A highway crash attenuator includes an array of resilient self-restoring polymeric tubes. Adjacent tubes are secured together by threaded fasteners, and the tubes of the rear row of the array are secured to a rigid object by threaded fasteners. The tubes form a rectangular array, without cables, frameworks or panels between the exterior surfaces of the array and oncoming traffic. The tubes of the front row of the array are provided with a greater wall thickness than the remaining tubes of the array to increase the mass and stiffness of the front of the array.
Stephens U.S. Pat. No. 5,314,261 discloses a vehicle crash cushion including an array of rubber cylinders that are secured together and to a wall. These cylinders are protected from contact with impacting vehicles by an array of panels 12 interposed between the rubber cylinders and the roadway. In the disclosed system, the rubber cylinders control the position of the panels 12, and it is the panels 12 that actually come into contact with an impacting vehicle.
In spite of the work described above, a need presently exists for a restorable crash attenuator that is simple to fabricate and to install, that provides an improved deceleration profile to an impacting vehicle, and that substantially restores itself to its original position after at least some impacts.
SUMMARY
The preferred crash attenuator described below includes an array of resilient, self-restoring, polymeric tubes. Each of these tubes is characterized by a respective longitudinal axis and a respective wall thickness. The array includes at least three rows of tubes, and each row includes at least three tubes. The rows include a back row positioned closest to a rigid object, and a front row positioned farthest from the rigid object. Adjacent ones of the tubes are secured directly to one another, preferably by threaded fasteners, and the tubes of the back row are secured to the rigid object by other fasteners.
The preferred highway crash attenuator described below uses tubes with a substantially greater wall thickness for the front row than for the remaining rows. Also, the preferred crash attenuator uses an equal number of tubes in each of the rows, such that the array is rectangular rather than triangular, and such that the array defines two opposed sides extending between the front and the back row and a front comprising the front row. The tubes themselves form the outermost surfaces of the crash attenuator at the two sides and at the front, and the need for a supporting or protecting framework such as the panels 12 of the Stephens patent is thereby eliminated. Other array shapes and other distributions of wall thickness in the array are possible.
The foregoing paragraphs have been provided by way of general introduction, and they are not intended to limit the scope of the following claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a highway crash attenuator that incorporates a preferred embodiment of this invention.
FIG. 2 is an exploded perspective view of the crash attenuator of FIG. 1.
FIG. 3 is an exploded perspective view of the rigid object that is positioned immediately behind the rear row of tubes in the embodiment of FIGS. 1 and 2.
FIG. 4 is an exploded perspective view of the back-up plate included in the rigid object of FIG. 3.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
Turning now to the drawings, FIGS. 1 and 2 show perspective views of a crash attenuator 10 that incorporates a preferred embodiment of this invention. The crash attenuator 10 includes an array 12 of resilient, self-restoring, polymeric tubes 14 positioned in front of a rigid object 16. Each of the tubes 14 defines a respective longitudinal axis A, and in this embodiment all of the axes A are oriented parallel to one another and substantially vertical.
As best shown in FIG. 2, the array 12 includes a front row 20, middle rows 22 and a back row 24 of the tubes 14. In this embodiment the array 12 is a rectangular array, and each of the rows 20, 22, 24 includes four of the tubes 14. In general, the array 12 preferably includes at least three rows of the tubes 14, and each row includes at least three tubes 14.
Each of the tubes 14 defines at least four holes 30, and the holes 30 of adjacent tubes 14 are aligned to receive first fasteners 32. Thus, each of the tubes 14 is secured to each adjacent tube 14 by two first fasteners 32. Similarly, each of the tubes 14 of the back row 24 is secured to the rigid object 16 by a pair of second fasteners 34. In this example, the first and second fasteners 32, 34 take the form of threaded fasteners such as 1/2 inch hex bolts, nuts, and washers (grade 5). Simply by way of example, the washers can have an outer diameter of 1 inch.
Thus, the fasteners 32 secure the tubes 14 to each other to form a self-supporting array that is in turn secured in place only to the rigid object 16, and only by the fasteners 34.
Various materials can be used for the tubes 14. In this example, the tubes 14 are formed from a high density polyethylene, such as the material commonly used for sewer pipe. Each tube defines a length L, an outer diameter D and a thickness T as shown in FIG. 2. Table 1 provides preferred dimensions for the tubes 14. As shown in Table 1, in this example all of the tubes 14 have the same outer diameter, and the tubes of the middle rows 22 and the back row 24 have the same wall thickness. The wall thickness of the tubes of the front row 20 is preferably at least 1.5 times and more preferably at least 1.8 times the wall thickness of the tubes of the rearwardly adjacent row. This provides the advantage of increasing the mass and the stiffness of the tubes of the front row 20, thereby providing increased deceleration at the beginning of an impact event, as described in U.S. Pat. No. 6,092,959, assigned to the assignee of the present invention and hereby incorporated by reference. The lengths of the tubes of the front row 20 and the middle rows 22 are equal, but the length of the tubes of the back row 24 is preferably somewhat less. This is done to create a space beneath the tubes of the back row 24 near the lower portion of the rigid object 16. This facilitates installation of the rigid object 16 as described below.
TABLE 1
Preferred Tube Dimensions (cm)
Length L Outer Diameter D Wall Thickness T
Front Row 20 99.1 32.4 4.1
Middle Rows 22 99.1 32.4 2.2
Back Row 24 91.4 32.4 2.2
As shown in FIGS. 1 and 2, in this preferred embodiment there an equal number of the tubes 14 in each of the rows 20, 22, 24, and the array 12 is therefore a rectangular array. This is quite different from triangular arrays of the prior art, because it increases the mass and the stiffness of the array 14 that contacts an impacting vehicle first in the event of a collision in the anticipated impact direction D.
The array 14 defines two opposed sides 40, 42 and a front 44. Note that in this preferred embodiment the sides 40, 42 are defined by outer ones of the tubes 14 and the front 44 is defined by the tubes of the front row 20. Since the tubes 14 form the outermost surfaces of the crash attenuator 10 at the two sides 40, 42 and the front 44, all external bracing, framework, panels, and cables are eliminated. This substantially simplifies installation of the attenuator and eliminates metallic elements that are positioned to engage an impacting vehicle.
The back row 24 of tubes 14 can be attached to any rigid object from which an impacting vehicle is to be protected. In this example, the rigid object 16 includes a back-up plate 50 as shown in FIG. 3 that includes a lower lip 52. In use, the lower lip 52 is bolted to a concrete pad to secure the lower edge of the back-up plate 50 in place. The upper portion of the back-up plate 50 is supported by two braces 54 that extend downwardly to respective anchors 56. Since the tubes 14 of the back row 24 are shorter than the remaining tubes 14 of the array, a space is left immediately above the lip 52. This facilitates access to the fasteners that secure the lip 52 to the back-up plate 50 and the lip 52 to the concrete apron.
FIG. 4 shows an exploded perspective view from the rear of the back-up plate 50, including the internal braces.
In alternative embodiments, the back row 24 of tubes 14 can be bolted directly to a concrete bridge pier for example, and the back-up plate 50, braces 54 and anchors 56 can be eliminated.
The crash attenuator 10 provides the important advantage that it is quick and easy to install, thereby subjecting installing personnel to the dangers of oncoming traffic for a relatively short time. Since the tubes 14 are self-restoring, the crash attenuator 10 is relatively low in maintenance requirements, and can often be re-used without any maintenance after an impact. As used herein, the term "self-restoring" is intended broadly to signify that the energy-absorbing elements of the crash barrier return to at least 80 percent of the original dimensions after a typical impact, and it should be understood that a self-restoring energy-absorbing element may not self-restore to precisely its original dimensions.
Of course, many changes and modifications can be made to the preferred embodiment described above. Other materials such as various rubbers and/or polymers can be used for the tubes 14, and the tubes 14 may be arranged and shaped in other sizes and proportions. For example, the array can be longer and wider than that shown. As other alternatives, the array may have a different number of tubes in various ones of the rows. For example, the array may taper from a narrower front (fewer tubes per row) to a wider center section or rear section (more tubes per row). Also, tube diameter may vary within the array, and wall thickness of the tubes may vary within the array in other ways than that listed in Table 1. For example, the tubes of the rear row may have a greater thickness than the tubes of the middle rows, and the tubes may vary in wall thickness within a row.
Though various features of the preferred embodiment described above are preferably used together, it should be understood that many of the features described above can be used separately.
The foregoing detailed description has discussed only a few of the many forms that this invention can take. For this reason, this detailed description is intended by way of illustration and not limitation. It is only the following claims, including all equivalents, that are intended to define the scope of this invention.
