Abstract:
A system and method for strengthening elongated members of a tower section is provided. A tower section includes a plurality of elongated members. At least one reinforcing member is employed to reinforce the tower section. A structural adhesive is applied to the elongated members and the reinforcing members. The reinforcing members are pressed or otherwise placed against corresponding elongated members. The structural adhesive is cured to thereby permanently attach the reinforcing members to the corresponding elongated members. The reinforcing members can be clamped, bolted or otherwise secured to the corresponding elongated members during curing of the structural adhesive.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Application Serial No. 60/415,906 filed on Oct. 3, 2002 entitled “A Method for Strengthening Tubular and Round Tower Members”, the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to structural reinforcement systems, and more particularly relates to a system and method for strengthening tubular and round tower members.  
         BACKGROUND OF THE INVENTION  
         [0003]    Existing systems and methods of reinforcing steel tubes or solid rounds of tower members require bolting or welding of heavy steel reinforcements which are difficult to position and install. Welding and bolting in the field is costly in both labor and time. When existing steel is galvanized, welding can often damage the galvanizing at locations that are not practical to repair later. Moreover, there is the risk that welding sparks dropping onto areas away from the tower can cause damage to property. When only bolting is used, high clamping forces are necessary to provide friction between the existing member and the new reinforcing member to transfer the shear forces between them. These clamping forces are questionable in their ability to be effective in reducing buckling behavior. Further, the application of weld joints, bolts or permanent clamps to a tower can significantly aesthetically detract from the appearance of the tower.  
           [0004]    Accordingly, it is a general object of the present invention to overcome the above-identified drawbacks of prior systems and methods for strengthening towers.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention resides in a system and method for strengthening elongated members of a tower section. A tower section includes a plurality of elongated members. At least one reinforcing member is employed to reinforce the tower section. A structural adhesive is applied to the elongated members and the reinforcing members. The reinforcing members are pressed or otherwise placed against corresponding elongated members. The structural adhesive is cured to thereby permanently attach the reinforcing members to the corresponding elongated members. The reinforcing members can be clamped, bolted or otherwise secured to the corresponding elongated members during curing of the structural adhesive. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a side elevational view of a tower section with reinforcing members in accordance with the present invention.  
         [0007]    [0007]FIG. 2 is a top plan view of a reinforcing member secured to a hollow pipe of a tower section and temporarily held in place by bolts.  
         [0008]    [0008]FIG. 3 is a top plan view of a reinforcing member secured to a solid round member of a tower section and temporarily held in place by bolts.  
         [0009]    [0009]FIG. 4 is a top plan view of an outside reinforcing member secured to a member of a tower section and temporarily held in place by a U-bolt clamp.  
         [0010]    [0010]FIG. 5 is a top plan view of outside and inside reinforcing sections secured to a member of a tower section and temporarily held in place by a full circle clamping device.  
         [0011]    [0011]FIG. 6 is a top plan view of a reinforcing member in the form of a clamp secured to a member of a tower section.  
         [0012]    [0012]FIG. 7 is a top plan view of a reinforcing member including overlapping parts secured to a member of a tower section.  
         [0013]    [0013]FIG. 8 is a top plan view of an outside reinforcing member secured to a member of a tower section with spacers interposed between the reinforcing member and the member of the tower section.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    With reference to FIG. 1, a tower section that is reinforced in accordance with the present invention is indicated generally by the reference number  10 . The reinforcement may be used for increasing the axial load carrying capacity of the legs of the tower section or increasing the buckling capacity by making the section more compact. The tower section includes a plurality of vertically extending elongated members or legs  12  which can be either hollow or solid in cross section. The elongated members  12  are preferably made of a metal such as steel, but may be fabricated from other relatively strong and durable materials without departing from the scope of the present invention.  
         [0015]    The tower section  10  can include leg splices  14  for coupling adjacent tower sections to one another. The elongated members  12  are coupled to one another by lateral supports or cross bracing members including horizontal members  16  and diagonal members  18  fabricated from the same or similar materials as the elongated members.  
         [0016]    Reinforcing members indicated generally by the reference number  20  are coupled to the elongated members  12 , as explained more fully below, for increasing structural integrity to the tower section  10 . A length of the reinforcing members  20  can vary, but is preferably nearly about a distance between lateral support connections along the elongated member  12  being reinforced. The reinforcing members  20  are preferably fabricated from metallic materials such as steel, or fiber reinforced polymer (FRP) materials such as carbon fibers encapsulated in a resin matrix. However, the reinforcing members  20  can be fabricated from other strong, durable and adherable materials without departing from the scope of the present invention.  
         [0017]    As shown in FIG. 1, each of the reinforcing members  20  is generally in the form of two half pipe sleeves which cooperate to form a circle in cross section and thereby extend substantially about the perimeter of a corresponding elongated member  12 . More specifically, a first semi-cylindrical or half pipe sleeve serves as an outwardly facing or outside reinforcing section  20   a , and a second semi-cylindrical or half pipe sleeve can optionally serve as an inwardly facing or inside reinforcing section  20   b . A cross-sectional diameter of the reinforcing member  20  can vary depending on the diameter of the elongated member  12  that is being reinforced. Moreover, the reinforcing members  20  can typically extend about 90 degrees to about 360 degrees around the perimeter of the corresponding elongated member  12  being reinforced without departing from the scope of the present invention.  
         [0018]    As shown in FIG. 1, the inside reinforcing sections  20   b  are discontinuous along portions  21  of the elongated member  12  that are coupled to cross bracing members  16 ,  18 . The reinforcing members  20  are adhered to the elongated members  12  with a structural adhesive. Moreover, the reinforcing members  20  can optionally be adhered to the cross bracing members including either or both of the horizontal members  16  and the diagonal members  18 . Clamps or thru-bolts indicated by the reference number  22  are temporarily or permanently applied to the reinforcing members  20  in order to hold the reinforcing members to the elongated members of the tower section  10  during adhesive curing. As explained more fully below, the reinforcing members  20  can be designed to self-clamp to an elongated member  12 .  
         [0019]    Although the elongated members  12  of the tower section  10  and the reinforcing members  20  are shown as circular or semi-circular in cross-section, the members can take other practical shapes or sections of shapes such as, for example, rectangles or squares without departing from the scope of the present invention.  
         [0020]    In operation, the reinforcing members  20  are adhered to the tower section  10  using conventional structural adhesives. The reinforcing members  20  are held in place during installation using bolts, clamping devices or other means that include overlapping portions of the reinforcing member. As shown in FIG. 2, for example, an elongated member in the form of a hollow pipe  12   a  has gussets  24  extending therefrom, and is reinforced by a reinforcing member  20  in the form of two half pipe sleeves. The half pipe sleeves serve as an outside reinforcing section  20   a  and an optional inside reinforcing section  20   b  which cooperate to extend substantially about the perimeter of the elongated member  12 . The reinforcing member  20  can define notches  26  for receiving optional step bolts  28  to hold the reinforcing member in place during adhesive curing. As shown in FIG. 3, the elongated member being reinforced can be in the form of a solid round member  12   b.    
         [0021]    A reinforcing member  20 , such as the outside reinforcing section  20   a  in the form of a half pipe sleeve shown in FIG. 4, can be secured to the elongated member  12  with a U-bolt clamp  30  or other clamping device. As further examples of clamping devices, FIG. 5 shows a reinforcing member  20  in the form of two half pipe sleeves  20   a ,  20   b  being held in place to the elongated member  12  with a clamping device  32  which extends substantially around a perimeter of the reinforcing member.  
         [0022]    The reinforcing member itself may serve as a clamp. As shown in FIG. 6, for example, the reinforcing member  20  includes two reinforcing sections each in the form of half pipe sleeves  20   c . Each half pipe sleeve  20   c  defines two opposing flanges  34  for being abutted to a corresponding flange of the other half pipe sleeve. The abutting flanges  34  are secured to one another by bolts  36 .  
         [0023]    Alternatively, as shown in FIG. 7, the reinforcing member  20  can include first and second reinforcing sections  20   d ,  20   e  each generally in the form of half pipe sleeves. The first reinforcing section  20   d  further defines two opposing overlap portions  38  each of which can be press fitted or otherwise secured over an adjacent portion of the second reinforcing section  20   e  to thereby self-clamp the reinforcing member  20  to the elongated member  12 .  
         [0024]    When FRP materials are used as a reinforcing member, the clamping device used is located on the outside of the reinforcing member to apply pressure onto the adhesive until it is cured. This allows the contractor installing the FRP pipe member to ensure that the adhesive is properly pressed against the existing member and the bond line thickness of the adhesive between the existing tower member and reinforcing member is correct. To provide additional accuracy in ensuring an accurate bond line thickness, a spacer made of plastic, string or metal can be placed behind the reinforcing member prior to tightening the clamping device. As shown in FIG. 8, for example, spacers  40  are interposed between a reinforcing member  20  in the form of a half pipe sleeve and the elongated member  12 .  
         [0025]    When metal is used as the reinforcing member on existing circular members in the vertical position (e.g. tower legs), the reinforcement may require a vertical support while the adhesive is curing.  
         [0026]    The structural adhesive is placed between the surface of the reinforcing member and the tower structure. The adhesive is placed onto the reinforcing member itself prior to placing onto the tower or directly onto the existing steel member prior to pressing the reinforcing member into it. The adhesive is the primary means of transferring loads between the reinforcing member and the tower structure. The loads are transferred in shear.  
         [0027]    The locations and requirements of the reinforcements are identified in the structural design. The reinforcements are cut to their correct lengths prior to delivery to the site or field cut. When the reinforcing member is made of an FRP material, the inside surface of the member is sanded or surface prepared in the molding to ensure a good bond transfer between the FRP and adhesive. When the reinforcing member is steel and hot dip galvanized, a surface preparation of the side to receive the adhesive may be required. Depending on the quality of the galvanizing and its bond to the steel, this surface preparation may entail cleaning and etching (chemical or abrasive) or removing the galvanizing layer altogether. When available, a primer may be applied to the bare steel after it has been exposed to reduce the amount of oxidation that will begin to occur.  
         [0028]    With the reinforcing members on site, the existing tower members to be reinforced are prepared for the adhesive by sanding, sandblasting or a chemical wash. Adhesive is next placed onto the surface and a spacer material can be placed on the adhesive. In lieu of spacer materials placed on the adhesive in the field, glass beads having the proper diameter may be mixed in with the adhesive at the time of mixing the adhesive components. The reinforcing members are then lifted into position and pressed onto the tower legs using a clamping device. Once installed, clamps or bolts can be placed and used to position and press the reinforcing members. The need to leave the clamping device in place is optional and depends on the design and construction methods used.  
         [0029]    The present invention utilizes structural adhesives to transfer the shear forces between the existing member and the new reinforcing member, eliminating the requirement for permanent welding or clamping. The elimination of welding and friction clamping in the field provides cost savings in labor and time. Eliminating field welding removes the risk of welding sparks dropping onto areas away from the tower and causing damage to property. It also eliminates welding damage to the galvanizing layer that exists on the inside of a tubular member when welded to the outside of the member. The latter is particularly important as inspection on the inside of a tubular member is impractical to accomplish.  
         [0030]    The completed retrofit reinforcement is low profile—meaning that no major projections exist from the tower when the retrofit work is complete. In addition to the aerodynamic advantages, this has benefits to tower owners and local communities who have aesthetic concerns about the appearance of their towers.  
         [0031]    As will be recognized by those of ordinary skill in the pertinent art, numerous modifications and substitutions may be made to the above-described embodiment of the present invention without departing from the scope of the invention. Accordingly, the preceding portion of this specification is to be taken in an illustrative, as opposed to a limiting sense.