BACKGROUND OF THE INVENTION
The major components of a W-beam type guardrail system include a standard guardrail section and terminals at each end of the standard section. The standard guardrail section shields errant vehicles from roadside hazards by containing and redirecting the vehicles on side impacts. A guardrail terminal section must safely accommodate errant vehicles for both end-on impacts and side impacts near the terminal ends. For side impacts beyond a specified point, which in the art is typically selected to be 12 ft-6 in. from the end of the terminal, the terminal section must also serve the function of containing and redirecting an errant vehicle and not allow it to gate or pass through. This specified point is known in the art as the “beginning of length-of-need.”
W-beam guardrails use tensile forces developed in the rail element as the means to contain and redirect errant vehicles during side impacts. The tensile force in the rail element is then transmitted to anchors in the ground via cables at the ends of both terminals. Thus, the anchor has to be strong enough to handle the tensile forces. Further, the anchor has to be of a breakaway design for the terminal to function properly upon end-on impacts and side impacts near the end of the terminal.
For end-on impacts, existing guardrail terminals may be grouped into two general categories: a) energy absorbing, and b) non-energy absorbing.
Energy absorbing terminals incorporate a mechanism for dissipating the impact energy to bring an errant vehicle to a controlled and safe stop. Examples of such energy absorbing terminals include: the Sequential Kinking Terminal (SKT), Flared Energy Absorbing Terminal (FLEAT), and ET-2000. It should be noted that energy absorbing terminals only dissipate large amounts of impact energy during low-angle end-on impacts. If a vehicle strikes the end of the terminal at an angle of 15 degrees or more, energy absorbing terminals will allow vehicles to safely pass or “gate” through the guardrail system.
Non-energy absorbing guardrail terminals are designed to allow the errant vehicle to safely pass or “gate” through the terminal and proceed behind the guardrail. The gating process does not dissipate much of the impact energy or slow down the vehicle significantly. The typical gating mechanism is to flare the end of the terminal away from the tangent section of the guardrail. Examples of existing non-energy absorbing guardrail terminals include: Breakaway Cable Terminal (BCT), Eccentric Loader Terminal (ELT), Modified Eccentric Loader Terminal (MELT), Slotted Rail Terminal (SRT), and the REGENT.
In end-on impacts with non-energy absorbing terminals, the rail element would be loaded eccentrically due to the end offset of the terminal from the tangent of the standard section. The eccentric loading causes the rail element to buckle without imparting excessive decelerations on the vehicle. After the rail element buckles, the vehicle gates through the terminal and proceeds behind the guardrail. Similarly, in side impacts near the ends of the terminals, the vehicle bends the end of the rail element and then proceeds behind the guardrail.
The High Flare Breakaway Guardrail Terminal of the present invention (herein referred to as the HFT), as described in this disclosure, is a non-energy absorbing or gating terminal. However, it utilizes a significantly higher effective flare rate of at least 5 to 1, or 4 ft or more of end offset effected over a distance of 20 ft or less. In comparison, existing gating terminals have an end offset of 4 ft typically effected over a distance of 37 ft-6 in. (see U.S. Pat. No. 4,678,166, Col. 4, lines 50-58), or an effective flare rate of about 10:1.
Full-scale crash testing has demonstrated that a 4-ft end offset distance is needed to provide sufficient eccentricity during end-on impacts to allow an unmodified W-beam rail element to buckle at a reasonable force level. Crash testing has also shown that a low flare rate of 10:1 is needed in order to successfully contain and redirect vehicles impacting at or downstream of the beginning of the length-of-need, again, typically selected to be 12 ft-6 in. from the end of the terminal. The high flare rate used with the present HFT is unique in the art.
With existing systems, there has been difficulty associated with containing vehicles impacting at the beginning of the length-of-need when the effective flare rate is higher than the typical 10:1. For example, an existing terminal design with a higher effective flare rate of 5 ft over 37 ft-6 in., or an effective flare rate of 7.5:1, fails to contain and redirect heavy passenger vehicles impacting at the beginning of the length-of-need.
With a long, low flare rate and the beginning of length-of-need set at 12 ft-6 in. from the end of the terminal, a terminal is flared for approximately 25 ft within the length-of-need. As a result, the beginning of length-of-need is offset approximately 21.7 in. from the tangent portion of the standard section of the guardrail barrier. In comparison, there is no offset at the beginning of length-of-need for the HFT terminal of the present invention. FIG. 1A illustrates the schematic layout for a prior art BCT terminal (a traditional flare terminal), and FIG. 1B shows the present inventive HFT terminal.
Offsetting the beginning of the length-of-need behind the tangent portion of the guardrail, as is the design of prior art systems, greatly aggravates the severity of length-of-need impacts and reduces the capacity of these non-energy absorbing terminals. It should be noted that W-beam guardrails contain and redirect errant vehicles using tensile forces developed in the rail element. Since a convex shape may be urged to a concave shape without any change in guardrail length, little tensile force is developed upon side impacts until the rail is in a concave shape. By the time sufficient tensile forces are developed in the rail upon impact, the rail has already deflected substantially and the vehicle is 2 to 3 feet behind the tangent section of the rail. This behavior, sometimes known as the “pop-through effect,” is illustrated in FIGS. 2A and 2B. FIG. 2A illustrates the long, low flare rate and a vehicle initially impacting at the beginning of the length-of-need 50. The convex shape of the flare is moved to a concave shape in FIG. 2B before full tensioning is produced in the guardrail. As may be seen, the vehicle is several feet behind the tangent. The offset at the beginning of length-of-need and the generally convex shape of the flared section of the rail in existing prior art systems create the pop-through effect, which in turn increases the potential for adverse situations, such as rail pocketing, post snagging, subsequent rail rupture or excessive occupant risk measures.
The present HFT system resolves problems in the prior art systems by shortening the flared section. Thus, the beginning of the length-of-need of the HFT system will be at or very near the downstream end of the terminal, where offset distances are very small. By eliminating the prior art approach of using long, low flare rates, the lateral offset of the beginning of length-of-need of the HFT system may be kept at or very near zero and the redirective capacity of the terminal may be maintained by eliminating or minimizing the pop-through effect.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a top plan view of a low flare rate guardrail system of the prior art.
FIG. 1B shows a top plan view of the high flare rate guardrail system of the present invention.
FIG. 2A is a top plan view of an initial vehicle impact on a prior art low flare rate guardrail system.
FIG. 2B illustrates a top plan view of the system of FIG. 2A after impact and at full tensioning of the guardrail.
FIG. 3A shows a top plan view of the high flare terminal of the present invention.
FIG. 3B shows a side elevation view of the system of FIG. 3A.
FIG. 4A is a top plan view of the high flare (linear) configuration of the present invention.
FIG. 4B shows a top plan view of the high flare (single curve/single radius) configuration of the present invention.
FIG. 4C shows a top plan view of the high flare (parabolic) configuration of the present invention.
FIG. 5A illustrates a side elevation view of the high flare terminal of the present invention with a shortened second breakaway post.
FIG. 5B shows a top plan view of a vehicle initially impacting the terminal of FIG. 5A at the beginning of the length-of-need.
FIG. 5C shows a top plan view of the terminal of FIG. 5A after the W-beam has passed over the shortened post, tensioning the guardrail, and containing and redirecting the vehicle.
FIG. 6A is a rear perspective view of an embodiment of the present high flare terminal with a strut extending between the first breakaway post and the second breakaway post.
FIG. 6B is a top, rear perspective view of the terminal of FIG. 6A viewing in the downstream direction.
FIG. 6C is a top plan view of the terminal of FIG. 6A upon initial impact of a vehicle with the strut between the first and second posts.
FIG. 6D is a top plan view of the terminal of FIG. 6A after the strut has been pushed backward, breaking the posts and releasing the anchor cable systems.
FIG. 6E shows an end-on impact of a vehicle with the terminal of FIG. 6A.
FIG. 6F illustrates first post breaking and initiating the first impact energy dissipation; and illustrates the strut telescoping (collapsing).
FIG. 6G shows that the collapsed strut has loaded and broken off the second post initiating the second impact energy dissipation.
FIG. 7A is a top, rear perspective view of another embodiment of the present invention viewing toward the upstream end of the terminal. The strut is attached to the first breakaway post and to the anchor cable bracket on the rail element.
FIG. 7B is a detailed perspective view of the side release mechanism of the terminal of FIG. 7A.
FIG. 7C is a top plan view of the terminal of FIG. 7A (without the rail element for clarity) upon initial impact by a vehicle. The second anchor cable mechanism is not shown.
FIG. 7D is a top plan view of the terminal of FIG. 7C after the initial impact and the strut pivoting at the first post and separated from the release mechanism.
FIG. 8A is a top, rear perspective view of another embodiment of the present invention. This embodiment shows the weld-plug, side release mechanism of the present invention.
FIG. 8B is a top plan view of the terminal of FIG. 8A (without the rail element for clarity) upon initial impact by a vehicle.
FIG. 8C is a top plan view of the terminal of FIG. 8B after the initial impact and the strut pivoting at the plug weld.
FIG. 9A illustrates a top, rear perspective view of another embodiment of the present invention. This embodiment utilizes square tabs and a shear pin side release mechanism.
FIG. 9B is a top plan view of the terminal of FIG. 9A (without showing the rail element) upon initial impact by a vehicle.
FIG. 9C is a top plan view of the terminal of FIG. 9B after the initial impact and the strut pivoting and shearing about the shear pin.
FIG. 10A is a top, rear perspective view of another embodiment of the present invention. This embodiment utilizes angled plates and a shear pin side releasing mechanism.
FIG. 10B is a bottom, rear perspective view of the embodiment of FIG. 10A showing the anchor cable passing through a hole in the bottom of the strut.
FIG. 10C is a top plan view of the terminal of FIG. 10A (without the rail element shown) upon initial impact by a vehicle.
FIG. 10D is a top plan view of the terminal of FIG. 10C after the initial impact.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
FIG. 3 illustrates a top plan view of HFT system 10 of the present invention showing a standard guardrail portion 12 with posts 13 and 15; a high flare rate end terminal section 14; a nose section 16 with a flat plate or thin gauge W-beam 17 with little bending strength and a side impact, cable anchor release mechanism 18 attached to a first breakaway end post 20; a second breakaway post 22 with a standard cable anchor mechanism 24; a third breakaway post 26; and a buffered end section 28 with shield 19 which shields the front edge of the W-beam rail so that the vehicle will not spear the W-beam when impacted between posts 20 and 22. FIG. 3 also illustrates the beginning of length of need point 50 and the tangent line 51 for measuring the end offset distances.
The high flare rate end terminal section 14 has a flare rate of 5:1 wherein the end offset is 4 feet or more over a distance D of 20 feet or less to the downstream end of the end terminal 14. FIGS. 4A-4C illustrate that the flare configuration may vary. FIG. 4A shows a linear (straight line) flare 40a configuration. FIG. 4B illustrates a single curve (single radius) flare 40b configuration. FIG. 4C shows a parabolic (decreasing radius toward the nose of the terminal) flare 40c configuration.
Turning again to FIG. 3, the nose section 16 is attached to a first breakaway end post 20 and has an arcuate metal impact head 21 which wraps around the post 20. Attached at the front side of the arcuate impact head, plate 17 extends from head 21 downstream to the W-beam 24 at buffer shield 19. Plate 17 may be a flat plate or a thin gauge W-beam section. Since plate 17 carries no tension load, has little bending strength, and merely spans the gap or spaces from the arcuate head 21 to the buffer shield 19, the nose section 16 of the present invention differs from other flat plate designs which shield the end of the rail element and distribute the impact load along the guardrail. These prior art flat plate designs include rounded and buffered W-beam or Thrie-beam end sections, the CAT crash cushion, and the design of U.S. Pat. No. 5,765,811. The latter patent discloses that “the end rail is formed by a flat plate maintained in tension along with the standard W-beam guardrail. The flat end rail possesses redirective capabilities when struck from the side by a vehicle and does so without distracting from the performance of the standard guardrail system with which it may be used.” (Column 1, line 66—Column 2, line 4.) The flat plate 17 of the present invention is not intended to dissipate any appreciable energy upon side impact. It allows the impacting vehicle to pass through the barrier.
Also illustrated in FIG. 3 is the placement of two separate anchor mechanisms 18 and 24. The use of a first, side-releasing anchor cable mechanism 18 in cooperation with a second standard anchor cable release mechanism 24 allows the present invention to utilize a high flare rate (defined as 4 feet or more end offset effected over a distance of 20 feet or less) and still ensure that an impacting vehicle will gate through the barrier for side impacts before the beginning of length-of-need. As should be understood from the disclosure herein that the present invention allows for tension in the end terminal to be released without the need to first break off the first breakaway post in the terminal.
Side impact cable anchor release mechanism 18 includes an anchor bracket 29 fabricated from a bent plate (see FIG. 6A) attached to the W-beam rail 23 with six standard splice bolts 31. Cable 27 is attached at a first end 27a to the first breakaway post 20 and at a second end 27b to the anchor bracket 29 through a variety of alternative side release mechanisms. The alternative embodiment release structures are disclosed below.
One of the purposes of the first anchor mechanism is to assure that the cable anchored to the first post 20 releases for side impacts near the upstream end of the terminal 14 allowing the impacting vehicle to gate through the barrier.
The second post 22 is also a breakaway post with a second cable anchor system 24 and a standard cable bracket 25 attached to the W-beam 23. A standard bracket releases the cable tension upon breaking of the post 22 and is not intended to release upon side impact as with first anchor mechanism 18.
FIG. 5 illustrates that second post 22 may be a shortened post 22a. The top of the post 22a is disposed below the bottom edge of the W-beam 23. Thus, the beam 23 is not attached to or resting against the post. It is free to move as the beam 23 is contacted or loaded. For side impacts at or downstream of the beginning-of-need 50 (post 26), the rail element 23 will be tensioned earlier in the process since the rail element 23 is not constrained by post 22a.
It should be noted that buffer shield 19 is intended to protect the front edge of the W-beam rail element 23 when there is an impact between posts 20 and 22a, so as to prevent the vehicle from “spearing” on the W-beam 23 and to improve the gate through of the vehicle in advance (upstream) of the beginning of need 50.
As previously indicated, several embodiments of a side impact releasing structure may be utilized to ensure that upon side impacts near the end of the terminal, the anchor cable 27 is released allowing for gate through of the vehicle. FIGS. 6A-6G illustrate a first embodiment.
FIGS. 6A and 6B show an upper strut 60 connecting posts 20 and 22 which facilitates the fracture of these posts during impacts on the end of the terminal and upstream of the beginning of the length-of-need. The strut 60 is designed with an inner telescoping tube 61 attached to post 20 which slides inside an outer tube 63 attached to post 22. The nose section 16 and the buffer shield 19 are not shown for clarity.
For side impacts between posts 20 and 22 as shown in FIGS. 6C and 6D (the rail elements are not shown for clarity), the vehicle 100 would impact the strut 60 and push the strut backward. As the strut is pushed backward, it loads and fractures posts 20 and 22 at the base, thus allowing the vehicle 100 to gate through the terminal. In such a case, a standard anchor cable mechanism may be used because tension is released when both posts fracture.
For end-on impacts as shown in FIGS. 6E-6G, the vehicle would first impact and fracture post 20, releasing the cable anchor 18A at post 20. As the vehicle proceeds forward, the inner tube 61 slides inside the outer tube 63, without loading post 22. When post 20 reaches the end of the outer tube 63 (FIG. 6G), post 22 would be loaded and fractured, thus releasing the cable anchor 24 at post 22. The sliding mechanism allows post 20 to fracture first before post 22 in order to produce two distinctly separate impacts and reduce the maximum force applied to the vehicle.
FIGS. 7A and 7B show schematic diagrams of another release mechanism and its major components. A special anchor bracket 29 fabricated from a bent plate is attached to the W-beam rail element 23 with standard splice bolts 31. Two triangular plates 54 and 55 are welded to the top of the bent plate to provide a flat surface for the bearing plate (not shown, see FIG. 8A) of the anchor cable 27 to rest against. The anchor cable 27 is held in place with a retainer/shear pin 57. The retainer/shear pin 57 holds the strut 60a to the bracket 29 in case tension on the cable is relaxed for whatever reason. The cable 27 then passes through the downstream end of strut 60a and comes out through a hole at the bottom of the strut for attachment to the end post 20. Strut 60a is attached at the upstream end to breakaway post 20. It is not connected directly to breakaway post 22. The strut 60a is designed with a slider mechanism similar to that for the strut between posts 20 and 22, as described previously. An inner tube 61 is attached to post 20, which slides inside an outer tube 63.
For side impacts between posts 20 and 22 as shown in FIGS. 7C and 7D, the vehicle would impact the strut 60a and push it back, rotating about post 20. As the strut 60a is pushed back, the retainer/shear pin 57 will be sheared, thus releasing the cable anchor 18A and allowing the vehicle 100 to gate through the terminal.
For end-on impacts, the vehicle 100 would first impact and then fracture post 20, thus releasing the cable anchor 27 at post 20. As the vehicle 100 proceeds forward, the inner tube 61 would slide inside the outer tube 63, without loading post 22. The sliding mechanism ensures that the strut 60a will not interfere with the fracture of post 20 and the release of the cable anchor 27. When the vehicle reaches the end of the outer tube 63, it will push the strut 60a into the post 22 and place a load on the post 22 until it fractures and releases cable anchor 24.
FIG. 8A shows a schematic diagram of a plug weld anchor release mechanism 18B and its major components. A special anchor bracket 29 fabricated from a bent plate is attached to the W-beam rail 23 element with six standard splice bolts 31. Two square tabs 70 (only one is shown in FIG. 8A) having a hole for setting a weld plug are welded to the top of the bent plate bracket 29 and a strut 72 is in turn attached to these tabs with plug welds 74. the strut 72 is a unitary, hollow tubular member which allows the cable 27 to pass through. The anchor cable 27 is bolted to the downstream end of the strut with a bearing plate 75. The anchor cable 27 then passes through the downstream end of the strut and comes out through a hole (not shown) at the bottom of the strut for attachment to the end post.
For side impacts between posts 20 and 22 as shown in FIGS. 8B and 8C, the vehicle 100 would impact the strut 72 and push it back. As the strut is pushed back, it rotates about the plug welds 74 and loads the weld material in torsion. The torsional shear stresses eventually fail the plug welds 70, thus releasing the cable anchor 27 and allowing the vehicle 100 to gate through the terminal.
For end-on impacts, the vehicle would first impact and fracture post 20, releasing the cable anchor 27 post 20. The vehicle would then contact the end of the strut 72 and push the strut 72 into post 22 until the post fractures and releases the cable anchor 24 at post 22.
FIG. 9A shows a schematic diagram of a plate/shear pin anchor release mechanism 18C and its major components. A special anchor bracket 29 fabricated from a bent plate is attached to the W-beam rail 23 element with standard splice bolts. The strut is attached to the anchor bracket 29 via a sliding locking mechanism. Two square tabs 80 (only one is seen in FIG. 9A) are welded to the top of the bent plate bracket 29. Two separate square tabs 81 are welded to the top and bottom of strut 72. When the cable is in tension, tabs 80 and 81 are urged together and hold the strut in place. Shear bolt 73 holds the strut 72 to the bracket 29 in case tension on the cable is relaxed for whatever reason. The anchor cable 27 is bolted to the downstream end of the strut with a bearing plate 75. The anchor cable then passes through the downstream end of the strut and comes out through a hole at the bottom of the strut for attachment to the end post.
For side impacts between posts 20 and 22 as shown in FIGS. 9B and 9C, the vehicle 100 would impact the strut 72 and push it back. As the strut 72 is pushed back, it rotates about the cable anchor end 79 and eventually fractures the shear bolt 73, allowing tabs 80 and 81 to disengage, thus releasing the cable anchor 27 and allowing the vehicle 100 to gate through the terminal.
For end-on impacts, the vehicle 100 would first impact and fracture post 20, releasing the cable anchor 27 at post 20. The vehicle 100 would then contact the end of the strut 72 and push strut 72 into post 22 until the post 22 fractures and releases the cable anchor 24 at post 22.
FIGS. 10A and 10B show schematic diagrams of an angled plate anchor release mechanism and its major components. A special anchor bracket 29 fabricated from a bent plate is attached to the W-beam rail 23 element with six standard splice bolts 31. A strut 72 is attached to the anchor bracket 29 via four angled plates 76, two on each side. The angled plates 76 are welded to the top of the bent plate bracket 29 on one end and attached to the strut by a shear bolt 77 through the upstream plates. Welded to the sides of the strut are cooperating angle plates 78 which engage with angled plates 76. The positions of the angled plates on the bracket and the strut match so that the strut 72 is held in place when tension is applied to the cable (see FIG. 10A). The bolt 77 holds the strut 72 to the bracket in case tension on the cable 27 is relaxed for whatever reason. The anchor cable 27 is bolted to the downstream end of the strut with a bearing plate. The anchor cable 27 then passes through the downstream end of the strut and comes out through a hole 80 at the bottom of the strut for attachment to the end post.
For side impacts between posts 20 and 22 as shown in FIGS. 10C and 10D, the vehicle 100 would impact the strut 72 and push it back. As the strut is pushed back, it rotates about the cable anchor end 79 and eventually breaks the shear bolt 77 and the angled plates 76 and 78 slide apart and disengage, thus releasing the cable anchor 27 and allowing the vehicle 100 to gate through the terminal.
For end-on impacts, the vehicle 100 would first impact and fracture post 20, releasing the cable anchor 27 at post 20. The vehicle 100 would then contact the end of the strut 72 and push the strut into post 22 until the post fractures and releases the cable anchor 24 at post 22.
As should be understood from the disclosure and drawings, the HFT terminal of the present invention has several advantages over other existing non-energy absorbing or gating terminals:
- 1. A shorter and thus less expensive terminal.
- 2. Only two or three posts to position for field installation instead of the typical six posts for existing terminals.
- 3. There effectively is no length-of-need section in the terminal, i.e., the beginning of length-of-need is at the end of terminal.
- 4. Higher anchorage capacity since there are two anchors instead of one for existing terminals. In addition, the anchor at post 22 is more in line with the tangent section of the guardrail and thus less lateral offset and pop through effect.
While the systems and methods of this invention have described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the systems, methods, and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain materials that are both functionally and mechanically related might be substituted for the materials described herein while the same or similar results would be achieved. All such similar substitutes and modifications to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.
Patent Application
20100314595
