Abstract:
A plastic standoff block having a substantially H-shape cross-section that is used for mounting a guardrail barrier to a vertical support post. The standoff block has horizontally disposed dual compression-resisting zones comprised of two back-to-back cavitated block modules joined by a common vertically disposed support base. In accordance with one embodiment, the support base extends outwardly from the modules to form a peripheral shoulder for a plurality of elongated horizontally disposed struts that buttress the modules against transverse buckling.

Description:
BACKGROUND 
     1. Field of the Invention 
     This invention relates generally to a plastic block apparatus. More particularly, this invention relates to a plastic standoff block that is used to mount a roadway guardrail to an upright support post. 
     2. Background Art 
     Conventional standoff blocks are typically composed of plastic or rubber materials and have been approved by the Federal Highway Administration (FHWA) of the U.S. Department of Transportation for mounting steel W-beam type guardrails to steel support posts. These guardrails find extensive use as barriers along roadways to prevent vehicles from veering off the roadway area. 
     Trinity Industries, Inc. of Dallas Tex., uses an injection molding process to produce one conventional standoff block. The Trinity block is composed of a mixture of recycled material that consists of approximately sixty-seven percent high density polyethylene (HDPE), approximately thirty percent granulated rubber, approximately two percent black color concentrate and approximately one percent, or less, of a blowing agent. This Trinity block has a cavitated or honeycomb-like interior region formed by injection molding constituent materials. Blocks of such compositions, approved for standoff usage, have external dimensions of approximately four inches in.width; approximately 7.3 inches in depth, or horizontal dimension; and, approximately 14 inches in height, or vertical dimension. The rearward, or post, end of the Trinity block includes a horizontal tab-like protrusion projecting rearward from the top edge to overlie a post top thereby enabling the block to be hung from the post substantially vertically during the installation of the W-beam type rail element. The:forward, or rail, face of the block mounting the rail element has a horizontal frontward projecting tab-like protrusion at its bottom edge that underlies the bottom edge of the rail and thereby temporarily supports the rail on the post for ease of installation with conventional through bolts. 
     Standard guardrail installations, with which the Trinity and other prior art plastic standoff blocks are designed, are required to pass certain high-impact tests approved by the FHWA. The specifics of these tests are available to standoff block manufacturers in published form and FWHA acceptance is based upon the monitored impact resistance of the tested block in a simulated barrier environment. 
     Because standoff blocks are required to sustain high horizontal directed compressed impact forces, they are molded with cavitated interiors that somewhat resemble a corrugated or honeycomb structure. 
     It is known to those working in the art of plastic injection molding that both compressive and torque resistance may be accorded rectangular-shaped injection-molded, structures by designing the structure with a honeycomb interior. This interior design is achieved by open-ended cavities formed by the injection molding process. These cavities, which are elongated in the general horizontal direction of the impact forces, are formed by a plurality of elongated, laterally spaced apart interior web-like walls depending at right angles from a common generally planar support base. One example of this type of cavitated structure is disclosed in U.S. Pat. No. 6,071,044, issued to Thomas E. Ricciardelli et al., and is assigned to the same assignee as the instant invention. U.S. Pat. No. 6,071,044 is hereby incorporated by reference in its entirety herein. 
     Conventional cavitated structures may be molded from virgin or recycled plastic compositions and may be characterized as having an overall U-shaped cross-section; such shape being defined by a pair of laterally spaced apart, parallel exterior side walls and a perpendicular support base or end wall. Thus, the design of conventional cavitated structures is essentially completely U-shaped. 
     The interior cavities of conventional cavitated structures are formed by injecting molten plastic into a series of parallel, elongated, closed-ended mold cores that extend like fingers from the planar core chambers. The plastic core chambers define the web base and extend perpendicular to the finger-like mold cores. The mold core fingers define the web-like cavity walls and extend forwardly from their base the remaining depth or horizontal dimension of the block. Thus, if the block depth is on the order of seven inches, the mold core fingers might have lengths on the order of six inches each. 
     A disadvantage of designing a conventional standoff block with a substantially U-shape and a single cavitated interior is that the substantial horizontal dimension of the block requires that the injection molding apparatus have lengthy mold cores for forming the cavity walls. These lengthy mold cores cause the molten plastic material to cool as it is injected into and fills the cores from the base channel. The extremities of the cores forming the open ends of the cavitated structure receive injected plastic at the lowest temperatures, which may be cool enough to cause solidification of the molten plastic before it completely fills the mold core ends. When such plastic solidification occurs before the core ends are completely filled, the web-like interior walls defined by the core will contract, or shrink, more rapidly causing possible deformation of the end product. Thus, a longer flow path will result in increased shrinkage during solidification of the molten plastic material, which may result in cavity walls and their compressive-resistant characteristics being non-uniform and, in some cases, reduced. Such non-uniformity is undesirable from a strength perspective, and moreover, makes the removal of the cavity walls from the mold more difficult. 
     Therefore, conventional U-shaped cross-section cores, which have relatively long, finger-like sections, cause the compression-resistant characteristics of the structures to be somewhat unpredictable and make the injection-molding process inefficient due to imperfect and/or deformed structures. 
     It would be desirable, and it is an object of the instant invention, to provide a standoff block design that does not suffer the aforementioned disadvantages of conventional standoff block designs. 
     SUMMARY OF THE INVENTION 
     The instant invention is directed to a guardrail block for joining a rail section to a vertically disposed support post. The standoff block is molded from plastic material into a substantially H-shaped cross-section, with a horizontal impact resistant cavitated module formed within each U-shaped half of the substantially H-shaped block. Upon installation, the outer.cavitated end of a first module abuts the rail and the outer cavitated end of a second module abuts the post. The inner ends of the modules join to form a vertical central support structure from which plural horizontal exterior struts extend toward the outer ends of the modules to buttress the block against transverse buckling. The struts may project horizontally beyond the post end of the module to straddle, and thereby position, the block on the post. 
     Accordingly, one embodiment of the instant invention is directed to a standoff block structure for mounting a rail structure of a roadway guardrail to a support post. The block piece mounted there between is composed at least partially of recycled plastic material and including first and second elongated block elements of substantially rectangular cross-sectional shape for providing impact resistance to the guardrail. Each of the block elements has a longitudinal axis, a cored interior formed by longitudinally extending open-ended cavities having open ends thereof at one end of each of the block elements. The open end of the first block element is adapted to abut the rail and the open end of the second block element is adapted to abut the post. The block includes a buttressing structure and a center plate is disposed substantially perpendicularly to the longitudinal axis and interposed between the ends of the block elements opposite the open ends thereof. The center plate joins the opposite ends of the block elements and defines the bottoms of the cavities. At least one bore extends through the block elements and the plate in a direction substantially parallel to the longitudinal axis for receiving a rail mounting fastener. 
     Another embodiment of the instant invention is directed to a plastic standoff block for mounting a guardrail to an upright support post. The block includes a pair of cavitated-open ended modules for resisting impact forces. Each of the modules is enclosed by a pair of spaced apart, substantially parallel sidewalls and a rearward end wall portion joining the sidewalls to provide a structure of substantially H-shaped cross-section. Each of the modules is further enclosed by respective upper and lower parallel edge walls joined to opposite respective ends of the structure. The sidewalls have a central axis extending there between in a vertical direction and the edge walls have a central axis extending there between in a horizontal direction and intersecting the central, vertically disposed axis at a substantially right angle thereto. A plurality of elongated, vertically spaced-apart interior walls extend from the rearward end wall portion substantially the length of the sidewalls to form the cavitated end of each of the modules, and the rearward end portions are joined together to mount the modules in longitudinal alignment with the cavitated ends thereof and are positioned to face the guardrail and post, respectively. 
     Yet another embodiment of the instant invention is.directed to a standoff block.molded from plastic material that includes first and second block elements, each block element having a honeycomb interior formed by plural, laterally spaced elongated interior walls having substantially parallel longitudinal axes. The block also includes a support wall interposed between the interior walls perpendicular to the longitudinal axes and joining the first and second block elements in a fixedly aligned relationship. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 shows an isometric perspective view of a standoff block constructed in accordance with this invention. 
     FIG. 2 shows an end elevation view of the block as viewed from the post module end. 
     FIG. 3 shows a sectional view of the block illustrated in FIG.  2 .taken through lines  3 — 3  thereof and shows one-half of the interior of the cavitated block. 
     FIG. 4 shows a cross-sectional side view of the block illustrated in FIG.  2 . 
     FIG. 5 shows a sectional side view of the block shown in FIG. 2 taken through section line  5 — 5  of FIG.  2 . 
     FIG. 6 shows a sectional side view of the block shown in FIG. 2 taken trough section line  6 — 6  of FIG.  2 . 
     FIG. 7 shows a side elevation view of the block shown in FIG. 1, showing horizontal reinforcing struts on the block exterior. 
     FIG. 8 shows a top view of the block illustrated in FIG. 1, showing the horizontal arrangement and extensions of the reinforcing struts. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will, nevertheless, be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments and further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
     As shown in FIG. 1, the standoff block according to this invention is composed primarily of recycled plastic material, so as to be environmentally friendly. The standoff block  10  has an overall rectangular shape with opposite parallel sidewalls  112  and  114 , each of which has a generally rectangular shape, and opposite parallel.top and bottom walls  116  and  118 , respectively. Frontward or rail surface portion  120  is designed to be positioned against a rearward surface of a section of a standard W-beam guardrail (not shown). Rearward or post surface portion,  122 , is disposed to abut the front surface of a vertical post, not shown. A pair of bolts (not shown) may be inserted in the horizontal direction through the rail section and with both holes provided in the post by way of throughbores  124 ,  126 , which extend horizontally through the block  10 . The diameter of the walls of the throughbores  124 ,  126  are slightly reduced approximately halfway through the horizontal length of the block  10  to slightly grip the bolts inserted into the throughbores  124 ,  126 , thereby facilitating bolt retention in the rail while the block mounting installation is being performed. (Reduced diameter of throughbores  124 ,  126  is shown in FIG. 4.) 
     The pair of flat, parallel exterior sidewalls  112 ,  114 , respectively, is intersected by a centrally disposed planar support base  136 . The base  136  is disposed in a plane perpendicular to a plane extending parallel to the planes of the sidewalls  112 ,  114  and spaced approximately halfway therebetween. (The latter plane containing the horizontal axis  5 — 5  and vertical axis  3 — 3  of the block  10 , which is shown in FIG. 2.) The sidewalls  112  and  114  have a width of approximately 7 inches, which is approximately equal to the spacing between the rail and the post. 
     The support base  136  divides the sidewall  112  into two equal sidewall sections  112 A and  112 B, respectively. The base  136  similarly divides the sidewall  114  into two equal sections  114 A and  114 B, respectively. The sidewalls  112 A and  114 A along with one-half of the thickness of the base  136  form the housing of the post-facing compression-resisting module  140 , which has substantially U-shaped cross-section, whereas the sidewalls  112 B and  114 B along with the opposite half of the base  136  thickness form the housing for the rail-facing compression-resisting module  142  of similar substantially U-shaped cross-section. With a common central base  136 , the overall cross-sectional shape of the block  10  resembles a substantially H-shaped cross section formed by the abutting substantially U-shaped compression-resisting modules  140  and  142 , commonly joined to the base  136 . Advantageously, the compression-resisting modules  140  and  142  are molded with honeycombed or corrugated interior structures that occupy each of the compression-resisting zones provided between the module sidewall pairs  112 A,  114 A and  112 B and  114 B, respectively. 
     The rail facing surface  120  has a recess adjacent each upper and lower wall  116 ,  118 , respectively, to provide a pair of slots  166 ,  168 , respectively having substantially cross-like shapes into which a pair of flat, rigid plates  170 ,  172  of similar cross-like shape may be inserted flush with the surface of the rail facing surface  120  and seated. The plates  170  and  172  may be stamped from a thin metal such as steel plate. The plates  170 ,  172  are provided to.resist the cutting action of the sharp rail edge from damaging block  10 . The plates  170 ,  172  are positioned at critical impact points on the surface  120  that are opposite points where upper and lower rail edges might cut into the standoff block  10  when the guardrail is bent inwardly during vehicle impact. 
     Each plate  170  and  172  may be affixed to the block  10  by a pair of fasteners  174 A,  174 B and  176 A,  176 B, respectively, which may be driven into the block adjacent the opposite inside corners formed by the cross-shape of the plates. Two sets of holes are molded into the block to facilitate the insertion of the fasteners  174  and  176  at two or more locations adjacent the plates. 
     Support struts  154 (A) . . . (N), where N is any number that comports with the design of block  10 , extend from base  136  on sidewall  112 B. Support struts  194 (A) . . . (N), where N is any number that comports with the design of block  10 , extend from base  136  on sidewall  112 A. Support struts  194  have corresponding terminal portions  161 (A) . . . (N) that enhance the stability of block  10  when it is mounted on a support post and supporting a section of guardrail. Support struts  196 A and  196 B are disposed on surface  118  and have terminal portions  151 A and  151 B, respectively, that extend to provide support for a section of guardrail, when the guardrail is mounted on block  10 . Support struts  198 A and  198 B extend in an opposite direction from base  136  on surface  118 . Surfaces  114  and  116  have similar struts, which are not shown in FIG.  1 . 
     Support struts  185 ,  187 ,  189 ,  191 ,  193  and  195  are mounted on edge portions of block  10 . 
     As seen in FIG. 2, the block  10  has dimensions so it fits against the vertically embedded support post and behind the rail section. Thus, a central-longitudinal axis, referred to herein as the vertical axis, of the block  10  is shown as section line  3 — 3 . A central-horizontal axis, referred to herein as horizontal axis is designated as section line  5 — 5 . Horizontal axis  5 — 5  perpendicularly intersects vertical axis  3 — 3  at the intersection of lines  3 — 3  and  5 — 5 . 
     The block  10  is usually mounted with its vertical axis  3 — 3  substantially parallel to a longitudinal axis of the post, which abuts block surface end (shown as surface  122  in FIG.  1 ). The horizontal axis  5 — 5  of the block is usually perpendicular to the vertical plane of the rail when the rail abuts block surface  120 . 
     Sidewalls  112 ,  114 , top and bottom surfaces  116 ,  118  and throughbores  124 ,  126  are also shown in FIG.  2 . 
     As seen in FIG. 3, the block  10  can be fabricated in a mold having an overall, substantially H-shaped cross-section with vertically spaced apart parallel, depending, closed-ended core that is designed to form the cavitated module interior. The parting line of the mold is the vertical axis at the midpoint of the base channel. The size and shape of the rectangular cavity webbing or sidewalls are determined by the core pattern of the fingers  182 (A) . . . (N) of module  140 . (N is any number that is compatible with the design of module  140 .) Module  142  has core fingers  184 (A) . . . (N), which are disposed opposite corresponding core fingers  182 (A) . . . (H), respectively. The core fingers, generally  182 ,  184 , have open ends extending perpendicularly from the vertical base channel defining the base and the crossbar of the H-shaped mold. These are used to direct the flow of the molten plastic material into the closed-ended core fingers  182 ,  184  where it knits with the plastic in the base channel upon cooling. Thus, the flow of molten plastic is from the center or parting line of the mold into the core fingers  182 ,  184  where cooling and solidification occur. Because.the different core fingers of each module  140 ,  142  are horizontally aligned with one another, and are almost one-half the length of core fingers of a conventional substantially U-shaped block having similar horizontal dimensions, the process of injecting the molten plastic into the mold is faster with less opportunity for premature cooling in the core fingers defining the cavity sidewalls and the outermost portions of the sidewalls. The subsequent removal of the solidified block is facilitated by opening the mold along a control parting line. The core fingers  182 ,  184  are slightly tapered from the base to facilitate their removal from the mold after solidification. 
     Rear terminal portions  161 (A) . . . (N) extend beyond surface  122  to enhance the stability when the block  10  is mounted to a support post. 
     Support member  151  on surface  120  supports a mounted section of guardrail. 
     As.seen.in FIG. 4, each of the modules  140  and  142  are molded with a plurality of open-ended cavities  146 (A) . . . (N), where N is.any suitable number that comports with the design of block  10 , and  144 (A) . . . (N), where N is any suitable number that comports with the design of block  10 , respectively. These cavities, generally referred to as  146 ,  144 , open in horizontally opposite directions and bottom out at the common, vertically disposed base  136 . The individual cavities  146  of module  140  are of similar size and shape as their horizontal counterpart cavities  144  of module  142  and are substantially symmetrical. The dimensions and arrangements of the individual cavities  144 ,  146  may vary from those explicitly depicted in FIG. 4 . Indeed, the dimensions and arrangements of the individual cavities may be any configuration that enhances the compression-resisting properties of the block  10 . Terminal portions  161  are also shown in FIG.  4 . 
     FIG. 5 shows a sectional side view of the block  10  shown in FIG.  2  through section line  5 — 5 . FIG. 5 shows modules  140  and  142 . Rail-facing surface  120  and post-facing surface  122  and cavities  144  and  146  are also shown. 
     FIG. 6 shows a sectional side view of the block  10  shown in FIG. 2 taken through section line  6 — 6 . FIG. 6 shows modules  140 ,  142 , surfaces  120  and  122 , support base  136 , cavities  144 ,  146  and core fingers  182 ,  184 . 
     As seen in FIG. 7, the edges of the base  136  may extend outwardly in a vertical plane from the sidewall  112 . Only surface  112  is shown in FIG. 7, and opposite surface  114  is shown in FIG.  1  and has a similar edge. This edge  136  also extends from respective top and bottom walls  116  and  118  of the block  10  thereby forming a.peripheral shoulder from which a plurality of horizontal support struts  154 (A) . . . (N) (where N is any number compatible with the design of the block) extend away from base  136  on surface  112 B. A plurality of support struts  194 (A) . . . (N) extend from base  136  on surface  112 A. Opposite surfaces shown herein as  114 A and  114 B have similar struts, which are not shown in FIG.  7 . The struts, generally  154 ,  194 , are molded integral with the modules  140 ,  142  and extend parallel to the horizontal axis of the block  10 . The struts  194  have terminal portions  161 (A) . . . (N) that are spaced apart in a lateral direction to span the opposite vertical edges of a support post (not shown) and serve to center the block  10  laterally on the post. 
     FIG. 7 also shows surfaces  166  and  168  and guardrail support member  151 . Struts  193  and  195  are in proximity to bottom surface  118  and struts  185  and  187  are in proximity to top surface  116 . 
     FIG. 8 shows a top view of block  10 . Struts  157 (A) and  157 (B) are disposed on the top surface of module  142  and struts  159 (A) and  159 (B) are disposed on top surface of module  140 . Terminal portions of struts  159 A and  159 B extend from module  142  to overlap the post top so as to support the block  10  vertically on the post during installation of the block on the post. Terminal portions  151 A and  151 B extend from module  142  to support the guardrail. 
     It is to be understood that the present invention is not to be considered as limited to the specific embodiments described above and shown in the accompanying drawings, which merely illustrate the best mode presently contemplated for carrying out the invention, and which is susceptible to such changes as may be obvious to one skilled in the art, but rather that the invention is intended to cover all such variations, modifications and equivalents thereof as may be deemed to be within the scope of the claims appended hereto.