Abstract:
Devices and methods for supporting guardrail terminal installations that incorporate safety end treatments such as the GET and the SRT. Preferred embodiments are described wherein guardrail terminal installations are primarily anchored to the ground using weak support posts that are preferably made of metal. The ends of the guardrail installation are secured to the ground using breakaway posts. In operation, the weak posts permit the central portion of the guardrail installation to contain and redirect the vehicle during a lateral collision to the rail member. The anchorage provided by the breakaway end posts helps prevent the guardrail from being excessively displaced, thus preventing the impacting vehicle from breaking through the guardrail. In operation, guardrail terminal assemblies constructed in accordance with the present invention provide an improved support system for the rail member which is more forgiving than conventional strong post anchorages, thereby providing an improvement in safety. At the present time, the invention has particular application in some non-U.S. countries, where it is required or highly preferred that metal support posts be used either completely or primarily within guardrail installations. However, the invention is also applicable to installation within the United States.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention generally relates to improvements for guardrail terminal installations and, in particular aspects, the invention relates to improved support posts and support systems for guardrail terminal systems that have safety end treatments. 
     2. Description of the Related Art 
     An important aspect of guardrail design is the ability of the guardrail to resist rupture and prevent penetration of the rail by a vehicle that impacts the guardrail end. For that reason, conventional guardrail installations are provided along their lengths with “strong” support posts that provide very little give when impacted by a vehicle. “Strong” support posts include 7″ diameter wood posts, W6×9 steel section posts and 6″ by 8″ wood posts. 
     Recently, it has also become important that a guardrail installation not present a hazard to a vehicle during an “end-on” impact where the guardrail installation is impacted from its end by a vehicle. As a result, a number of solutions have been proposed and used for eliminating the upraised end of the guardrail for making it safer. 
     The guardrail extruder terminal (GET) and slotted rail terminal (SRT) are known safety end treatments for a guardrail assembly that permit the guardrail assembly to safely absorb some or all of the vehicle&#39;s kinetic energy during an end-on collision, thereby eliminating the hazard associated with the upraised end. These end treatments are desirable because they absorb the energy of an end-on collision in a controlled manner to help bring an impacting vehicle to a safe stop or they allow the vehicle to safely “gate” through the terminal after absorbing some of the vehicle&#39;s energy. The GET is described in U.S. Pat. Nos. 5,078,366 and 4,928,928. The SRT is described in U.S. Pat. Nos. 5,547,309 and 5,407,298. Those patents are incorporated herein by reference. These end treatments were originally designed so that the support posts of the terminal would be readily frangible, “breakaway” posts made of wood. Holes were usually drilled through the post near the ground line in order to weaken the post at that point. Guardrail support posts downstream from the terminal are typically solid wooden posts used to securely anchor the midportion of the guardrail assembly to the ground. As the guardrail collapsed or became flattened by the end treatment, the breakaway posts would be broken at or around the ground line. 
     There are, however, drawbacks to using strong posts along the length of the end-treatment terminal. The strong posts must be weakened in some manner to accommodate end on impacts to the terminal. These modifications are costly and time consuming and, if done improperly or forgotten, can result in a significant safety hazard for motorists. 
     The inventors believe that, to date, guardrail terminals have used entirely strong support posts that have been modified by drilling holes or using other means to cause the post to breakaway. An improved guardrail installation would be desirable. 
     SUMMARY OF THE INVENTION 
     The present invention provides new and innovative devices and methods for supporting guardrail in guardrail terminals that incorporate safety end treatments such as the GET and the SRT. Preferred embodiments are described wherein the guardrail in a terminal is primarily supported above the ground using weak support posts that are preferably made of metal. The ends of the terminal installation are secured to the ground using breakaway posts and other accessories. 
     In operation, the weak posts in the downstream portion of the guardrail installation help to contain and redirect a vehicle during a lateral collision to the rail member. The anchorage in part provided by the breakaway end posts helps prevent excessive guardrail displacements that will allow the impacting vehicle to pass over to the opposite side of the guardrail during side or lateral impacts along the length of the terminal. 
     In other aspects, the invention provides an alternative to use of post weakening mechanisms which results in savings of costs. In operation, terminal assemblies constructed in accordance with the present invention provide an improved support system for the rail member which is more forgiving than conventional strong post support systems, thereby providing an improvement in safety. 
     At the present time, the invention has particular application in some non-U.S. countries, where it is required or highly preferred that metal support posts be used either completely or primarily within guardrail installations. However, the invention is also applicable to installation within the United States. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall plan view of an exemplary guardrail system constructed in accordance with the present invention having a guardrail extruder terminal-type end treatment. 
         FIG. 2  is a perspective view of the upstream end of the exemplary guardrail system illustrated in  FIG. 1 . 
         FIG. 3  is a cutaway detail illustrating interconnection of the rail member to a support post. 
         FIG. 4  is a plan view illustrating disconnection of a weak support post from the rail member during an end-on collision. 
         FIG. 5  illustrates an exemplary S3×5.7 steel section post supporting a rail. 
         FIG. 6  depicts an alternative guardrail installation constructed in accordance with the present invention and having a slotted rail terminal-type end treatment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to  FIGS. 1 and 2 , there is shown an exemplary guardrail assembly  10  that is constructed in accordance with the present invention. The guardrail assembly  10  runs longitudinally along a section of roadway  12  and has a first, upstream end  14  and a second, downstream end  16 . Although the guardrail installation  10  is depicted as being disposed along a straight line, it will be understood that it may be curved as well to conform to the shape of the roadway  12  and may be made of any desired length. The guardrail installation  10  has a central standard guardrail section  11  with guardrail safety end terminals  13  located on either end of the standard section  11 . The boundaries between the terminals  13  and the standard guardrail section  11  are illustrated by lines  15  in  FIG. 1 . The standard section  11  includes a corrugated rail  17  that is supported, in most instances, by strong posts  19 . 
     Each of the guardrail terminals  13  include a substantially continuous, corrugated rail  18  that is supported at its end  14  or  16  by a pair of support posts  20 . The rail  18  is supported in each terminal  13  by support posts  22 . 
       FIG. 2  depicts the upstream end  14  of one of the guardrail terminals  13  in greater detail. It is noted that the construction and operation described for the upstream end  14  is representative of both the upstream and downstream ends  14 ,  16 .  FIG. 2  illustrates that the rail  18  is made up of corrugated rail members  24 ,  26  that are interconnected, or spliced, to one another using nut and bolt assemblies  27 . 
     Each terminal  13  of the rail installation  10  includes a safety device, generally depicted at  28  in  FIG. 2  which is used to reduce the hazard associated with an upraised guardrail end. In this embodiment, the safety device  28  provides a guardrail extruder terminal impact head  30 . The structure and operation of these type of terminal heads  30  is generally described in U.S. Pat. Nos. 5,078,366 and 4,928,928.  FIGS. 2 and 4  illustrate the fact that the traffic side  32  of the head  30  has reduced profile as compared to the non-traffic side  34  of the head  30 . The head  30  is composed of an impact portion  36  and a feeder chute  38  that fits over the end of the rail  18 . As  FIG. 4  shows, the head  30  encloses a throat  40  that receives the rail  18  and helps flatten the corrugations in the rail  18 . Additionally, the head  30  includes a curved bending plate  42  that bends and further flattens the rail portion  18 , displacing it laterally away from the head  30 .  FIG. 4  illustrates a flattened portion  44  of the rail  18  being displaced laterally away from the head  30 . 
     Preferably, up to three types of support posts,  20 ,  22 , and  19  may be used to support the rails  17  and  18 . Moving downstream from the impact head  30  along the terminal  13 , the first two support posts  20  (only one shown in  FIG. 2 ) are breakaway post members that provide secure anchorage of the rail  18  to the ground  46 . The anchorage provided by the support posts  20  is required for redirection of vehicles that might impact the rail assembly  10  from the side proximate the end  14 . 
     A tension cable assembly  48  (shown in  FIG. 2 ) is disposed through the lead breakaway post  20 . Tension cable assemblies such as assembly  48  are well known in the art and operate to transmit tensile forces applied longitudinally to the rail  18  to the lower end of the lead support post  20 . As a result, the force from lateral impacts to the rail  18  are, in part, transmitted to the lower end of the support posts  20  at either end  14 ,  16  of the installation  10 . This helps to securely anchor the rail  18  during such lateral impacts. 
     The support posts  20 , which are the one or two most extreme posts at either end  14  or  16  of the installation are, as noted, frangible or breakaway in nature. During an end-on impact, then, the supports posts  20  will easily breakaway near the ground line of the post  20  to release the cable  48  and the rail  18  from their anchorage. With when the lead post broken away, the cable assembly  48  will also be released from its attachment to the post  20 . There are a number of post structures that are suitable for use as breakaway posts  20 . In certain, non-U.S. countries, for example, it is desirable and sometimes required to use non-wooden posts for guardrail installations. Thus, a breakaway steel post assembly would be particularly desirable. One example of a suitable steel breakaway post is described in U.S. Pat. No. 5,988,598. Another suitable steel breakaway post is the HBA post, which is Marketed commercially by Trinity Industries of Dallas, Tex. In other instances, a wooden breakaway post may be used, although this is not preferred, particularly in many non-U.S. countries where the use of wooden support posts must be minimized or eliminated. The structure and operation of wooden breakaway posts is known and described in U.S. Pat. No. 5,547,309. 
     Posts  22  located along the length of each terminal  13  downstream from posts  20  along assembly  10 , are unmodified yielding, or “weak,” support posts. The term “unmodified,” as used herein, refers to a post that has not been subjected to any weakening mechanisms, whether by mechanical, chemical or other means, such as by drilling holes in the post, by notching the post, by incorporating mechanical breakaway devices such as frangible connections, or by incorporating bolts that shear upon impact. The unmodified weak post, by its inherent cross-sectional properties and material properties, readily yields or is deflected in a collision. It is preferred that the weak posts  22  be formed of metal rather than of wood. An unmodified “weak” support post is a support post that readily yields or is deflected in a collision. Further, an unmodified weak support post is one that will meet “preferred” occupant impact velocity and occupant ridedown acceleration limits, as recommended in NCHRP Report 350 or its successor, when impacted in a direction consistent with the direction it would be impacted in end-on tests of a guardrail terminal by design vehicles recommended in NCHRP Report 350 or its successor, traveling at speeds of approximately 15 mph or greater with the post embedded in soils as recommended in NCHRP Report 350 or its successor. Weak support posts are further characterized by a greater amount of deflection upon impact than strong posts. 
     In addition, an unmodified weak guardrail post is one that will meet Impact Severity Class A, as specified in CEN prEN 1317-4, Trento, June 1999, or its successor, when impacted in end-on tests of a guardrail terminal by test vehicles specified in CEN prEN 1317-4, Trento, June 1999, or its successor, traveling at speeds or approximately 25 km/h or greater, with the posts embedded in soils as recommended in CEN prEN 1317-4, Trento, June 1999, or its successor. 
     Examples of commercially available unmodified weak posts are 4″ diameter circular wood posts, 4″×6″ rectangular wood posts and S3×5.7 steel section posts. It is preferred, particularly for application in many non-U.S. countries, that the weak posts comprise either C-120 or S3×5.7 steel section posts since these posts are not made of wood. Presently, it is highly preferred that the weak posts  22  comprise a C-120-type post, which is a standard Spanish support post. A U-shaped post is illustrated in  FIGS. 2 ,  3  and  4 . It can be seen that the U-shaped post has a U-shaped cross-section. This U-shape has a weak axis  61  running parallel to the cross-member  25  of the post  22 , and a strong axis  63  running parallel to the two legs  23  of the post  22 . The U-shaped post is, therefore, more easily bent around the weak axis  61  than around the strong axis  63 . As a result, the U-shaped post has the advantageous property of yielding more easily in response to an end-on impact than to a lateral impact upon the rail  18 . 
       FIG. 5  illustrates an embodiment of the invention wherein the rail  18  is being supported by unmodified posts  22 ′ that comprise S 3×5.7 steel section post members. The S 3×5.7 steel section post has an H-shaped cross-section made up of a central web  27  and two end flanges  29 . Two connectors  31  are used to affix the rail  18  and bracket  50  to one of the end flanges  29 . As can be seen, the S 3×5.7 post provides the same sort of weak and strong axes as the C-120 post member, and it will also provide the advantage of more readily yielding in response to an end-on collision than a lateral impact to the rail  18 . 
     Posts  19  located along the central portion of the guardrail installation may be the same as posts  22  or  22 ′, or they may be different in size, shape or material. 
       FIGS. 2 and 3  illustrate the details of attachment of the rail  18  to U-shaped post  22 . A U-shaped standoff bracket  50  is disposed between the rail  18  and each post  22 . The U-shaped bracket  50  has a central web  52  and two legs  54 , as  FIG. 3  shows. The bracket  50  is located so that the rail  18  is engaged by portions of the web  52  and each leg  54 . A connector  56 , such as a nut-and-bolt assembly, is disposed through the post  22 , bracket  50  and rail  18  to securely affix the rail to the post  22 . The legs  54  of the bracket  50  provide stiffness to the rail  18  and help to distribute the force of a lateral impact upon different areas of the support post  22 . In testing, the presence of the bracket  50  has been shown to reduce the amount of deflection of the rail  18  in response to a lateral impact. Therefore, the brackets  50  compensate somewhat for the weakness of the weak support posts  22  and help ensure that a laterally impacting vehicle will not rupture or penetrate the rail  18 . In a preferred embodiment of the invention, the support posts  22  that are located 3rd, 5th and 7th from each end  14 ,  16  of the rail assembly  10  are not affixed to the rail  18  with connectors. This makes it easier for the rail  18  to feed properly into the impact head  30  since the rail is typically spliced together at these posts. An example of a splice in the rail  18  is shown in  FIG. 2  where rail members  24  and  26  are joined by connectors  27 . 
       FIG. 4  depicts the release of the rail  18  from a weak support post  22  during an end-on impact. As shown there, the impact head  30  has received an end-on impact from vehicle  58  that has driven the head  30  down along the rail  18  thereby flattening and displacing the rail  18  to provide flattened portion  44 . In the position shown, the head  30  has traveled downstream past the locations of the two breakaway posts  20 . The feeder chute  38  of the head  30  has contacted the bracket  50  and the connector  56  passing through the bracket  50  that interconnects the rail  18  to the post  22 . The feeder chute  38  has released the connection. Typically, the connection is released as the connector  56  is pulled through the rail  18 . It is noted that the bracket  50  provides a surface upon which the downstream end of the feeder chute  38  is contacted during the downstream movement of the head  30 . The weak support post  22  will later be bent down from the rail  18  by the impact portion  36  and vehicle  58 . The unmodified weak post  22  typically yields by bending proximate the point at which it is buried in the ground. This bending down is very advantageous as it permits support posts to be readily bent down permitting the impacting vehicle  58  to easily traverse the post in the collision. 
     Referring now to  FIG. 6 , a second embodiment of the invention is described. Like components between the two embodiments are numbered alike. Guardrail installation  100  includes a rail-collapsing slotted rail terminal (SRT)-type end treatment  102  at its upstream end  14 . The construction and operation of SRT end treatments is, as noted previously, described in U.S. Pat. Nos. 5,547,309 and 5,407,298. The SRT end treatment  102  features several slotted sections  104  (only one shown) in the rail  18 . The slotted section  102  contains three longitudinal slots  106  that are cut into the rail  18  to weaken its ability to structurally withstand an end-on impact. Slot guards  108  are located at the downstream end of the slots  106 . 
     The guardrail installation  100  should, in response to a lateral impact upon the rail  18 , react in the same manner as the installation  10  described earlier. The weak posts  22  will yield or be deflected thereby softening the impact for the impacting vehicle. In an end-on impact, the SRT end treatment  102  will result in axial collapse of the rail  18 . The rail  18  will be released from the weak support posts  22  as the connectors  56  are pulled out of the rail  18 . 
     A principal advantage is that guardrail installations constructed in accordance with the present invention are more forgiving during an impact to the lateral side thereby resulting in less damage to impacting vehicles and their passengers. Strong wooden support posts used in conventional systems do not easily yield in a collision and thus cause significant damage to the impacting vehicle. At the same time, the weak posts  20  used in the invention are capable of arresting an impacting vehicle that would impact the lateral side of the rail  18 . This capability is provided, in part, by the brackets  50  and the anchorage afforded the system by the tension cable assembly  48 . A further considerable advantage provided by the present invention is the savings in cost over installations that utilize more expensive strong wooden posts. 
     While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to other various changes without departing from the scope of the invention.