Fences – Highway guard
Reexamination Certificate
2001-01-02
2003-03-18
Hartmann, Gary S. (Department: 3671)
Fences
Highway guard
C404S006000
Reexamination Certificate
active
06533249
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to roadway safety devices and more particularly, to a guardrail beam having enhanced stability which minimizes failure and provides for more reliable, predictable response of the guardrail beam during a vehicle collision or impact.
BACKGROUND OF THE INVENTION
A goal of roadway safety is to provide a forgiving roadway and adjacent roadside for errant motorists. Guardrail systems are employed along a roadside to accomplish multiple tasks associated with roadway safety. Upon vehicle impact, a guardrail must react as a brake and shock absorber to dissipate kinetic energy of the vehicle. Subsequently, the guardrail acts as a mechanical guide to redirect the vehicle away from hazards during deceleration and to prevent the vehicle from leaving the roadway, becoming airborne or rebounding into lanes of moving traffic. For many years, standard heavy gauge metal guardrail, often referred to as the “W-beam”, has been used on the nation's roadways to accomplish these tasks and others. Named after its characteristic shape, a W-beam guardrail system is typically anchored to the ground using posts made of metal, wood or a combination of both.
Recently, there has been a vigorous effort to raise performance standards which guardrails must satisfy. Increasingly stringent testing criteria have uncovered some deficiencies in performance of standard W-beam guardrails. Considering the pervasive extent of use of standard W-beam guardrails, performance deficiencies, that have come to light as more comprehensive and rigorous test specifications are implemented, must be addressed.
A typical highway guardrail system is formed from a plurality of standard heavy gauge metal W-beams or panels which are overlapped with respect to each other at a standard splice. Depending upon the location of impact and kinetic energy associated with an impacting vehicle, interlocking or overlapping standard W-beams or panels may rotate relative to each other at the splice.
Upon a vehicle's impact with a guardrail, a dynamic response is obtained from the guardrail. The response may include vibration of the guardrail in a direction parallel to the ground and perpendicular to the direction of the vehicle. A standard W-beam guardrail may respond somewhat effectively when the waves are in a direction away from the vehicle. However, as the standard W-beam guardrail returns in a direction toward the vehicle, standard W-beams tend to buckle or crimp at the top and bottom edges. At this point, the standard W-beam's ability to absorb energy by plastic moment is significantly deteriorated. Furthermore, as the vehicle continues its path along the guardrail, it interacts with the edge of any buckled W-beam sections. This may result in tearing of the associated W-beam material starting at the top edge or bottom edge and may often occur in the region where two standard W-beams are overlapped.
Accordingly, recent efforts have focused on the development of a new guardrail system that will accomplish safety goals more effectively. One such design included a deeper and wider “W-beam.” However, this change in geometry generally requires a significant increase in hardware to attach adjacent beams or panels at each splice. Such alternative systems have not gained widespread industry acceptance because they have typically lacked the ability to efficiently interface with existing guardrail systems.
Other efforts have attempted to address typical failure modes associated with standard W-beams through system changes without changing the guardrail panel design itself. As a result, these efforts have met with only limited success, since the combination of crash event variables which may produce typical failure modes are both numerous and diverse. Thus, simply changing the configuration of a guardrail system or installation in this way generally offers little promise of significant improvement during vehicle impact.
SUMMARY OF THE INVENTION
The present invention achieves significant guardrail system performance enhancements by improving the guardrail panel design itself. Simple, precise design changes in specifically combined ratios according to the present teachings provide the basis for these novel and unexpectedly synergistic enhancements to stability and strength during service. The significance of the present invention is amplified by the ability of the new improved designs to be retrofitable, and thus to be used for both the repair and replacement of existing installations.
One aspect of the present invention is to provide an improved guardrail system for use in various locations such as median strips and adjacent to roadways. The improved guardrail system is preferably formed from a plurality of guardrail beams having a first edge region and a second edge region formed in accordance with teachings of the present invention. Guardrail beams or panels having such edge regions are generally more fracture resistant and tend to more evenly spread stresses sustained during impact between a vehicle and the associated guardrail system. Guardrail beams or panels incorporating teachings of the present invention may thus withstand significant forces of vehicle impact while maintaining adequate safety for vehicles, passengers, and bystanders.
Another aspect of the present invention is providing cost-effective, retrofitable guardrail beams or panels which may be employed interchangeably along with, or in lieu of existing guardrail systems. Still another aspect is to provide a guardrail system capable of dissipating impact energy of a vehicle collision more effectively than existing guardrail systems.
A guardrail beam or panel incorporating teachings of the present invention typically has an elongated, rectangular configuration defined in part by a first edge region and a second edge region with a front face and a rear face disposed therebetween. At least two folds are formed in the guardrail beam and extend outwardly from the rear face to provide a typical W-beam cross-section between the first edge region and the second edge region.
The first edge region is defined in part by a first flange or edge flange and a second flange or slot flange extending generally parallel with and adjacent to the first flange. The second edge region is defined in part by a corresponding edge flange and slot flange. The edge regions cooperate with each other to create a more uniform, stable and predictable response during vehicle impact. A plurality of post bolt holes and splice bolt slots are preferably provided to allow the guardrail beam to be used interchangeably with existing guardrail systems.
Technical advantages of a guardrail beam having edge regions formed in accordance with teachings of the present invention include better stabilization against crack growth that may originate near a bolt hole, a splice bolt slot or at other locations along the length of the guardrail beam. This enhanced fracture resistance is enabled by the combined effect of radius and angle between two adjacent flanges, and is still further enhanced in a compounding manner by the appropriate choice of radius to thickness ratio. This ratio serves to accomplish the dual role, first of maximizing the amount of strain hardening in the radius region which itself serves as a barrier to crack growth, and second, of emphasizing the stiffening and constraining role of one flange with respect to the other which serves as an additional crack barrier. This dual stabilization has a compounding effect against the growth of cracks that may originate near bolt holes, splice bolt slots, and other locations along the length of the guardrail beam or panel. It results in a stronger guardrail beam which is better able to resist damage resulting from impact by a vehicle. The combined effect is so significant that for some applications the strength of resulting splice bolt slots may be increased by as much as a factor of about three (3).
Another technical advantage of a guardrail system formed in accordance with teachings of the prese
Baker & Botts L.L.P.
Hartmann Gary S.
ICOM Engineering, Inc.
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