Patent Publication Number: US-6902150-B2

Title: Steel yielding guardrail support post

Description:
RELATED APPLICATION 
   This application claims the benefit of U.S. Provisional Application Ser. No. 60/334,286 filed Nov. 30, 2001. 

   TECHNICAL FIELD OF THE INVENTION 
   The present invention relates generally to guardrail systems and more particularly, to a steel yielding guardrail support post. 
   BACKGROUND OF THE INVENTION 
   Guardrail systems are widely used along heavily traveled roadways to enhance the safety of the roadway and adjacent roadside. Guardrail beams and their corresponding support posts are employed to accomplish multiple tasks. Upon vehicle impact, a guardrail acts to contain and redirect the errant vehicle. 
   For many years, a standard heavy gauge metal guardrail known as the “W-beam” has been used on the nation&#39;s roadways to accomplish these tasks and others. Named after its characteristic shape, the “W-beam” is typically anchored to the ground using posts made of metal, wood or a combination of both. 
   Wood posts are more readily available and more economical than metal posts in some geographical areas. In other areas, metal (e.g., steel) posts are more readily available and more economical, and are preferred for their ease of installation using driving methods. 
   Wood posts used in a terminal portion of a guardrail have been made to break away upon impact, thus producing a desired behavior during a collision by a vehicle at the end of the terminal section. However, in some environments, wood posts deteriorate more rapidly and alternate materials are sought. Commonly used steel posts do not break away in the desired fashion, and are not suitable for use in the terminal section of a guardrail system. 
   Break away steel support posts that are modified to allow for failure during a collision have recently become available. Examples include a “hinged breakaway post” and the “energy absorbing breakaway steel guardrail post” described in U.S. Pat. No. 6,254,063. Many such prior attempts require substantial time, money, and resources during fabrication, modification, and/or installation. 
   SUMMARY OF THE INVENTION 
   A guardrail support post is provided, for use in securing guardrail beams adjacent roadways. The guardrail support post has been modified to weaken the support post along a direction generally parallel to the flow of traffic. This allows for failure, or yielding of the guardrail support post during a head-on collision of a vehicle with a guardrail terminal, or other guardrail section. Accordingly, the support posts of a guardrail system will yield as a vehicle impacts consecutive support posts, and absorb kinetic energy of the vehicle, until the vehicle is brought to a stop. 
   In accordance with a particular embodiment of the present invention, a guardrail support post includes a continuous structural member having a top edge, a bottom edge, and a generally uniform cross section from the top edge to the bottom edge. The structural member includes first and second generally parallel flanges, and a web forming a coupling between, and extending generally perpendicular to the first and second flanges. The structural member may have a lower portion for installing below grade adjacent a roadway, and an upper portion configured to be coupled with a guardrail beam. A mid portion of the structural member is disposed between the upper portion and the lower portion. In accordance with at least one embodiment of the present invention, the first and second flanges include first and second cutouts, respectively, that occur within the mid portion. The cutouts may be operable to weaken the structural member about the axis generally perpendicular to the flanges without excessively weakening the structural member about an axis generally parallel to the flanges. 
   In accordance with another embodiment of the present invention, each of the cutouts includes a vertical dimension and a horizontal dimension. A ratio of the vertical dimension to the horizontal dimension may be approximately equal to or less than one. 
   In accordance with yet another embodiment of the present invention, the cutouts comprise generally circular cutouts. Each generally circular cutout may include a diameter of approximately thirteen millimeters. 
   In accordance with still another embodiment of the present invention, the generally circular cutouts may be sized approximately equal to bolt holes configured to receive fasteners for coupling the guardrail beam with the support member. For example, the generally circular cutouts may include a diameter of approximately twenty-one millimeters. 
   Technical advantages of particular embodiments of the present invention include a guardrail support post that is weakened about a “weak axis” such that the guardrail support post will fail or yield during a head-on collision with a terminal section of the guardrail. The guardrail support post may also have sufficient strength to redirect vehicles that collide along the length of the guardrail system at an angle to the flow of traffic. 
   Another technical advantage of particular embodiments of the present invention includes a support post that has been weakened at a particular point along its mid section. This allows the most likely point of failure of the support post during a head-on collision (parallel to the direction of traffic) to be predetermined and/or controlled. 
   Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some or none of the enumerated advantages. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following brief descriptions, taken in conjunction with the accompanying drawings and detailed description, wherein like reference numerals represent like parts, in which: 
       FIG. 1  illustrates a side view of a guardrail system that incorporates aspects of the present invention; 
       FIG. 2  is a side view, with portions broken away, illustrating an enlarged section of a portion of the guardrail system of  FIG. 1 ; 
       FIG. 3  illustrates a guardrail support post suitable for use with the guardrail system of  FIG. 1 , in accordance with a particular embodiment of the present invention; and 
       FIG. 4  illustrates another guardrail support post suitable for use with the guardrail system of  FIG. 1 , in accordance with another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2  illustrate portions of a guardrail safety system  10  that incorporates aspects of the present invention. Guardrail system  10  may be installed adjacent a roadway, to protect vehicles, drivers and passengers from various obstacles and hazards, and prevent vehicles from leaving the roadway during a traffic accident or other hazardous condition. Guardrail systems incorporating aspects of the present invention may be used in median strips or shoulders of highways, roadways, or any path that is likely to encounter vehicular traffic. Guardrail system  10  includes a guardrail beam  12 , and support posts  14  that anchor guardrail beam  12  in place along the roadway. 
   In accordance with the teaching of the present invention, support posts  14  have been modified to decrease the strength of support posts  14  in a direction generally parallel to axis  16  (generally along the direction of traffic) without substantially decreasing its strength in a direction generally perpendicular to axis  16  (out of the page in FIG.  1 ). Accordingly, if a vehicle impacts guardrail system  10  “head-on” adjacent terminal post  18 , support posts  14  will tend to fail (e.g., buckle), while allowing the vehicle to decelerate as it impacts consecutive support posts. However, if a vehicle strikes guardrail system  10  along the face of and at an angle to guardrail beam  12 , support posts  14  will provide sufficient resistance (strength) to redirect the vehicle along a path generally parallel with guardrail beam  12 . 
   Guardrail system  10  is intended to keep errant vehicles from leaving the roadway during a crash or other hazardous situation. In many instances, guardrail  10  is installed between a roadway and a significant hazard to vehicles (e.g., another roadway, a bridge, cliff, etc.). Therefore, guardrail system  10  should be designed to withstand a significant impact from a direction generally perpendicular to the roadway, without substantial failure. It is this strength that allows guardrail system  10  to withstand the impact, and still redirect the vehicle so that it is once again traveling generally in the direction of the roadway. 
   However, testing and experience has continuously shown that guardrail systems may actually introduce additional hazards to the roadway and surrounding areas. This is particularly true with respect to vehicles that impact the guardrail system adjacent its terminal section, in a direction generally parallel to the roadway. For example, if the guardrail system were rigidly fixed in place during a crash, serious injury and damage may result to the errant vehicle, its driver and passengers. Accordingly, many attempts have been made to minimize this added risk. 
   One such method used to reduce the frequency and amount of damage/injury caused by head on collisions with a guardrail system included a terminal portion that was tapered from the ground up. This effectively reduced the impact of head on collisions, but also created a ramp-like effect that caused the vehicles to go airborne during a crash. 
   Other methods include breakaway cable terminals (BCT), vehicle attenuating terminals (VAT), SENTRE end treatments, breakaway end terminals (BET) and the breakaway support posts of U.S. Pat. No. 6,398,192 (“&#39;192 Patent”). Many such terminals, supports, end treatments and the like are commercially available from various organizations. Examples include the HBA post by Exodyne Technologies and Trinity Industries, and a breakaway support post similar in configuration to that described in the &#39;192 Patent. 
     FIG. 2  illustrates a portion of the terminal section of guardrail system  10 , in more detail. This is referred to the terminal section since the guardrail section terminates at this point. The terminal section includes an end terminal assembly  20  that is specially configured to absorb the impact of a head on collision, to minimize damage and injury caused by such a collision. 
   End terminal assembly  20  is anchored to the ground using break away terminal post  18 . End terminal assembly  20  is slidably coupled with a section of guardrail beam  22 . Terminal post  18  is coupled with guardrail beam  22  using a cable  24  and coupling assembly  26 . A ground strut  28  couples terminal post  18  with guardrail support post  40 . As discussed above, guardrail support post  40  is configured to break away when a significant force is applied along its weak direction. The specifics of guardrail support post  40  will be addressed in more detail with respect to  FIGS. 3 and 4 . 
   Referring again to  FIG. 1 , guardrail system  10  includes one terminal post  18 , and seven guardrail support posts  40 . Collectively, this configuration forms the terminal section of guardrail system  10 . Standard guardrail support posts  41  may be used for the balance of guardrail system  10 . However, it should be recognized by those of ordinary skill in the art that support post  40  described herein is suitable for installation at any location within a guardrail system, within the teachings of the present invention. 
     FIG. 3  illustrates a guardrail support post  40 , in accordance with a particular embodiment of the present invention. Support post  40  includes an elongate, continuous structural member of a standard Wide flange configuration. Support post  40  includes two flanges  36  and  38 , that are generally parallel with one another, and in a spaced relation. A web  37  forms the coupling between flanges  36  and  38 . Flanges  36  and  38  include a generally identical configuration of boltholes  48  and cutouts  50 , therein. 
   With regard to a Wide flange shape used as a guardrail post, the cross section is typically shaped like the letter “H”. The cross section has two major axes for bending. The “weak” axis generally refers to a central axis that extends through the web and is perpendicular to the flanges. The “strong” axis generally refers to a central axis that is perpendicular to the web and parallel to the planes of the flanges. The weak axis for a conventional installation of guardrail extends generally transversely to the road. The strong axis extends generally along the roadway. 
   In the illustrated embodiment of  FIG. 3 , the Wide flange is a standard W6×9, which is commonly used in fabricating support posts for guardrail installations. In fact, one advantage of the present invention is the ability to re-use existing, standard equipment to fabricate, modify, and install support post  40 , without substantial modification to the equipment. Those of ordinary skill in the art will recognize that wide flange beams may be available in many different sizes. For example, a standard W6×9 Wide flange may have a nominal six-inch depth and weigh nine pounds per foot. However, a Wide flange having a six-inch depth and weighing eight and one-half pounds per foot may also be referred to as a W6×9 Wide flange and they are considered equivalent in the trade. The term “W6×9 Wide flange” is intended to refer to all sizes and configurations of guardrail posts that may be referred to as “W6×9” by a person of ordinary skill in the art. In addition, persons skilled in the art recognize other names used for wide flanges include but are not limited to “I-beam,” “H-beam,” “W-beam,” “S-beam,” “M-beam,” or the term “shape” may be substituted for “beam.” 
   Support post  40  includes a relatively “weak” axis W, and a relatively “strong” axis S. For the reasons described above, support post  40  is normally installed along a roadway such that weak axis W is generally perpendicular to the direction of traffic, and strong axis S is generally parallel to the direction of traffic. Accordingly, support post  40  is typically able to withstand a significant impact (e.g., with a car travelling at a high rate of speed) about the strong axis S without substantial failure. However, support post  40  is intentionally designed such that failure will more readily occur in response to an impact about the weak axis W. 
   Support post  40  is approximately 1,830 mm long, and includes an upper portion  42 , a lower portion  44 , and a mid portion  46  which couples upper portion  42  with lower portion  44 . Upper portion  42  includes two boltholes  48  that are adapted to receive connectors for the installation of a guardrail beam (e.g., guardrail beam  12 ) upon support post  40 . Lower portion  44  is suitable for installation below grade, as part of a guardrail support system. Mid portion  46  includes two cutouts  50 , which are configured to further weaken support post  40  about the weak axis W, to more readily allow for failure due to impact from a vehicle along that direction. The overall length of support post  40 , and its upper, lower and mid portions may vary significantly, within the teachings of the present invention. 
   Bolt holes  48  include a standard configuration that allow for the installation of widely used guardrail beams, upon support posts  40 . In general, bolt holes  48  align with the center of the guardrail beam, and maintain the center of the guardrail beam approximately five hundred and fifty millimeters above grade. However, the number, size, location and configuration of boltholes  48  may be significantly modified, within the teachings of the present invention. 
   Cutouts  50  are positioned within mid portion  46  to weaken support post  40  about weak axis W, adjacent grade (when installed). This will accommodate failure of support post  40  approximately at grade, allowing support post  40  to “fold” over from the point of failure, upward. Since lower portion  44  is below grade, it is not expected that the ground, or lower portion  44  of support post  40  will appreciably deflect during an impact. 
   Since cutouts  50  are intended to occur approximately at grade, and the center of bolt holes  48  are intended to occur five hundred and fifty millimeters above grade, bolt holes  48  occur five hundred and fifty millimeters above cutouts  50 , in the illustrated embodiment. It will be recognized by those of ordinary skill in the art that the size, configuration, location and number of bolt holes, cutouts, and their relationship with each other, may be varied significantly within the teachings of the present invention. 
   In the illustrated embodiment of  FIG. 3 , cutouts  50  occur approximately seven hundred and twenty-five millimeters below a top edge  52  of support post  40 . However, the location of cutouts  50  may vary in accordance with the teachings of the present invention. The configuration of  FIG. 3  envisions that cutouts  50  will occur approximately at grade level. In other embodiments, cutouts  50  may occur below grade or above grade. The depth of cutouts  50  below grade should not exceed an amount that will prevent support post  40  from failing at or near the location of cutouts  50 . At some depth below grade, the surrounding earthen (or other) material will reinforce lower portion  44  of support post  40  to an extent that will no longer accommodate such failure to occur. 
   The height of cutouts  50  above grade should not exceed a point at which support post  40  will fail at cutouts  50 , and leave a “stub” above grade which can snag vehicles, and otherwise cause excessive injury and/or excessive damage. Such a stub could be detrimental to the redirective effect of the guardrail system in which support post  40  is operating. 
   As described above, several attempts have been made in the past to allow for failure of a terminal guardrail post in the weak direction. Such attempts often include two-piece sections of support post that are welded or otherwise fastened together using plates, bolts etc. Such efforts have been focused upon accommodating failure of the support post at a certain area of the support post, when impacted in the weak direction. The present invention provides an enhanced alternative to such techniques. 
   For example, support post  40  is a single, continuous structural member that does not require any labor in field assembly, welding, or special handling. With the exception of boltholes  48  and cutouts  50 , support post  14  has a continuous, generally uniform cross-section from top edge  52 , to bottom edge  54 . Therefore, fabrication of support post  40  is simplified, with respect to other multiple component products. Furthermore, support post  40  can be shipped as one piece, and installed as one piece. Many prior attempts that included multiple components that were hinged, or otherwise connected could not be shipped, and/or installed as a single unit without damaging the support post. 
   Similarly, many such prior efforts required specialized equipment for proper installation, and often required a significant amount of field labor to perform such installation. In contrast, support post  40  of the present invention can be installed using traditional guardrail post installation equipment (e.g., guardrail post drivers). 
   Cutouts  50  of support posts  40  are configured to reduce the strength of support post  40  about weak axis W, without substantially weakening support post  40  about strong axis S. In the illustrated embodiment, cutouts  50  comprise generally circular openings that have been punched or drilled through support post  40 . 
   Previous attempts to accommodate failure of a guardrail support post have often weakened the support post about the strong axis S, which impacts the support post&#39;s ability to redirect a vehicle that collides with the support in a direction generally perpendicular to the roadway. For this reason, such support posts may be unacceptable for use along a roadway, and may fail to comply with governing federal standards bodies&#39; requirements. 
   Patent Application PCT/US98/09029 (&#39;029 Application) illustrates a support post having slotted openings disposed therein. These slots are substantially longer (vertically) than they are wide (horizontal). 
   Cutouts  50  provide an enhanced ability to control the point of failure of support post  40  during a collision with a vehicle. For example, the support post of the &#39;029 Application may fail at any point along the slots, and failure may be based upon imperfections in the material adjacent the slots. By limiting the vertical dimension of cutout  50 , it is easier to dictate the precise point of failure of support post  40  along its vertical length. 
   Furthermore, the slots of the &#39;029 Application require the removal of a substantial amount of material from the flange. This weakens the flange along directions other than perpendicular to the web. Furthermore, during a dynamic crash situation, in which the impact may come from any angle, twisting or bending of the flange may result in the flange changing its orientation in response to the initial impact. Accordingly, the support post having vertical slots similar to the &#39;029 Application may fail prematurely along the strong axis and lose its ability to redirect the vehicle. 
   In accordance with the teachings of the present invention, the vertical dimension of cutout  50  is limited based upon the horizontal dimension of cutout  50 . For example, a ratio of the vertical dimension of any particular cutout may be equal to, or less than three times the horizontal dimension. Alternatively, the ratio may be limited to two times the horizontal dimension. In the illustrated embodiment of  FIG. 3 , the ratio is 1:1, since cutout  50  is generally a circular opening in the support post. The smaller the vertical dimension of the cutout, the more precisely the designer may dictate the point of failure along the vertical length of support post  40 . 
   Various configurations of cutouts  50  are available to a designer of support post  40 , in accordance with the teachings of the present invention. For example, rather than circular openings, cutouts  50  may comprise square, rectangular, triangular, oval, diamond shaped, or practically any other geometric configuration, and still obtain some or all of the benefits described herein. 
   The horizontal orientation of cutouts  50  within flanges  36  and  38  may also be altered significantly, within the teachings of the present invention. In the illustrated embodiment of  FIG. 3 , cutouts  50  are located approximately twenty millimeters from outer edges of flanges  36  and  38 . However, in alternative embodiments, cutouts  50  may be located closer to such edges, or further from such edges. In one embodiment, cutouts  50  may be configured such that they extend all the way to the edge of the flange, such that there is a break in material beginning at the edge. In this manner, a traditional punch could be employed at the edge, to form a semi-circular opening that extends to the edge of the flange. 
   Alternatively, a sawcut could be employed from the outer edge of the flange, and extending inward, to form cutouts  50 . In this manner, the sawcut would form the starting point of the likely point of failure along the weak axis of the support post. Rather than a sawcut, a similar configuration may include a slot in which the longest dimension extends horizontally through the flange. Such a slot may begin or terminate at the edge of the flange, or otherwise be disposed completely within the material of the flange. 
     FIG. 4  illustrates a support post  70 , in accordance with another embodiment of the present invention. Support post  70  is a W8×10 Wide flange, and is therefore slightly larger and heavier than the W6×9 Wide flange of FIG.  3 . Support post  70  is very similar in configuration to support post  40 , although many of the dimensions of relative aspects and components are slightly different. Therefore, support post  70  will not be described in significant detail. 
   Cutouts  72  of support post  70  are slightly larger than cutouts  50  of FIG.  3 . In the illustrated embodiment of  FIG. 4 , cutouts  72  are approximately twenty-one millimeters in diameter. In this configuration, cutouts  72  are the same size as boltholes  74 . Accordingly, fabrication of support post  70  is simplified, since the same tools that are used to punch bolt holes  74  may be used to punch cutouts  72 . Tooling costs are thereby reduced, since the tools need only be re-indexed to provide additional holes for cutouts  72 . 
   Two types of guardrail support members are described and illustrated within this specification: (I) W6×9; and (II) W8×10 Wide flanges. It should be recognized by those of ordinary skill in the art that practically any size guardrail support post may be enhanced by incorporating the teachings of the present invention. The size, weight and configuration of the support post are just a few factors to be considered to determine the appropriate location of cutouts, to allow failure along the weak axis, while maintaining sufficient strength along the strong axis to redirect impacting vehicles. 
   Although the present invention has been described by several embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as fall within the scope of the present appended claims.