Fences – Highway guard
Reexamination Certificate
1999-08-23
2001-07-03
Browne, Lynne H. (Department: 3629)
Fences
Highway guard
C256S001000, C256SDIG005, C052S098000, C403S002000
Reexamination Certificate
active
06254063
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to breakaway steel posts for use with a highway guardrail end terminal system or a crash attenuation system. More particularly, the invention relates to a supplemental energy-absorbing mechanism affixed to such steel posts.
Existing highway guardrail end treatment systems include: the breakaway cable terminal (BCT), the eccentric loader terminal (ELT), the modified eccentric loader terminal (MELT), the vehicle attenuating terminal (VAT), the extruder terminal (ET), the slotted rail terminal (SRT), the sequential kinking terminal (SKT), and the flared energy absorbing terminal (FLEAT).
In all of these systems, breakaway wooden posts, either inserted in foundation tubes (known as BCT breakaway post) or directly installed in the ground (known as controlled release terminal CRT post), are used to facilitate proper breaking of the posts to minimize the potential for snagging on the posts and excessive decelerations on the vehicles in end-on impacts with the terminals. Holes are drilled into the wooden post at and/or below ground level to reduce the cross-sectional area of the post, thus reducing the force required to break the post. Steel breakaway posts based on the slip-base concept have also been developed, but did not receive widespread acceptance due to maintenance problems and higher initial costs.
However, there are situations in which a transportation agency may choose not to use wooden posts for environmental concerns or as a matter of policy. In such situations, breakaway steel post would be an alternative. A prior patent of the inventors relates to various conceptual designs for breakaway posts suitable for use with highway guardrail and end terminal systems. These designs have a predictable breakaway force threshold when impacted along the weak axis (in the direction of end-on impacts with the terminal system) while maintaining a sufficiently high bending force in the strong axis (perpendicular to the weak axis in the direction of side impacts) to provide the required lateral stiffness to the terminal system for side impacts.
The present invention relates to an improved steel post for use with a highway post-and-beam type guardrail at locations where deflection of the post in the soil is limited or not allowed, e.g., posts embedded in concrete or asphalt in such applications as mow strips.
Existing standard guardrail line posts, either wood or steel, require some deflection in the soil to function properly. When a guardrail is impacted, the posts in the immediate vicinity of the impact would typically deflect and absorb some of the impact energy. Deflection of the posts would allow the rail to go into tension and act like a ribbon to contain and redirect the vehicle. If deflection of the posts in the soil is not allowed or limited in such applications as mow strips where the posts are embedded in concrete or asphalt, wooden posts would fracture and steel posts would bend or twist at the base.
The present invention relates to various conceptual designs for energy-absorbing breakaway steel guardrail posts suitable for use at locations where deflection of the post in the soil is limited or not allowed. These designs provide a predictable failure or yielding force threshold when impacted to maintain the required lateral stiffness; a mechanism for adequate energy dissipation by the post; and a limit beyond which the lateral resistance of the post is eliminated.
SUMMARY OF THE INVENTION
The improved breakaway guardrail post of the present invention includes upper and lower post sections which are connected by a specially designed breakaway joint. The guardrail may be provided with a various number of alternative embodiments of controllers attached to the upper post member and lower post member to control the energy dissipation of the guardrail about the breakaway joint at a predetermined rate. The failure or yield is at a predictable force threshold when impacted along either the strong or weak axis while maintaining a sufficiently high bending force in the strong axis to provide the required lateral stiffness to the terminal system for side or strong axis impacts.
The present invention discloses several energy-absorbing controller alternatives for breakaway posts used with a highway guardrail or crash attenuation system. All breakaway alternatives involve joining of two sections (upper and lower) of structural steel shape (e.g., I-beam) posts in such a manner that the joint will fail or yield at a predictable force threshold when impacted along the weak axis while maintaining a sufficiently high bending force in the strong axis to provide the required lateral stiffness to the terminal system for side impacts. The lower section of the post is installed in the ground by either means of driving or drill and backfill. The rail element for the guardrail or crash attenuation system is attached to the upper portion of the post. The energy absorbing dissipation controlling mechanisms include: a cable restraint member; a strap attached along the post web; a strap having a U-shaped portion; and straps with slotted openings for receiving fasteners.
REFERENCES:
patent: 3820906 (1974-06-01), Katt
patent: 5160111 (1992-11-01), Hugron
patent: 5484217 (1996-01-01), Carroll et al.
patent: 6065894 (2000-05-01), Wasson et al.
Reid John D.
Rohde John R.
Sicking Dean L.
Browne Lynne H.
Cottingham John R.
Jackson Walker L.L.P.
Safety by Design, Inc.
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