REPAIR OF HOLLOW TUBULAR STRUCTURES

Abstract: A method of increasing the structural strength of a hollow load bearing member such as a pile (12), particularly for the purpose of repairing a damaged pile, includes the steps of fitting a rigid structural insert (17) into 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 pile (12) and corresponding compressive hoop stresses in the insert (17), to enhance the load transfer between the pile (12) and the insert (17)

Description: REPAIR OF HOLLOW TUBULAR STRUCTURES 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 tubular structural members including steel jacket offshore structures, structural members on bridges or the like, 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 tubular concrete 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 outside of 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. In our Australian Patent Specification No. 72002/98, we. describe a method of increasing the strength of a pile using an external sleeve. In some instances, however, it is not possible to use an external sleeve in the manner described. For example, some piles are braced with welded bracing such that it is impractical to incorporate an external sleeve. Other factors may also prevent or mitigate against the use of an external sleeve in the manner described in our Australian patent specification. Summary 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. In accordance with one aspect of the invention there is provided a method of increasing the structural strength of a hollow, load bearing member, such as a pile, including the steps of fitting a rigid, structural insert into the member, the insert having external dimensions less than the internal dimensions of the hollow member to provide an interspace between the member and the insert, supporting the insert so that it is spaced from the member, and filling the interspace between the insert and the member with an expansive filler, and allowing the filler to set, cure and thereby expand in such a way as to generate tensile forces on the member and compressive forces on the insert. The insert may be a single piece insert for those applications where a single piece insert is able to be engaged within the member. Otherwise, the insert 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 insert is preferably spaced from the member by the use of spacer means, which may include spacing tabs, indentations or other deformations of the insert material or separate spacers including spacers formed of synthetic plastic or rubber materials or the like attached to the outer surfaces of the insert. Alternatively, spacer means may be attached to the member prior to engagement of the insert thereon or spacer means may be inserted between the member and the insert after the engagement of the insert within the member. In one arrangement, a seal is provided between the lower edge of the insert and the member to seal the interspace between the insert 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 insert. The seal or seals act to retain the expansive filler within the space between the insert and the member before the filler has set and expanded. When the insert is composed of two or more parts, seals may also be used between the parts of the insert, depending on the means of fixing the insert 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 tensile hoop stresses in the member and compressive hoop stresses in the insert so that loading actions on the member are able to be transferred between the member and the insert. 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 insert is effected primarily by friction across the grout to member interface and across the grout to insert interface. The invention also includes the apparatus for repairing a damaged pile or otherwise increasing the strength of a load bearing member comprising an insert adapted to engage within the member, means to space the insert from the member, and an expansive filler adapted to fill the space and to expand on setting and curing to post-tension the insert, the filler forming a rigid interface between the insert and the member. In one form of the invention, shear keys are provided to positively and rigidly connect the insert with the expansive filler and to connect the filler with the member. The shear keys may comprise studs, bolts, including coach bolts or the like fastened to the member. The insert itself may also have outwardly extending shear keys formed by any suitable means including bolts, punched or pressed deformations of the insert, 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 insert means within the member, the insert means having an axial length to extend in both directions beyond the area of damage on the member and have an outer diameter smaller than the inner diameter of the member, spacer means to space the insert 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 member and apply compressive forces to the insert whereby the set grout facilitates load transfer between the member and the insert primarily by friction across the member/grout/insert interfaces. In order that the invention may be more readily understood, embodiments thereof will now be described with reference to the accompanying drawings wherein: Brief Description of the Drawings Fig. 1 is a part sectional view of a jetty pile and an encasing repair insert in accordance with the present invention; and Fig. 2 is a cross-sectional plan view of a cylindrical, tubular pile and an insert in accordance with one embodiment of the invention; Description of the Preferred Embodiment Referring to the drawings, the embodiments illustrated in Figs. 1 and 2 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, it is necessary to secure an insert 17 to the pile 12 so that the insert 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 insert 17 in the pile 12 and spacing the insert 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 compressing the insert 17 and tensioning the pile thereby to form a substantially firm or rigid interface between the pile 12 and the insert 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 insert 17 to extend between the insert 17 and the pile 12. The seal shown in Fig. 1 is formed by a flexible, deformable rubber ring engaged on the end of the insert 17. 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 insert 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 insert. 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 compressive hoop stresses in the insert 17 and tensile hoop stresses in the pile 12. A pre-stress of 12 MPa or more is achievable. Further, by roughening the outer surface of the insert 17, a greater degree of resistance to slip between the grout and the insert is achieved. The surface roughness may be increased by any suitable means including machining, stamping, shot blasting or the like. The proportion of the additive in the grout mix is a key design variable in order to achieve a specific pre-stress through expansion in curing of the grout. Referring to Fig. 2, an insert 17 is illustrated assembled within the pile 12 and is spaced therefrom by a series of internal deformable rubber spacers 27 which are fixed to the outside surface of the insert such as by adhesive or mechanical fastening. The spacers 27 are provided at several locations along the length of the inserts whereby, when the insert is located as illustrated, the spacers act to centre the insert 17 on the pile 12 so that a substantially annular space 18 exists between the insert 17 and the pile 12. This space is then filled with the expansive grout mixture aforesaid which, on setting, expands and produces compressive stresses in the insert 17 and tensile stresses in the pile 12, the grout being of a material which facilitates load transfer between the pile and the insert. An alternate form of spacer (not shown) may comprise a ring formed of a flexible material, such as a spring steel or the like, and which is able to be clipped around the insert 17. The ring has a number of depending, outwardly extending legs the edges of which are adapted to engage the surface of the pile so that the body of the ring is spaced therefrom. The ring engages over the lower end of the insert 17 thereby supporting that end such that the insert 17 is evenly spaced from the pile. The lower seal may also be formed of one or more pockets of a flexible material, such as rubber, synthetic plastic material, fabric or the like, which are open at their upper end and are secured to the lower edge portion of the insert 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 causing the face thereof to engage and seal against the surface of the pile. The grouted pockets 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 insert 17 is formed of two or more interconnected parts, the pockets are provided on each of the individual insert parts and end pockets abut each other when the insert parts are interconnected. It will be appreciated that the insert may be of solid construction or tubular as illustrated, and may be formed of metal, timber or the like. It will also be appreciated that variations in the construction of the invention, the seals, the spaces and the like may be adapted from those disclosed in the International patent application aforesaid. The disclosures in that specification are incorporated herein by reference.

Claims: CLAIMS: 1. A method of increasing the structural strength of a hollow load bearing member, including the steps of fitting a rigid, structural insert into the member, the insert having external dimensions less than the internal dimensions of the member to provide an interspace between the member and the insert, supporting the insert so that it is spaced from the member, filling the interspace with an expansive filler, and allowing the filler to set or cure and thereby expand in such a way that the expansion of the filler generates tensile forces on the member and at least radial compressive forces on the insert. 2. A method according to Claim 1 including the step of securing two or more parts together to form the insert within the member. 3. A method according to Claim 2 wherein the insert is formed of two parts secured together longitudinally by mechanical means, chemical bonding or adhesive. 4. A method according to any one of Claims 1 to 3 including the step of providing spacers to evenly space the insert 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 includes 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 insert and the member to key into the filler. 9. Apparatus for carrying out the method of any one of Claims 1 to 8 including, a rigid, structural insert formed of one, two or more elongate sections adapted to be engaged within a hollow load bearing member, a plurality of spacers adapted to space the insert 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 insert and the member such as to set up compressive hoop stresses in the insert and tensile hoop stresses in the member, the filler forming a rigid interface between the insert and the member. 10. Apparatus according to Claim 9 wherein said seal comprises one or more flexible bag-like part-toroidal bladders attached to the lower end of the respective insert 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 insert part. 11. A method of repairing a structural member, such as a pile, having a damaged area, including, the steps of securing an insert within the member, the insert having an axial length to and being secured so as to extend beyond the area of damage in both longitudinal directions, said insert having outer dimensions smaller than inner dimensions of the member, providing spacers to space the insert 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 thereby expand within the space such that the expansion of the filler generates at least radial forces to thereby tension the member and apply compressive forces to the insert and produce compressive hoop stresses in the insert such as to set up compressive hoop stresses in the member and tensile hoop stresses in the insert and tensile hoop stresses in the member, and whereby the filler facilitates load transfer primarily by friction across the filler-to-member and filler-to-insert interfaces. 12. A method according to Claim 11 wherein the expansive filler is a cementitious grout containing an expansive agent of a calcium-sulpho-aluminate structure or a lime based agent. 13. A method according to Claim 11 or Claim 12 wherein the lower end of the interspace is sealed by flexible, bag-like bladders attached to the lower end of the insert 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. 14. A method according to Claim 11 or Claim 12 wherein the lower end of the interspace is sealed by a plurality of pocket seals attached to the insert 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: 2000
Main classification: E02D5
IPC codes: E02D5