Patent Application
20070102689
The present invention relates generally to guardrail systems and more particularly, to a cable barrier guardrail system with steel yielding support posts.
Guardrail systems are widely used along heavily traveled roadways to enhance the safety of the roadway and adjacent roadside. For example, guardrail systems may be used to accomplish multiple tasks, such as containing and redirecting an errant vehicle upon impact. One such system includes a guardrail beam, such as a “W-beam” (named after its characteristic shape), and corresponding support posts. Other systems may utilize cables and corresponding support posts.
Support posts may be made of metal, wood, plastic, composites, or other materials. The material(s) forming the support posts may depend upon design and/or economical factors. For example, wood 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 and durability.
To avoid undesirable effects, it may be desirable that the support posts yield or break away upon impact in the longitudinal direction, thus producing a desired behavior during a collision by a vehicle at the impact site. Steel support posts that are modified to produce desired behavior during a collision have recently become available. Examples include a “hinged breakaway post” described in U.S. Pat. No. 6,886,813, an “energy absorbing breakaway steel guardrail post” described in U.S. Pat. No. 6,254,063, and a “support post” described in U.S. Patent Application No. 2003/0222254. Many such prior attempts require substantial time, money, and resources during fabrication, modification, and/or installation, however. Furthermore, wood posts may not provide sufficient strength to limit lateral deflections to desired levels. Such posts may also deteriorate rapidly from exposure to the elements. As a result, alternate materials are sought.
In accordance with a particular embodiment of the present invention, a guardrail system includes at least one cable operable to contain and redirect an errant vehicle. The guardrail system also includes a plurality of guardrail support posts spaced apart in relation to one another. Each support post includes a lower portion, a mid portion, and an upper portion. The lower portion is for installing below grade adjacent the roadway. The mid portion lies substantially adjacent the grade and includes a weakened section operable to weaken the support post about a longitudinal axis. The upper portion is releasably coupled to the at least one cable such that the upper portion is uncoupled from the at least one cable when the support post is displaced.
In accordance with another embodiment, a guardrail support post includes a continuous structural member having 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 has a lower portion for installing below grade adjacent the roadway, an upper portion configured to couple with at least one cable, and a mid portion between the upper portion and the lower portion. The upper portion includes a cable slot formed in the web of structural member. The cable slot includes a first portion comprising a plurality of enlarged openings. Each pair of adjacent enlarged openings are separated by a restriction. Each of the plurality of enlarged openings are adapted to receive a cable. A second portion includes a substantially U-shaped configuration and is adapted to receive at least one cable.
Technical advantages of particular embodiments of the present invention include a guardrail support post that has sufficient lateral strength to redirect vehicles that collide along the length of the guardrail system at an angle to the flow of traffic with limited deflection and reduced longitudinal strength that mitigates the severity of the interaction (snagging) between an impacting vehicle and the post. Accordingly, a guardrail system of the present invention may provide benefits in terms of space (reduced deflection for a given post spacing) and cost savings (as a result of fewer posts required to achieve a desired deflection).
Other technical advantages may include increased flexibility with respect to design requirements of support posts. For example, wood support posts may be utilized in a cable guardrail system, in particular embodiments. Where wood support posts include a modified section, larger posts may be used than in conventional guardrail systems using wood posts. As a result of the increased lateral stiffness of the larger posts, the spacing between support posts may be increased, and less support posts may be required in the overall guardrail system without a resulting increase in deflection. Accordingly, a further technical advantage may include reduced costs associated with the installation and repair of the cable guardrail system. Similarly, if the spacing between support posts is left unchanged, the increased lateral stiffness of the larger posts may result in reduced lateral deflection. Accordingly, the cable guardrail system can be used at more restrictive locations.
Additional advantages may be realized by the mechanical coupling of the guardrail support posts to one or more cables used to contain and redirect errant traffic. In particular embodiments, a modified slot may releasably secure the cables with respect to the support post. A first portion of the modified slot may maintain the cables at a desired elevation with respect to the ground. The first portion may also maintain one or more cables in a position that is resistant to release from the support post. A second, generally U-shaped portion may similarly maintain a cable at a desired elevation with respect to the ground. However, the U-shaped portion may increase the strength of the web of the support post and thus provide resistance to the yielding of the support post. Accordingly, the second portion may reduce deflection of the support post.
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:
The illustrated portion of cable guardrail system 10 includes a terminal section 12 and a length-of-need (LON) section 14. Generally, the LON section 14 extends adjacent to a desired length of the roadway. The LON section 14 includes a cable system 16 comprised of at least one cable 18 that operates to redirect errant vehicles. The cable system 16 is supported by support posts 20. In the illustrated embodiment, cable system 16 includes three cables 18 (upper cable 18a, middle cable 18b, and lower cable 18c). Other embodiments, however may include a cable system 16 that has as few as one cable 18 and as many as five or more cables 18. It is generally recognized that the number of cables may vary depending upon factors such as the type of vehicles using the associated roadway and the hazard which requires installation of cable guardrail system 10.
In particular embodiments, cables 18 comprise wire rope cables; however, other embodiments may include other types of cables, wire rope, or steel strands. One example cable for use in cable guardrail system 10 includes a 0.75″ diameter 3×7 wire rope. Other cables that may be used in cable guardrail system 10 may include wire rope having a diameter of ¼″ to 2″, or any other size suitable for use in cable-type guardrail systems.
Although all cables 18 in cable system 16 may be of a common size, one of ordinary skill in the art may recognize that the size of each cable 18 may vary, in certain embodiments. For example, top cable 18a may be of a larger diameter than middle cable 18b and lower cable 18c. Such an embodiment may provide additional resistance for accommodating taller and heavier vehicles, such as semi trailer trucks. For similar reasons, middle cable 18b may be of a larger diameter than lower cable 18c to provide greater resistance to larger vehicles, such as sport utility vehicles.
Terminal section 12 includes cable anchor posts 22, which each anchor an initiation point of a cable 18 within cable system 16. In the illustrated embodiment, each cable 18 is anchored or secured by, or coupled to, a separate cable anchor post 22 proximate a ground surface 24. For example, cable 18a is coupled to cable anchor post 22a, cable 18b is coupled to cable anchor post 22b, and cable 18c is coupled to cable anchor post 22c. Accordingly, since the illustrated cable system 16 includes three cables 18, terminal section 12 includes three cable anchor posts; however, other embodiments may include a terminal section with fewer or greater than three cable anchor posts. For example, some embodiments of the present invention may include four cable anchor posts that each anchor one of four cables. Cable guardrail systems in accordance with other embodiments may also include terminal systems with more than one cable coupled to a single cable anchor post. For example, one embodiment may include a terminal section with four cables and two cable anchor posts, in which case each cable anchor post may anchor two cables. In such situations, it may be desirable to separately anchor at least some cables to facilitate construction and repair of the system.
It should be understood that cable anchor posts 20 of
As described above, cables 18 are also each secured to support posts 20, which support such cables 18 in a generally horizontal and parallel relation above ground surface 24. In the illustrated embodiment, cable anchor posts 22 and support posts 20 are securely anchored in concrete footers 26. However, other embodiments may utilize other mechanisms or methods to anchor cable anchor posts 22 and support posts 20. For example, some embodiments may utilize sleeves, foundation tubes, ground struts, or trapezoidal soil plates to secure posts of a cable guardrail system.
The orientation and spacing of cable anchor posts 22 and support posts 20 may vary in various embodiments. As illustrated in
Cable guardrail system 10 is intended to keep errant vehicles from encountering roadside hazards and opposing traffic during a crash or other hazardous situation. In many instances, cable guardrail system 10 is installed between a roadway and a significant hazard to vehicles (e.g., another roadway, a bridge, cliff, etc.). Therefore, cable guardrail system 10 should be designed to withstand a significant impact from a vehicle leaving the roadway and striking the guardrail at an angle, without substantial failure.
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 cable guardrail system 10 adjacent its terminal section 12, in a direction generally parallel to the roadway. For example, if the cable guardrail system 10 were rigidly fixed in place during a crash, serious injury and damage may result to the errant vehicle, its driver and passengers.
In particular embodiments, cable anchor posts 22 may include releasable cable anchor posts such as those described in U.S. Pat. No. 6,932,327 (“'327 patent”). As a result, each releasable cable anchor post may yield or break-away and release its respective cable in the event of an impact by a vehicle striking the post. The performance of cable guardrail system 10 may be improved since the vehicle is less likely to become hung up on the cable anchored post. Conversely, in the event that a vehicle strikes cable guardrail system 10 at a location other than a particular releasable cable anchor post, then releasable cable anchor posts resist release of their respective cables and hold and anchor their respective cables. Thus, if a vehicle impacts cable guardrail system 10 at an angle to the flow of traffic at any point along its length-of-need (“LON”), then each releasable cable anchor post may be designed to hold their respective cables to aid in the redirection of the vehicle toward the roadway. In particular embodiments, each releasable cable anchor post may hold and anchor the cable(s) that it secures in the event of an impact to a separate releasable cable anchor post. Furthermore, having particular cables of the system separately anchored and released may facilitate construction and repair of the system and reduce cost.
Improperly designed posts in the LON section 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 guardrail system at an angle along the LON section. The vehicle may encounter (contact) numerous support posts which if not properly designed may induce and increase risk to the driver and passengers. Additionally, the guardrail may fail in its purposes of containing and redirecting the errant vehicle.
In accordance with the teaching of the present invention, support posts 20 in LON section 14 have been modified to decrease the strength of support posts 20 in a direction generally parallel to axis 28 (generally along the direction of traffic) without substantially decreasing its strength in a direction generally perpendicular to axis 28 (out of the page in
Although support post 20 has buckled, cables 18 remain in substantially the same position with respect to the road as the position of cables 18 prior to the collision. The position of cables 18 is maintained due to the uncoupling of support post 20 with cable system 16 upon impact. Specifically, and as will be described in more detail below, support post 20 is configured to releasably couple to cable system 16. Upon impact, the coupling mechanism releases cables 18 such that cable system 16 remains intact and in position to operate to redirect the errant vehicle to prevent the vehicle from encountering roadside hazards and opposing traffic. Thus, the impact performance of cable system 16 of guardrail system 10 is not compromised by the modified support post 20.
With regard to a Wide flange shape used as a guardrail post, the cross section is typically shaped like the letter “I” as shown in
In a particular embodiment, the Wide flange comprising support post 40 is a standard S4×7.7, which has a nominal four-inch depth and weighs 7.7 pounds per foot. Those of ordinary skill in the art will recognize, however, that wide flange beams may be available in many different sizes, and many different sizes may be appropriate for use as a support post 40. Accordingly, in alternative embodiments, support post 40 may include a standard W6×9, which may have a six-inch depth and weigh from eight and one half pounds per foot to nine pounds per foot. The standard W6×9 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. In still other embodiments, support post 40 may include a standard W8×10, which may have an eight-inch depth and weigh approximately ten pounds per foot. As a further modification, it is recognized that persons skilled in the art may utilize other structural shapes for the support posts. Such shapes may 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.” Additionally, a non-wide flange such as a “C-channel” may be substituted for the wide flange support post.
Support post 40 is relatively “weak” about axis W, and relatively “strong” about 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 traveling 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 such that damage and deceleration of the impacting vehicle are minimized.
In particular embodiments, support post 40 may have a length on the order of approximately 3′-11¼″ and includes an upper portion 48, a lower portion 50, and a mid portion 52 which spans between upper portion 48 and lower portion 50. Upper portion 48 includes a cable slot 54 that is adapted to releasably couple to a cable system (e.g., cable system 16 that includes cables 18) upon support post 40. Lower portion 50 is suitable for installation below grade, as part of a guardrail support system. Mid portion 52 includes two cutouts 56, which are configured to weaken support post 40 about the weak axis W, to more readily allow for buckling 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.
Cutouts 56 are positioned within mid portion 52 to weaken support post 40 about weak axis W, substantially adjacent to or near grade (when installed). When cutouts 56 are positioned at or near grade, the configuration of support post 40 may accommodate yielding of support post 40 approximately at or near grade, allowing support post 40 to “fold” over from the point of yield, upward or otherwise be displaced. It will be recognized by those of ordinary skill in the art that the size, configuration, location and number of cutouts may be varied significantly within the teachings of the present invention.
In a particular embodiment, cutouts 56 may be positioned approximately 2′-7¾″ below a top edge 58 of support post 40. However, the location of cutouts 56 may vary in accordance with the teachings of the present invention. As described above, the configuration of
The height of cutouts 56 above grade should not exceed a point at which support post 40 will yield or break-away at cutouts 56, 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.
Support post 40 includes a modified cable slot 54 having a configuration that allows for the releasable coupling of support post 40 with one or more cables. In the illustrated embodiment, cable slot 54 is formed in web 46 of the wide flange support post. Forming cable slot 54 in web 46 eliminates requirements for bolts, hooks, or other mechanical attachments to releasably secure cable system 16 to support post 40. Furthermore, in the illustrated embodiment, modified cable slot 54 comprises an open slot since it is open at top edge 58 of support post 40. Because cable slot 54 is open, cables 18 may be slid into cable slot 54 during assembly of cable guardrail system 10. Thus, cable slot 54 aids in the efficient installation of cable guardrail system 10.
Modified cable slot 54 is an elongated slot extending from top edge 58 towards bottom edge 60 of support post 40. The length of modified cable slot 54 may be selected in part based on desired vertical spacing of cable system 16 relative to the adjacent roadway. The length of modified cable slot 54 may also be selected to accommodate the number of cables 18 which will be installed therein and desired vertical spacing between each cable 18.
In the illustrated embodiment, modified cable slot 54 is of a modified U-shaped configuration that is defined in part by first edge 61, second edge 62 and bottom edge 63. A first portion 64 of each of first edge 61 and second edge 62 is of a wave-like configuration. Thus, one or more restrictions 65 are formed within cable slot 54.
Restrictions 65 of cable slot 54 may be defined in part by corresponding projections 66 on first and second edges 61 and 62. First and second edges 61 and 62 of cable slot 54 preferably include alternating tapered or sloping surfaces which form projections 66. The same tapered or sloping surfaces also form enlarged openings 67 within cable slot 54. The location of enlarged openings 67 are preferably selected to correspond with approximate desired locations for cables 18. Thus, in the illustrated embodiment, each of first and second edges 61 and 62 include three projections 66, defining two openings 67 there between. As will be described in more detail below, such a configuration allows the assembly of three or fewer cables 18 within cable slot 54.
In various embodiments, the gap or spacing formed between corresponding projections 66 on first and second edges 61 and 62, respectively, is generally selected to be greater than the outside diameter of cables 18. Specific dimensions between the respective projections are selected to facilitate disengagement between cables 18 as support post 40 with cable slot 54 is bent from a generally vertical position towards a horizontal position while allowing easy installation of cables 18 in cable slot 54.
A second portion 68 of each of first edge 61 and second edge 62 is of a U-shaped configuration. Thus, first and second edges 61 and 62 of second portion 68 have a generally smooth profile and extend generally parallel with each other in a direction that is generally parallel to the longitudinal axis of support post 40. In particular embodiments the width of the space formed between first and second edges 61 and 62 is the same as the width of the space formed between restrictions 65 of first portion 64. Generally, the width of the space is selected to be slightly greater than the outside diameter of cables 18. The bottom edge of second portion 68 of cable slot 54 corresponds generally with bottom edge 63 and includes but is not limited to a substantially round radius of curvature. The radius of curvature may be such as to support a cable 18 within cable system 16 in second portion 68 of modified cable slot 54.
In the illustrated embodiment, modified cable slot 54 includes three restrictions 65 formed within cable slot 54. In particular embodiments, the first (or upper) restriction 65 may be formed approximately ⅝″ from the top edge 58 of support post 40. The second (or middle) restriction 65 may be formed approximately 4 5/16″ below the first restriction. The third (or lower) restriction 65 may be formed approximately 4 5/16″ below the second restriction.
Restrictions 65 are formed by projections 66 in first and second edges 61 and 62, respectively. In particular embodiments, the width of the space defined by restrictions 65 may be approximately 13/16″. Similarly, the width of the U-shaped slot defined by first and second edges 61 and 62 of second portion 68 may also be on the order of approximately 13/16″. Conversely, the width of the space defined by openings 67 may be approximately 1⅜″. Thus, modified cable slot 54, as illustrated, is configured to secure any size cable 18 that may be slightly smaller than 13/16″.
As stated above, the location of cables 18 is related to the location of openings 67 within cable slot 54. Specifically, a first (or upper) opening 67 may be located approximately 2 25/32″ from top edge 58 of support post 40. Thus, upper cable 18a may be supported at an elevation that is approximately 2 25/32″ from the top edge 58 of support post 40. Second (or lower) opening 67 may be approximately 4 5/16″ below the first opening 67. As a result, middle cable 18b may be supported at an elevation that is approximately 7 3/32″ below top edge 58 of support post 40. Finally, lower cable 18c, which may rest on lower edge 63 of cable slot 54, may be supported at an elevation that is approximately 11 13/16″ from the top edge 58 of support post 40. The radius of curvature corresponding to bottom edge 63 of cable slot 54 is approximately 13/32″ in the illustrated embodiment.
Support post 40 is a single, continuous structural member that does not require any labor in field assembly, welding, or special handling, in particular embodiments. With the exception of modified cable slot 54 and cutouts 56 support post 40 has a continuous, generally uniform cross-section from top edge 58, to a bottom edge 60. 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).
As described above, cutouts 56 of support post 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 56 comprise generally circular openings that have been punched or drilled through support post 40. In the illustrated embodiment of
Previous attempts to accommodate yielding 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 at an angle relative 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). The support post of the '029 Application may yield at any point along the slots, and yielding may be based upon imperfections in the material adjacent the slots. By contrast, cutouts 56 provide an enhanced ability to control the point of yield of support post 40 during a collision with a vehicle. By limiting the vertical dimension of cutouts 56, it is easier to dictate the precise point of yielding of support post 40 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 and/or result in increased deflections of cable guardrail system 10.
In accordance with the teachings of the present invention, the vertical dimension of each cutout 56 is limited based upon the horizontal dimension of cutout 56. 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
Modifications, additions, or omissions may be made to support post 40 without departing from the scope of the invention. For example, it will be recognized by those of ordinary skill in the art that the size, configuration, location and number of cutouts, cable slots, and their relationship with each other may be varied significantly within the teachings of the present invention. Additionally, various configurations of cutouts 56 and cable slot 54 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 56 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.
As a further modification, the horizontal orientation of cutouts 56 within flanges 42 and 44 may also be altered significantly, within the teachings of the present invention. In the illustrated embodiment of
Alternatively, a saw cut could be employed from the outer edge of the flange, and extending inward, to form cutouts 56. In this manner, the saw cut would form the starting point of the likely point of yield along the weak axis of the support post. Rather than a saw cut, 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.
As still another modification, various configurations of cable slot 54 are available to a designer of support post 40, in accordance with the teachings of the present invention. Thus, the modified cable slots illustrated in
In still other embodiments, cable slot 54 may be omitted. Cables 18 of cable system 16 may be fastened to flanges 42 and 44 or to another component of support post 40 using J bolts, I bolts, U bolts, locking hook bolts, bent pieces of plate, or another fastener or mechanical connection. Where cables 18 of cable system 16 are attached to an I-beam support post such as the one illustrated in
In the illustrated embodiment, support post 70 is slightly longer than support post 40 of
Upper portion 78 includes a modified cable slot 84 that is adapted to releasably couple to a cable system (e.g., cable system 16 that includes cables 18) upon support post 70. Like modified cable slot 54 of FIGURES 3A-3C, modified cable slot 84 has a configuration that allows for the releasable coupling of support post 70 with one or more cables. In the illustrated embodiment, modified cable slot 84 is formed in web 76 of the wide flange support post. Like modified cable slot 54, modified cable slot 84 comprises an open, elongated slot extending from top edge 86 towards bottom edge 88 of support post 70.
In the illustrated embodiment, the length of modified cable slot 84 is slightly longer than modified cable slot 54 of
In the illustrated embodiment, modified cable slot 84 is defined in part by first edge 91, second edge 92 and bottom edge 93. A first portion 94 of each of first edge 91 and second edge 92 is of a wave-like configuration and includes five restrictions 95. Restrictions 95 are defined in part by corresponding projections 96 on first and second edges 91 and 92. Restrictions 95 are separated by enlarged openings 97 within cable slot 84.
As described above, cables 18 within a cable system 16 are preferably disposed at different heights relative to the ground and relative to each other. Varying the vertical spacing between cables 18 often provides a much wider lateral catch area for vehicles impacting with cable guardrail system 10. The vertical spacing between cables 18 may be selected to satisfactorily contain both pickups and, to some extent, even larger trucks with a relatively high center of gravity, as well as vehicles with a low front profile and low center of gravity. Thus, in particular embodiments, the location of at least a portion of enlarged openings 97 are preferably selected to correspond with approximate desired locations for cables 18. In the illustrated embodiment, each of first and second edges 91 and 92 include five projections 96, defining four openings 97 there between. Where a cable 18 is supported in each opening 97, such a configuration allows the assembly of as many as five cables 18 within cable slot 84 (one cable per opening 97 and one cable per elongated U-shaped slot within second portion 98 of cable slot 84).
It is recognized, however, that the ratio of openings 97 to cables within cable system 16 is not necessarily 1:1. Accordingly, modified cable slot 84 may include more openings 97 than there are cables 18 within cable system 16. In such embodiments, spacers (described in greater detail below with respect to
Support posts such as support post 102 may be installed at desired locations adjacent to a roadway and/or median. Various techniques may be used to anchor support post 102 with respect to the ground. For example, support post 102 may be securely anchored in a concrete footer, such as concrete footer 30 illustrated in
After the installation of support post(s) 102 and terminal posts, cables 18a, 18b, and 18c (or any number of desired cables) may be rolled out and placed on the ground extending generally longitudinally the desired length of the cable guardrail system. One end of each cable 18 may be connected with a respective cable anchor post (not shown).
Lower cable 18c may be inserted into modified cable slot 108 and may be slid down modified cable slot 108 until lower cable 18c rests on the bottom edge 110 of cable slot 108. A spacer 104a may then be inserted or dropped into cable slot 108 to rest on lower cable 18c.
Spacer 104a may be formed from a wide variety of materials including polymeric materials, elastomeric materials, recycled materials, structural foam materials, composite materials, wood, and/or lightweight metal alloys. In particular embodiments, spacer 104a may be injection molded from rubber and/or other plastic materials. The present invention is not limited, however to forming spacer 104a from any specific type of material or with any specific dimensions or configurations.
Web 116 of spacer 104a has a width that is narrower than the narrowest portion of modified cable slot 108 of support post 102. Accordingly, where support post 102 includes an S4×7.7, the width of web 116 may be on the order of or less than approximately ¾″. As a result, spacer 104a and, specifically, web 116 of spacer 104a may be slid through the opening of modified cable slot 108 such that flanges 112 and 114 of spacer 104a are disposed on opposite sides of the web member of support post 100.
Additionally, each of flanges 112 and 114 have a width that is greater than the widest portion of modified cable slot 108. As a result, flanges 112 and 114 operate to secure spacer 104a in modified cable slot 108. In the illustrated example, where support post 102 comprises an S4×7.7, flanges 112 and 114 may have a width on the order of approximately 2″. However, other configurations may be suitable for spacer 104a. It is only material, however that flanges 112 and 114 are wider than the widest portion of modified cable slot 108 and narrower than the length of the web portion of the support post 102.
As illustrated, web 116 of spacer 104a is tapered at both a first (upper) end 118 and a second (lower) end 120. Accordingly, web 116 of spacer 104a includes a first tapered portion 122 and a second tapered portion 124, which are separated by a substantially vertical portion 126. Thus, while the substantially vertical portion 126 of web 116 may have a width on the order of approximately ¾″, the tapered portion 122 of web 116 at upper edge 118 may have a width on the order of approximately ½″. Similarly, tapered portion 124 of web 116 at lower edge 120 may have a width on the order of approximately ½″. When configured as described or similarly configured, tapered portions 122 and 124 may improve the ease with which spacer 104a may be slid onto support post 102.
Returning to
After the insertion of middle cable 18b, a spacer 104b may then be inserted or dropped into modified cable slot 108 to rest on middle cable 18b. In particular embodiments, spacer 104b may be configured substantially similar to spacer 104a described above. Upper cable 18a may then be inserted into modified cable slot 108 of support post 102. Upper cable 18a may be slid down modified cable slot 108 until upper cable 18a rests on the upper edge 118 of spacer 104b. Thus, middle cable 18b and upper cable 18a are separated by spacer 104b. Accordingly, the height of spacer 104b (3 9/16″ in a particular embodiment) is preferably selected to correspond with the desired vertical spacing between middle cable 18b and upper cable 18a.
One or more retaining bands 106 may then be secured around the exterior of support post 102 between upper cable 18a and middle cable 18b and/or between middle cable 18b and lower cable 18c. In particular embodiments, retaining band(s) 106 may be placed on the exterior of support post 102 to provide additional strength to support post 102. For example, retaining band(s) 106 may increase the strength of support post 102 and compensate for the weakened web that results from material being removed for modified cable slot 108. Retaining band(s) 106 may also operate to keep the cable-support post connection intact longer when impacted by an errant vehicle.
Retaining band(s) 106 may be formed from various types of metals, elastomeric materials and/or composite materials. For some applications, retaining band(s) 106 may be formed from a relatively strong steel alloy to provide additional support to allow post 30 to handle forces imposed on support post 102 by cables during a vehicle impact with cable guardrail system 10.
In a particular embodiment, retaining band(s) 106 may comprise a metal strap having a total length of approximately 14 13/16″ before being wrapped around support post 102. The width of the metal strap may be on the order of approximately 1¼″ and the depth (or thickness) may be on the order of approximately 0.04″. After installation around support post 102, the opposites ends of a metal strap having a total length of approximately 14 13/16″ may overlap by approximately 11/16.
After the assembly of retaining band(s) 106 around support post 102, a first end of each cable 18 may be secured to a cable anchor post of a first terminal section, such as cable anchor post 22 of terminal section 12 illustrated in
When installed adjacent a roadway, support post 102, as part of an overall cable guardrail system, protects vehicles, drivers, and passengers from various obstacles and hazards. Specifically, and as described above, support post 102 is intentionally designed to preferably buckle about a weakened section when struck by an errant vehicle. However, cables 18 may remain in substantially the same position with respect to the road as the position of cables 18 prior to the collision. The position of cables 18 is maintained due to the uncoupling of support post 102 with the cables 18 upon impact. Specifically, as support post 102 buckles, cables 18 slip out of modified cable slot 108 through the open area at top edge 54. In the process, retaining band(s) 106 and spacers 104 may be disengaged from support post 102. Because cables 18 may remain in substantially the same position as their original position with respect to the roadway, cables 18 may operate to redirect the errant vehicle to prevent the vehicle from encountering roadside hazards and opposing traffic. Repair of the support system may involve the isolated replacement of support post 102 and any damaged components such as spacers 104 and retaining band 106.
Support post 150 is approximately 6′ long, and includes an upper portion 152, a lower portion 154, and a mid portion 156. In the illustrated embodiment, upper portion 152 includes three pairs of bolt holes 152 that are adapted to receive connectors for the installation of cables 18 of cable system 16. For example, bolt holes 152 may be adapted to receive U-shaped bolts, hook bolts, or other fasteners. Lower portion 154 is suitable for installation below grade, as part of a guardrail support system. Mid portion 156 comprises a weakened section 160 which is configured to weaken support post 150 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 150, and its upper, lower, and mid portions may vary significantly, within the teachings of the present invention.
Bolt holes 158 include a standard configuration that allow for the installation of cables 18, upon support post 150. In general, each pair of bolt holes 158 maintain a cable 18 at a desired distance above grade. However, the number, size, location, and configuration of bolt holes 158 may be significantly modified, within the teachings of the present invention. As just one possible modification, in particular embodiments, each pair of bolt holes 158 may be replaced with a single bolt hole 158. Such a configuration may be compatible with fasteners such as J bolts in which only one leg of the bolt may penetrate support post 150. Additionally, it is recognized that while all cables 18 may be support on one side of support post 150 in certain embodiments, other embodiments may include alternating the installation of cables 18 on opposing sides of support post 150.
Weakened section 160 is positioned within mid portion 156 to weaken support post 150 about weak axis W, adjacent to or near grade (when installed). This will accommodate yielding of support post 150 approximately at grade or near grade, allowing support 150 to fracture or otherwise yield at the point of failure.
In the illustrated embodiment, weakened section 160 includes a pair of cutouts or notches disposed in opposing sides of support post 150. Specifically, weakened section 160 comprises a saw cut that extends inward to form cutouts in opposing sides of support post 150. In particular embodiments, the saw cut may include a 45 degree notch. However, one of ordinary skill in the art will recognize that notches or saw cuts of other angles may also be employed where appropriate. It will also be recognized by those of ordinary skill in the that the size, configuration, and location of weakened section 160 may be varied significantly within the teachings of the present invention. For example, in addition to or in lieu of saw cuts, weakened section 160 may include one or more circular cutouts similar to those described above with respect to I-beam type support posts. Thus, weakened section 160 may include one or more holes drilled in the longitudinal axis of support post 150. In other embodiments, weakened section 160 may comprise one or more square, rectangular, triangular, oval, diamond shaped, or other geometric configuration of apertures.
By weakening support post 150, wood posts of greater dimensions may be used than in conventional guardrail systems using unmodified wood posts. As a result, the spacing between support posts 150 may be increased, and less support posts 150 may be required in the cable guardrail system to achieve a desired deflection. Such a design may reduce the costs associated with the installation and repair of the cable guardrail system. Specifically, longer spacing between support posts generally affects the total cost of the cable safety system, not only material, but also installation time and cost.
At least three types of guardrail support members are described and illustrated within this specification: (I) S4×7.7 Wide flanges; (II) W6×9 Wide flanges; (III) W8×10 Wide flanges; and (IV) 4×6 wood post. It should be recognized by those of ordinary skill in the art that practically any size, shape, or configuration of guardrail support post may be enhanced by incorporating the teachings of the present invention. Any material including wood, metal, plastic, composite materials, or any combination of these or other suitable materials may be used to form support posts. Additional examples of the types of support posts that may be used may include steel pipe and square tubing. Furthermore, 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 cables to the support posts and the hole/slot patterns in the support posts through which these connecting bolts pass may be varied in any manner suitable for enabling the cables to release from the support posts upon impact with an errant vehicle.
