Patent Publication Number: US-9890546-B2

Title: Reinforcement and repair of structural columns

Description:
CROSS-REFERENCE(S) TO RELATED APPLICATION(S) 
     This application is related to U.S. patent application Ser. No. 13/409,688, filed on Mar. 1, 2012, and U.S. patent application Ser. No. 13/439,722, filed on Apr. 4, 2012, and U.S. patent application Ser. No. 13/859,596, filed on Apr. 9, 2013, and U.S. patent application Ser. No. 12/618,358, filed on Nov. 13, 2009. 
     TECHNICAL FIELD 
     This application relates generally to construction. More specifically, this application relates to a method and apparatus for reinforcing and/or repairing structural columns. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings, when considered in connection with the following description, are presented for the purpose of facilitating an understanding of the subject matter sought to be protected. 
         FIGS. 1A-1C  show example “columns” suitable to be reinforced and/or repaired by the present methods and apparatus; 
         FIGS. 2A-2C  show example components employed to reinforce the columns illustrated in  FIGS. 1A-1C , using the present methods; 
         FIGS. 3A and 3B  show cross-sectional areas of two example reinforced columns; and 
         FIG. 4  shows an example process of reinforcing a column using the present method. 
     
    
    
     DETAILED DESCRIPTION 
     While the present disclosure is described with reference to several illustrative embodiments described herein, it should be clear that the present disclosure should not be limited to such embodiments. Therefore, the description of the embodiments provided herein is illustrative of the present disclosure and should not limit the scope of the disclosure as claimed. In addition, while the following description often references using fibrous materials, it will be appreciated that the disclosure may include other materials to add to the tensile or compressive strength of the column in different or multiple directions. 
     Briefly described, a method and an article of manufacture are disclosed for reinforcing various structural columns of various materials, such as wood or concrete columns of electric poles, steel or concrete poles and towers for support of cellular phone antennas, concrete columns between different floors of buildings, columns of large billboards, etc., but not limited to steel, concrete, masonry, wood, plastics, and the like. Multiple layers of various material sheets, each sheet having substantially the same or different properties, may be used as an outer shell for pouring of filler materials, such as concrete or adhesive, into the cavity between the column and the outer shell. The outer shell itself can be intended and designed to add to the tensile strength of the surface of the completed and reinforced column. It can also be designed to provide confining pressure around the column being repaired. In many embodiments, since it is preferable not to substantially add to the diameter of the column and since much of the reinforcement tensile or compressive strength is accomplished by components placed in the cavity between the outer shell and the column, a single thin sheet of semi-rigid outer shell suffices. In some embodiments improving the “ring stiffness” is less important than improving the bending capacity and strength of the column. 
     Structural repair can be expensive, cumbersome, and time consuming. Structures can get damaged due to a variety of factors, such as earthquakes, overloading, weight of traffic, wear and tear, corrosion, explosions and the like. One of the problems with existing concrete columns or wooden poles is that they are subject to corrosion and/or natural elements that weaken these structures. The disclosed methods may be employed as a preventive measure and/or for repair of a damaged column. However, it is generally easier and more cost-effective to strengthen a structure that may be exposed to damaging forces and loads, than waiting to repair such eventual damages after they occur. Intentional damage inflicted upon infrastructure, by terrorism or vandalism, is another way that structural damage may result. For example, recently, there has been growing interest to strengthen the above-mentioned structures for blast loading, such as terrorist attacks, which may seek to blow up a building or topple a power pole by placing a bomb adjacent to the column and detonating it. In addition to prevention, if damage does occur to a structure, a cost-effective and speedy method of repair is clearly desirable. 
       FIGS. 1A-1C  show example “columns” suitable to be reinforced by the present methods and apparatus.  FIG. 1A  shows a wooden electric pole that is constantly exposed to natural elements which weakens the wood in addition to forcing it to bend, such as by wind or by tension in its electrical wires.  FIG. 1B  illustrates a typical concrete column between two floors of a building. Different forces acting on the building, such as those resulting from an earthquake or a storm, will create different moments and forces in different sections of each of the building columns.  FIG. 1C  shows an advertisement billboard that is frequently exposed to winds from different directions which induce simple or complex moments and forces in the billboard&#39;s supporting columns. The columns in these structures, regardless of the geometry of their cross-section, can benefit from reinforcement by the present methods, whether they are damaged or as a preventive measure. 
       FIG. 2A  shows example components employed to reinforce column  200  (electric pole) illustrated in  FIG. 1A , using an embodiment of the present methods. In this embodiment tension bearing elements  202  are longitudinally placed against column  200 . In some embodiments the tension bearing elements  202  may be in the form of ribbons or straps of fibrous materials such as GU50C Carbon Strips sold by QuakeWrap Inc. of Tucson, Ariz.; in other embodiments they may be rebars. In various embodiments, the tension bearing elements  202  may be adhered to column  200 , for example by glue or epoxy, or may be merely held against or at a relatively small distance from the column  200  by a tie-wrap or rope  204 . It is important to note that the width of a tension bearing strap may be equivalent or even more than the circumference of column  200  and be able to even completely wrap around column  200  widthwise. 
     In various embodiments it may be desirable to have tension bearing components wrapped around the column instead or in addition to the longitudinal tension bearing components. An example of such circumferential tension bearing components is component  208  shown in  FIG. 2A . This is different from the above mentioned longitudinal tension bearing strap  202  which, because of its wide width, may be also wrapped around column  200 . The circumferential components may be wrapped in simple loops or spirally along part or the entire length of the column  200 . If used in addition to the longitudinal components, the circumferential components may be wrapped directly around the column—between the longitudinal components and the column—or wrapped over the longitudinal components after the longitudinal components are attached to the column, such that the longitudinal components are between the circumferential components and the column. 
     As further illustrated in  FIG. 2A , a semi-rigid/semi-flexible sheet  206  is wrapped around the assembly/combination of the column  200  and the tension bearing component(s)  202  and  208  to form a shield. In some embodiments edges  212  of sheet  206  meet, overlap and are glued together to create a complete shell around column  200 . As an example, sheet  206  can be a carbon laminate PLC100.60 or a glass laminate PLG60.60 sold by PileMedic, LLC in Tucson, Ariz. When sheet  206  is wrapped continuously one or more time around the column, it creates a confining pressure that further strengthens the column. In other embodiments edges  212  of sheet  206  may be butt-joined and in some embodiments these edges may not even be permanently connected, as will be discussed below. After completion of the shield, desired filler material  210  is poured in the cavity between the shield (sheet  206 ) and column  200 . 
     In some embodiments the tension bearing elements, for example rebars, may be firmly connected to the foundation over which the column is erected. Some examples of the tension bearing elements are steel reinforcing bars, prestressing or post-tensioning strands and wires, nonmetallic rods and strips such as Carbon FRP, etc. In columns, such as the one shown in  FIG. 1B , the ends of the tension bearing elements may be embedded in the floor and/or the ceiling between which the column stands. 
     In the embodiment shown in  FIG. 2B , column  220  is constructed over floor  224  and under ceiling  226 . In this embodiment one end of rebars  221  is fixed by epoxy or any other appropriate glue in a hole in floor  224  and the other end of rebars  221  is fixed by epoxy or any other appropriate glue in another hole in ceiling  226 . In another embodiment it may be easier to epoxy anchor shorter rebars in the ceiling and floor and then overlap a third piece of rebar with these two shorter bars to create a continuous rebar piece. This is illustrated by three-piece-rebar  222  in  FIG. 2B . In some embodiments it may be possible to run a long rebar  223 , for example even as long as the height of a building, through floors and ceilings of multiple floors of the building to reinforce multiple columns that are placed on top of each other. 
     “Anchor” means fix or fasten to mainly resist a pulling force to the degree that the anchoring means fails before it dislodges from the anchoring point. For example, the following quotes are from chapter 17 of “Building Code Requirements for Structural Concrete (ACI 318-14)” which is dedicated to “anchoring.” Section 17.2.3.4.3 (a) states: “For single anchors, the concrete-governed strength shall be greater than the steel strength of the anchor . . . .” (This means the concrete must be strong enough to allow the steel anchor to yield in tension). Section 17.2.3.4.3 (b) states: “The anchor or group of anchors shall be designed for the maximum tension that can be transmitted to the anchor or group of anchors based on the development of a ductile yield mechanism . . . .” (Again, this is requiring the anchor or group of anchors to yield in tension before it gets pulled out of the group). Section 17.2.3.5.3 (a) states: “The anchor or group of anchors shall be designed for the maximum shear that can be transmitted . . . based on the development of a ductile yield mechanism . . . .” And in section 17.4.1.2 the Code provides an equation for how to calculate the strength of an anchor in tension by taking the cross sectional area of the anchor multiplied by a value that is 1.9 times the yield strength of the anchor. All of the above indicate the significance of anchorage and the measures that must be taken to prevent premature (pullout) of the anchor. 
     The other source is a textbook on “Reinforced Concrete Mechanics and Design.” 5 th  edition, by Wight and MacGregor. This book discusses how steel stirrups must be anchored so that they fail by yielding of the steel, which is to make sure the steel reaches its ultimate strength before it pulls out of the concrete block. Here are a few quotes from this book: “Equations 6-21 and 6-18 (which are used in the ACI Building Code) are based on the assumption that the stirrups will yield at ultimate . . . .” “Assuming that all the stirrups yield at failure, the shear resisted by stirrup is . . . .” Also on  FIG. 6-26  it can be seen that the force shown on each stirrup is equal to the area of stirrup times its yield strength. 
     As illustrated in  FIG. 2B , a semi-rigid/semi-flexible sheet  230  is wrapped around the assembly/combination of column  220  and the tension bearing component(s)  221 ,  222 , and/or  223 . In some embodiments the edges  232  of sheet  230  overlap and are glued together to create a complete shell around column  220 . In other embodiments the edges  232  of sheet  230  may be butt-joined and in some embodiments the edges  232  of sheet  230  may not be permanently joined or adhered to each other, as will be discussed below. In some embodiments the edges  232  may be placed side by side and a tape, overlapping both edges, be placed over both edges  232  to keep them adjacent to each other. 
     In  FIG. 2C , the radial distance of shell-section  242  from the column surface  240  creates a cavity  244  that is filled by any desired kind of filler materials, such as concrete, grout, polymer-modified grout, epoxy grout, just epoxy, or the like. It is preferable to have mounted tensile straps  241  on column  240  before the filler material is poured or even before shell-section  242  is created. In various embodiments the semi-rigid/semi-flexible shell material may be chosen so that shell-section  242  itself contributes noticeably to the strengthening of the reinforced column. As an example, the sheet  206  can be a carbon laminate PLC100.60 or a glass laminate PLG60.60 sold by PileMedic, LLC in Tucson, Ariz. In some embodiments, such as the one illustrated by  FIG. 2C , the shell-section  242  may be formed by wrapping the semi-rigid/semi-flexible sheet, overlappingly, around column  240 . As can be clearly seen in  FIG. 2C , edges  246  show the limits of the overlapping area of shell-section/shield-section  242 , which may be held together by epoxy, glue, screws, tong and groove joints or the like. The semi-rigid/semi-flexible sheet may be wrapped around column  240  one or more times, or different or separate sheets may be used to wrap around column  240 . The semi-rigid/semi-flexible sheet may even be wrapped spirally around column  240 . 
     The process of wrapping the semi-rigid/semi-flexible sheet around column  240 , or even pouring of the filler material, may be performed in sections along the length of the column in an incremental manner until the entire column or a desired part of it is reinforced. The circular/circumferential edges  252  of the adjacent shell sections may be overlapped, as shown in  FIG. 2C , and adhered to each other to ensure the tensile (and compressive, if desired) integrity of the completed shell, while at the same time sealing the shell to prevent leakage of the filler material during construction and intrusion of moisture and oxygen once the shell is installed. Those skilled in the art recognize that such oxygen or moisture intrusion serves as a fuel to the corrosion process which can continue the deterioration of the column. The joints between shell sections may be joined shut using epoxy, chemical, or thermal techniques. In  FIG. 2C , the overlap width  250  shows the extent of overlap of shell-section  242  and shell-section  248 . While butt-joining these two sheets is another possibility, overlapping them is simpler in practice. The filler material may be poured after completing each shell-section  242  and  248  or after completing all shell-sections including  242  and  248 . 
     After the filler and other adhesive material are cured, the completed reinforced assembly of column  240 , the tension components  241 , the filler material, and the joined shell-sections  242  and  248  is a new and stronger column which contains the original column  240  in its core. Each component of this assembly is a degree of freedom for designing the reinforcement and/or the repair of column  240  and for accomplishing a desired final shape, size, and strength. It is known to those skilled in the art that by appropriate choice of these reinforcement components, the desired improvement in the axial, shear and flexural strength of a column can also be achieved. Additionally, all reinforcement components of the present method may be designed such that they also contribute to the axial, shear and flexural strengthening of a column. 
     In various embodiments in which the filler material adheres/attaches to the shield, the edges of the sheet forming the shield may be permanently left unattached to each other. In such embodiments a curved sheet of semi-flexible material may be placed around the column, and because such a sheet can keep its cylindrical shape, there may be no need to permanently attach its longitudinal edges together; especially if there is no need for confining pressure around the column. 
     In various embodiments, the shell sheet is constructed from fiber-reinforced material, such as Fiber Reinforced Polymer (FRP) to give the sheets more resistance against various types of loading, such as blast loading. Those skilled in the art will appreciate that many types of reinforcement fibers may be used for reinforcement including polymer, fiberglass, metal, cotton, other natural fibers, and the like. The sheet materials may include fabrics made with fibers such as glass, carbon, Kevlar, basalt, Nomex, aluminum, and the like; some saturated with a polymer such as polyester, vinyl ester, or epoxy for added strength, wear resistance, and resilience. The fibers within a reinforcement sheet may be aligned in one direction, in cross directions, randomly oriented, or in curved sections to provide various mechanical properties, such as tearing tendency and differential tensile strength along different directions, among others. Different reinforcement layers may use sheets with fibers oriented in different directions, such as orthogonal directions, 3-D fabrics, etc. with respect to other sheets to further reinforce the shell or, in other words, the Structural Reinforcement Wrap (SRW). 
     The semi-flexible or semi-rigid sheets from which shells/shields are formed, are preferably manufactured, transported, and stored as flat sheets, although curved sheets may also be used. 
     In various embodiments, multiple honeycomb laminates may be employed to further reinforce the SRW. Various layers in the SRW may be glued to each other to form one integral laminate wrap. In some embodiments, each layer in the SRW may be made from a different or same type of reinforcement sheet to develop different costs, performances, and mechanical properties for the SRW. For example, the outer layers may be made from thicker and tougher reinforcement sheets while the inner layers (closer to the structure) may be made from thinner and more flexible sheets to save material and installation or construction costs. Other variations in sheet layers are possible, such as fiber types and orientations, sheet materials, sheet material properties like chemical resistance, heat resistance, gas and fluid impermeability, and the like. Shells made with such variations in reinforcement layers will exhibit different mechanical and chemical properties suitable for different applications, costs levels, and considerations such as environmental and public safety considerations. 
     Shorter shells (shorter than the desired height of the completed/final shell) may be wrapped around the column at one elevation and then pushed up or down to their final elevation before grout is placed. This offers unique advantages, for example for repair of submerged piles where the shell is created above the water and then it is pushed down into water, eliminating the need for costly divers on such repairs. 
     The multi-layer embodiments may be pre-glued and integrated prior to application to a structure or be integrated during the application to the structure. 
     When concrete is poured in the cavity between the shell and the column to reinforce the structure, a stiff SRW may be used to support the weight of the fresh concrete or grout before the concrete or grout sets and cures. SRW eliminates the framework sometimes needed to support concrete repair and/or reinforcement. In rare cases when additional support is needed while the concrete or grout is being cured, temporary support may be used around the shell. In some embodiments a ring, ledge or a lip near the bottom of the shell may also be used to support the weight of the fresh concrete or grout, at the bottom of the shell, before the concrete or grout sets and cures. 
     In various embodiments the shell-based/SRW-based outer lining may have very high ring stiffness and may prevent further erosion and deterioration of the column. In an optional step of reinforcement process, one or both ends of a shield may be connected to or embedded in the floor and/or ceiling on which or between which the column is built. This is in addition or instead of connecting the reinforcement straps/rebars to the floor and/or the ceiling, as mentioned above. 
     Those skilled in the field know that the reinforcement sheet may be kept at a distance from the column, while being wrapped around it, by different conventional means or by using a reinforcement sheet that includes protrusions on one side. By using such sheets the shell/SRW becomes an integral part of the filler material and a much stiffer system results, while eliminating the need for temporary or permanent spacers otherwise needed. 
       FIG. 3A  shows example cross-sectional area of a reinforced column  300 . In this embodiment column  300  is hollow, such as a pipe. As can be seen in  FIG. 3A , the combination of column  300 , straps  310 , filler material  340 , and shell  320  creates a thicker-walled column that can withstand higher compressive forces while bending or under axial pressure. In this example shell  320  is axially/longitudinally sealed by overlap  330 . Additionally in this example, the tension bearing elements  310 , which are also a part of the above mentioned combination of column  300 , filler material  340 , and shell  320 , will add to the tensile capacity of the column under bending moments. While the tension bearing elements  310  may be even attached to the inside or the outside surface of shell  320 , attaching them to the outside surface of column  300  is more practical. 
       FIG. 3B  shows example cross-sectional area of a rectangular reinforced concrete column  350  that was originally constructed with longitudinal reinforcing steel bars  360  and lateral steel ties  365 . In many cases it is desirable to strengthen such columns with as little enlargement of the original cross section as possible. In one embodiment, the corners  370  of the column  350  can be cut and removed to reach new sides  375 . The shell  380  is wrapped around the column and it is axially/longitudinally sealed by overlap  385 . Tension reinforcing elements  395  can be positioned along the axis of the column and the annular space between the shell  380  and the column is filled with a filler material  390 . Those skilled in the art recognize that by designing the number of layers of overlap of shell  380  and the length of overlap  385 , the shell can offer very high confining pressure and can also eliminate the need for new lateral ties. The shell  380 , the reinforcing elements  395  and the filler material  390  all contribute to the increase in axial, flexural and shear capacity of the original column  350 . For a video of testing the disclosed methods on concrete and wood columns please visit http://goo.gl/HRHzjr and http://goo.gl/vxf1Mx respectively. 
     In the embodiments in which the reinforcement rebars or other reinforcement members are securely attached inside holes that are drilled in the floor and/or ceiling, a slightly larger size column will result that will have a construction similar to the original column but with more reinforcement components. Especially in such reinforced concrete columns the completed column is not a combination of an original column and a reinforcement cover, but a new column with same construction as the original column with more reinforcement members. In effect, with such concrete reinforced columns there is no distinction between the original column and the reinforcement part. 
       FIG. 4  shows an example process of reinforcing a column using the presented method. Process  400  proceeds to block  410  where one or more reinforcement straps/ribbons/rebars are longitudinally and/or circumferentially attached to the column&#39;s surface. As described above with respect to  FIGS. 2A and 2B , different numbers and types of straps may be used during this step. In various embodiments these reinforcement straps may be attached to the column surface using adhesives, attachment components, fasteners, a combination thereof, and the like. The process proceeds to block  420 . 
     At the optional block  420 , one or both ends of the reinforcement rebars or straps are connected to or embedded in the floor and/or ceiling on which or between which the column is built. The process proceeds to block  430 . In some embodiments this step may not be optional and one or both ends of the reinforcement rebars or straps may have to be connected to or embedded in the floor and/or ceiling on which or between which the column is built. 
     At block  430 , at least one semi-rigid reinforcement sheet is wrapped (overlappingly or otherwise) around the column and strap assembly to create a shield around the column, such that there remains a cavity between the wrapped sheet (shield) and the column. The process proceeds to block  430 . 
     At another optional block  440 , one or both ends of the shield may be connected to or embedded in the floor and/or ceiling on which or between which the column is built. This is in addition or instead of connecting the reinforcement straps/rebars to the floor and/or the ceiling, as mentioned in block  420 . The process proceeds to block  450 . 
     At block  450 , additional reinforcement sheet layers may be attached on top of the primary shield. The above procedure may be repeated several times in different sequences to construct an SRW of the thickness, composition, and stiffness desired. Such SRW may include many layers of reinforcement sheets and many layers of honeycomb laminate structures or 3D fabric, which may or may not be adjacent to each other. The process proceeds to block  440 . 
     At block  460 , filler material such as those enumerated above is poured in the cavity between the shield and the column. 
     At block  470 , the process terminates. 
     Changes can be made to the claimed invention in light of the above Detailed Description. While the above description details certain embodiments of the invention and describes the best mode contemplated, no matter how detailed the above appears in text, the claimed invention can be practiced in many ways. Details of the system may vary considerably in its implementation details, while still being encompassed by the claimed invention disclosed herein. 
     Particular terminology used when describing certain features or aspects of the invention should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the invention with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the claimed invention to the specific embodiments disclosed in the specification, unless the above Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the claimed invention encompasses not only the disclosed embodiments, but also all equivalent ways of practicing or implementing the claimed invention. 
     The above specification, examples, and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. It is further understood that this disclosure is not limited to the disclosed embodiments, but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements. 
     While the present disclosure has been described in connection with what is considered the most practical and preferred embodiment, it is understood that this disclosure is not limited to the disclosed embodiments, but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.