Patent Application
20070063179
The present invention relates generally to guardrail systems and more particularly, to a weakened guardrail mounting connection.
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, standard heavy gauge metal guardrails known as “W-beams” have been used on the nation's roadways to accomplish these tasks and others. Named after its characteristic shape, the “W-beam” is typically anchored to the ground using support posts made of metal, wood, or a combination of both. A terminal post is used at or near the terminal end of the guardrail system. Support posts other than the terminal posts are termed “length-of-need” (LON) posts. LON posts support the W-beam along the intermediary portion of the guardrail system between opposing terminal ends of the guardrail system.
Wood support posts may be more readily available and more economical than metal posts in some geographical areas. In other areas, metal (e.g., steel) posts may be more readily available and more economical and may be preferred for their ease of installation using driving methods. As an additional benefit, wood support posts used in a LON or terminal portion of a guardrail system have been made to break away upon impact, thus producing a desired behavior during a collision by a vehicle at the impact site. 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 optimal for use in the guardrail system and especially 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.
In accordance with a particular embodiment of the present invention, a guardrail safety system includes a guardrail beam and a plurality of support posts in spaced apart relation to one another. Each support post is configured to be releasably coupled to the guardrail beam. A plurality of connectors couple the plurality of support posts to the guardrail beam. Each connector includes a head portion that is configured to provide a sufficiently strong connection between the guardrail beam and the support post to support the guardrail beam and a sufficiently weak connection between the guardrail beam and the support post to enable the support post to detach from the guardrail beam when struck by the errant vehicle.
Technical advantages of particular embodiments of the present invention include a guardrail support post that has sufficient strength to redirect vehicles that collide along the length of the guardrail system at an angle to the flow of traffic. As a result, the guardrail system may fail in a designed manner even at a low level of tension.
A further technical advantage of particular embodiments of the present invention may include a weakened connection between the support post and guardrail beam such that the support post detaches from the guardrail beam when struck by an errant vehicle. Specifically, a connector may be provided that adequately supports the guardrail beam while releasing from the guardrail beam when a lateral force is applied to the guardrail beam. Accordingly, in particular embodiments, an advantage may be that the connection is strong in shear and weak in tension.
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.
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:
Support posts 14 have been modified to decrease the strength of support posts 14 in a direction generally parallel to axis 20 (generally along the direction of traffic) without substantially decreasing its strength in a direction generally perpendicular to axis 20 (out of the page in
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 that forms an angle to the roadway without substantial failure. It is this lateral 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.
Testing and experience have continuously shown, however, 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 16 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. Such methods generally include the use of terminal portions that are tapered from the ground up to effectively reduce the impact of head on collisions and to create a ramp-like effect that causes 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 (“'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 '192 Patent.
Improperly designed posts in the LON portion of a guardrail system may also introduce additional hazards to the roadway and surrounding areas. This is particularly true with respect to vehicles that impact the LON portion of the guardrail system at a substantial angle to the guardrail beam. In such a scenario, snagging or contact between the vehicle and posts can cause severe vehicle damage, deformation to the occupant compartment, high vehicle decelerations, and failure or rupture of the guardrail beam. Additionally, the guardrail may fail in its purposes of containing and redirecting the errant vehicle.
Referring again to
Support posts 14 may be embedded in the ground, a concrete footing, or a metal socket. Support posts 14 may be made of wood, metal, plastic, composite materials, or any combination of these or other suitable materials. It is also recognized that each support post 14 within guardrail system 10 need not necessarily be made of the same material or include the same structural features. Furthermore, the cross-section of support posts 14 may be any engineered shape suitable for releasably supporting guardrail beam 12. Such cross-sectional shapes may include, but are not limited to, square, rectangular, round, elliptical, trapezoidal, solid, hollow, closed, or open.
Although
In such an embodiment, guardrail beam 12 may include multiple 12-gauge W-beam rail elements of a length on the order of approximately 3.8 meters (12.5 feet) or 7.6 meters (25 feet). The guardrail beam sections may be mounted at a height of 78.74 centimeter (31 inch) with rail splices positioned mid-span between the support posts 14. While guardrail beam 12 may include W-beam rail elements, it is generally recognized that the illustrated guardrail beam 12 is merely an example of a beam that may be used in a guardrail system. Guardrail beams 12 may include conventional W-beam guardrails, thrie beam guardrails, box beams, wire ropes, or other structural members suitable for redirecting an errant vehicle upon impact. It is also recognized that the configuration and dimensions of any of the above-described elements within guardrail system 10 may vary as desired.
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
Support post 34 includes a relatively “weak” axis W and a relatively “strong” axis S. For the reasons described above, support post 34 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 34 is typically able to withstand a significant impact (e.g., with a car traveling at a high rate of speed) about the strong axis S without substantial failure. However, support post 34 is intentionally designed such that yielding will more readily occur in response to an impact about the weak axis W.
In the illustrated embodiment, support post 34 has a length on the order of approximately 1,830 mm (6 feet), and it includes an upper portion 42, a lower portion 44, and a mid portion 46 that couples upper portion 42 with lower portion 44. Upper portion 42 includes two boltholes 48 in each of flanges 36 and 38 that are adapted to receive connectors for the installation of a guardrail beam (e.g., guardrail beam 12) upon support post 34. Lower portion 44 is suitable for installation below grade as part of a guardrail support system. Mid portion 46 includes two cutouts 50 in both flanges 36 and 38, which are configured to further weaken support post 34 about the weak axis W, to more readily allow for yielding due to impact from a vehicle along that direction. The overall length of support post 34 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 34. In general, bolt holes 48 align with the center of the guardrail beam and maintain the center of the guardrail beam at a distance that is between 550 and 750 millimeters (1.8-2.5 feet) above grade. In the particular embodiment illustrated, bolt holes 48 maintain the center of the guardrail beam at a distance that is on the order of 550 (1.8 feet) above grade. Bolt holes 48 have a diameter on the order of approximately 21 millimeters. However, it is generally recognized that the illustrated dimensions are for example purposes only; 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 34 about weak axis W adjacent grade (when installed). This will accommodate yielding of support post 34 approximately at grade, allowing support post 34 to “fold” over from the point of yielding, upward. Since lower portion 44 is below grade, it is not expected that the ground or lower portion 44 of support post 34 will appreciably deflect during an impact about the weak axis of the post. In the illustrated embodiment of
Since cutouts 50 are intended to occur approximately at grade and the center of bolt holes 48 are intended to occur between 550 and 750 millimeters (1.8-2.5 feet) above grade, bolt holes 48 occur between 550 and 750 millimeters (1.8-2.5 feet) above cutouts 50. In the illustrated embodiment, bolt holes 48 occur at approximately 550 millimeters (1.8 feet) above cutouts 50. It will be recognized by those of ordinary skill in the art, however, 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.
Additionally, the location of cutouts 50 may vary in accordance with the teachings of the present invention. The configuration of
The height of cutouts 50 above grade should not exceed a point at which support post 34 will yield at cutouts 50 and leave a “stub” above grade that 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 34 is operating.
Support post 34 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 34 has a continuous, generally uniform cross-section from top edge 52 to bottom edge 54. Therefore, fabrication of support post 34 is simplified with respect to other multiple component products. Furthermore, support post 34 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 34 can be installed using traditional guardrail post installation equipment (e.g., guardrail post drivers).
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's ability to redirect a vehicle that collides with the support in a direction generally perpendicular to or at an angle 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' requirements. Patent Application PCT/US98/09029 ('029 Application) illustrates a support post having slotted openings disposed therein. These slots are substantially longer (vertically) than they are wide (horizontal).
Cutouts 50 of support posts 34 are configured to reduce the strength of support post 34 about weak axis W, without substantially changing the behavior of the support post 34 about strong axis S. In the illustrated embodiment, cutouts 50 comprise generally circular openings that have been punched or drilled through support post 34. Cutouts 50 provide an enhanced ability to control the point of yielding of support post 34 during a collision with a vehicle. For example, the support post of the '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 34 along its vertical length.
Furthermore, the slots of the '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 '029 Application may fail prematurely along the strong axis and lose its ability to redirect the vehicle.
In accordance with certain example embodiments 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
Various configurations of cutouts 50 are available to a designer of support post 34, in accordance with the teachings of the present invention. For example, rather than circular openings, cutouts 50 may comprise square, rectangular, triangular, oval, semi-circular, diamond shaped, or practically any other geometric configuration and still obtain some or all of the benefits described herein. Cutouts 50 are positioned, shaped, and sized such that support post 34 retains sufficiently high strength in the lateral direction (the direction perpendicular to the guardrail beam 12) to capture and redirect an impacting vehicle with reasonable dynamic deflection.
The horizontal location 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
Alternatively, a sawcut, diamond shaped notch, or other notch or cut could be employed from the outer edge of the flange and extended inward to form cutouts 50. In this manner, the sawcut, diamond shaped notch, or other notch or cut would form the starting point of the likely point of yielding 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.
Support post 70 is very similar in configuration to support post 34, 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
As shown in
Similar to the support posts described above, LON support post 100 has adequate strength in the lateral direction and sufficiently low strength in the longitudinal direction. LON support post 100 may be embedded in the ground, a concrete footing, or a metal socket. LON support post 100 may be made of wood, metal, plastic, composite materials, or any combination of these or other suitable materials. Furthermore, the cross-section of LON support post 100 may be any engineered shape suitable for releasably supporting a guardrail beam, such as guardrail beam 12. Such cross-sectional shapes may include, but are not limited to, square, rectangular, round, elliptical, trapezoidal, solid, hollow, closed, or open.
Similar to previously described embodiments, LON support post 100 includes a weakened section, such as cutouts 108, that provide reduced strength in the longitudinal direction but maintained strength in the lateral direction. The weakened section may include one or more openings in the form of round or elliptical holes, notches, vertical slots, horizontal slots, saw cuts, or any combination of these or other openings. Alternatively, a sawcut, diamond shaped notch, or other notch or cut could be employed from the outer edge of the flange and extended inward to form cutouts 50. As discussed above, the weakened section is generally at ground level such that LON support post 100 will yield at ground level but may vary above or below grade. The opening or other weakened section may be located on the interior of the post or may intersect an exterior edge. The geometry and size of the opening is as is required for a given post cross section such that the force required to fail, fracture, or yield the post about its strong axis is reduced such that the magnitude and severity of vehicle contact or snagging forces are reduced to safe levels that mitigate the potential for occupant injury and vehicle instability. Where the weakened section includes one or more sawcuts, diamond shaped notches, or other notches or cuts, the weakened section may be cut into the side of the post in one embodiment. Where the weakened section includes a slot, the slot may include a sharp or rounded edge bottom.
As shown in
As shown in
LON support post 186 is formed of wood, plastic, or a composite material and may be embedded in the ground, a concrete footing, a metal socket, or a foundation tube. Although illustrated as having a 6×8 rectangular shape, the cross-section of LON support post 186 may be any engineered shape suitable for releasably supporting a guardrail beam, such as guardrail beam 12. Such cross-sectional shapes may include, but are not limited to, square, rectangular, round, elliptical, trapezoidal, solid, hollow, closed, or open.
Similar to the support posts described above, LON support post 186 has adequate strength in the lateral direction and sufficiently low strength in the longitudinal direction. Specifically, LON support post 186 includes a weakened section, such as a cutout 190, that provide reduced strength in the longitudinal direction but maintained strength in the lateral direction. As shown in
As discussed above, the weakened section is generally at ground level such that LON support post 186 will yield at ground level, but may vary above or below grade. The opening or other weakened section may be located on the interior of the post or may intersect an exterior edge. The geometry and size of the opening is as is required for a given post cross section such that the force required to fail, fracture, or yield the post about its strong axis is reduced such that the magnitude and severity of vehicle contact or snagging forces are reduced to safe levels that mitigate the potential for occupant injury and vehicle instability. Where the weakened section includes one or more notches, the notches may be cut into the side of the post in one embodiment. Where the weakened section includes a slot, the slot may include a sharp or rounded edge bottom.
In operation, the LON support posts described above in
Many advantages may be realized by the use of modified, engineered LON support posts of
Other modifications to support posts and LON support posts in particular, may further prevent tearing of the guardrail beam upon impact. For example,
With regard to the modified Wide flange shape used as support post 200, the cross section of support post 200 is shaped like a modified letter “H” or a modified letter “I”. Specifically, a first flange 202 is substantially straight and, thus, forms a standard leg of an “H” or “I”. A second flange 204 includes a substantially rounded surface such that a first edge 210 and a second end 212 of second flange 204 is curved inward toward web 206 and first flange 202. Second flange 204 forms the face of the support post 200 that couples to and lies adjacent to a guardrail beam 208.
In particular embodiments, second flange 204 may slightly longer than first flange 202. For example, in a particular embodiment, support post 200 is formed from a modified W6×8.5. Whereas a standard W6×8.5 member may include two flanges that are each approximately four inches long, second flange 204 is slightly longer than the standard flange and, thus, slightly longer than first flange 202. For example, in a particular embodiment, second flange 204 may have a length that is approximately six inches long.
In operation, because second flange 204 is rounded toward first flange 202, no sharp edges of support post 200 are adjacent to guardrail beam 208. As a result, second flange 204 forms a cushion at the interface between guardrail beam 208 and support post 200. Accordingly, guardrail beam 208 is not susceptible to rupture by the sharp edges of support post 200 when an errant vehicle comes into contact with the support post-guardrail beam combination.
Despite some structural and orientation differences discussed above, flanges 202 and 204 of support post 200 may include, in particular embodiments, a weakened section such that, similar to the support posts discussed above, modified support post 200 includes a relatively “weak” axis W and a relatively “strong” axis S. For the reasons described above, modified support post 200 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, modified support post 200 is typically able to withstand a significant impact (e.g., with a car traveling at a high rate of speed) about the strong axis S without substantial failure. However, modified support post 200 is intentionally designed such that yielding will more readily occur in response to an impact about the weak axis W.
The modification of the support post to include a curved flange as shown in
In the absence of an offset or spacer block, a flange protector may be positioned at the interface of the guardrail beam and support post. The flange protector may extend beyond the edges of both the post and the rail element to shield the rail element from the edges of the support post and, thus, prevent initiation of cuts or tears in the guardrail beam in the vicinity of the support post as the guardrail system deforms during an impact. The flange protector may take the form of a plate fabricated from metal, wood, plastic, rubber elastomer, or composite materials. When used in conjunction with a corrugated rail element, such as a W-beam or thrie beam, the plate may be fabricated to conform to the shape of the rail element such that it can nest inside the rail element. The dimensions of the plate are such that the edges of the plate extend to or beyond the edges of the support post.
Flange protector 250 includes a body portion that is substantially rectangular. In particular embodiments, flange protector 250 may comprise a substantially flat plate. In other embodiments and in the illustrated embodiment, flange protector 250 includes an indentation 254 in the a first surface 256 that is proximate to support post 252 when the flange protector 250 and support post 252 are assembled together. Specifically, when assembled together, a flange 258 of support post 252 that is proximate flange protector 250 fits into indentation 254. Accordingly, the dimensions of flange protector 250 and the size of indentation 254 may vary as is appropriate for the particular size and shape of support post 252. It is generally recognized, however, that indentation 254 is optional, and flange protector 250 may or may not include such an indentation.
In various embodiments, the depth of flange protector 250 may be selected based on the depth of support post 252. For example, in a particular embodiment, the depth of flange protector 250 may be selected to be less than the predetermined depth of the support post and may be selected to be less than half of the predetermined depth of the support post. As another example, the depth of flange protector 252 may be selected to be less than three inches.
In particular embodiments, for example, where support post 252 includes a W6×8.5 Wide flange, flange protector 250 has a length on the order of approximately 360 millimeters (14.17 inches) and a width on the order of approximately 131 millimeters (5.16 inches). The depth of flange protector 250 may vary within a range on the order of approximately 13 to 62 millimeters (0.5 to 2.4 inches). Indentation 254 in first surface 256 may have a depth of approximately 10 millimeters (0.39 inches), in a particular embodiment. Thus, lips on either side of flange protector 250 may be raised approximately 10 millimeters (0.39 inches) to protect the guardrail beam from the edges of the abutted flange 258 of support post 252 and to keep flange protector 250 from rotating once connected to support post 252. The width of the lips on either side of indentation 254 may be on the order of approximately 13 mm (0.5 inches). For connection between support post 252 and the guardrail beam (not shown), flange protector 250 includes one or more boltholes 260 that are approximately 21 millimeters (0.82 inches) in diameter, in the illustrated embodiment.
The dimensions of flange protector 250 may also be varied. The combination of flange protector 250 with the frangibility of support post 252 in a LON section of guardrail system 10 may provide enhanced impact performance and reduced installation cost. Specifically, a flange protector 250, as an alternative to the standard offset block, may cost much less than the cost of a deep offset block and may be attractive to a number of highways and roads agencies where it is anticipated that the omission of both may result in a system with an increased potential for incidence of rupture of the guardrail beam when contacted with flange 258 of support post 252.
As described above, flange protector 250 shields the guardrail beam from the sharp edges of support post 252 to prevent rupturing of the guardrail beam. Furthermore, a structure such as flange protector 250 may be used as a retrofit spacer block when steel-yielding support post 252 is placed in a foundation tube as an alternative to a wood post. Thus, anywhere it is desirable to protect the guardrail beam from the flanges of support posts, a flange protector 250 may be used. As an additional variation, it is recognized that support post may in particular embodiments include a structural member that of a different cross-sectional shape than that described. For example, and as discussed above, support post may comprise a rectangular, a tubular member, or any other appropriate shape. Where support post does not include flanges such as flanges 258, it is recognized that flange protector may be selected to accommodate the selected cross-sectional shape of the support post and may be termed “a guardrail beam protector.” Returning to
It is desirable for the connectors to sufficiently support guardrail beam 12 but to be readily released upon load being directly applied to support post 14 or upon deflection of the rail element and rotation of the support post in surrounding soil. For example, the connectors may enable support posts 14 to readily release from guardrail beam 12 when support post 14 is contacted by a vehicle.
In particular embodiments, connector 300 includes a bolt with a tapered or wedge-shaped head 302, such as a countersunk bolt. Connector 300 provides sufficiently low force against guardrail beam 12 to release support post 14 from guardrail beam 12 when an errant vehicle contacts and displaces support post 14. Stated differently, the connection formed between guardrail beam 12 and support post 14 by connector 300 is strong in shear and weak in tension. The shape of countersunk head 302 allows connector 300 to pull through the mounting slot on the guardrail beam 12. Connector 300 may then be displaced with support post 14 upon impact.
Such a connector is improved over oval shoulder button head bolts that provide adequate support for the guardrail beam but do not provide sufficiently low release strength. Connector 300 is also improved over small diameter bolts, which are typically used with several washers. Small diameter bolt-washer combinations provide only a limited ability to support the guardrail beam (not strong in shear) and have variable release strengths.
In a particular embodiment, connector 300 may include slotted countersunk bolts such as, for example, 16 mm (⅝-inch) diameter by 38 mm (1-½-inch) long slotted flat countersunk head machine screws. The countersunk head 302 of connector 300, in such an embodiment, may have a diameter on the order of approximately 25 millimeters (1 inch) and have a length on the order of 13 millimeters (½ inch). Other embodiments may include a countersunk head 302 having a diameter on the order of 25 millimeters (1 inch) and a length on the order of 6.5 millimeters (¼ inch). It is generally recognized, however, that these are merely two examples of connectors 300 that may be used to releasably engage guardrail beam 12 with support post 14. Other connectors that may be used in place of connector 300 include those specified by ANSI/ASME B18.5.
Still other, alternative embodiments of possible connectors may include appropriately sized standard bolts that will tear through the guardrail beam without rupturing the guardrail beam. For example, the standard bolts may select such that a head portion of the bolt is of a size that overlaps an edge of the aperture by a distance that generates a desired pullout resistance. In particular embodiments, the size of the head portion selected as a function of a thickness of the guardrail beam. Such bolts may include ⅝-inch bolts, ¼-inch bolts, or 3/16-inch bolts with or without washers. A plow bolt may also be used where the resulting connection is weak in tension such as to release when a lateral load is applied. In still other embodiments, connector 300 may release through fracture, shear, or tensile failure.
Additionally, the configuration of connector 400 prevents connector 400 from rotating when connector 400 is used to couple support post 14 with guardrail beam 12. Specifically, head 402 of connector 400 includes a first surface 404 and a second surface 406. Whereas first surface 404 comprises the outer surface of connector 400, second surface 406 is proximate threaded shaft 408. In the illustrated embodiment, first surface 404 of head 402 is of a substantially round configuration. By contrast, second surface 404 is of a substantially oval configuration. Thus a portion of head 402 includes a shoulder 410. Where guardrail beam 12 includes a slotted hole through which connector 400 is placed, the oval shape of shoulder 404 prevents connector 400 from rotating in the slotted hole. The shoulder 410 of connector 400 also limits the horizontal movement of connector 400 within the slotted hole of guardrail beam 12. This, in turn, limits the amount of overlap of head 402 of connector 400 with the edge of the slotted hole of guardrail beam 12. The result is that the pullout force required to disengage connector 400 from guardrail beam 12 is further reduced.
In a particular embodiment, connector 400 may include slotted countersunk bolts such as, for example, 16 mm (⅝-inch) diameter by 38 mm (1-½-inch) slotted flat countersunk head machine screws. The countersunk head 402 of connector 400, in such an embodiment, may have a diameter on the order of approximately 25 millimeters (1 inch) and have a length on the order of 13 millimeters (½ inch). The diameter of the longer dimension of oval shoulder 406 may correspond generally with the diameter of head 402 or approximately 1 inch, and the diameter of the shorter dimension of oval shoulder 406 may correspond generally with the diameter of the bolt shaft or approximately ⅝ inch. It is generally recognized, however, that this merely one example of a connectors 400 that may be used to releasably engage guardrail beam 12 with support post 14. Other connectors may be used in place of connector 400.
Technical advantages of particular embodiments of the present invention include a LON guardrail support post that has sufficient strong axis strength to redirect vehicles that collide along the length of the guardrail system at an angle to the flow of traffic. As a result, the guardrail system may readily yield to an impacting vehicle at low force levels.
A further technical advantage may include a weakened connection between the support post and guardrail beam such that the support post detaches from the guardrail beam when struck by an errant vehicle. Specifically, a connector may be provided that adequately supports the guardrail beam while releasing from the guardrail beam when a lateral force is applied to the guardrail beam. Accordingly, in particular embodiments, an advantage may be that the connection is strong in shear and weak in tension.
At least four types of guardrail support members are described and illustrated within this specification: (I) W6×9 Wide flanges; (II) W8×10 Wide flanges; (III) W6×8.5 Wide flanges; and (IV) weakened wood posts. 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 yielding 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. For example, the features described above may be used independently and/or in combination with each other or other design modifications. Changes in the size or strength of the bolts connecting the rail to the offset blocks or flange protectors and support posts and the hole/slot pattern in the rail through which these connecting bolts pass may be varied in any manner suitable for enabling the post to release from the guardrail element.
This patent application claims priority from Patent Application Ser. No. 60/718,679, filed Sep. 19, 2005, entitled A Weakened Guardrail Mounting Connection, attorney docket no. 017575.1083.
| Number | Date | Country | |
|---|---|---|---|
| 60718679 | Sep 2005 | US |
