Abstract:
A method of building a structure, the method including the steps of: 1. fabricating a generally longitudinal, steel sub-structure of the structure with a cable retainer attached to, or forming part of, the substructure and that extends substantially longitudinally therealong; 2. assembling the sub-structure into a structure; 3. inserting a cable into the cable retainer; 4. after step 2, applying a tensile force to the cable relative to the cable retainer; and 5. after step 4, bonding the cable to the cable retainer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 11/572,407, filed Jan. 19, 2007, which is a national phase application of International Application No. PCT/AU2005/001077, filed Jul. 21, 2005, designating the United States and claiming priority to Australian Patent Application No. 2004904034, filed Jul. 21, 2004, both of which are incorporated by reference herein in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method of building a structure and also to a method to strengthening, or reducing the deflection of, a built structure. 
     The invention has been primarily developed for use in relation to steel portal frame structures and will be described hereinafter with reference to this application. However, the invention is not limited to this field of use and is also applicable for other structural and architectural works. 
     BACKGROUND OF THE INVENTION 
     When designing a structure or building, consideration must be given to, amongst others requirements, the requirements of strength, deflection and dynamics. It is common for additional material to be required in a structure to satisfy deflection requirements, when compared to the material required to satisfy strength requirements. The additional material increases material and construction costs and can also adversely affect the building&#39;s dynamic response (particularly to earthquakes) and also requires a corresponding increase in the building&#39;s foundations. 
     It is important that the amount of materials used in building structures is minimised from a cost and environmental standpoint. It is an object of the present invention to reduce the material required in a building whilst still satisfying deflection criteria. 
     SUMMARY OF THE INVENTION 
     Accordingly, in a first aspect, the present invention provides a method of building a structure, the method including the steps of:
         1. fabricating a generally longitudinal, steel sub-structure of the structure with a cable retainer attached to, or forming part of, the sub-structure and that extends substantially longitudinally therealong;   2. assembling the sub-structure into a structure;   3. inserting a cable into the cable retainer;   4. after step 2, applying a tensile force to the cable, relative to the cable retainer; and   5. after step 4, bonding the cable to the cable retainer.       

     In a second aspect, the present invention provides a method of building a structure, the method including the steps of:
         1. fabricating a generally longitudinal, steel sub-structure of the structure with a cable retainer attached to, or forming part of, the sub-structure and that extends substantially longitudinally therealong;   2. inserting cable into the cable retainer;   3. after step 2, applying a tensile force to the cable, relative to the cable retainer; and   4. after step 3, bonding the cable to the cable retainer; and   5. assembling the sub-structure into a structure.       

     In a third aspect, the present invention provides a method of strengthening, or reducing the deflection of, a built structure, the method including the steps of:
         1. attaching a cable retainer to a generally longitudinal, steel sub-structure of the structure with the cable retainer extending substantially longitudinally therealong;   2. inserting cable into the cable retainer;   3. applying a tensile force to the cable, relative to the cable retainer; and   4. after step 3, bonding the cable to the cable retainer.       

     The cable retainers are adapted to follow the tensile line of resistance the sub-structure is subjected when loaded during use. 
     Preferably, the method includes assembling at least two sub-structures into a structure. 
     Preferably also, the method includes inserting at least two cables into the cable retainer. 
     The cable is preferably bonded to the cable retainer by any one of the following: welding, gluing (including grouting, most preferably with cementitous grout), or by expanding the cable retainer relative to the cable or shrinking the cable relative to the cable retainer (for example by heating the cable retainer and/or by cooling the cable and thereafter allowing them to shrink and/or expand into engagement with one another) prior to inserting the cable into the cable retainer. 
     The tensile force is preferably applied to the cable by jacking. 
     The structure is preferably a steel portal frame structure, more preferably produced from I or T section beams or from tubular truss assemblies. 
     When the sub-structure is in the form of an I or T section beam, the cable retainer are attached to the web of the beam and, most preferably, passes through the flange of the beam. When the sub-structure is a truss assembly, the cable retainer is in the form of one of the tubular members integral with the truss. 
     The sub-structure is preferably utilised in the centre span of the structure. However, the sub-structure can also be used in the columns or walls of the structure. 
     In one form, the cable retainer extends within the boundaries of its associated sub-structure. In another form, the cable retainer is attached to the sub-structure external the boundaries of sub-structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings wherein: 
         FIGS. 1 to 11  are each schematic cross-sectional drawings of structures utilising an embodiment of the invention; 
         FIG. 12  is an exploded view of the sub-structures comprising the structure shown in  FIG. 11 ; 
         FIG. 13  is a cross-sectional end view of an embodiment of an I beam suitable for use in the structures shown in earlier drawings; 
         FIG. 14  is a cross-sectional end view of another embodiment of an I beam suitable for use in the structures shown in earlier drawings; 
         FIG. 15  is a cross-sectional end view of a further embodiment of a rectangular beam suitable for use in the structures shown in earlier drawings; and 
         FIG. 16  is a cross-sectional end view of an embodiment of a truss assembly suitable for use in the structures shown in earlier drawings. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a steel portal frame structure  20  formed from a centre span  22 , two columns  24  and two foundations  26 . Each half of the centre span  22  and each of the columns  24  represent a sub-structure of the steel portal frame structure  20 . 
     The centre span  22  has a first cable retainer  28  attached thereto, by welding in the regions  30  and via the struts  32  in the region  34 . Each of the columns  24  also have cable retainers  36  attached thereto by welding. 
     Cables, represented by double headed arrows  38  and  40 , are passed through the cable retainers  28  and  36  respectively. The cables  38 ,  40  are tensioned relative to the cable retainers  28 ,  36  respectively then bonded to the cable retainers  28 ,  36  respectively, prior to releasing the tension in the cables. The tensioning, bonding and releasing steps shall be described in more detail below. 
     The cable retainers  28 ,  36  extend generally along the longitudinal direction of their associated centre span (sub-structure)  22  or column (sub-structure)  24 . More particularly, the cable retainers  28 ,  36  are positioned to follow the tensile line of resistance of their associated sub-structure when the structure  20  is subjected to its intended load during use. 
     For example, the steel portal frame structure  20  shown in  FIG. 1  is designed to be subject to a downward and horizontal load/use and the cable retainers  28 ,  36  are thus oriented as shown to best resist deflection caused by that load. 
     The resulting structure is able to better resist deflection under its designed load conditions as the tension applied to the cables relative to their associated sub-structure stores strain energy in the resulting sub-structure. Accordingly, as forces are applied to structure, the counter strain stored in the sub-structure resists the application of that load. 
     The resulting structure can, within certain boundaries, accept load with reduced strain and thus has an increased load carrying capacity for a given deflection. A 50-100% reduction in deflection can result compared to a similar sized existing structure. 
     The steel portal frame structures shown in  FIGS. 2-12  each have their components and sub-structures identified with like reference numerals to those used in  FIG. 1 . However, in each structure, the cable retainers follow a different path compared to the columns and centre span so as to suit differing load conditions. 
     The structure  50  shown in  FIG. 2  is designed to resist upward and horizontal load conditions/usage. 
     The structure  60  shown in  FIG. 3  is designed to resist downward and horizontal load conditions/usage. 
     The structure  70  shown in  FIG. 4  is designed to resist upward and horizontal load conditions/usage. 
     The structure  80  shown in  FIG. 5  is designed to resist upward and horizontal load conditions/usage. 
     The structure  90  shown in  FIG. 6  is designed to resist downward and horizontal load conditions/usage. 
     The structure  100  shown in  FIG. 7  is designed to resist upward and horizontal load conditions/usage. 
     The structure  110  shown in  FIG. 8  is designed to resist downward and horizontal load conditions/usage. 
     The structure  120  shown in  FIG. 9  is designed to resist upward and horizontal load conditions/usage. 
     The structure  130  shown in  FIG. 10  is designed to resist downward and horizontal load conditions/usage. 
     The structure  140  shown in  FIG. 11  is designed to resist upward and horizontal load conditions/usage. 
       FIG. 12  shows the various sub-structures that comprise the structure  140  shown in  FIG. 11 . As shown, the centre span  22  is formed from three sub-structures  22   a ,  22   b  and  22   c . The structure  140  is preferably built by assembling all of the sub-structures into the final form shown in  FIG. 11 , inserting cables through the cable retainers, jacking the cables into a state of tension, bonding the cables to the cable retainers (for example with cementitous grout) and then releasing the jacking load on the cables. 
     As an alternative, one or more of the sub-structures can be assembled and tensioned according to the method described above, and then subsequently attached to the sub-structures. For example, the centre span sub-structure can be assembled on the ground and, after tensioned cables have been bonded thereto, be raised into its final position and connected to the column sub-structures. 
     As a further alternative, cable retainers can be added to a pre-existing structure, or a new structure built without them, which are then tensioned and bonded in the manner described above. This finds particular application in improving the strength and/or deflection performance of an existing built structure or structure whose design is complete. 
       FIGS. 13 and 14  show examples of cable retainers  28 ,  36 , in the form of steel tubes, being attached to beams  150  and  152 , for example by welding, which are suitable for use in the previously described structures (for example, those structures shown in  FIGS. 1 to 6 ). 
       FIG. 15  shows an alternative beam  154  in which the cable retainer  28 ,  36  is in the form of an opening or hole or channel through the beam which is suitable for use in a previously described structure (for example, the structure shown in  FIG. 10 ). 
       FIG. 16  shows an example of cable retainers  28 ,  36 , in the form of steel tubes, being part of a truss assembly  156 , which is suitable for use in the previously described structures (for example, those structures shown in  FIGS. 7 to 10 ). 
     The structures described above can be designed to meet strength and dynamic requirements, whilst reducing the need to increase the material added to the structure to satisfy deflection requirements. The embodiments described previously advantageously enable the span of a structure to be increased whilst using the same amount of materials to thus provide a larger structure for the same material cost. Conversely, a structure with a like span to an existing structure can be produced using a reduced amount of materials. The structures described above are also lighter and cheaper than existing comparable structures, particularly when foundation saving are taken into account. 
     Although the invention has been described with reference to specific embodiments, it would be appreciated by those skilled in the art that the invention can be embodied in many other forms. For example, the cable retainers can be of any shape and any number of cables can be inserted therein.