Abstract:
A composite structure that can serve as a cushion or fender piling for moored or passing ships includes an elongate tubular member having a radially projecting resilient cushion extending over an upper portion of its length. In one embodiment, the material of the cushion also fills the tubular member, encapsulating an upper extremity of the tubular member. In another embodiment, the tubular member is filled with a different material such as concrete, and the material of the cushion can also encapsulate upper extremities of both the tubular member and the different filler material. Optionally, a reinforcing member such as a helically formed length of reinforcing bar engages an inside surface of the tubular member for resisting inward deflection of the tubular member when the piling is subjected to high bending and shear loading.

Description:
BACKGROUND  
       [0001]     The present invention relates to elongated structures such as pilings of the type used in marine applications for protecting piers, docks and similar structures from being damaged by passing and docking ships, and methods for making such pilings.  
         [0002]     Concrete, steel, and wood are conventionally used for pilings, telephone poles, and the like. However, each of these materials has disadvantages. Concrete and steel pilings are heavy and awkward to maneuver. Neither concrete nor steel pilings make good fender pilings because neither is “forgiving” when impacted. Under impact steel bends and buckles and concrete shatters. Both concrete and steel pilings are expensive to repair. Furthermore, steel, either standing alone or as a reinforcement in porous concrete, is subject to corrosion.  
         [0003]     Wood pilings are plagued by wear and tear and are attacked by wood-boring marine organisms. Wood pilings are typically treated with creosote, but even this material can be ineffective against modern marine borers. These marine borers can only be stopped by wrapping the wood pilings in plastic coverings. However, these plastic coverings cannot withstand much wear and tear, especially abrasion from normal vessel contact. So in addition to a thin plastic wrap, wooden fender piles often require thick plastic wrappings, which are expensive to put in place. Wood used for telephone poles is subject attack from environmental hazards such as woodpeckers, and in desert locations, there can be severe erosion from sandstorms.  
         [0004]     Composite pilings are also known, being disclosed for example in U.S. Pat. No. 5,180,531 to Borzakian, that document being incorporated herein by this reference. The &#39;531 patent discloses a plastic pipe having an inner pipe core or mandrel being 6 inches or less in diameter, and a substantially homogenous coating being at least two inches thick. The thick plastic coating provides the bulk of the mechanical strength, being formulated with a desired combination of flexibility, brittleness, and impact resistance for use as pilings including fender pilings of docks, telephone poles, light standards, etc. The plastic pipe of the prior art is not entirely satisfactory in that uniform thick coatings that are free of voids are somewhat difficult to achieve, and longer lengths of the pilings such as from 20 feet to 60 feet normally require assembly of shorter length segments, with consequent degradation of structural and environmental integrity and increased cost of fabrication. Also, when the plastic pipe is provided with the homogenous plastic coating having with a desired flexibility and impact resistance for fender piling applications, the bending strength is less than desired for withstanding side loads that are produced by contact with approaching vessels. Pilings of similar construction incorporating larger pipe mandrels are also known.  
         [0005]     U.S. Pat. No. 5,766,711 to Barmakian discloses a composite camel structure including a pipe mandrel and a thermally bonded plastic cushion surrounding the mandrel, that patent being incorporated herein by this reference. A mold having the mandrel centered therein is filled with molten plastic, the plastic being cooled and solidified by feeding water into the mandrel for progressively solidifying the cushion member along mandrel for producing a thermal bond without excessive tensile strain in the plastic material, thereby to achieve a substantially unbroken outside surface.  
         [0006]     Another known form of composite piling, which is described in U.S. Pat. No. 6,244,014 to Barmakian and incorporated herein by this reference, incorporates a welded cage structure including longitudinal bars that are connected by a spiral member, the cage structure being encapsulated in a resilient plastic.  
         [0007]     A further form of composite pilings incorporates a thin-wall cylindrical tubular member formed of carbon filament-reinforced plastic that is filled with concrete. Unfortunately, it is prohibitively expensive to orient the carbon filament diagonally. Commercially available tubular members of this type have a substantially purely circumferential filament orientation and consequently this type has little bending and shear strength, even in combination with the concrete core. Further, these pilings are quite brittle, having little ability to withstand side impacts by ships and other vessels in marine applications.  
         [0008]     In view of these problems with existing thin-wall pilings, there is a need for elongated structures for marine use that are inexpensive to provide, yet have a long life, are easily installed, environmentally sound, durable in use, having high bending and shear strength. There is a further need for such structures having great energy absorbing capacity when subjected to side impact loads.  
       SUMMARY  
       [0009]     The present invention meets these needs by providing a composite structure that is low in cost and has particularly high bending and shear strength. In some preferred configurations the structure also has a very great ability to withstand high energy side impact loading. In one aspect of the invention, the reinforced composite structure includes an elongate tubular member having first and second ends, a second end portion near the second end, a length of at least 10 feet, an outside surface defining an outer cross-sectional area of at least 28 square inches at a first location along the tubular member, and an inside surface defining a wall thickness of not more than 10 percent of an equivalent diameter of the outer cross-sectional area at the first location; and a resilient plastic body encapsulating only a portion of the outside surface of the tubular member including a portion near the first end, the plastic body extending on the outside surface of the tubular member not closer to the second end than 20 percent of the length of the tubular member for facilitating secure and rigid planting of the composite structure in soil. Preferably the encapsulation extends lengthwise on the outside surface of the tubular member for at least three equivalent diameters of the outer cross-sectional area outside and inside surfaces for enhanced structural integrity of the plastic body. The encapsulated portion of the tubular member can extend to the first end of the tubular member, it can be approximately flush with the first end of the tubular member, or it can encapsulate the upper end of the tubular member. Also, the plastic body can substantially fill the tubular member.  
         [0010]     The tubular member can include a fiber-reinforcing material, such as fiberglass.  
         [0011]     Preferably the composite structure includes a reinforcing element contacting the inside surface of the tubular member. The reinforcing element can include a shear-resistant material substantially filling the tubular member. The shear-resistant material can be concrete. Also, or in the alternative, the reinforcing element can include an elongate reinforcing member extending within the tubular member and being in proximate contact with a portion only of its inside surface. The reinforcing member can include a longitudinally distributed plurality of loop elements. Adjacent loop elements of the reinforcing member can have a pitch spacing between approximately 25 percent and approximately 70 percent of the equivalent outside diameter of the tubular member, and the loop elements can be helically formed. The reinforcing member can include a material selected from steel, nickel, carbon fiber, and fiberglass. The reinforcing member can have a cross-sectional area of between 0.02 percent and approximately 0.2 percent of the overall cross-sectional area of the tubular member.  
         [0012]     Preferably at least a portion of the plastic body has a radial thickness outside of the tubular member that is not less than approximately 5 percent of a co-located circumference of the tubular member, the term co-located meaning located along the tubular member within the portion of the plastic body.  
         [0013]     Preferably the plastic body consists of a main polymeric component and an additive component, the main polymeric component consisting of low-density polyethylene of which at least 60 percent is linear low density stretch film polyethylene, the additive component including an effective amount of an ultraviolet inhibitor. More preferably, the main polymeric component is at least 90 percent of the plastic body, the plastic body including not more than 5 percent by weight of high-density polyethylene.  
         [0014]     In another aspect of the invention, a method for forming a composite structure includes the steps of providing an elongate tubular member; and encapsulating an end portion of the tubular member in a plastic body, the tubular member having an overall length of not less than approximately 10 feet, an overall cross-sectional area of at least 28 square inches at an axial extremity of the plastic body closest to the second end of the tubular member, and a wall thickness being not more than 10 percent of a diameter equivalent to said overall cross-sectional area.  
         [0015]     The method can include the further step of inserting a reinforcing element into the tubular member, the reinforcing element contacting the inside surface for stiffening the tubular member. The reinforcing element can include a reinforcing member, the method including the further steps of forming the reinforcing member as a rod member having a longitudinally spaced plurality of loop elements and, prior to the encapsulating, inserting the rod member into the tubular member with at least a portion of each of the loop elements contacting circumferentially spaced locations on the inside surface of the tubular member.  
         [0016]     Alternatively, or additionally, the step of inserting can include feeding a liquidic reinforcing material into the tubular member, and solidifying the liquidic material. The liquidic material can include material of the plastic body and/or concrete.  
         [0017]     The encapsulating can include the steps of providing an injection mold having an elongate cylindrical cavity; loading the mold with the tubular member such that a portion of the tubular member projects from a main cavity portion of the mold; injecting a polymeric composition into the mold thereby encapsulating a portion of the tubular member; and cooling the mold to form the composite structure. Preferably the step of injecting includes formulating the polymeric composition to consist of low density polyethylene, at least 60 percent of the polymeric composition being linear low-density stretch film polyethylene for resisting cracking of the material.  
         [0018]     In a further aspect of the present invention, a method for forming a cushioned fender in a marine environment having underwater soil, includes the steps of selecting a reinforced composite structure as first given above; and driving the second end of the tubular member into the soil to a depth effective for stabilizing the tubular member and for positioning the plastic body as a cushioned barrier above the soil. 
     
    
     DRAWINGS  
       [0019]     These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings, where:  
         [0020]      FIG. 1  is a sectional elevational view of a reinforced composite piling according to the present invention, the piling being installed in a marine environment for fending off passing vessels;  
         [0021]      FIG. 2  is a bottom view of the piling of  FIG. 1 ;  
         [0022]      FIG. 3  is a sectional elevational view as in  FIG. 1 , showing an alternative configuration of the composite piling;  
         [0023]      FIG. 4  is a lateral sectional view of a mold assembly in use making the composite piling of  FIG. 1 , illustrating the flow of extruded plastic within and around a spiral reinforcing member thereof; and  
         [0024]      FIG. 5  is a flow chart for a process of forming the piling structure of  FIG. 1 . 
     
    
     DESCRIPTION  
       [0025]     The present invention provides a novel reinforced composite structure that is particularly effective as a fender in association with a ship mooring or other harbor structure. With reference to  FIGS. 1 and 2  of the drawings, a composite structure or piling  10  according to the present invention includes an elongate tubular member  12  and a resilient plastic material forming a plastic body  14  encapsulating an upper portion of the tubular member. As shown in  FIG. 1 , the piling  10  can be implanted in soil  16  under a body of water  18  such that the plastic body  14  is positioned for blocking the hull of a ship  20  in a cushioned manner, the plastic body being confined to that portion of the tubular member  12  that is not in the soil  16 .  
         [0026]     An exemplary configuration of the piling  10  has the tubular member  12  and an outer perimeter of the plastic body  14  formed generally circularly cylindrical with a diameter B at a distance W outwardly from the tubular member  12  as shown in  FIG. 2 , the tubular member having an outside diameter D (See  FIG. 1 .) that is typically between 8 and 36 inches, and a length L that is typically between approximately 10 feet and approximately 60 feet. Even longer lengths such as 100 feet are also contemplated, although coupling to extension pilings in locations of deep mud deposits is generally preferred. A preferred embodiment of the tubular member  12  is formed of glass fiber-reinforced epoxy (referred to herein as “fiberglass”), having a wall thickness T that can be from approximately 0.125 inch up to approximately 2 inches. As used herein, the term “cylindrical” means having a surface that is generated by a straight line that moves parallel to a fixed line. Thus, although the tubular member  12  and the perimeter surface of the body  14  are shown in the drawings as being circularly cylindrical, other cross-sectional shapes such as elliptical, polygonal, and rounded polygonal are also contemplated within the scope of the present invention. In these alternatives, the tubular member  14  typically has an overall cross-sectional area of at least approximately 50 square inches, although smaller sections such as having approximately 28 square inches are contemplated, being equivalent to approximately 6 inches diameter. Further, this invention is not limited to cylindrically shaped cores, as axially tapered and other tubular shapes are contemplated. Moreover, other materials are contemplated for the tubular member, including carbon filament-reinforced plastic and steel.  
         [0027]     Also, although the plastic body  14  is shown radially projecting a uniform distance W outwardly from the tubular member  12  to a body diameter B for a distance or encapsulated length l downwardly from the upper extremity of the tubular member, the body  14  need not be concentric with the tubular member  12 . Further, the perimeter surface of the body  14  is not required to be circular or even cylindrical; a variety of other shapes such as frusto-conical and ellipsoidal are contemplated within the scope of the present invention, although at least a portion of the plastic body preferably has a radial thickness outside of the tubular member being not less than approximately 5 percent of a co-located circumference of the tubular member. Moreover, the plastic body  14  projects outwardly from the tubular member over a body length C, which can extend a distance E beyond the upper end of the tubular member  12 , the piling  10  having an overall length F. As further shown in  FIG. 1 , the composite piling  10  extends to a height H above the soil  16  when driven a sink distance S into the soil. The sink distance S will normally be at least 20 percent of the length L of the tubular member  12 . Accordingly, the encapsulated length l is normally less than 80 percent of the length L, preferably less than 75 percent of the length L for avoiding contact with or partial penetration with the soil, with consequent potential for partial separation of the plastic body from the tubular member and/or reduced stiffness of the implantation of the piling  10 . Also, the encapsulated length l is normally not less than approximately 3 times the diameter D of the tubular member. More generally for tubular members of non-circular cross-section, the encapsulated length l is not less than 3 equivalent diameters of the tubular member, the term equivalent diameter being the diameter of a circular cross-section having the same area as that of the non-circular cross-section. More preferably, the encapsulated length l is between approximately 30 percent and approximately 50 percent of the length L for providing effective cushioning over an expected range of contact locations while avoiding the use of ineffective quantities of material of the plastic body  14 .  
         [0028]     An optional feature of the composite piling  10  is a reinforcing element that extends proximate an inside surface  24  of the tubular member for resisting inward deformation of the tubular member under high transverse loading such as when the piling  10  is subjected to impact contact by the ship  20 , or in the event that the ship  20  being restrained by the piling is subjected to high winds. In the exemplary configuration of  FIGS. 1 and 2 , the reinforcing element is a reinforcing member  22  in the form of rod of generally uniform cross-section having helically formed loop elements  23  that contact the inside surface  24  of the tubular member  24  along substantially the full length thereof.  
         [0029]     In the exemplary configuration of  FIGS. 1 and 2 , the plastic body  14  substantially fills the space inside the tubular member  12  that is not occupied by the reinforcing member  22 . In applications wherein bending loading is not severe, the reinforcing member  22  can be omitted and the plastic body  14  filling at least a portion of the tubular member functions as the reinforcing element. In applications having severe bending loads, a reinforcing structure (incorporating the reinforcing member  22  or in addition thereto) can be imbedded in the tubular member. (The glass fibers of the exemplary fiberglass tubular member  12 , described above, serve as such a reinforcing structure.) The reinforcing member  22  can be a conventional formed steel reinforcing rod of the type commonly used for reinforcing concrete (available, for example from J.L. Davidson Co. of Rialto, Calif.). Other suitable forms of the reinforcing member  22  include nickel reinforcing rod (available from MMFX Steel Corp. of America, Charlotte, N.C.), fiberglass reinforcing rod (available from Hughes Brothers fiberglass of Seaward, Nebr., and carbon fiber reinforcing rod (available from Aero Space Composite Products of San Leandro, Calif.).  
         [0030]     In a preferred configuration wherein the outside diameter D of the tubular member  12  is on the order of 8 or 10 inches, the thickness T being between approximately 0.12 inches and approximately 0.25 inches, a suitable diameter of the reinforcing member  22  is nominally ⅜ inch in diameter. A suitable spacing or pitch P of the loop elements  19  is approximately 5 inches, or about half of the outside diameter D. More generally, the diameter of the reinforcing member  22  can be from approximately 0.25 inch to approximately 0.75 inch.  
         [0031]     In a variety of applications, it is contemplated that the outside diameter D of the tubular member  12  can be from approximately 8 inches to approximately 36 inches. The radial thickness W of the plastic body  14  can range from approximately 0.25 inch to approximately 24 inches. Practical combinations of these dimensions include the wall thickness T of the tubular member being from approximately 1.5% to approximately 10% of D, the radial thickness W of the plastic body  14  being from approximately 3% to approximately 100% of the diameter D of the tubular member  12 .  
         [0032]     With further reference to  FIG. 3 , an alternative configuration of the composite piling, designated  10 ′, incorporates a shear member  30  that preferably fills the space within the tubular member  12  that is not occupied by the reinforcing member  22 . A suitable and preferred material for the shear member  30  is concrete. It will be  
         [0033]     An important feature of the present invention is a formulation of polymeric material that is suitable for encapsulating the tubular member  12  and that does not form voids and cracks due to tensile thermal strains being generated during solidification. This problem is exacerbated by the absence of a tubular mandrel that can receive cooling water as disclosed in the camel structure of the above-referenced &#39;711 patent. As described in the above referenced U.S. Pat. No. 6,244,014 which is incorporated herein, it has been discovered that a particularly suitable composition for forming the plastic body  14  as an uninterrupted covering that also fills the tubular member  12  is a main first quantity of low density polyethylene of which at least 60 percent and preferably 65 percent is linear low-density polyethylene (LLDPE), the balance being regular low-density polyethylene (LDPE), and a process additive second quantity which may include a foaming or blowing agent, a coupling agent, a fungicide, an emulsifier, and a UV inhibitor such as carbon black, the composition not having any significant volume of filler material such as calcium carbonate. Preferably, the first quantity is at least 90 percent of the total volume of the plastic body  14 , approximately 5 percent of the total volume being a mixture of coloring, foaming agent, and UV inhibitor. Preferably the composition is substantially free (not more than 5 percent) of high density polyethylene.  
         [0034]     Thus the composition of the cushion member  14  has polymeric elements being preferably exclusively polyethylene as described above (substantially all being of low-density and mainly linear low-density), together with process additives. As used herein, the term “process additive” means a substance for enhancing the properties of the polymeric elements, and does not include filler material such as calcium carbonate.  
         [0035]     With further reference to  FIG. 4 , a mold apparatus  40  for encapsulating the cage  12  to form the plastic body  14  of the piling  10  includes a mold assembly  42 , a mold cradle  44 , and a conventional extruder press having an outlet  46 . The mold assembly  42  includes a flanged tubular mold segment  48 , an inlet plate  50  having an injection point  52  for connection to an outlet of the extruder press, and a back plate  54  through which the tubular member  12  projects, the back plate  54  having an exhaust vent  55 .  
         [0036]     As further shown in  FIG. 4 , the mold segment  48  has an inside diameter D′ and a length L′, being a weldment of a mold tube  78  and a pair of perforate flanges  80 . The diameter D′ and the length L′ of the mold segment  48  correspond to the body diameter B and length C, but with allowance for shrinkage of the material of the plastic body  14 . For example, with the inside diameter D′ being 13.25 inches, the body diameter B subsequent to cooling of the plastic body  14  is approximately 13.0 inches. Respective pluralities of flange fasteners  84  provide removable connections between the flanges  80  and the corresponding inlet and back plates  50  and  54 . Suitable materials for the mold tube  78  and the flanges  80  include mild steel of 0.25 inch and 1 inch thickness, respectively. It will be understood that additional counterparts of the mold segment  48  can be connected end-to-end with the segment  48  for selectively varying the length C of the body member  14 .  
         [0037]     Also shown in  FIG. 5  is the tubular member  12  centered within a main cavity  60  of the mold assembly  42 , being supported relative to the back plate  54  and a rear element  62  of the mold cradle  44  that also supports the mold assembly  42 . The back plate  54  is provided with a plurality of flanged inserts  56  that are fastened thereto by fasteners  58  for facilitating insertion of the tubular member  12  as well as for providing an effective seal between the back plate  54  and the tubular member. The rear element  62  has a cavity  64  formed therein for locating the projecting extremity of the tubular member  12 , the cavity  64  closely fitting the outside of the tubular member to provide a seal for the material of the body member  14  being molded therein, and having a counterpart of the exhaust vent, designated  55 ′. The mold cradle  44  also includes a medial element  66  and a front element  68  on which rests the mold tube  78 , the medial element also engaging the perforate flange  80  to which the back plate  54  is fastened for limiting the projection of the tubular member from the mold assembly  42 . Further, the rear element  62  is stepped as indicated at  70  for facilitating location of the tubular member  12  first by lowering the member and then by axially displacing the member outwardly from the mold assembly  42 . Alternatively, the rear element  62  can be assembled from a cradle portion and a cavity portion, the cavity portion being attached subsequent to positioning of the mold assembly  42  and the tubular member, and this form of the rear element  62  can be made a part of the mold assembly  42 . Additionally or alternatively to the centering by the rear element  62 , the tubular member can be centered within the mold assembly  42  by means described in the above-referenced U.S. Pat. No. 6,244,014, provided that a suitable means for keeping the tubular member axially located is included.  
         [0038]     The mold assembly  42  and the mold cradle  44  can also be used in formation of the composite piling  10 ′ of  FIG. 3 , the shear member  30  having been formed by conventional means prior to molding the plastic body  14 . In this embodiment, there is no need for sealing engagement at the projecting extremity of the tubular member  12  or for the exhaust vent  55 ′.  
         [0039]     With further reference to  FIG. 5 , a molding process  100  for forming the composite structure or piling  10  includes inserting the reinforcing member  22  into the tubular member  12  in a load reinforcing step  102 , a form shear member step  103  (when the process  100  is for forming the piling  10 ′), a load mold step  104  wherein the tubular member  12  is placed within the mold assembly  42  with one end thereof projecting from the back plate  54 , a cradle step  106  wherein the tubular member  12  is coaxially centered within the mold tube  78  by being supported, for example, by the rear element  62  of the mold cradle in combination with the back plate  54 , the tubular member also projecting a predetermined distance from the back plate  54  corresponding to the extension distance E being that desired. The mold assembly  42  is closed, for example, by installing the inlet and/or back plates  50  and  54 , in a close mold step  108  and, optionally in an incline mold step  110 , the mold assembly  42  is propped up on a suitable support for elevating the exhaust vents  55  and  55 ′. It will be understood that the back plate can be attached to the medial element  66  prior to connecting the mold tube  78 . Also, the mold cradle  44  can be constructed so as to support the mold assembly  42  in an inclined condition initially. Further, it may be desirable to bond or otherwise fixably locate the reinforcing member to the inside surface  24  of the tubular member  12  for increased bending strength of the composite piling  10 .  
         [0040]     Next, the material of the plastic body  14  is fed into the main cavity  60  in an inject body step  112 . Then in a cooling step  114 , the mold assembly  42  with its contents is submerged in cooling water for solidifying the material of the plastic body  14 , after which the assembly  42  is removed from the water (step  116 ), opened and the completed piling  10  is withdrawn in a remove structure step  118 .  
         [0041]     If desired or needed, the tubular member  12  and/or the mold assembly  42  can be preheated to be certain that the plastic material of the cushion member  14  flows to the cover plate  54  of the mold assembly  42  and completely fills the main cavity  60  as well as the tubular member  12 .  
         [0042]     The piling  10  of the present invention is immune to marine borer attack, and thus requires no further protection, such as creosote or plastic sheathing, being practically maintenance free. The piling  10  is abrasion resistant, and thus has excellent effectiveness as a marine fender piling without any added protective covering.  
         [0043]     The composite piling  10  is chemically inert, so it can last indefinitely. It does not react with sea water, is corrosion free, is substantially immune to the effects of light, is not bothered by most petroleum products, and is not subject to dry rot. Because it can be made with recycled plastic, it is an environmentally sound investment.  
         [0044]     In some military based naval applications, it is undesirable for a piling to be electro-magnetically sensitive. In such applications the reinforcing member  22  can be formed with non-magnetic materials, such as carbon-reinforced plastic.  
         [0045]     Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. For example, the tubular member  12  can be flush with one end of the plastic body  14 , or the tubular member project from both ends of the plastic body. In the first case, the inlet plate  50  would be formed for feeding the material for the plastic body  14  of the piling  10  of  FIGS. 1 and 2  both outside and inside of the tubular member  12 . In the second case, separate paths for the material for the plastic body  14  would be provided, either in a single operation or separate molding operations. Similarly for the piling  10 ′ of  FIG. 3 , the inlet plate  50  would be formed for feeding material outside of the tubular member only, such as by incorporating a pair of injection points  52  on opposite sides of counterparts of the flanged inserts  56 . Therefore, the spirit and scope of the appended claims should not necessarily be limited to the description of the preferred versions contained herein.