Patent Publication Number: US-6666233-B1

Title: Tendon receiving duct

Description:
RELATED U.S. APPLICATIONS 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 09/752,126, filed on Dec. 29, 2000, and entitled “TENDON-RECEIVING DUCT WITH LONGITUDINAL CHANNELS”, presently pending. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     REFERENCE TO MICROFICHE APPENDIX 
     Not applicable. 
     FIELD OF THE INVENTION 
     The present invention relates to ducts as used in post-tension construction. More particularly, the present invention relates to the formation of a polymeric duct used for retaining multi-strand tensioning systems within an encapsulated environment. 
     BACKGROUND OF THE INVENTION 
     For many years, the design of concrete structures imitated the typical steel design of column, girder and beam. With technological advances in structural concrete, however, its own form began to evolve. Concrete has the advantages of lower cost than steel, of not requiring fireproofing, and of its plasticity, a quality that lends itself to free flowing or boldly massive architectural concepts. On the other hand, structural concrete, though quite capable of carrying almost any compressive load, is weak in carrying significant tensile loads. It becomes necessary, therefore, to add steel bars, called reinforcements, to concrete, thus allowing the concrete to carry the compressive forces and the steel to carry the tensile forces. 
     Structures of reinforced concrete may be constructed with load-bearing walls, but this method does not use the full potentialities of the concrete. The skeleton frame, in which the floors and roofs rest directly on exterior and interior reinforced-concrete columns, has proven to be most economic and popular. Reinforced-concrete framing is seemingly a quite simple form of construction. First, wood or steel forms are constructed in the sizes, positions, and shapes called for by engineering and design requirements. The steel reinforcing is then placed and held in position by wires at its intersections. Devices known as chairs and spacers are used to keep the reinforcing bars apart and raised off the form work. The size and number of the steel bars depends completely upon the imposed loads and the need to transfer these loads evenly throughout the building and down to the foundation. After the reinforcing is set in place, the concrete, a mixture of water, cement, sand, and stone or aggregate, of proportions calculated to produce the required strength, is placed, care being taken to prevent voids or honeycombs. 
     One of the simplest designs in concrete frames is the beam-and-slab. This system follows ordinary steel design that uses concrete beams that are cast integrally with the floor slabs. The beam-and-slab system is often used in apartment buildings and other structures where the beams are not visually objectionable and can be hidden. The reinforcement is simple and the forms for casting can be utilized over and over for the same shape. The system, therefore, produces an economically viable structure. With the development of flat-slab construction, exposed beams can be eliminated. In this system, reinforcing bars are projected at right angles and in two directions from every column supporting flat slabs spanning twelve or fifteen feet in both directions. 
     Reinforced concrete reaches its highest potentialities when it is used in pre-stressed or post-tensioned members. Spans as great as one hundred feet can be attained in members as deep as three feet for roof loads. The basic principle is simple. In pre-stressing, reinforcing rods of high tensile strength wires are stretched to a certain determined limit and then high-strength concrete is placed around them. When the concrete has set, it holds the steel in a tight grip, preventing slippage or sagging. Post-tensioning follows the same principle, but the reinforcing tendon, usually a steel cable, is held loosely in place while the concrete is placed around it. The reinforcing tendon is then stretched by hydraulic jacks and securely anchored into place. Pre-stressing is done with individual members in the shop and post-tensioning as part of the structure on the site. 
     In a typical tendon tensioning anchor assembly used in such post-tensioning operations, there are provided anchors for anchoring the ends of the cables suspended therebetween. In the course of tensioning the cable in a concrete structure, a hydraulic jack or the like is releasably attached to one of the exposed ends of each cable for applying a predetermined amount of tension to the tendon, which extends through the anchor. When the desired amount of tension is applied to the cable, wedges, threaded nuts, or the like, are used to capture the cable at the anchor plate and, as the jack is removed from the tendon, to prevent its relaxation and hold it in its stressed condition. 
     Multi-strand tensioning is used when forming especially long post-tensioned concrete structures, or those which must carry especially heavy loads, such as elongated concrete beams for buildings, bridges, highway overpasses, etc. Multiple axially aligned strands of cable are used in order to achieve the required compressive forces for offsetting the anticipated loads. Special multi-strand anchors are utilized, with ports for the desired number of tensioning cables. Individual cables are then strung between the anchors, tensioned and locked as described above for the conventional monofilament post-tensioning system. 
     As with monofilament installations, it is highly desirable to protect the tensioned steel cables from corrosive elements, such as de-icing chemicals, sea water, brackish water, and even rain water which could enter through cracks or pores in the concrete and eventually cause corrosion and loss of tension of the cables. In multi-strand applications, the cables typically are protected against exposure to corrosive elements by surrounding them with a metal duct or, more recently, with a flexible duct made of an impermeable material, such as plastic. The protective duct extends between the anchors and in surrounding relationship to the bundle of tensioning cables. Flexible duct, which typically is provided in 20 to 40 foot sections is sealed at each end to an anchor and between adjacent sections of duct to provide a water-tight channel. Grout then may be pumped into the interior of the duct in surrounding relationship to the cables to provide further protection. 
     Various patents have issued, in the past, for devices relating to such multi-strand duct assemblies. For example, U.S. Design Pat. No. 400,670, issued on Nov. 3, 1998, to the present inventor, shows a design of a duct. This duct design includes a tubular body with a plurality of corrugations extending outwardly therefrom. This tubular duct is presently manufactured and sold by General Technologies, Inc. of Stafford, Tex., the licensee of the present inventor. In particular, FIGS. 1 and 2 are illustrations of the prior art duct that is being manufactured by General Technologies, Inc. 
     As can be seen in FIG. 1, the tubular duct  10  has a tubular body  12  and a plurality of corrugations  14  which extend radially outwardly from the outer wall  16  of the tubular body  12 . The tubular body  12  includes an interior passageway  14  suitable for receiving multiple post-tension cables and strands therein. The interior passageway  18  of the tubular body  12  is suitable for receiving a grout material so as to maintain the multiple strands in a liquid-tight environment therein. FIG.  2  shows the tubular body  12  as having the corrugations  14  extending outwardly in generally spaced parallel relationship to each other and in transverse relationship to the longitudinal axis of the tubular body  12 . A wall  16  will extend between the corrugations  14 . The tubular body  12 , along with the corrugations  16 , are formed of a polymeric material. The duct  12  can be any length, as desired. Couplers can be used so as to secure lengths of duct  10  together in end-to-end relationship. 
     One of the problems associated with the prior art duct  10  is that it is not stiff enough in the longitudinal direction. The duct  10  will flex too easily. It becomes difficult to profile such an easily flexible duct. When the cables are being installed in the interior passageway  18 , the cablepusher that is used to install the cable within the interior passageway  18  is likely to strike the walls of the interior passageway  18  when the duct is flexed. Because of the force used to install the cable through the duct  10 , the walls of the duct can break or become damaged if the cable strikes the walls of the duct. It is desirable to manufacture a duct  10  with greater stiffness and rigidity in the longitudinal direction so as to avoid the flexing and deflection of the duct. 
     An additional problem with the duct  10 , as shown in FIGS. 1 and 2, is that air has a possibility of being trapped in the corrugations. When air bubbles form within the interior of the corrugations, the grout used to seal the interior  18  does not effectively encapsulate the cable on the interior  18 . As such, it is desirable to manufacture the duct  10  such that the potential for trapped air bubbles within the corrugations  14  is reduced. 
     The present inventor is also the inventor of U.S. Pat. No. 5,474,335, issued on Dec. 12, 1995. This patent describes a duct coupler for joining and sealing between adjacent sections of duct. The coupler includes a body and a flexible cantilevered section on the end of the body. This flexible cantilevered section is adapted to pass over annular protrusions on the duct. Locking rings are used to lock the flexible cantilevered sections into position so as to lock the coupler onto the duct. U.S. Pat. No. 5,762,300, issued on Jun. 9, 1998, to the present inventor, describes a tendon-receiving duct support apparatus. This duct support apparatus is used for supporting a tendon-receiving duct. This support apparatus includes a cradle for receiving an exterior surface of a duct therein and a clamp connected to the cradle and extending therebelow for attachment to an underlying object. The cradle is a generally U-shaped member having a length greater than a width of the underlying object received by the clamp. The cradle and the clamp are integrally formed together of a polymeric material. The underlying object to which the clamp is connected is a chair or a rebar. 
     U.S. Pat. No. 5,954,373, issued on Sep. 21, 1999 to the present inventor, shows another duct coupler apparatus for use with ducts on a multi-strand post-tensioning system. The coupler includes a tubular body with an interior passageway between a first open end and a second open end. A shoulder is formed within the tubular body between the open ends. A seal is connected to the shoulder so as to form a liquid-tight seal with a duct received within one of the open ends. A compression device is hingedly connected to the tubular body for urging the duct into compressive contact with the seal. The compression device has a portion extending exterior of the tubular body. 
     U.S. patent application Ser. No. 09/752,126, filed on Dec. 29, 2000 filed on by the present inventor, does describe a tendon-receiving duct having longitudinal channels. In this patent application, two forms of the duct are described. One form has a generally circular section and the other form has a generally oval cross section. The longitudinal channels are evenly spaced around the duct. These longitudinal channels extend for the length of the duct and allow each of the corrugations to connect with each other. As a result, when grout is introduced into the interior passageway of the duct, it will flow between the corrugations along the longitudinal channels so as to effectively fill the interior of the duct with grout. The longitudinal channels provide a certain amount of rigidity and straightness to the duct so as to facilitate installation of cables therein. 
     A difficulty associated with the product of U.S. patent application Ser. No. 09/752,126 is that the even placement of the channels around the circumference of the duct does not assure that any particular channel resides in the uppermost position. The orientation of the duct is subject to random placement upon underlying rebars or other structures. If the orientation of the channels is such that no channel appears at the direct top of the duct, then would be a possibility of air bubbles migrating to the inner wall of the duct in the area between the channels. Under conditions of great load capacities, the duct could hinge in the areas of the channels. Since the duct experiences large forces on the bottom thereof, the random orientation of the channels would not assure proper support for the bottom surfaces of the duct. As such, a need developed to slightly improve the construction of this prior duct of the present inventor. 
     It is an object of the present invention to provide a tendon-receiving duct which improves the rigidity of the duct in the longitudinal direction. 
     It is another object of the present invention to provide a tendon-receiving duct which facilitates the removal of air bubbles within the interior of the duct. 
     It is a further object of the present invention to provide a tendon-receiving duct apparatus which facilitates the ability to install the cable within the duct. 
     It is still a further object of the present invention to provide a tendon-receiving duct which is easy to manufacture, easy to use, and relatively inexpensive. 
     It is a further object of the present invention to provide a tendon-receiving duct which provides an automatic orientation of the duct so that a channel is formed at the top of the duct. 
     It is an other object of the present invention to provide a tendon-receiving duct which reduces undulations along the length of the duct. 
     It is a further other object of the present invention to provide a tendon-receiving duct which minimizes restrictions during the installation of cables or tendons on the interior of the duct. 
     It is a further object of the present invention to provide a tendon-receiving duct which provides a structure which avoids hinging in the areas of the channels. 
     These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a tendon receiving duct comprising a tubular body having a longitudinal axis and plurality of corrugations extending radially outwardly therefrom. Each of the corrugations is in spaced relationship to an adjacent corrugation. The tubular body has an interior passageway suitable for receiving cables therein. Each of the plurality of corrugations opens to the interior passageway. The tubular body has a first longitudinal channel extending between adjacent pairs of the plurality of corrugations on a one side of the tubular body. The tubular body has a pair of longitudinal channels extending between adjacent pairs of the plurality of corrugations on an opposite side of the tubular body. 
     The pair of longitudinal channels are in spaced parallel relationship to each other. Each of the pair of longitudinal channels is spaced by approximately 160° in respective opposite directions from the first longitudinal channel around the circumference of the tubular body. The pair of longitudinal channels have an exterior surface that is co-planar with each other and also co-planar with an exterior surface of the tubular body. 
     The first longitudinal channel is positioned at a top of the tubular body. The pair of longitudinal channels are positioned at a bottom of the tubular body. The first longitudinal channel and the pair of longitudinal channels extend for an entire length of the tubular body. Each of the channels opens at opposite ends of the tubular body. The tubular body has a wall extending between the adjacent corrugations. Each of the first longitudinal channel and the pair of longitudinal channels extends outwardly of this wall. The longitudinal channels open to the interior passageway of the tubular body. Each of the first longitudinal channel and the pair of longitudinal channels has one end opening to one of the pair of corrugations and an opposite end opening to the other of the pair of corrugations. The longitudinal channels connect the plurality of corrugations in fluid communication. The longitudinal channels extend outwardly of the tubular body by a distance equal to the distance that the plurality of corrugations extend outwardly of the tubular body. 
     The tubular body has a circular cross section in a plane transverse to a longitudinal axis of the tubular body. The tubular body, the plurality of corrugations, the first longitudinal channel and the pair of longitudinal channels are integrally formed together of a polymeric material. 
     In an alternative form of the present invention, a plurality of tendons will extend through the interior passageway of the tubular body. A grout material fills the interior passageway of the tubular body. This grout material will also fill the plurality of corrugations and the longitudinal channels. As used herein, the term “tendons” can refer to various items, such as construction cables, wire rope, rebar and related items. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is an upper perspective view showing a prior art tendon-receiving duct. 
     FIG. 2 is a side elevational view of the prior art tendon-receiving duct shown in FIG.  1 . 
     FIG. 3 is an upper perspective view of the tendon-receiving duct in accordance with the teachings of the present invention. 
     FIG. 4 is an end view of the tendon-receiving duct in accordance with the teachings of the present invention. 
     FIG. 5 is a cross-sectional view as taken across lines  5 — 5  of FIG.  4 . 
     FIG. 6 is a cross-sectional view as taken across lines  6 — 6  if FIG.  4 . 
     FIG. 7 is a side elevational view of the tendon-receiving duct of the present invention as partially sectioned so as to show the tendons therein. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 3, there is shown the tendon-receiving duct  20  in accordance with the teachings of the preferred embodiment of the present invention. The tendon-receiving duct  20  includes a tubular body  22  having a plurality of corrugations  24  extending radially outwardly of the tubular body  22 . Each of the corrugations  24  is in spaced relationship to an adjacent corrugations  24 . The tubular body has an interior passageway  26  suitable for receiving tendons (or post-tension cables) therein. Each of the plurality of corrugations  24  open within the tubular body  22  to the interior passageway  26 . A first longitudinal channel  28  is formed on the top side of the tubular body  22  and extends so as to communicate between the corrugations  24 . A pair of longitudinal channels  30  and  32  are formed on the bottom side of the tubular body  22 . This pair of longitudinal channels  30  and  32  also communicate between the corrugations  24 . 
     The tubular body  22  has a wall section  34  formed between adjacent pairs of corrugations  24  on the tubular body  22 . The wall portion  34  defines the inner wall of the interior passageway  26 . The longitudinal channel  28  will extend between the corrugations  24  in parallel relationship to the longitudinal axis of the tubular body  22 . Similarly, the pair of longitudinal channels  30  and  32  will extend between the corrugations  24 . Each of the longitudinal channels  28 ,  30  and  32  has an interior which opens to the interior passageway  26 . 
     As can be seen in FIG. 3, the first longitudinal channel  28  and the pair of longitudinal channels  30  and  32  extend for the entire length of the tubular body  20 . The first longitudinal channel  28  will have one end  36  opening at the end  38  of the tubular body  22 . Similarly, the first channel  28  will have an opposite end  40  opening at the opposite end  42  of the tubular body  22 . Each of the pair of longitudinal channels  30  and  32  will have a first end opening at the end  38  of the tubular body  22  and an opposite end opening at the opposite end  42  of the tubular body  22 . The longitudinal channels  28 ,  30  and  32  extend outwardly of the wall portion  34 . The longitudinal channels  28 ,  30  and  32  will serve to connect the plurality of corrugations  24  in fluid communication with each other. The longitudinal channels  28 ,  30  and  32  extend outwardly of the wall portion  34  of the tubular body  22  by a distance equal to the distance that the plurality of corrugations  24  extend outwardly of the tubular body  22 . It can be seen that the tubular body  22  has a circular cross section in a plane transverse to the longitudinal axis of the tubular body  22 . Each of the tubular body  22 , the plurality of corrugations  24 , the first longitudinal channel  28 , and the pair of longitudinal channels  30  and  32  are integrally formed together of a polymeric material in an injection molding process. 
     In normal use, when grout is introduced into the interior passageway  26 , it will begin to fill the void within the interior passageway  26 . The grout will initially fill the interior of the adjacent corrugation  24  and push air bubbles upwardly and outwardly therefrom. These air bubbles can migrate along the first longitudinal channel  28  toward the next corrugation  24 . The grout can then flow between the corrugations  24  along the pair of longitudinal channels  30  and  32  at the bottom of the duct  20 . Eventually, the grout will fill the channels  28 ,  30  and  32  and slowly move along the length of the tubular body  22 . As a result of the uppermost positioning of the first longitudinal channel  28 , it can be assured that the air bubbles will migrate into the channel  28  so as to be properly pushed by the grout toward the end of the duct  20 . A suitable valve, or other device, can be used so as to release the migrated air from the interior passageway  26  at the end of the duct  20 . 
     Importantly, the longitudinal channels  28 ,  30  and  32  provide rigidity and stiffness along the longitudinal axis of the tubular body  22 . As a result, the tubular body  22  is less likely to curl up, whip or wobble during the installation of the tendons or cable by a cablepusher. The added stiffness provided by the longitudinal channels  28 ,  30  and  32  allows cables to be installed in a quicker and more convenient manner. There is less likelihood of duct breakage when the tendons are installed. The minimization of whip, wobble, and undulations caused by the construction of the channels  28 ,  30  and  32  will further reduce the likelihood of duct breakage. 
     It is important to note that the duct  20  will typically rest on underlying surface, such as rebars or post-tension cables. Such structures provide a relatively small point of contact with the relatively thin walls of the duct  20 . As a result, in prior art ducts, there was a possibility of indentations created by the strong forces imparted by the weight supported by the duct  20  and the contact force with the underlying structures. The present invention addresses this problem by providing the pair of longitudinal channels  30  and  32  at the bottom of the duct  20 . As a result, three points of contact will be provided with the underlying surface. These points of contact include the surfaces of the channels  30  and  32  and the lowermost portion of the wall  34 . As a result, undulations and indentations are prevented. The arrangement of the top longitudinal channel  28  and the bottom longitudinal channels  30  and  32  are configured so as to eliminate “hinging” in the areas of the channels. It can be seen that the top channel  28  is positioned in an offset relationship from the bottom channels  30  and  32 . The lack of direct alignment of the channels will prevent hinging from occurring. 
     Importantly, the present invention provides an automatic centering effect. Unlike prior art ducts, it is relatively easy for the worker at the construction site to determine the top and the bottom of the duct  20 . The single channel  28  will appear at the top of the duct  20  and the pair of channels  30  and  32  will appear at the bottom of the duct  20 . As a result, the duct  20  will always be installed in its desired orientation so that the support channels  30  and  32  will contact the underlying surface. 
     Referring to FIG. 4, the end view of the duct  20  is particularly shown. The first longitudinal channel  28  is illustrated as formed in the direct top of the tubular body  22 . The first longitudinal channel  28  has a height which is generally equal to the height of the outer surface of the corrugation  24 . The first longitudinal channel  28  opens to the interior passageway  26  of the tubular body  22 . The pair of longitudinal channels  30  and  32  are formed adjacent to the bottom of the tubular body  22 . In particular, the pair of longitudinal channels  30  and  32  are spaced by approximately 160-170°, in opposite directions, respectively, from the first longitudinal channel  28  around the circumference of the tubular body  22 . Each of the pair of longitudinal channels  30  and  32  extends outwardly from the wall  34  by a distance equal to the distance that the corrugation  24  extends outwardly from wall  34 . Each of the longitudinal channels  30  and  32  opens to the interior passageway  26  of the tubular body  22 . An underlying surface  44  is particularly shown in FIG.  4 . It can be seen that the pair of longitudinal channels  30  and  32  will rest in co-planar relationship with the surface  44 . It can be also seen that a point of contact  46  on the outer surface of wall  34  would also contact the underlying surface  44 . As a result, there are three points of contact between the bottom surface of the duct  20  and the underlying surface  44 . This will provide a suitable rigidifying effect and will avoid indentations through the wall  34  created by forces between the underlying surface  44  and the weight supported by the duct  20 . 
     FIG. 5 is a cross-sectional view of the duct  20 . In particular, it can be seen that the first longitudinal channel  28  extends generally centrally between the side  50  and  52  of the tubular body  22 . Corrugations  24  extend in generally spaced parallel relationship to each other in transverse orientation to the longitudinal axis of the tubular body  22 . The longitudinal channel  28  is illustrated as having its ends, along its length, opening to the corrugations  24 . As a result, grout and air bubbles will naturally migrate along the length of the tubular body  22 . 
     FIG. 6 shows a detailed view of a particular corrugation  24 . Corrugations  24  are illustrated as having walls that extend at an approximately 60° angle with respect to each other. This angled orientation of the walls facilitates manufacturing and also facilitates air bubble migration to the outermost regions of each corrugation  24 . The 60° angle will tend to “funnel” air bubbles to the outermost surfaces and also funnel such air bubbles upwardly toward the first longitudinal channel  28 . 
     FIG. 7 shown an alternative embodiment of the present invention in which the duct  60  has corrugations  62  with a first longitudinal channel  64  and a pair of longitudinal channels  66 . The first longitudinal channel  64  is at top of the tubular body  68 . The pair of channels  66  are located at the bottom of the tubular body  68 . In FIG. 7, a further stiffening effect is created by the formation of small ribs  70  extending transversely to the longitudinal axis of the tubular body  68 . Each of the ribs  70  is in spaced parallel relationship to each other and will extend around the diameter of the tubular body  68 . In FIG. 7, it can be seen that the tubular body  68  has an interior passageway  72  into which a plurality of tendons or cables  74  extend. A suitable grout material  76  fills the interior passageway  72  of the tubular body  68  and will surround the tendons  74  within the tubular body  68 . As a result, a relatively air and water tight relationship is established between the duct  60  and those tendons  74  extending within the duct  60 . 
     The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction can be made within the scope of the appended claims without departing from the true spirit of the invention. The present invention should only be limited by the following claims and their legal equivalents.