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 repairing 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 a prestress of at least 3 MPa and 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 ).

The claims defining the invention are as follows:  
     
         1 . A method of increasing the structural strength of a load bearing member including the steps of: 
 (a) fitting a rigid, structural sleeve to the member, with the sleeve having internal dimensions greater than the external dimensions of the member;    (b) supporting the sleeve so that it is spaced from the member whereby to provide a continuous interspace from the member to the sleeve;    (c) sealing the continuous interspace at its lower end;    (d) filling the continuous interspace with an expansive filler; and    (e) allowing the filler to set, or cure, and expand within the confines of the continuous interspace to generate an expansive pressure of at least 3 MPa which imparts at least radial prestress forces on the member and tensile hoop stresses in the sleeve, whereby the generated forces effect a transition of loading forces from one section to another of the load bearing member through the sleeve and expansive filler.    
     
     
         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 1  wherein the interspace is filled from its upper end.  
     
     
         4 . A method according to  claim 1  including the step of providing spacers to evenly space the sleeve from the member.  
     
     
         5 . A method according to  claim 1  including the steps of providing at least one toroidal bladder attached to the lower end of the sleeve with a filler tube extending to the upper end of the sleeve, and filling the bladder with expansive filler through the filler tube before filling the interspace.  
     
     
         6 . A method according to  claim 1  including the step of sealing the interspace at its upper end.  
     
     
         7 . A method according to  claim 1  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  claim 1  including the step of providing shear keys on either or both the member and the sleeve to key into the filler.  
     
     
         9 . A method according to  claim 1  wherein the step of filling the interspace with an expansive material results in direct contact between the filler and the member and between the filler and the sleeve.  
     
     
         10 . Apparatus for increasing the structural strength of a load bearing member including a rigid, structural sleeve formed of one, two or more elongate sections to be fastened about a load bearing member, a plurality of spacers adapted to space the sleeve from the member to form a continuous interspace from the member to the sleeve, a seal around the lower end of the continuous interspace, and a set or cured expansive filler to fill the continuous interspace which generates and imparts at least radial prestress compressive forces of at least 3 MPa 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.  
     
     
         11 . Apparatus according to  claim 10  wherein the sleeve is formed of two parts adapted to be connected together.  
     
     
         12 . Apparatus according to  claim 10  wherein said seal comprises at least one flexible toroidal bladder attached to the lower end of the respective sleeve part and adapted to be filled with said filler, the bladder having a filler line or tube extending from an upper end of the respective sleeve part.  
     
     
         13 . Apparatus according to  claim 10  wherein said sleeve is formed of two parts hinged together along one longitudinal edge and adapted to be fastened together along another longitudinal edge.  
     
     
         14 . Apparatus according to  claim 10  wherein the expansive filler is a cementitious grout containing an expansive agent of a calcium-sulpho-aluminate structure.  
     
     
         15 . A method of repairing a pile having a damaged area including the steps of: 
 (a) securing a sleeve which has inner dimensions greater than outer dimensions of the pile around the pile, the sleeve having an axial length to, and being secured so as to, extend beyond the area of damage in both directions;    (b) providing spacers to space the sleeve from the pile to form a continuous interspace from the pile to the sleeve;    (c) sealing a lower end of the continuous interspace;    (d) introducing an expansive filler through the upper end of the continuous interspace, displacing any water or air in the continuous interspace, to thereby fill the interspace with the expansive filler;    (e) permitting the filler to set, or cure, and to expand within the confines of the continuous interspace to generate a compressive pressure of at least 3 MPa and impart at least radial prestress forces which tension the sleeve and apply compressive forces to the pile and produce compressive hoop stresses in the pile and tensile hoop stresses in the sleeve, whereby the filler facilitates load transfer primarily by friction across the filler-to-pile and filler-to-sleeve interfaces.    
     
     
         16 . A method according to  claim 15  wherein the expansive filler is a cementitous grout containing an expansive agent of a calcium-sulpho-aluminate structure or a lime based agent.  
     
     
         17 . A method according to  claim 15  wherein the lower end of the interspace is sealed by at least one flexible bladder attached to the lower end of the sleeve and having a filler line or tube extending from an upper end of the respective sleeve, the bladder being filled with the expansive filler or grout so as to expand and seal against the pile and retain said filler in the interspace.  
     
     
         18 . A method according to  claim 15  wherein the lower end of the interspace is sealed by a plurality of pocket seals attached to the sleeve at its lower end, the pockets 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 pile.