therefore able to conform to the surface of the pile 12 to which the sleeve part 17a is to be fitted. A grout line 38 extends from an upper end of the sleeve part 17a to the bag structure 36 and through which the bag 36 is adapted to be filled with grout. In use, the sleeve 17a is connected with a corresponding sleeve (not shown) about a pile 12, the two parts being secured together by bolts passing through the holes 25. Grout is introduced into the opening 39 of the grout line 38 and fills the bag structure 36 thus forming a close fitting seal against the pile. Adjacent ends of the bag structures of the co-operating sleeve parts abut when the sleeve parts are assembled and the respective bag structures 36 are filled with grout material. It will be appreciated that any suitable seal may be provided at the lower end of the annular space 18 to support the expansive grout within that space until such time as the grout has set. Such a seal may be formed of any suitable material, including synthetic plastic material, foamed plastics material, or even welding. Similarly, the upper end of the annular interspace 18 may be sealed by welding (in the case of a steel pile 12) or other sealing means. It will also be appreciated that the features of the invention can be applied to piles or other structures of non-circular cross-section. In this case, the shape of the sleeve 17 may, if desired, be made to correspond to the shape of the structural member and to provide a space therebetween into which an expansive filler material can be introduced. Referring to Fig. 6, the sleeve 17 illustrated is used to repair a damaged timber pile 12. In this embodiment, shear keys 42 are embedded in the pile 12 and extend into the substantially annular interspace 18. If desired, the sleeve parts 17a and 17b may also be formed with internally extending shear key formations 43. It will be understood that such shear keys 42 and 43 may be used in the embodiments of Figs. 1 to 5. The sleeve 17 is spaced from the pile 12 by deformable spacers 27, and a seal, similar to that shown in Fig. 5, is used to seal the lower end of the interspace. The filler material 19 is introduced into the interspace 18 through the upper end thereof. The filler may be introduced through one or more tubes or pipes 44 which can extend to the lower end of the interspace to ensure delivery of the filler 19 to that lower end. Any water or air in the interspace 18 is displaced by the filler 19 as it is delivered thereto. When filled, the interspace may be sealed at its upper end to retain the filler during setting or curing. The filler, on curing or setting over a period of time such as between five (5) minutes and twelve (12) hours, generates tensile hoop stress in the sleeve and corresponding compressive stress in the member. These stresses enhance the load transfer between the member and the sleeve which is primarily effected by friction across the interfaces. It will be understood that features described in relation to any of the described embodiments may be used in the other of the embodiments. For the purposes of this specification, including the claims, the term "comprising" wherever used shall be taken to have the meaning "including".

Claims: CLAIMS: 1. A method of increasing the structural strength of a load bearing member including, inter alia, the steps of fitting a rigid, structural sleeve to the member, the sleeve having internal dimensions greater than the external dimensions of the member to provide an interspace between the member and the sleeve, supporting the sleeve so that it is spaced from the member, filling the interspace with an expansive filler, allowing the filler to set or cure and expand to produce at least radial forces on the member and tensile hoop stresses in the sleeve. 2. A method according to Claim 1 including the step of securing two or more parts together to form the sleeve about the member. 3. A method according to Claim 2 wherein the sleeve is formed of two parts secured together longitudinally by bolts. 4. A method according to any one of Claims 1 to 3 including the step of providing spacers to evenly space the sleeve from the member. 5. A method according to any one of Claims 1 to 4 including the step of sealing the interspace at its lower end. 6. A method according to Claim 5 including the step of sealing the interspace at its upper end. 7. A method according to any one of Claims 1 to 6 wherein the step of filling the interspace with an expansive filler comprises filling the space with a cementitious grout containing an expansive agent of a calcium-sulpho- aluminate structure. 8. A method according to any one of Claims 1 to 7 including the step of providing shear keys on either or both the member and the sleeve to key into the filler. 9. Apparatus for carrying out the method of any one of Claims 1 to 8 including, inter alia, a rigid, structural sleeve formed of one, two or more elongate sections adapted to be fastened about a load bearing member, a plurality of spacers adapted to space the sleeve from the member to form an interspace therebetween, a seal around the lower end of the interspace, and an expansive filler to fill the interspace and, when set or cured, to produce at least radial compressive forces on the member and the sleeve such as to set up compressive hoop stresses in the member and tensile hoop stresses in the sleeve, the filler forming a rigid interface between the member and the sleeve. 10. Apparatus according to Claim 9 wherein the sleeve is formed of two parts adapted to be connected together by bolts. 11. Apparatus according to Claim 9 or Claim 10 wherein said seal comprises one or more flexible bag-like part-toroidal bladders attached to the lower end of the respective sleeve part and adapted to be filled with said filler, the or each bladder having a filler line or tube extending from an upper end of the respective sleeve part. 12. Apparatus according to Claim 9 wherein said sleeve is formed of two parts hinged together along one longitudinal edge and adapted to be fastened together along another longitudinal edge. 13. A method of repairing a structural member, such as a pile, having a damaged area, including, inter alia, the steps of securing a sleeve around the member, the sleeve having an axial length to extend beyond the area of damage in both directions, said sleeve having inner dimensions greater than outer dimensions of the member, providing spacers to space the sleeve from the member to form an interspace, sealing a lower end of the interspace, filling the interspace with an expansive filler by introducing the filler through the upper end of the interspace displacing any water or air in the interspace, permitting the filler to set or cure and expand within the space to thereby tension the sleeve and apply compressive forces to the member such as to set up compressive hoop stresses in the member and tensile hoop stresses in the sleeve, and whereby the filler facilitates load transfer primarily by friction across the grout to member and grout to sleeve interfaces. 14. A method according to Claim 13 wherein the expansive filler is a cementitious grout containing an expansive agent of a calcium-sulpho- aluminate structure or a lime based agent. 15. A method according to Claim 13 or Claim 14 wherein the lower end of the interspace is sealed by flexible, bag-like bladders attached to the lower end of the sleeve and adapted to be filled with an expansive filler or grout so as to expand and seal against the member and retain said filler in the interspace. 16. A method according to Claim 13 or Claim 14 wherein the lower end of the interspace is sealed by a plurality of pocket seals attached to the sleeve at its lower end, the pocket seals being open at their upper end to receive the filler introduced into the interspace, the filler filling the pockets causing inner edges thereof to engage and seal against the member.

Inventors: POTTS ANDREW ELMHIRST, SINCOCK PAUL, POTTS, ANDREW, ELMHIRST, SINCOCK, PAUL
Applicants: AMOG TECHNOLOGIES PTY LTD, POTTS ANDREW ELMHIRST, SINCOCK PAUL, AMOG TECHNOLOGIES PTY. LTD., POTTS, ANDREW, ELMHIRST, SINCOCK, PAUL
Application year: 1998
Main classification: E02D5
IPC codes: E02B17, E02D5, E02D15