WO2007137152A2

WO2007137152A2 - Composite structure

Info

Publication number: WO2007137152A2
Application number: PCT/US2007/069223
Authority: WO
Inventors: Robert Greene
Original assignee: Lancaster Composite, Inc.
Priority date: 2006-05-19
Filing date: 2007-05-18
Publication date: 2007-11-29
Also published as: WO2007137152A3

Abstract

A composite structure having a fiber reinforced resinous structure, a core within a hollow portion of the fiber reinforced resinous structure, a tendon under stress and disposed in the core, the tendon exerting stress on the core, and a driving tip attached to the fiber reinforced resinous structure is disclosed. A composite structure having a fiber reinforced resinous structure and a core within a hollow portion of the fiber reinforced resinous structure wherein the fiber reinforced resinous structure is configured to emulate the appearance of a palm tree is also disclosed.

Description

COMPOSITE STRUCTURE

FIELD OF THE INVENTION

[0001] The invention relates to a composite structure and more particularly to a composite pile.

BACKGROUND

[0002] While many designs of composite piles are known, there still remains room for improvement in both the functional and aesthetic aspects of composite piles.

SUMMARY

[0003] In one embodiment, the present invention relates to a composite structure having a fiber reinforced resinous structure, a core within a hollow portion of the fiber reinforced resinous structure, a tendon under stress and disposed in the core, the tendon exerting stress on the core, and a driving tip attached to the fiber reinforced resinous structure. In another embodiment, the present invention relates to a composite structure having a fiber reinforced resinous structure and a core within a hollow portion of the fiber reinforced resinous structure wherein the fiber reinforced resinous structure is configured to emulate the appearance of a palm tree.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Exemplary embodiments of the present invention are explained below with reference to the drawings, in which:

[0005] FIG. 1 is an end view across the axis of an embodiment of the invention;

[0006] FIG. 2 is an end view across the axis of another embodiment of the invention;

[0007] FIG. 3 is an end view across the axis of yet another embodiment of the invention;

[0008] FIG. 4a is a partial end view of concave ridges formed in a pole of the invention;

[0009] FIG. 4b is a partial end view of convex ridges formed in a pole of the invention;

[0010] FIG. 5a is a front view of a lower portion of another embodiment of the invention showing an abrasive adhesive coating thereon.; [0011] FIG. 5b is a front view of a lower portion of another embodiment of the invention, showing fiber ravings wrapped so as to extend from an outer surface thereof;

[0012] FIG. 6 is an end view across the axis of another embodiment of the pipe of the invention which incorporates tendons under stress;

[0013] FIG. 7 is a front view of the invention of FIG. 6 showing circumferentially wrapped fibers of the pipe;

[0014] FIG. 8 is an orthogonal view of another embodiment of a composite structure according to the present invention;

[0015] FIG. 9 is a cross-sectional view of the composite structure of FIG. 8 taken at cutting plane A-A of FIG. 8;

[0016] FIG. 10 is a cross-sectional view of the composite structure of FIG. 8 taken at cutting plane B-B of FIG. 8;

[0017] FIG. 11 is a cross-section view of the composite structure of FIG. 8;

[0018] FIG. 12 is a partial cut-away view of the composite structure of FIG. 8; and

[0019] FIG. 13 is a partial orthogonal view of a composite structure according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

[0020] FIG. 1 shows an end view across the axis of a pole 10 of an embodiment of the invention. The invention may be formed of four distinct materials, one of which, the core 12, takes on a particular significance because of the manner in which it is formed. Core 12 is encased within pipe 14 which is covered by veil 16, on top of which is placed protective surface coating 18. Each of the four parts of composite pole structure 10 adds a particular characteristic to the pole structure, and together they furnish a pole of superior strength and durability which can be produced economically. In the broadest aspect of the invention, the veil 16 and coating 18 need not be provided.

[0021] The construction of a composite structure such as a pole 10 is essentially based upon the filling of pipe with a core 12, but core 12 has unique properties which produce a non-metallic pole with strength equivalent to that of steel poles. Core 12 is a Portland cement based product with admixtures which enables the mixture to expand as it hardens, or at least limit shrinkage of the mixture as it hardens. [0022] An improvement of the core materials over previous composite poles and pilings is the inclusion of additional admixtures to the Portland based concrete core. These admixtures are relatively new to the concrete industry. They are known as corrosion inhibitors.

[0023] They may be used in the invention in its best and most durable form but they are not essential in the fabrication of the invention.

[0024] In some applications, the pole according to the invention will utilize steel inserts to connect the top of the vertical pole to a horizontal deck and the bottom of the pole to a hard rock base. Where steel is added to the pole and where the pole is being installed it a salt laden corrosive environment the concrete core material might use the corrosion inhibitor admixture to help protect the steel connections. [0025] Another improvement of the new pole core material is the inclusion of fly ash, silica fume and other small particulate to the concrete mix designed to make the finished concrete core material much denser and accordingly more impervious to the migration of chlorides, sulfates and other soil and water corrosive agents. [0026] The use of corrosion inhibitor admixtures and silica fume and other densifϊers are very helpful in insuring the integrity of steel reinforcement inserts within the pole. The use of inhibitors and densifϊers in the invention are also advantageous to the core material even where there are no steel inserts but not as useful as when steel is included.

[0027] Though the above improvements are good for the durability of the new pole structure they are not absolutely critical.

[0028] In one embodiment of the invention, it is important that the core material normally expand in order that it have a permanent positive stress and produce a force fit with exterior pipe 14. It is also vital that the hardened core 12 have significant strength, which is best indicated by a compressive strength rating of about 1500 psi or more, so that it adds significant strength to the structure and does not act to merely fill the interior space of the pipe. The load/force developed as the core hardens must, however, be less than the structural strength of pipe in order to prevent the forces produced by the attempted expansion during hardening of core from distorting and/or substantially weakening pipe as it restrains the expansion of core.

In an embodiment, cylindrical pipe has a two inch outer diameter with 0.030 inch wall thickness up to a ninety-six inch diameter with at least 0.500 inch wall thickness. The pipe is constructed with a standard polyester, epoxy or vinyl ester resin base, reinforced with fibrous roving, chop, or woven mat throughout its entire thickness. In this embodiment, the material that forms the pipe 14 has a tensile strength of about 30,000 psi. Of course, in other embodiments of the present invention, the tensile strength of the material that forms the fiber reinforced pipe may be substantially less than or greater than 30,000 psi. Added bending strength can be attained if the significant portion of the fibrous roving are oriented to be at an angle of at least 45 degrees to the axis of the pole or oriented generally along the axis of the pole. The fibrous rovings in the illustrated embodiment is fiberglass. It can be appreciated that other fibrous rovings such as carbon, etc. may be used. [0029] As with all fiberglass and resin structures, color pigments may be added during manufacture of pipe to produce consistent color throughout the entire pipe.

[0030] It is also advantageous to produce veil 16 on the exterior surface of pipe when it is being manufactured. Veil 16 is a layer of polyester or other material cloth impregnated with resin. The production of such a veil 16 is well understood by those skilled in the art of fiberglass construction. Veil 16 protects the fiberglass against ultraviolet radiation, provides a moisture barrier, protects against blooming of the surface fibers of the fiberglass and also adds strength to pole. [0031] Another improvement over the existing pole design is the aesthetic improvement of the outside surface of the pole that is developed by use of thick textured veils. This is a welcome improvement as architectural designers desire more "natural" looking piling.

[0032] The pipe component parts of the poles are made with different production equipment and methods. The different manufacture methods provide for different texture finishes. By adjusting the various manufacture techniques and by making various adaptations to the manufacturing equipment one can create textured finishes that resemble the bark finish of wooden tree pilings. By adjusting and adapting the production equipment and including special heavy, textured and thick veils natural tree trunk appearances can be achieved.

[0033] For example, palm tree trunks are used throughout the world as marine piling to support buildings, roads, piers, docks and walkways. As the palm tree grows the large leafs of the tree die off and form a Crosshatch bark pattern. This pattern can be emulated by applying broad widths of rough textured veils at various and repeating angles about the axis of the pole utilizing the filament winding manufacture method for the fabrication of the FRP pipe portion of the pole (discussed infra and with reference to FIG. 13).

[0034] Another improvement that is added to the palm tree texturing technique is that the various angles of the roving and veil lay-up pattern is that the pattern can appear to be random as is the true palm tree growth pattern. The angled overlap pattern can be repeated with the exact repeated angle but the production machinery can be programmed to carry 4-5 slightly different angles where some repeat each rotation of the mandrel but where other angles repeat only every fifth revolution for example. The machines can be set up to repeat what appears to be a random Crosshatch pattern like a real palm tree.

[0035] By applying heavy veils in this fashion there is another benefit and improvement in the pole design. The Crosshatch "v" pattern wicks the water off of the pole surface and causes the water to rest in the "v". This allows for small pockets of water to form the gather dust and dirt particulate. The particulate mixed with more water forms a friendly environment for the growth of small marine life. This promotion of natural growth further enhances the aesthetic appeal for the architectural designer who is trying to create a warm natural environment but can't sacrifice the need for a durable piling product. Even though the promotion of marine life growth on the piling as mentioned above is to some extent a corrosive agent itself it is no match for the highly corrosion resistant qualities found in the extra heavy thick veil wrap. The various acids that are produced by the excrement of the marine life is easily shielded by the FRP veil system. The corrosive biological agents that are easily resisted by the FRP veil system are highly corrosive and destructive for steel, steel reinforced concrete and wood piles

[0036] Another improvement and benefit of the new pole design is that the extra thick veil materials described above are saturated in resin and adds significantly more protection from all of the corrosive agents that are found in aggressive salt laden marine environments. Normal veils are about 30 mils in thickness where the new thick veils are more than 30 mils and can be as much as .25 inches thick. Veils that are this thick are unprecedented in FRP pipe fabrication. Their inclusion is a significant corrosion resistance benefit.

[0037] Another benefit of the thick veils improvement is that it can also be pigmented for color that will be fast over time. [0038] The core is composed primarily of a mixture of stone, sand, water, and

Portland-type cement. In one embodiment of the invention, the specific material used is Type I Portland-type cement as manufactured by the Lehigh Cement Co. The stone component could be solid limestone, as commonly found at many local quarries, or lightweight type aggregate as produced, for example, by Solite Corp. The sand component is clean washed and specifically graded round silica material as is available from many local sand quarries. Normal potable water is used and other cementitious products may be employed to promote expansion or at least limit shrinkage of the core upon hardening. For example, expansion additives such as INTRAPLAST N manufactured by Sika (plastic state expansion), or CONEX, as manufactured by IM Cement Co. (early hardened state expansion) may be used in the core. Alternatively, a standard expansion agent such as alumina hydrate may be employed in the core, or the core may comprise Type K cement. [0039] When hardened, this formula yields a compressive strength of about

1500-15,000 psi. Of course, in other embodiments, the formula may yield a compressive strength of significantly less than 1500 psi or significantly more than 15,000 psi. Moreover, one particular formula normally expands about 0.1-10 percent upon hardening, except that it is restrained by the hollow tube 14 and therefore provides an exceptionally strong force fit with hollow tube or pipe 14. The density of such a core is about 35 pounds per cubic foot or more. Of course, the density of the core in alternative embodiments may be significantly less than 35 pounds per cubic foot. Instead of expanding, the mixture may be formulated such that shrinkage is limited or made to be generally negligible, unlike shrinkage which may occur.

Protective coating 18 may also be added to pole 10, for the purpose of enhancing ultraviolet protection and corrosion resistance and to produce a smooth surface. The coating 18 is applied during the manufacture of the pipe and is at least 0.001 inch thick. Protective coating 18 is clear, can be made with or without pigments, and includes specific ultraviolet absorbers and/or shields. An example of such a coating could be "Amerishield" as manufactured by Ameron Corp. or "Tufcote" as manufactured by DuPont or a variety of gel-coat products.

The composite pole of the present invention can furnish bending strength equal to or greater than Schedule 40 steel pipe (ASTM F- 1083) of the same diameter, and its inherent corrosion resistance is far superior to that of steel. Moreover, the present invention actually furnishes a pole which will flex more than twice as far as steel and return to its original shape without failure. [0040] FIG. 2 shows another embodiment of a composite pole structure 100 of the invention. As shown, the inner surface 110 of the pipe 140 is roughened to form a regular or irregular pattern therein. In the illustrated embodiment, the inner surface 100 includes an irregular pattern defining a plurality of recesses 112 which increases the surface area contact between the core 120 and the pipe 140 when the core 120 hardens within in the pipe 140. Thus, a portion of the core 120 is disposed in the recesses 112 defining a mechanical lock between the core 120 and the pipe 140. The core 120, pipe 140, veil 160 and coating 180 are otherwise identical to the embodiment of FIG. 1. Alternatively, as shown in FIGS. 4a and 4b, instead of the recesses, ridges 112' or 112 can be molded or otherwise formed into the inner surface 110 of the pipe 140'. The ridges may be concave 112' (FIG. 4a) or convex 112' FIG. 4b) and may be in a regular or an irregular pattern. It can be appreciated, however, that the core 120 need not be of the type which expands its volume when it hardens to provide a force fit with the pipe 140, since the mechanical lock provides the desired locking of the core 120 to the pipe 140. Thus, a conventional type cement material may be employed as the core material in this embodiment of the invention. It can also be appreciated that the core material may be of the type discussed above, in which shrinkage is limited during hardening thereof

FIG. 3 shows yet another embodiment of a composite pole structure 200 of the invention. As shown, an adhesive 250 is coated on the inner surface 212 of the tube 240 such that when the core 220 hardens it is chemically locked with respect to the pipe via the adhesive 250. The adhesive 250 is preferably SIKADUR 32 .RTM. manufacture by Sika. However, any type of adhesive suitable for securing the resin pipe 240 to the hardened core may be employed. The core 220, pipe 240, veil 260 and coating 180 are identical to the embodiment of FIG. 1. It can be appreciated, however, that the core 220 need not be of the type which expands its volume when it hardens to provide a force fit with the pipe 240, since the chemical lock provides the desired locking of the core 220 to the pipe 240. Thus, a conventional type of cement material may be used as the core material in this embodiment of the invention. It can also be appreciated that the core may be of the type discussed above, in which shrinkage is limited during hardening thereof

Tests were performed to determine the push-out strength or frictional resistance of the core material to the inner wall of the composite pole structure. The total load in pounds required to dislodge the core from the hollow tube was measured and divided over the unit area and represented in units of psi. The average frictional resistance of the core made in accordance with the embodiment of FIG. 1, (no mechanical or chemical locking of the core) was measured to be on average 25 psi over the entire inner wall surface of the pipe. With the addition of an adhesive 250 bonding the core 220 to the pipe 240 (FIG. 3) the average frictional resistance of the core was determined to be approximately 90 psi. Thus, there is a corresponding minimum increase in bending strength of approximately 30% as a result of a better bond between the core and the pipe which provides for a better transfer of shear between the structural component parts. With both expansion of the core 220 and the use of the adhesive 250 (FIG. 3), failure of the composite structure is often in the cohesive strength of the core 220 itself. Namely, the cohesive strength of the bond between the core and pipe can be stronger than the cohesive strength of the core 220.

Additives 20 may be included in the core of the invention to improve the composite pole structure. For example, silica fume, an extremely fine aggregate that fills tiny voids in the core may be added to the core to improve the compressive thus, making he composite pole structure even stronger. Steel, glass or polymer fibers additives mixed into the core could also be employed. The fibers deter cracking which cause premature failures, provide higher stiffness, provide higher compressive strength and provide higher bending strength, all of which enhance the performance of the composite pole structure.

FIGS. 5a and 5b show other embodiments of the invention, each having a roughened portion on at least a portion of an outside surface of at least one of the ends of the filled structure. It can be appreciated that the poles or filled structures of FIGS. 5a and 5b may be configured as disclosed in any of the embodiments of FIGS. l-4b, but also include a roughened portion on an outside surface thereof, as explained below.

As shown in FIG. 5a, the fiber reinforced pipe 140 of pole 300 has an outer surface 310. In the illustrated embodiment, the outside surface 310 includes an abrasive adhesive 320 coated on at least one end of the pole 300. The abrasive adhesive 320 includes an abrasive such as a grit material, e.g., sand, in an epoxy, and defines a roughened portion on the outside surface 310. When the pole 300 is driven into the ground, the roughened portion creates skin friction with the ground which increases the bearing load capabilities of the pole 300 as compared to that of a smooth pole. Thus, the pole 300 may be relatively shorter than traditional material pole (smooth steel and/or concrete poles) since it does not have to be driven as deep as the traditional poles to achieve the same load bearing. The abrasive adhesive defining the roughened surface works well in mounting the pole 300 in sandy ground, particularly when the size of the grits of the abrasive closely match the size of the grits of sand in the ground.

FIG. 5b shows a pole 400 having a plurality of fiber rovings 412 wrapped about a lower portion of the fiber reinforced pipe 140 so as to extend from outside surface 410 thereof. Each of the fiber rovings 412 may be a singular fiber roving strand or may comprise a group of smaller roving strands. Thus, during manufacture of the fiber reinforced pipe 140, the fiber rovings 412 may be wrapped to extend from the outside surface 410 and cured to be integral with the pipe 140. In the illustrated embodiment, the fiber rovings 412 are disposed in spaced relation thereby defining a roughened portion on the outside surface 310. The fiber rovings 412 may be evenly or unevenly spaced. Further, the fiber rovings 412 are arranged so as to be generally perpendicular to the longitudinal axis 420 of the pole 400 so as to create more driving friction than would be created if the rovings 412 were more vertically oriented with respect to the longitudinal axis 420. The fiber rovings 412 create increased skin friction when driven into the ground, resulting in the advantages noted above, with reference to the embodiment of FIG. 5a. The fiber rovings 412 have been found to provide a pole having good load bearing capabilities in muddy soil or clay.

In the illustrated embodiments, only a portion of poles 300 and 400 near an end thereof is roughened since one end portion is typically driven into the ground when the pole is used as a piling. In piling applications under water, the portion of the pole exposed to water is preferably smooth to prevent biological attack from mollusks, barnacles and the like, which have a more difficult time attaching to a smooth surface.

Although two examples of surface roughening have been described above, it can be appreciated that the pole of the invention may be roughened any amount to produce increased skin friction with the ground.

It is to be understood that the form of this invention as shown is merely an embodiment. Various changes may be made in the function and arrangement of parts; equivalent means may be substituted for those illustrated and described; and certain features may be used independently from others without departing from the spirit and scope of the invention as defined in the following claims.

For instance, structures may be produced without either veil 14 or protective coating 16 when the application does not require ultraviolet protection. Moreover, the diameter and cross sectional configuration of the external member may, of course vary, and the particular formula of the core could be changed as long as the requirements of the claims are retained. Further, although a generally round cross-sectioned pipe is disclosed, the composite structure may be in any shape or closed section, such as, for example a square, rectangular, oval etc, cross-section. [0041] With reference to FIG. 6, another embodiment of a composite structure of the invention is shown, generally indicated at 500. The structure 500 is similar to that of FIG. 1 and includes a core 512 encased within pipe 514 which is covered by a veil 516, on top of which is a protective surface coating 518. In the broadest aspect of the invention, the veil 16 and coating 18 need not be provided. [0042] The pipe 514 is constructed with a standard polyester, epoxy or vinyl ester resin base, reinforced with fibrous roving, chop, or woven mat throughout its entire thickness. In this embodiment, the material that forms the pipe 514 has a tensile strength of about 30,000 psi. Of course, in other embodiments of the present invention, the tensile strength of the material that forms the fiber reinforced pipe may be substantially less than or greater than 30,000 psi. In the embodiment illustrated in FIG. 7, the fibrous roving includes circumferential fiber wraps 522 such as fiberglass, carbon, aramid, kelvar, graphite or other strong, fibrous material. The fiber wraps 522 are provided in multiple layers of the pipe 514 and may overlap with fiber wraps of other layers. In the illustrated embodiment, the fiber wraps 522 are oriented at an angle of about five degrees or more (up to ninety degrees) with respect to base plane A. When driving concrete piles, failure may occur at the top of the pile as it is being driven. The fiber wraps 522 are provided to increase the circumferential or hoop strength of the structure 500 so as to reduce failure at the driven end and/or the tip end when the structure 500 is used as a pile.

[0043] The core 512 is of the cementitous type discussed above with regard to

FIG. 1. More particularly, in the preferred embodiment of FIG. 6, the core 512 is of the type which expands or limits shrinkage thereof as it hardens so as to securely engage the inner wall of the pipe 514 for improved bending properties. However, if the structure 500 is to be used when bending is not a major concern, the core 512 need not have expansion properties and need not engage the inner wall of the pipe 514. [0044] In accordance with the invention and as shown in FIG. 6, at least one pre-stressed and/or post-tensioned tendon 524 is provided in the core 512 and extends along a longitudinal axis B of the structure 500. The term pre-stress or post-tensioned used herein means that the tendons 524 are under stress. In the illustrated embodiment, a plurality of tendons 524 are provided and extend substantially the entire length of the structure 500. The tendons 524 may extend only partially the length of the structure 500. The tendons 524 can be of steel or fiber reinforced plastic (FRP) material. In the preferred embodiment, the tendons 524 are pre-stressed in a conventional manner and the cementitious material of the core 512 is poured into the pipe 514 and permitted to harden about the tendons 524 such that the tendons 524 apply stress in the longitudinal direction on the core 524. Steels can be in the form of standard cable or solid bar stock. The steel cable tendon 524 has up to 250 ksi-rating with the solid bar tendon being rated as low as 80 ksi and as high as 150 ksi. The FRP material such as glass, aramid, kelvar, carbon, graphite, etc., can be rated as low as 50 ksi and as high as 400 ksi.

[0045] The tendons 524 may be highly tensioned or moderately tensioned.

The higher the tension, the more stress is induced onto the core 512 and thus the structure 500. The more stress on the core 512, the more dense the core becomes which essentially increases the physical properties of the structure 500 and hence increases the stiffness of the structure 500. It is noted that normal "rebar" reinforcement of concrete piles does not induce a stress on the concrete as does the pre-stressed or post-tensioned tendons 524.

[0046] Steel tendons 524 under stress greatly add stiffness and tensile strength to the structure 500 as well as increasing the overall bending strength of the structure 500.

[0047] It is known that concrete cracks as a result of excessive bending load.

The cracking cannot be avoided with the given normal tensile strength of a particular concrete mix. In many instances, the additional tensile strength induced by the pre- stressed, or post-tensioned tendons 524 is enough to avoid cracking of the cementitious core 512 and the overall negative effects on performance of the structure 500. For example, during handling (loading and unloading) of piles, fewer pick-up points are needed and there is less worry of cracking with piles having stressed tendons. Furthermore, more tensile stress can be tolerated in pile driving abuse if the pile is under stress.

[0048] As with the other disclosed embodiments, additives 520 may be included in the core 512 of the invention to improve the composite pole structure. For example, silica fume, an extremely fine aggregate that fills tiny voids in the core may be added to the core to improve the compressive thus, making he composite pole structure even stronger. Steel, glass or polymer fibers additives mixed into the core could also be employed. The fibers deter cracking which cause premature failures, provide higher stiffness, provide higher compressive strength and provide higher bending strength, all of which enhance the performance of the composite pole structure.

Referring to FIGS. 8-12, another embodiment of a composite structure according to the present invention is shown. FIG. 8 shows a composite pile 700 comprising a central portion 702, a pile cap 704 at a top of the pile 700 above the central portion 702, and a driving tip 706 at a bottom of the pile 700 below the central portion 702.

[0049] The central portion 702 comprises an outer pipe 708 substantially similar in construction to pipe 514. More specifically, the pipe 708 is constructed with a standard polyester, epoxy or vinyl ester resin base, reinforced with fibrous roving, chop, or woven mat throughout its entire thickness. However, it will be appreciated that other embodiments of the present invention may include a pipe 708 formed of a different material and through a different process. In this embodiment, the pipe 708 is approximately 11 meters in length. Further, while not shown, pipe 708 may alternatively be produced with a veil substantially similar to veil 14, may be produced with a protective coating substantially similar to protective coating 16, or may even be provided with a texture which emulates the texture of a palm tree (as discussed previously and infra). Most generally, central portion 702 is constructed by providing pipe 708 and filling pipe 708 with a cementious core 709 substantially similar to cementious core 512. The pipe 708 which serves as a casing around the prestressed central portion 702 provides a tremendous corrosion resistant barrier for keeping outside elements from the core 709 while also providing excellent hoop-strength reinforcement for the containment and/or confinement of the core 709. The hoop- strength reinforcement properties of the pipe 708 aid in preventing diagonal cracking or shear failure of the core 709. The hoop-strength provided by the pipe 708 also reduces or eliminates the need for hoop steel as a source of hoop-strength as used in standard ASSHTO / PCI prestressed concrete pile designs. [0050] Other elements are also provided within the cementious core 709, specifically, as shown in FIG. 9 (a cross-sectional view taken at cutting plane labeled A-A in FIG. 8), tendons 710 substantially similar to tendons 524, ties 712, and prestressed strands 714 are provided in the core 709 along various portions of the longitudinal length of central portion 702 and pile cap 704. In this embodiment, tendons 710 are constructed of threaded bar. More specifically, in this embodiment, tendons 710 are constructed of hot dipped galvanized, Grade 75, #14, DYWIDAG THREADB AR^® of the DYWIDAG Threaded Reinforcing System produced by DYWIDAG Systems International which comply with the ASTM A615 standard. The tendons 710 are optionally selectively post-stressed. Of course, in other embodiments of the present invention the tendons 710 may be constructed differently or provided by a different manufacturer. Use of tendons 710 that are threaded provides the benefit of allowing selective stressing of the tendons 710. For example, where appropriate fasteners 716 are used to interface tendons 710, a hydraulic jack may be used to adjust the fasteners 716 along the longitudinal length of the tendons 710 to increase or decrease the stress imposed on the core 709 by the tendons 710. In this embodiment, the tendons 710 are stressed to approximately 520N/mm². [0051] In this embodiment, the pile cap 704 is a portion of the core 709 extending above the central portion 702 and is not encased within pipe 708. As most clearly shown in FIG. 8, pile cap 704 has a smaller outside diameter than the remainder of the core 709. One advantage of the smaller diameter pile cap 704 is that a shoulder 718 formed at the junction between the central portion 702 and the pile cap 704 provides a surface upon which a load may be caused to bear down onto composite structure 700 from above. Further, the shoulder 718 provides a convenient surface upon which subsequent cementious mixtures may be cast onto and generally around the pile cap 704. A first set 720 of six tendons 710 are disposed substantially in an equally spaced radial array within the core 709 and the array is substantially centered along the longitudinal axis of the pipe 708. The first set 720 of tendons 710 protrude from the top of the pile cap 704 and also extend downward along the longitudinal length of the composite structure 700 until they terminate at a depth of about 3 meters beyond the shoulder 718. The portions of the tendons 710 protruding upward out of the pile cap 704 provide an interface for the above described threaded couplings or fasteners 716 which generally act against the core 709 and allow selective stressing of the tendons 710.

[0052] A second set 722 of tendons 710 are provided at the bottom of the central portion 702. The second set 722 of tendons 710 are embedded from the bottom of the central portion 702 about 2 meters into the core 709. A disk-shaped plate 724 is disposed at the bottom end of the central portion 702 and, in this embodiment, has an outside diameter closely matched to the outside diameter of the pipe 708. The tendons 710 extend from within the core 709 through the plate 724 and extend a sufficient distance beyond the plate 724 to allow fasteners 716 to be applied to the tendons 710 in a manner similar to the fasteners 710 of the first set 720 of tendons 710. Specifically, fasteners 716 are applied to the tendons 710 of the second set 722 so that the fasteners 716 may be caused to selectively increasingly or decreasingly bear against the bottom surface of the plate 724, thereby increasing or decreasing the stress of the tendons 710 of the second set 722. Alignment plates 726 are provided on the top surface of the plate 724 to aid in the alignment between the pipe 708 and plate 724, thereby providing a substantially close fit between the two and resulting in substantially coaxial placement.

[0053] Ties (or stirrups) 712 are substantially ring-shaped and, in this embodiment, are constructed of #3 steel rebar. Along the first set 720 and second set 722 of tendons 710, ties 712 are provided such that the tendons 710 lie generally adjacent to or abut the innermost surface of the ties 712. In this embodiment where the outside diameter of the pipe 708 is approximately 762mm (and the pipe 708 has a wall thickness of about 9mm), the ties are disposed generally coaxial with the longitudinal axis of the pipe 708 and have a diameter of approximately 457mm. Along the first set 720, ties 712 are provided near the top of the composite structure 700 within the core 709 of the pile cap 704 and at approximately 100mm intervals downward along the length of the tendon 710. Along the second set 722, ties 712 are provided near the plate 724 within the core 709 of the central portion 702 and at approximately 100mm intervals upward along the length of the tendon 710. Of course, in other embodiments of the present invention, the ties 712 may be constructed of different materials, be formed in different shapes, and be disposed differently along the tendons 710.

[0054] Prestressed strands 714 are also disposed within the core 709 along the length of the central portion 702. More specifically, twenty- five 13mm prestressed strands 714 are disposed substantially in an equally spaced radial array within the core 709 and the array is substantially centered along the longitudinal axis of the pipe 708. The prestressed strands 714 are generally located substantially equidistant between the ties 712 and the pipe 708 such that they lie lengthwise along the longitudinal length of the composite structure 700, generally parallel to the central axis of the composite structure 700, and between the ties 712 and the pipe 708. Of course, in other embodiments, the prestressed strands 714 may be differently shaped and sized, differently disposed within the core 709 and/or a different number of strands 714 may be provided. Further, in alternative embodiments, the prestressed strands 714 may run substantially beyond the full length of the central portion 702 and into the pile cap 704 or not run the full length of the central portion 702. The prestressed strands 714 add significant longitudinal strength and stiffness to the composite structure, however, in this embodiment, the pipe 708 still contributes between about 50-55% of the overall bending strength or moment capacity of the composite structure and also provides additional stiffness.

[0055] In this embodiment, driving tip 706 connected at a bottom of the composite structure 700 is substantially constructed of an open ended tube 728 having an outer diameter similar to the outer diameter of the pipe 708 and a wall thickness of approximately 13mm. In this embodiment, the driving tip 706 is approximately 3 meters in length and is welded to the plate 724 with a full penetration weld so that the driving tip 706 is substantially coaxial with the pipe 708. In this embodiment, the plate 724 has a thickness of about 38mm. The bottom end of the driving tip 706 located opposite the end connected to the plate 724 is substantially open. In other embodiments, the driving tip 706 may be differently shaped, for example, as an "H" beam, "W" beam, "S" beam, a square tube, or other suitable sectional shape. The joinder between the central portion 702 and the driving tip 706 is a so-called "full- moment" splice insofar as the moment connection between the central portion 702 and the driving tip 706 is as stronger or stronger than the central portion 702. [0056] In another embodiment of a composite structure according the present invention, the composite structure may be constructed substantially similar to the composite structure 700 but with a few differences. A first difference is that a pipe substantially similar to pipe 708 may extend only about 4-12 feet downward from a should substantially similar to the shoulder 718, leaving the remainder of the core of the central portion unsheathed by the shorter pipe. Accordingly, to provide additional hoop-strength, steep hoop reinforcements may be applied along that same remainder of the core of the central portion which is not sheathed by the shorter pipe. In this arrangement, the shorter pipe is located at the top of the central portion for instances where, particularly in on-land applications of the composite structure, the corrosion problems combated by the shorter pipe are only present on the top portion of the composite structure which interacts with the salt water table in the soil close to the surface. Further, the shorter pipe is well suited for accommodating heavy loads due to seismic forces such as those attributable to an earthquake.

[0057] Referring to FIG. 13, a composite pile 1300 formed to appear as a palm tree (as described previously) has broad widths of rough textured veils 1312 on the outside surface 1310 of the pole 1300. The cross-hatch design provides a pocket 1314 (the above described "v"of the pattern) which wicks the water off of the pole surface 1310 and causes the water to rest in the pocket 1314. As explained above, this allows for small pockets of water to form the gather dust and dirt particulate in the pocket 1314 and promote marine life and a more natural appearance.

Claims

WHAT IS CLAIMED IS:

1. A composite structure, comprising: a fiber reinforced resinous structure; a core within a hollow portion of the fiber reinforced resinous structure; a tendon under stress and disposed in the core, the tendon exerting stress on the core; and a driving tip attached to the fiber reinforced resinous structure.

2. The composite structure according to claim 1, wherein the driving tip is attached to the fiber reinforced resinous structure with a full moment splice.

3. The composite structure according to claim 1, the driving tip comprising: a tube.

4. The composite structure according to claim 1, wherein an outside diameter of the driving tip is substantially the same size as an outside diameter of the fiber reinforced resinous structure.

5. The composite structure according to claim 1, wherein the driving tip has an open end opposite an end of the driving tip attached to the fiber reinforced resinous structure.

6. The composite structure according to claim 1, further comprising: a plate secured to the fiber reinforced resinous structure; wherein the driving tip is attached to the plate.

7. The composite structure according to claim 6, wherein the driving tip is attached to the plate with a full penetration weld.

8. The composite structure according to claim 1, wherein an outside of the fiber reinforced resinous structure is configured to emulate the appearance of a palm tree.

9. The composite structure according to claim 8, the fiber reinforced resinous structure comprising: a pocket.

10. The composite structure according to claim 9, wherein the pocket is formed by overlapping veils.

11. The composite structure according to claim 1, further comprising: a prestressed strand disposed within the core.

12. The composite structure according to claim 1, further comprising: a pile cap located at a top end of the composite structure.

13. The composite structure according to claim 11, wherein the pile cap has an outside diameter less than an outside diameter of the fiber reinforced resinous structure.

14. A composite structure, comprising: a fiber reinforced resinous structure; and a core within a hollow portion of the fiber reinforced resinous structure; wherein the fiber reinforced resinous structure is configured to emulate the appearance of a palm tree.

15. The composite structure according to claim 14, further comprising: a selectively stressed tendon disposed within the core for selectively stressing the core.

16. The composite structure according to claim 14, further comprising: a prestressed strand disposed within the core for stressing the core.

17. The composite structure according to claim 14, wherein the fiber reinforced resinous structure comprises a pocket on an outside surface of the fiber reinforced resinous structure.

18. The composite structure according to claim 17, further comprising: a driving tip attached to the fiber reinforced resinous structure.

19. The composite structure according to claim 18, the driving tip comprising: a tube.

20. A filled structure, comprising: a fiber reinforced resinous hollow structure having a tensile strength of at least 30,000 psi, and an inside surface forming a boundary which defines a space; a hard core within said space, the hard core having a density of at least 35 pounds per cubic foot and a compressive strength of at least 1500 psi, the hard core being formed from a mixture of particulate cementitious material and liquid; at least one tendon under stress and disposed in said hard core, said tendon being constructed and arranged to exert stress on said hard core; and a driving tip attached to the fiber reinforced resinous hollow structure.

21. The filled structure according to claim 20, the driving tip comprising: a tube.

22. The filled structure according to claim 20, wherein the fiber reinforced resinous hollow structure is configured to emulate the appearance of a palm tree.