Abstract:
An efficient structural composite suitable for a cantilever applications in nonomnidirectional uses, such as that of highway guardrail posts, assembled from recycled plastic or rubber material as compressive elements with embedded formed sheet steel as tensile elements and shear transfer by encapsulation of said tensile elements in said compressive elements. Structural integrity and/or specific maximum service loads can be achieved through design sizing of shear-transfer elements allowing for intended catastrophic structural failure, which is useful in highway guardrail system design.

Description:
BACKGROUND OF THE INVENTION 
     Foundation posts for highway safety guardrails are typically made of wood or steel, both of which are relatively inexpensive, readily available, and sufficiently strong to support the guardrail. 
     Recycled plastics are currently in wide use as a compressive structural member “spacer-block” component between a guardrail and post. The plastic spacer block is used as a substitute for the traditional wood or steel spacer block in W-beam highway-roadside guardrail systems. While the concept of using plastics as guard rail post components has been disclosed, plastics generally have not been selected for use in guardrail posts due in part to five structural considerations. 
     First, the most widely used highway guardrail system is the “strong-post” design. Strong-post guardrail systems resist impacting vehicles in a rigid-manner providing little deflection of the support posts. The standard guardrail posts presently used are 6″ by 8″ timber or 6″ wide-flange steel beams. Both the wood post and the steel post carry the lateral design loadings with very little deflection vis-á-vis plastic matrix posts of similar dimensions. 
     Second, the most widely used guardrail installation method is the “drop-hammer.” The typical truck-mounted guardrail post-driver is a gravity-dead-weight which is dropped on the top of an individual post driving the post into the soil. The post is driven by successive blows of the drop-hammer to the depth desired. Unlike typical foundation pile driving, the guardrail post must be driven to a specific depth as the W-beam rail must be at a specific height above the road surface. Posts in current use that are formed of wood or steel have significant rigidity under the impact of the drop-hammer allowing for transmission of the vertical applied force through the post to the soil matrix. Due to plastic&#39;s significantly higher elasticity, the use of a drop-hammer is impaired as the vertical applied force is dissipated due to the rubbery nature of plastic. 
     Third, plastics tend to have lower overall tensile and compressive strengths vis-á-vis steel. Plastics when dimensioned to that of wood posts still remain inferior in tensile strength. As such, to meet the strength requirements of the standard “strong-post” guardrail post, the dimensional size exceeds the maximum allowable for the typical installation-equipment of the present art. 
     Fourth, the standard “strong-post” guardrail system requires the use of a “post-bolt” (sometimes known as the “thru-bolt”). The post-bolt is passed through the W-beam rail component, then the spacer-block and finally, through the post. That is, the head of the post-bolt is in contact with the traffic-side of the rail-section and the threaded end of the post-bolt is on the “away-side” of the system&#39;s post. At issue is the incompatibility of a plastic post and the standard steel post-bolt. When the strong-post guardrail is impacted by a crashing vehicle, the W-beam rail and spacer-block and post are usually subjected to torque. The rail, spacer-block, post system resists the applied torque by way of the post-bolt. Due to significant “hardness” differential vis-á-vis a steel post-bolt and a plastic post, the steel post-bolt tends to knife or cut through the plastic post. 
     Fifth, a plastic guardrail post, of dimensional size suitable for use with the state-of-the-art installation-equipment, provides significantly less resistance to torque loads due to impacting crashing vehicles. 
     In one disclosure (U.S. Pat. No. 5,507,473, issued to Hammer et al.), plastic guardrail posts are strengthened by providing a reinforcing member in the plastic extending along a neutral axis of the guardrail post. 
     SUMMARY OF THE INVENTION 
     The present invention relates to and addresses concerns inherent to plastics virgin and/or recycled) and/or rubber (virgin and/or recycled) and its use as a structural post component, particularly for highway safety guardrails. 
     A composite foundation post of this invention includes a reinforcement in or attached to the tensile region of a polymer matrix. Preferably, the post is a highway guardrail post, and the reinforcement includes perforated U-channel sheet steel. 
     In a method of the invention, a drive cap is positioned on the post before the post is driven into a support matrix (e.g., soil). 
     The present invention offers a number of advantages. The use of reinforcement in the tensile region of the post remedies the lack of tensile strength in the polymer matrix. The use of one or more perforated steel U-channel beams in a highway guardrail post of this invention also imparts strength perpendicular to the run-of-rail but allows the post to shear off if a tire, for example, snags on a post, which would otherwise bring the vehicle and its passenger to a catastrophic stop. Posts of this invention also strongly resist torque so as to minimize “pocketing” of the guardrail system when impacted between posts. Further, the polymer matrix can be formed from recycled plastics thereby reducing waste, disposal costs and environmental damage. Moreover, methods of this invention allow the plastic composite post to be driven into the ground without shredding the plastic. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
     FIG. 1 is a view of a foundation post of this invention with a guardrail attached. 
     FIG. 2 is a cross-sectional, downward view of the post and guardrail shown in FIG.  1 . 
     FIG. 3 is a view of the tensile face of a foundation post of this invention. 
     FIG. 4 is a view of the compressive face of a foundation post of this invention. 
     FIG. 5 is a cross-sectional view into the tensile region of a foundation post of his invention with sheet-steel U-channel reinforcements exposed. 
     FIG. 6 is an exposed view of shear studs in a post of this invention. 
     FIG. 7 is an exploded view of a foundation post of this invention including a girdle. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A description of preferred embodiments of the invention follows. 
     A foundation post (or pile; these terms are used interchangeably herein) of this invention is formed of a polymer matrix and a reinforcement material extending through a tensile region (i.e., the region of the post that is in tension when a designed-for lateral load is applied) of the foundation post. The polymer matrix can be plastic (virgin and/or recycled) and/or rubber (virgin and/or recycled). Preferably, the polymer comprises polyethylene from recycled wire housings, as described in U.S. Pat. No. 5,951,712 issued Sep. 14, 1999, which is incorporated herein by reference in its entirety. The reinforcement can be, for example, sheet steel, or fiber (cloth or strands), such as fiberglass or carbon fiber. The sheet steel is preferably in the form of one or more thin, galvanized, perforated U-channel steel sheet(s). In further preferred embodiments, the post is formed by casting the polymer in a mold with the reinforcement positioned in the mold so as to be in the post&#39;s tensile region. Where the foundation post is for a highway guardrail, the post is configured using pre-approved U.S. Transportation Department components and U.S. Federal Highway Administration required crash-tested sub-systems. In particular, the U-channel steel sheets act as break-away devices conforming with regulations set forth in National Cooperative Highway Research Program Report  350 . 
     A preferred embodiment of a foundation post  10  of this invention connected to a guardrail  11  is illustrated from a front view (facing the tensile face of the pile) in FIG.  1 . In addition to carrying design lateral loads, the post  10  should have sufficient hardness at its foot  12  to cut through a soil matrix  14  it is driven into without significant physical deformation. To advance this goal, a post-drive shoe  16  that reinforces and protects the post&#39;s matrix material during handling and driving is provided at the foot  12  of the post  10 . The post-drive shoe  16  can be cast in the mold and/or attached after the post  10  is molded. FIG. 2 provides a cross-sectional view looking down at the same post  10  and guardrail  11  and also illustrating sheet steel reinforcements  18  proximate the tensile face  20  of the post  10  and a post-bolt  22  passing through the post  10  and securing the guardrail  11  to the post  10 . A spacer-block can be provided between the guardrail  11  and post  10 , with the post-bolt  22  likewise passing through the spacer-block. 
     The sheet steel  18  can extend down, then across the post&#39;s foot  12  and may then extend back up a certain length of the compressive face  24  or back of the post  10 . The sheet steel  18  can also extend up, then across the post&#39;s top  26  and/or extend down the compressive face  24  of the post  10 . The sheet steel  18  can also extend down farther to include and reinforce the post-bolt hole. In fact, in the event that the polymer  28  in question lacks sufficient compressive strength, the post  10  is preferably designed with sheet steel  18  extending completely around the post  10 , with or without identical sheet steel thicknesses at various locations. In the event that the polymer  28  in question lacks shear strength, banding can be applied. Actual compositing of the sheet steel  18  to the polymer  28  can be by way of pressure and/or heat forcing the polymer  28  into and/or through the sheet steel  18  perforations, thus assuring good shear transfer. Another means and method is to partly or completely encapsulate the sheet steel  18  by applying a layer of polymer  28  over the exposed side(s) of the sheet steel and apply pressure and/or heat to melt the two plastic surfaces into one through the sheet steel perforations. Similar approaches use fiberglass and/or carbon fiber, either individually and/or combined and/or in concert with sheet steel. 
     Other examples of laterally-loaded foundation piles of this invention include permanent retaining walls, permanent sea walls and temporary trench walls. Each includes the polymer matrix and reinforcement material mounted proximately to the tensile face of the pile, as described above. Further, in each case, the tensile face of the post is the face that is put in tension when an intended lateral load is applied. E.g., where the post is part of a retaining wall, the tensile face is the face that is proximate to the retained mass. 
     Laterally loaded shallow foundation piles, such as permanent retaining walls, permanent sea walls, temporary trench walls and highway guardrail posts tend to be designed as cantilevers. That is, one end of the pile or post is considered “fixed” in a Ad support matrix (e.g., soil) and the other end is “not-fixed”; the “not-fixed” end is allowed to deflect when under design loadings. In the case of a retaining wall, the design load is usually applied over the length of the pile with higher design loadings at the pile&#39;s “fixed” end. The design load usually tapers off as one moves toward the “not-fixed” end of the pile. In the case of a “strong-post” guardrail system, the design load is usually a “point-load” applied via the W-beam rail, through the “spacer-block” to the “not-fixed” end (in normal guardrail applications the “not-fixed” end is the top of the post). 
     In any of these case loadings, or similar loadings, the face of the pile or post facing toward the loadings tend to be in tension when under design loads. The opposite face of the pile or post tends to be in compression when design loads are applied. To maintain structural integrity, the pile or post transfers shear between the opposing faces (tensile/compression) without change in distance between the faces. Use of polymer usually provides significant compressive strength but not tensile strength. The placement of reinforcement, such as sheet steel and/or strands of fiberglass and/or carbon fiber in a tensile region of the post and/or attached to the pile&#39;s or post&#39;s tensile face redresses the lack of tensile strength in the polymer. An important structural issue is establishing a bond between the tensile face and the compressive face via shear transfer from the tensile face material and the polymer matrix of the pile&#39;s or post&#39;s material. Gluing is an option when the polymer is of sufficient shear strength and both the tensile face material and the polymer are compatible for gluing. If the polymer is not of sufficient shear strength and/or if a chemical bond, such as that formed by gluing, is not practical, and/or if there is incompatibility of materials for chemical bonding between the reinforcement and the polymer, the physical shear connection is provided either by extending the reinforcement into the polymer to a depth compatible with shear transfer requirements or by extending the polymer into and/or encapsulating all or part of the reinforcement. Alternatively, the fibers can be applied to a preform tensile face, which is then put in an injection mold where another polymer layer is molded on top of the fibers. 
     FIGS. 3 and 4 respectively illustrate a view of the front, or tensile, lateral-load bearing face  20  of the post  10  and a view of the back, or compressive, face  24  of the post  10 . FIGS. 3 and 4 also illustrate a post crown  30  formed of steel or carbon cloth and including a band wrapping around the top end of the post  10  for reinforcing the post  10  both for pile-driving activities, discussed below, and also for torque resistance to a lateral load (e.g., a vehicle impact). The post crown  30  can also include a top cover. If a standard spacer block is positioned between the post  10  and a guardrail secured to the post  10 , the tensile-face side of the post-crown band can be eliminated to accommodate placement of the spacer block flush with the post  10 ; in which case, the post crown  30  acts to resist rotation of the spacer block during, e.g., a vehicle impact. Further, the post crown  30  can be cast in the mold and/or attached after the post  10  is molded. 
     FIG. 4 also illustrates post-bolt reinforcement strip  32  that may be cast in the mold and/or attached after the post  10  is molded. The strip  32  can wrap completely around the post  10  if a spacer block is not used. If the strip  32  is attached after the post  10  is molded and spacer block is to be used, then the spacer block can be modified to accommodate the reinforcement strip  32 . 
     In FIG. 5, a cross-sectional view of a post  10  of this invention is provided, looking at a pair of perforated sheet-steel, U-channel reinforcements  18  embedded in the tensile region of the post  10 , proximate the tensile face of the post  10 . The reinforcements  18  preferably run the entire length of the post  10 . The perforations  34  in the steel provide for polymer flow process and to provide shear transfer and/or to attach shear studs. The bolt hole  36  can be cast in the polymer or bored out of the polymer after casting. The hole  36  can be made with or without making contact with the reinforcement  18 . 
     Shear studs, in the form of bolts  38  with nuts  40  are passed through the U-channel sheet steel reinforcement  18  in FIG.  6 . The bolts  38  extend through the polymer  28  to resist shear stress in the post  10  and to prevent delamination at the interface of the sheet steel  18  and the polymer  28  when a lateral load is applied. 
     As shown in FIG. 7, which is cut away to show relative placement, a girdle  42  can be provided at ground  14  level to provide additional lateral support for the post  10 . The girdle  42  can be placed inside the mold or attached after the post  10  is formed. Holes  44  are provided in the girdle  42  to provide for polymer flow process and to provide shear transfer and/or to attach shear studs. In alternative embodiments, bonding around other parts or all of the post between the ground and a spacer block to supply additional lateral support. 
     The pile&#39;s or posts lateral resistance should not exceed the soil matrix&#39;s lateral resistance to the design loads in question. That is, failure of the soil matrix to resist the design lateral loadings is usually a result of either inferior soil conditions for the design loads in question, or failure of the pile&#39;s or post&#39;s compressive face to fully develop the strength of the soil matrix due to less than optimal “spade” dimension aspects of the pile or post. Failure of the soil matrix in contact with the pile&#39;s or post&#39;s tensile face should be considered but is usually rare in short piles. 
     In addition to the requirement that the pile&#39;s or post&#39;s foot retain its structural shape during its installation of being driven through the soil matrix in question, the pile&#39;s or post&#39;s top must also retain its structural integrity to as to fully develop the load transfer from the system&#39;s spacer-block. Retaining the structural integrity of the post&#39;s top through the driving operation of placing the post to the appropriate depth into the soil matrix can be achieved by one or both of the following. First, a drive-cap can be temporarily placed of the top of the post, thereby distributing more evenly the vertically applied driving force of the drop-hammer. Second, the top of the post can be specifically reinforced or banded around the top and/or extended down the sides. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.