U.S. patent application number 11/532751 was filed with the patent office on 2007-03-22 for yielding post guardrail safety system.
Invention is credited to Dean C. Alberson, Roger P. Bligh, D. Lance JR. Bullard, C. Eugene Buth.
Application Number | 20070063177 11/532751 |
Document ID | / |
Family ID | 37883164 |
Filed Date | 2007-03-22 |
United States Patent
Application |
20070063177 |
Kind Code |
A1 |
Alberson; Dean C. ; et
al. |
March 22, 2007 |
YIELDING POST GUARDRAIL SAFETY SYSTEM
Abstract
In accordance with a particular embodiment of the present
invention, a guardrail safety system includes a guardrail beam
having a length-of-need (LON) portion spanning between two terminal
portions. The guardrail safety system also includes a plurality of
guardrail support posts in spaced apart relation to one another. At
least a portion of the plurality of support posts include a lower
portion for installing below grade adjacent the roadway, a mid
portion that lies substantially adjacent the grade, and an upper
portion releasably coupled to the LON portion of the guardrail
beam. The mid portion includes a weakened section operable to
weaken the support post about a first axis without substantially
changing the behavior of the support post about a second axis that
is generally perpendicular to the first axis.
Inventors: |
Alberson; Dean C.; (Bryan,
TX) ; Bullard; D. Lance JR.; (College Station,
TX) ; Buth; C. Eugene; (Wellborn, TX) ; Bligh;
Roger P.; (College Station, TX) |
Correspondence
Address: |
BAKER BOTTS L.L.P.
2001 ROSS AVENUE
SUITE 600
DALLAS
TX
75201-2980
US
|
Family ID: |
37883164 |
Appl. No.: |
11/532751 |
Filed: |
September 18, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60718644 |
Sep 19, 2005 |
|
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Current U.S.
Class: |
256/13.1 |
Current CPC
Class: |
E01F 9/635 20160201;
E01F 15/0453 20130101; E01F 15/0461 20130101 |
Class at
Publication: |
256/013.1 |
International
Class: |
E01F 15/00 20060101
E01F015/00 |
Claims
1. A guardrail safety system, comprising: a guardrail beam
comprising a length-of-need (LON) portion spanning between two
terminal portions; and a plurality of guardrail support posts in
spaced apart relation to one another, at least a portion of the
plurality of support posts comprising: a lower portion for
installing below grade adjacent the roadway; a mid portion that
lies substantially adjacent the grade, the mid portion including a
weakened section operable to weaken the support post about a first
axis without substantially changing the behavior of the support
post about a second axis that is generally perpendicular to the
first axis; and an upper portion releasably coupled to the LON
portion of the guardrail beam.
2. The guardrail safety system of claim 1, wherein the weakened
section comprises at least one cutout formed in the mid portion of
the support post.
3. The guardrail safety system of claim 1, wherein the weakened
section comprises at least one aperture selected from the group
consisting of a square, rectangle, circle, oval, ellipse, and
trapezoid.
4. The guardrail safety system of claim 1, wherein the weakened
section comprises at least one cutout selected from the group
consisting of a notch, a diamond-shaped notch, a semi-circle
opening, and a sawcut.
5. The guardrail safety system of claim 4, wherein the cutout is
formed in a surface of the support post proximate an outer edge of
the support post.
6. The guardrail safety system of claim 1, wherein the support post
is comprised of steel.
7. The guardrail safety system of claim 6, wherein the support post
is selected from the group consisting of an I-beam, an H-beam, a
C-channel, an S-beam, a W-beam, and a M-beam.
8. The guardrail safety system of claim 6, wherein the support post
is selected from the group consisting of a W6.times.9 Wide flange,
a W8.times.10 Wide flange, and a W6.times.8.5 Wide flange.
9. The guardrail safety system of claim 1, wherein the support post
is comprised of wood.
10. The guardrail safety system of claim 1, wherein the support
post is comprised of plastic.
11. A guardrail safety system, comprising: a terminal section
comprising: a terminal portion of a guardrail beam; and a plurality
of terminal support posts installed adjacent a roadway in spaced
apart relation to one another, each terminal support post coupled
to the terminal portion of the guardrail beam; and a length-of-need
(LON) section comprising: a LON portion of the guardrail beam; and
a plurality of LON support posts installed adjacent the roadway in
spaced apart relation to one another, each LON support post coupled
to the LON portion of the guardrail beam and comprising: a lower
portion for installing below grade adjacent the roadway; a mid
portion that lies substantially adjacent the grade, the mid portion
including a weakened section operable to weaken the support post
about a first axis without substantially changing the behavior of
the support post about a second axis that is generally
perpendicular to the first axis; and an upper portion releasably
coupled to the LON portion of the guardrail beam.
12. The guardrail safety system of claim 11, wherein the weakened
section comprises at least one cutout formed in the mid portion of
the LON support post.
13. The guardrail safety system of claim 11, wherein the weakened
section comprises an aperture selected from the group consisting of
a square, rectangle, circle, oval, ellipse, and trapezoid.
14. The guardrail safety system of claim 11, wherein the weakened
section comprises at least one cutout selected from the group
consisting of a notch, a diamond-shaped notch, a semi-circle
opening, and a sawcut formed in a surface of the LON support
post.
15. The guardrail safety system of claim 14, wherein the cutout is
formed in a surface that is proximate an outer edge of the support
post.
16. The guardrail safety system of claim 11, wherein each LON
support post is comprised of steel.
17. The guardrail safety system of claim 16, wherein each LON
support post is selected from the group consisting of an I-beam, an
H-beam, a C-channel, an S-beam, a W-beam, and a M-beam.
18. The guardrail safety system of claim 16, wherein each LON
support post is selected from the group consisting of a W6.times.9
Wide flange, a W8.times.10 Wide flange, and a W6.times.8.5 Wide
flange.
19. The guardrail safety system of claim 11, wherein each LON
support post is comprised of a material selected from the group
consisting of plastic and wood.
20. A guardrail safety system, comprising: a terminal section
comprising: a terminal portion of a guardrail beam; and a plurality
of terminal support posts installed adjacent a roadway in spaced
apart relation to one another, each terminal support post coupled
to the first terminal portion of the guardrail beam; and a
length-of-need (LON) section comprising: a LON portion of the
guardrail beam; and a plurality of LON support posts installed
adjacent the roadway in spaced apart relation to one another, each
LON support post selected from the group consisting of a W6.times.9
Wide flange, a W8.times.10 Wide flange, and a W6.times.8.5 Wide
flange, each LON support post coupled to the LON portion of the
guardrail beam and comprising: a lower portion for installing below
grade adjacent the roadway; a mid portion that lies substantially
adjacent the grade, the mid portion including a weakened section
selected from the group consisting of at least one cutout, at least
one notch, at least one diamond-shaped notch, at least one sawcut,
and at least one aperture, and at least one semi-circular opening,
the weakened section operable to weaken the support post about a
first axis without substantially changing the behavior of the
support post about a second axis that is generally perpendicular to
the first axis; and an upper portion releasably coupled to the LON
portion of the guardrail beam.
Description
RELATED APPLICATION
[0001] This patent application claims priority from patent
application Ser. No. 60/718,644, filed Sep. 19, 2005, entitled
Steel Yielding Guardrail Safety System, attorney docket no.
017575.1081.
TECHNICAL FIELD
[0002] The present invention relates generally to guardrail systems
and more particularly to a yielding post guardrail safety
system.
BACKGROUND
[0003] Guardrail systems are widely used along heavily traveled
roadways to enhance the safety of the roadway and adjacent
roadside. Guardrail beams and their corresponding support posts are
employed to accomplish multiple tasks. Upon vehicle impact, a
guardrail acts to contain and redirect the errant vehicle.
[0004] For many years, standard heavy gauge metal guardrails known
as "W-beams" have been used on the nation's roadways to accomplish
these tasks and others. Named after its characteristic shape, the
"W-beam" is typically anchored to the ground using support posts
made of metal, wood, or a combination of both. A terminal post is
used at or near the terminal end of the guardrail system. Support
posts other than the terminal posts are termed "length-of-need"
(LON) posts. LON posts support the W-beam along the intermediary
portion of the guardrail system between opposing terminal ends of
the guardrail system.
[0005] Wood support 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
using driving methods. As an additional benefit, wood support posts
used in a LON or terminal portion of a guardrail system have been
made to break away upon impact, thus producing a desired behavior
during a collision by a vehicle at the impact site. However, in
some environments, wood posts deteriorate more rapidly and
alternate materials are sought.
[0006] Commonly used steel posts do not break away in the desired
fashion and are not optimal for use in the guardrail system and
especially not suitable for use in the terminal section of a
guardrail system. Break away steel support posts that are modified
to allow for failure during a collision have recently become
available. Examples include a "hinged breakaway post" and the
"energy absorbing breakaway steel guardrail post" described in U.S.
Pat. No. 6,254,063. Many such prior attempts require substantial
time, money, and resources during fabrication, modification, and/or
installation.
SUMMARY
[0007] In accordance with a particular embodiment of the present
invention, a guardrail safety system includes a guardrail beam
having a length-of-need (LON) portion spanning between two terminal
portions. The guardrail safety system also includes a plurality of
guardrail support posts in spaced apart relation to one another. At
least a portion of the plurality of support posts include a lower
portion for installing below grade adjacent the roadway, a mid
portion that lies substantially adjacent the grade, and an upper
portion releasably coupled to the LON portion of the guardrail
beam. The mid portion includes a weakened section operable to
weaken the support post about a first axis without substantially
changing the behavior of the support post about a second axis that
is generally perpendicular to the first axis.
[0008] Technical advantages of particular embodiments of the
present invention include a LON guardrail support post that has
sufficient strength to redirect vehicles that collide along the
length of the guardrail system at an angle to the flow of traffic.
Additionally, the modified support post as used in a LON portion of
a guardrail system mitigates the severity of the interaction
(snagging) between an impacting vehicle and the post without
changing the deflection characteristics of the guardrail system.
For example, LON support posts configured to include a weakened
section that, upon release from the guardrail beam during impact,
may readily yield or breakaway when contacted by the vehicle. Still
another advantage may include, in particular embodiments, the
removal or reduction in size of an offset block between the
guardrail beam and the LON support post. Accordingly, particular
embodiments of a guardrail system of the present invention may
provide benefits in terms of space and cost savings.
[0009] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] 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:
[0011] FIG. 1 illustrates a side view of a guardrail safety system
that incorporates certain aspects of the present invention;
[0012] FIGS. 2A-2C illustrate a guardrail support post suitable for
use with the guardrail system of FIG. 1, in accordance with a
particular embodiment of the present invention;
[0013] FIGS. 3A-3C illustrate another guardrail support post
suitable for use with the guardrail system of FIG. 1, in accordance
with another embodiment of the present invention;
[0014] FIGS. 4A-4C illustrate a LON guardrail support post suitable
for use with the guardrail system of FIG. 1, in accordance with a
particular embodiment of the present invention;
[0015] FIGS. 5A-5C illustrate another LON guardrail support post
suitable for use with the guardrail system of FIG. 1, in accordance
with another embodiment of the present invention;
[0016] FIGS. 6A-6C illustrate another LON guardrail support post
suitable for use with the guardrail system of FIG. 1, in accordance
with another embodiment of the present invention;
[0017] FIG. 7 illustrates a support post that includes a modified
flange for the protection of a guardrail beam, in accordance with
one embodiment of the present invention;
[0018] FIGS. 8A and 8B illustrate a flange protector for attachment
to a support post for the protection of a guardrail beam, in
accordance with one embodiment of the present invention;
[0019] FIG. 9 illustrates a connector for coupling a guardrail beam
with a support post, in accordance with a particular embodiment of
the present invention; and
[0020] FIGS. 10A-10C illustrate a connector for coupling a
guardrail beam with a support post, in accordance with an
alternative embodiment of the present invention.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0021] FIG. 1 illustrates a guardrail safety system 10 that
incorporates certain aspects of the present invention. Guardrail
system 10 may be installed adjacent a roadway to protect vehicles,
drivers, and passengers from various obstacles and hazards and
prevent vehicles from leaving the roadway during a traffic accident
or other hazardous condition. Guardrail systems that incorporate
certain aspects of the present invention may be used in median
strips or shoulders of highways, roadways, or any path that is
likely to encounter vehicular traffic. Guardrail system 10 includes
a guardrail beam 12 and support posts 14 that anchor guardrail beam
12 in place along the roadway. As illustrated, guardrail system 10
includes three sections. Two terminal sections 16 are located on
opposing ends of guardrail system 10 and are separated by an
intermediary length-of-need (LON) section 18.
[0022] Support posts 14 have been modified to decrease the strength
of support posts 14 in a direction generally parallel to axis 20
(generally along the direction of traffic) without substantially
decreasing its strength in a direction generally perpendicular to
axis 20 (out of the page in FIG. 1). Stated differently, support
posts 14 exhibit adequate strength in the lateral direction but
sufficiently low strength in the longitudinal direction.
Accordingly, if a vehicle impacts guardrail system 10 "head-on"
adjacent an end terminal post 22, support posts 14 will tend to
yield (e.g., buckle), while allowing the vehicle to decelerate as
it impacts consecutive support posts 14. However, if a vehicle
strikes guardrail system 10 along the face of and at an angle to
guardrail beam 12, support posts 14 will provide sufficient
resistance (strength) to redirect the vehicle along a path
generally parallel with guardrail beam 12.
[0023] Guardrail system 10 is intended to keep errant vehicles from
leaving the roadway during a crash or other hazardous situation. In
many instances, guardrail 10 is installed between a roadway and a
significant hazard to vehicles (e.g., another roadway, a bridge,
cliff, etc.). Therefore, guardrail system 10 should be designed to
withstand a significant impact from a direction that forms an angle
to the roadway without substantial failure. It is this lateral
strength that allows guardrail system 10 to withstand the impact
and still redirect the vehicle so that it is once again traveling
generally in the direction of the roadway.
[0024] Testing and experience have continuously shown, however,
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 guardrail system adjacent its
terminal section 16 in a direction generally parallel to the
roadway. For example, if the guardrail system were rigidly fixed in
place during a crash, serious injury and damage may result to the
errant vehicle, its driver, and passengers. Accordingly, many
attempts have been made to minimize this added risk. Such methods
generally include the use of terminal portions that are tapered
from the ground up to effectively reduce the impact of head on
collisions and to create a ramp-like effect that causes vehicles to
go airborne during a crash. Other methods include breakaway cable
terminals (BCT), vehicle attenuating terminals (VAT), SENTRE end
treatments, breakaway end terminals (BET) and the breakaway support
posts of U.S. Pat. No. 6,398,192 ("'192 Patent"). Many such
terminals, supports, end treatments and the like are commercially
available from various organizations. Examples include the HBA post
by Exodyne Technologies and Trinity Industries and a breakaway
support post similar in configuration to that described in the '192
Patent.
[0025] Improperly designed posts in the LON portion 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 LON portion of the guardrail system at a
substantial angle to the guardrail beam. In such a scenario,
snagging or contact between the vehicle and posts can cause severe
vehicle damage, deformation to the occupant compartment, high
vehicle decelerations, and failure or rupture of the guardrail
beam. Additionally, the guardrail may fail in its purposes of
containing and redirecting the errant vehicle.
[0026] Referring again to FIG. 1, each terminal section 14 includes
a terminal portion of guardrail beam 12, one terminal end post 22,
and five terminal support posts 14a. LON guardrail support posts
14b may be used for the balance of guardrail system 10 to support a
LON portion of guardrail beam 12. As will be described in more
detail below, it should be recognized that terminal support posts
14a and LON support posts 14b may be identical or may differ where
desired. In particular embodiments, for example, terminal support
posts 14a and LON support posts 14b may differ in size and
configuration where the terminal sections 16 and LON section 18 are
designed for different impact conditions. In other embodiments,
terminal support posts 14a and LON support posts 14b may be
identical or substantially identical such that any support post 14
described herein is suitable for installation at any location
within guardrail system 10. In such embodiments, terminal support
posts 14a and LON support posts 14b may be interchangeable within
guardrail system 10.
[0027] Support posts 14 may be embedded in the ground, a concrete
footing, or a metal socket. Support posts 14 may be made of wood,
metal, plastic, composite materials, or any combination of these or
other suitable materials. It is also recognized that each support
post 14 within guardrail system 10 need not necessarily be made of
the same material or include the same structural features.
Furthermore, the cross-section of support posts 14 may be any
engineered shape suitable for releasably supporting guardrail beam
12. Such cross-sectional shapes may include, but are not limited
to, square, rectangular, round, elliptical, trapezoidal, solid,
hollow, closed, or open.
[0028] Although FIG. 1 is illustrated without dimensions, in a
particular embodiment, it is understood that guardrail system 10
may be of different lengths depending on the nature of the roadside
hazard being shielded. Each terminal section 16 may have a length
on the order of approximately 11.4 meters (37.5 feet),
respectively, and LON section 18 will have a length that varies as
needed. In such an embodiment, support posts 14 may be placed along
guardrail beam 12 at a spacing on the order of approximately 1.9
meters (6.25 feet) or other distance as required to obtain the
desired deflection and impact performance.
[0029] In such an embodiment, guardrail beam 12 may include
multiple 12-gauge W-beam rail elements of a length on the order of
approximately 3.8 meters (12.5 feet) or 7.6 meters (25 feet). The
guardrail beam sections may be mounted at a height of 78.74
centimeter (31 inch) with rail splices positioned mid-span between
the support posts 14. While guardrail beam 12 may include W-beam
rail elements, it is generally recognized that the illustrated
guardrail beam 12 is merely an example of a beam that may be used
in a guardrail system. Guardrail beams 12 may include conventional
W-beam guardrails, thrie beam guardrails, box beams, wire ropes, or
other structural members suitable for redirecting an errant vehicle
upon impact. It is also recognized that the configuration and
dimensions of any of the above-described elements within guardrail
system 10 may vary as desired.
[0030] FIGS. 2A-2C illustrate a guardrail support post 34, in
accordance with a particular embodiment of the present invention.
Support post 34 includes an elongate continuous structural member
of a standard Wide flange configuration. Support post 34 includes
two flanges 36 and 38 that are generally parallel with one another
and in a spaced relation. A web 40 forms the coupling between
flanges 36 and 38. Flanges 36 and 38 include a generally identical
configuration of boltholes 48 and cutouts 50, therein.
[0031] With regard to a Wide flange shape used as a guardrail post,
the cross section is typically shaped like the letter "H". The
cross section has two major axes for bending. The "weak" axis
generally refers to a central axis that extends through the web and
is perpendicular to the flanges. The "strong" axis generally refers
to a central axis that is perpendicular to the web and parallel to
the planes of the flanges. The weak axis for a conventional
installation of guardrail extends generally transversely to the
road. The strong axis extends generally along the roadway.
[0032] In the illustrated embodiment of FIGS. 2A-2C, the Wide
flange is a standard W6.times.8.5, which is commonly used in
fabricating support posts for guardrail installations. In
particular embodiments, the W6.times.8.5 such as that illustrated
in FIGS. 2A-2C may be particularly well suited for installation as
a support post 14a in terminal section 16 of guardrail system 10.
One advantage of some embodiments is the ability to re-use existing
standard equipment to fabricate, modify, and install support post
34 without substantial modification to the equipment. Those of
ordinary skill in the art will recognize that wide flange beams may
be available in many different sizes. For example, a standard
W6.times.8.5 Wide flange may have a nominal six-inch depth and
weigh nine pounds per foot. However, a Wide flange having a
six-inch depth and weighing eight and one-half pounds per foot may
also be referred to as a W6.times.8.5 Wide flange and is considered
equivalent in the trade. The term "W6.times.8.5 Wide flange" is
intended to refer to all sizes and configurations of guardrail
posts that may be referred to as "W6.times.8.5" by a person of
ordinary skill in the art. In addition, persons skilled in the art
recognize other names used for wide flanges 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." Support post 34
includes a relatively "weak" axis W and a relatively "strong" axis
S. For the reasons described above, support post 34 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 34 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 34
is intentionally designed such that yielding will more readily
occur in response to an impact about the weak axis W.
[0033] In the illustrated embodiment, support post 34 has a length
on the order of approximately 1,830 mm (6 feet), and it includes an
upper portion 42, a lower portion 44, and a mid portion 46 that
couples upper portion 42 with lower portion 44. Upper portion 42
includes two boltholes 48 in each of flanges 36 and 38 that are
adapted to receive connectors for the installation of a guardrail
beam (e.g., guardrail beam 12) upon support post 34. Lower portion
44 is suitable for installation below grade as part of a guardrail
support system. Mid portion 46 includes two cutouts 50 in both
flanges 36 and 38, which are configured to further weaken support
post 34 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 34 and its upper, lower, and mid portions
may vary significantly within the teachings of the present
invention.
[0034] Bolt holes 48 include a standard configuration that allow
for the installation of widely used guardrail beams upon support
posts 34. In general, bolt holes 48 align with the center of the
guardrail beam and maintain the center of the guardrail beam at a
distance that is between 550 and 750 millimeters (1.8-2.5 feet)
above grade. In the particular embodiment illustrated, bolt holes
48 maintain the center of the guardrail beam at a distance that is
on the order of 550 (1.8 feet) above grade. Bolt holes 48 have a
diameter on the order of approximately 21 millimeters. However, it
is generally recognized that the illustrated dimensions are for
example purposes only; the number, size, location and configuration
of boltholes 48 may be significantly modified within the teachings
of the present invention.
[0035] Cutouts 50 are positioned within mid portion 46 to weaken
support post 34 about weak axis W adjacent grade (when installed).
This will accommodate yielding of support post 34 approximately at
grade, allowing support post 34 to "fold" over from the point of
yielding, upward. Since lower portion 44 is below grade, it is not
expected that the ground or lower portion 44 of support post 34
will appreciably deflect during an impact about the weak axis of
the post. In the illustrated embodiment of FIGS. 2A-2C, cutouts 50
are approximately thirteen millimeters in diameter. It is generally
recognized, however, that the provided dimensions of cutouts 72 are
provided for example purposes only; cutouts 72 may be of any
appropriate size and may vary between approximately 13 and 21
millimeters, in various embodiments.
[0036] Since cutouts 50 are intended to occur approximately at
grade and the center of bolt holes 48 are intended to occur between
550 and 750 millimeters (1.8-2.5 feet) above grade, bolt holes 48
occur between 550 and 750 millimeters (1.8-2.5 feet) above cutouts
50. In the illustrated embodiment, bolt holes 48 occur at
approximately 550 millimeters (1.8 feet) above cutouts 50. It will
be recognized by those of ordinary skill in the art, however, that
the size, configuration, location and number of bolt holes,
cutouts, and their relationship with each other may be varied
significantly within the teachings of the present invention.
[0037] Additionally, the location of cutouts 50 may vary in
accordance with the teachings of the present invention. The
configuration of FIGS. 2A-2C envisions that cutouts 50 will occur
approximately at grade level. In other embodiments, cutouts 50 may
occur below grade or above grade. The depth of cutouts 50 below
grade should not exceed an amount that will prevent support post 34
from yielding at or near the location of cutouts 50. At some depth
below grade, the surrounding earthen (or other) material will
reinforce lower portion 44 of support post 34 to an extent that
will no longer accommodate such yielding to occur.
[0038] The height of cutouts 50 above grade should not exceed a
point at which support post 34 will yield at cutouts 50 and leave a
"stub" above grade that 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 34 is operating.
[0039] Support post 34 is a single, continuous structural member
that does not require any labor in field assembly, welding, or
special handling. With the exception of boltholes 48 and cutouts
50, support post 34 has a continuous, generally uniform
cross-section from top edge 52 to bottom edge 54. Therefore,
fabrication of support post 34 is simplified with respect to other
multiple component products. Furthermore, support post 34 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.
[0040] 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 34 can be installed using traditional guardrail post
installation equipment (e.g., guardrail post drivers).
[0041] Previous attempts to accommodate failure 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 in a direction generally
perpendicular to or at an angle 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).
[0042] Cutouts 50 of support posts 34 are configured to reduce the
strength of support post 34 about weak axis W, without
substantially changing the behavior of the support post 34 about
strong axis S. In the illustrated embodiment, cutouts 50 comprise
generally circular openings that have been punched or drilled
through support post 34. Cutouts 50 provide an enhanced ability to
control the point of yielding of support post 34 during a collision
with a vehicle. For example, the support post of the '029
Application may fail at any point along the slots, and failure may
be based upon imperfections in the material adjacent the slots. By
limiting the vertical dimension of cutout 50, it is easier to
dictate the precise point of failure of support post 34 along its
vertical length.
[0043] 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.
[0044] In accordance with certain example embodiments of the
present invention, the vertical dimension of cutout 50 is limited
based upon the horizontal dimension of cutout 50. 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 FIGS. 2A-2C, the ratio
is 1:1 since cutout 50 is generally a circular opening in the
support post. The smaller the vertical dimension of the cutout, the
more precisely the designer may dictate the point of yielding along
the vertical length of support post 34.
[0045] Various configurations of cutouts 50 are available to a
designer of support post 34, in accordance with the teachings of
the present invention. For example, rather than circular openings,
cutouts 50 may comprise square, rectangular, triangular, oval,
semi-circular, diamond shaped, or practically any other geometric
configuration and still obtain some or all of the benefits
described herein. Cutouts 50 are positioned, shaped, and sized such
that support post 34 retains sufficiently high strength in the
lateral direction (the direction perpendicular to the guardrail
beam 12) to capture and redirect an impacting vehicle with
reasonable dynamic deflection.
[0046] The horizontal location of cutouts 50 within flanges 36 and
38 may also be altered significantly, within the teachings of the
present invention. In the illustrated embodiment of FIGS. 2A-2C,
cutouts 50 are located approximately twenty millimeters (0.79
inches) from outer edges of flanges 36 and 38. However, in
alternative embodiments, cutouts 50 may be located closer to such
edges or further from such edges. In one embodiment, cutouts 50 may
be configured such that they extend all the way to the edge of the
flange such that there is a break in material beginning at the
edge. In this manner, a traditional punch could be employed at the
edge to form a semi-circular opening that extends to the edge of
the flange.
[0047] Alternatively, a sawcut, diamond shaped notch, or other
notch or cut could be employed from the outer edge of the flange
and extended inward to form cutouts 50. In this manner, the sawcut,
diamond shaped notch, or other notch or cut would form the starting
point of the likely point of yielding along the weak axis of the
support post. Rather than a sawcut, 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.
[0048] FIGS. 3A-3C illustrate a support post 70, in accordance with
another embodiment of the present invention. Support post 70 is a
W8.times.10 Wide flange and is therefore slightly larger and
heavier than the W6.times.8.5 Wide flange of FIGS. 2A-2C. In
particular embodiments, the W8.times.10, such as that illustrated
in FIGS. 3A-3C, may be particularly well suited for installation as
a support post 34 in terminal portion 16 of guardrail system 10.
Additionally or alternatively, support post 70 may be used when
additional strong axis strength is desired to, for example, reduce
deflection of guardrail system 10 while sufficiently reducing the
strength of the post about the weak axis to maintain vehicle
contact forces and damage at acceptable levels.
[0049] Support post 70 is very similar in configuration to support
post 34, although many of the dimensions of relative aspects and
components are slightly different. Therefore, support post 70 will
not be described in significant detail. Cutouts 72 of support post
70 are slightly larger than cutouts 50 of FIGS. 2A-2C. In the
illustrated embodiment of FIGS. 3A-3C, cutouts 72 are approximately
twenty-one millimeters in diameter. It is generally recognized,
however, that the provided dimensions of cutouts 72 and bolt holes
74 are provided for example purposes only; cutouts 72 and bolt
holes 74 may be of any appropriate size. It is anticipated that the
diameter of cutouts 72 may vary between approximately 13 and 21
millimeters, in various embodiments. Where as in the illustrated
configuration cutouts 72 are the same size as bolt holes 74,
fabrication of support post 70 is simplified since the same tools
that are used to punch bolt holes 74 may be used to punch cutouts
72. Tooling costs are thereby reduced since the tools need only be
re-indexed to provide additional holes for cutouts 72.
[0050] FIGS. 4A-4C illustrate a support post 100, in accordance
with another embodiment of the present invention. In the
illustrated embodiment, support post 100 is a W6.times.8.5 Wide
Flange configured such that support post 100 may be particularly
well suited for installation as a LON support post 14b in LON
portion 18 of guardrail system 10. Accordingly, support post 100
may also be described herein as "LON support post 100." LON support
post 100 is very similar in configuration to support post 34,
although many of the dimensions of relative aspects and components
are slightly different. The illustrated embodiment may provide
optional weakening about the weak axis without appreciably
affecting the strong axis strength of the post. It is also one of
the most economical embodiments for achieving satisfactory impact
performance of guardrail system 10.
[0051] As shown in FIGS. 4A-4C, LON support post 100, which
supports a guardrail beam, such as guardrail beam 12, has a length
of approximately 1.8 m (6 ft). When incorporated into a guardrail
system, such as guardrail system 10, multiple LON support posts 100
may be spaced approximately 1.9 m (6 ft-3 inches) on center, in a
particular embodiment. Although bolt holes 110 are depicted as
maintaining the center of the guardrail beam at a distance that is
on the order of 635 millimeters (25 inches) above grade, it is
generally recognized that the illustrated dimensions are for
example purposes only; the number, size, location, and
configuration of boltholes 48 may be significantly modified within
the teachings of the present invention. In various embodiments, it
is anticipated that bolt holes 110 may maintain the center of the
guardrail beam at a distance that is between 550 and 750
millimeters (1.8-2.5 feet) above grade.
[0052] Similar to the support posts described above, LON support
post 100 has adequate strength in the lateral direction and
sufficiently low strength in the longitudinal direction. LON
support post 100 may be embedded in the ground, a concrete footing,
or a metal socket. LON support post 100 may be made of wood, metal,
plastic, composite materials, or any combination of these or other
suitable materials. Furthermore, the cross-section of LON support
post 100 may be any engineered shape suitable for releasably
supporting a guardrail beam, such as guardrail beam 12. Such
cross-sectional shapes may include, but are not limited to, square,
rectangular, round, elliptical, trapezoidal, solid, hollow, closed,
or open.
[0053] Similar to previously described embodiments, LON support
post 100 includes a weakened section, such as cutouts 108, that
provide reduced strength in the longitudinal direction but
maintained strength in the lateral direction. The weakened section
may include one or more openings in the form of round or elliptical
holes, notches, vertical slots, horizontal slots, saw cuts, or any
combination of these or other openings. Alternatively, a sawcut,
diamond shaped notch, or other notch or cut could be employed from
the outer edge of the flange and extended inward to form cutouts
50. As discussed above, the weakened section is generally at ground
level such that LON support post 100 will yield at ground level but
may vary above or below grade. The opening or other weakened
section may be located on the interior of the post or may intersect
an exterior edge. The geometry and size of the opening is as is
required for a given post cross section such that the force
required to fail, fracture, or yield the post about its strong axis
is reduced such that the magnitude and severity of vehicle contact
or snagging forces are reduced to safe levels that mitigate the
potential for occupant injury and vehicle instability. Where the
weakened section includes one or more sawcuts, diamond shaped
notches, or other notches or cuts, the weakened section may be cut
into the side of the post in one embodiment. Where the weakened
section includes a slot, the slot may include a sharp or rounded
edge bottom.
[0054] As shown in FIG. 4A, the weakened section includes cutouts
108 of support post 100, which are approximately 21 millimeters (
13/16 of an inch) in the illustrated embodiment. Like support post
70, cutouts 108 are the same size as boltholes 110 in this
configuration. Accordingly, fabrication of LON support post 100 is
simplified since the same tools that are used to punch bolt holes
110 may be used to punch cutouts 108. Tooling costs are thereby
reduced since the tools need only be re-indexed to provide
additional holes for cutouts 108. It is generally recognized,
however, that the provided dimensions of cutouts 72 and bolt holes
74 are provided for example purposes only; cutouts 72 and bolt
holes 74 may be of any appropriate size. It is anticipated that the
diameter of cutouts 72 may vary between approximately 13 and 21
millimeters, in various embodiments.
[0055] FIGS. 5A-5C illustrates a LON support post 180, in
accordance with an alternative embodiment of the present invention.
LON support post 180 is a W8.times.10 Wide flange and is,
therefore, larger and heavier than the W6.times.8.5 Wide flange of
FIGS. 4A-4C. LON support post 180 is very similar in configuration
to previously described support posts, although many of the
dimensions of relative aspects and components may be slightly
different. For example, cutouts 182 of LON support post 180 are
approximately 13 millimeters (1/2 inch) in diameter. In this
configuration, cutouts 182 are slightly smaller than bolt holes
184, which are approximately 21 millimeters (0.82 inches) in
diameter. It is generally recognized, however, that the provided
dimensions of cutouts 182 and bolt holes 184 are provided for
example purposes only; cutouts 182 and bolt holes 184 may be of any
appropriate size. Like the embodiments described above, it is
anticipated that the diameter of cutouts 182 may vary between
approximately 13 and 21 millimeters, in various embodiments.
[0056] FIGS. 6A-6C illustrate a LON support post 186, in accordance
with an alternative embodiment of the present invention. As
illustrated, LON support post 186 is a 6.times.8 wood post. Thus,
LON support post 186 has a nominal width of approximately 6 inches
and a nominal depth of approximately 8 inches. Although formed of
wood, it is anticipated that support post 186 may be particularly
well suited for installation as a LON support post 14b in LON
portion 18 of guardrail system 10. The illustrated embodiment may
provide optional weakening about the weak axis without appreciably
affecting the strong axis strength of the post.
[0057] As shown in FIGS. 6A and 6B, LON support post 186, which
supports a guardrail beam, such as guardrail beam 12, has a length
of approximately 1830 mm (6 ft). Bolt holes 188 have a diameter on
the order of approximately 13/16 of an inch. Although bolt holes
188 are depicted as maintaining the center of the guardrail beam at
a distance that is on the order of 550 millimeters (21 inches)
above grade, it is generally recognized that the illustrated
dimensions are for example purposes only; the number, size,
location, and configuration of bolt holes 188 may be significantly
modified within the teachings of the present invention. In various
embodiments, it is anticipated that bolt holes 188 may maintain the
center of the guardrail beam at a distance that is between 550 and
750 millimeters (1.8-2.5 feet) above grade.
[0058] LON support post 186 is formed of wood, plastic, or a
composite material and may be embedded in the ground, a concrete
footing, a metal socket, or a foundation tube. Although illustrated
as having a 6.times.8 rectangular shape, the cross-section of LON
support post 186 may be any engineered shape suitable for
releasably supporting a guardrail beam, such as guardrail beam 12.
Such cross-sectional shapes may include, but are not limited to,
square, rectangular, round, elliptical, trapezoidal, solid, hollow,
closed, or open.
[0059] Similar to the support posts described above, LON support
post 186 has adequate strength in the lateral direction and
sufficiently low strength in the longitudinal direction.
Specifically, LON support post 186 includes a weakened section,
such as a cutout 190, that provide reduced strength in the
longitudinal direction but maintained strength in the lateral
direction. As shown in FIGS. 6A-6C, cutout 190 of support post 186
is of a circular shape and has a diameter on the order of
approximately 89 millimeters (3.5 inches). It is generally
recognized, however, that the provided dimensions of cutout 190 is
provided for example purposes only. Further, the weakened section
may include one or more openings in the form of round or elliptical
holes, semi-circular openings, diamond notches, notches, vertical
slots, horizontal slots, saw cuts, or any combination of these or
other openings.
[0060] As discussed above, the weakened section is generally at
ground level such that LON support post 186 will yield at ground
level, but may vary above or below grade. The opening or other
weakened section may be located on the interior of the post or may
intersect an exterior edge. The geometry and size of the opening is
as is required for a given post cross section such that the force
required to fail, fracture, or yield the post about its strong axis
is reduced such that the magnitude and severity of vehicle contact
or snagging forces are reduced to safe levels that mitigate the
potential for occupant injury and vehicle instability. Where the
weakened section includes one or more notches, the notches may be
cut into the side of the post in one embodiment. Where the weakened
section includes a slot, the slot may include a sharp or rounded
edge bottom.
[0061] In operation, the LON support posts described above in FIGS.
4A-4C, 5A-5C, and 6A-6C are connected to the guardrail beam such
that upon impact, the connection between the LON support posts and
guardrail beam will yield in preferred embodiments. Because the LON
support posts include weakening cutouts at approximately the ground
elevation, the LON support posts may bend at the weakened section
upon vehicular impact. Despite the deflection of LON support posts
upon impact, however, the guardrail beam may remain at the
originally designed elevation. As a result, the guardrail beam may
substantially prevent an errant vehicle from running over the
guardrail beam and/or becoming unstable.
[0062] Many advantages may be realized by the use of modified,
engineered LON support posts of FIGS. 4A-4C, 5A-5C, and 6A-6B.
First, use of modified, engineered posts in the standard LON or
non-terminal portion of the guardrail system mitigates the severity
of the interaction (snagging) between an impacting vehicle and the
post without changing the deflection characteristics of the
guardrail system. Second, because the LON support posts release
from the guardrail beam, the flanges of the LON support posts may
be prevented from tearing the guardrail beam. As a result, offset
blocks (spacers placed between the flanges of the LON support post
and the guardrail beam) may be reduced in size or removed
altogether, which can provide benefits in terms of space and cost
savings.
[0063] Other modifications to support posts and LON support posts
in particular, may further prevent tearing of the guardrail beam
upon impact. For example, FIG. 7 illustrates a support post 200
that includes a modified flange for the further protection of the
guardrail beam. It is generally recognized that support post 200
may include a terminal support post 14a or a LON support post 14b.
In the illustrated embodiment, support post 200 includes an
elongate, continuous structural member of a modified Wide flange
configuration. Similar to the support posts described above,
support post 200 includes two flanges 202 and 204 that are coupled
at their respective midpoints by a web 206. Flanges 202 and 204 at
their respective midpoints are generally parallel with one another
and in a spaced relation.
[0064] With regard to the modified Wide flange shape used as
support post 200, the cross section of support post 200 is shaped
like a modified letter "H" or a modified letter "I". Specifically,
a first flange 202 is substantially straight and, thus, forms a
standard leg of an "H" or "I". A second flange 204 includes a
substantially rounded surface such that a first edge 210 and a
second end 212 of second flange 204 is curved inward toward web 206
and first flange 202. Second flange 204 forms the face of the
support post 200 that couples to and lies adjacent to a guardrail
beam 208.
[0065] In particular embodiments, second flange 204 may slightly
longer than first flange 202. For example, in a particular
embodiment, support post 200 is formed from a modified
W6.times.8.5. Whereas a standard W6.times.8.5 member may include
two flanges that are each approximately four inches long, second
flange 204 is slightly longer than the standard flange and, thus,
slightly longer than first flange 202. For example, in a particular
embodiment, second flange 204 may have a length that is
approximately six inches long.
[0066] In operation, because second flange 204 is rounded toward
first flange 202, no sharp edges of support post 200 are adjacent
to guardrail beam 208. As a result, second flange 204 forms a
cushion at the interface between guardrail beam 208 and support
post 200. Accordingly, guardrail beam 208 is not susceptible to
rupture by the sharp edges of support post 200 when an errant
vehicle comes into contact with the support post-guardrail beam
combination.
[0067] Despite some structural and orientation differences
discussed above, flanges 202 and 204 of support post 200 may
include, in particular embodiments, a weakened section such that,
similar to the support posts discussed above, modified support post
200 includes a relatively "weak" axis W and a relatively "strong"
axis S. For the reasons described above, modified support post 200
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, modified support post 200 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, modified support post 200 is intentionally
designed such that yielding will more readily occur in response to
an impact about the weak axis W.
[0068] The modification of the support post to include a curved
flange as shown in FIG. 7 is merely one method of protecting a
guardrail beam from potential tearing by the support post. Previous
methods for preventing the rupturing of the guardrail beam by the
sharp edges of the support post flanges include the positioning an
offset block between the flange of support post 14 and guardrail
beam 12. Recent trends in guardrail systems include increasing the
depth of offset blocks to prevent post snagging. When a frangible
or yielding post such as support post 14 is used to support the
guardrail beam, however, the offset block need only prevent contact
between the guardrail beam and post flanges.
[0069] In the absence of an offset or spacer block, a flange
protector may be positioned at the interface of the guardrail beam
and support post. The flange protector may extend beyond the edges
of both the post and the rail element to shield the rail element
from the edges of the support post and, thus, prevent initiation of
cuts or tears in the guardrail beam in the vicinity of the support
post as the guardrail system deforms during an impact. The flange
protector may take the form of a plate fabricated from metal, wood,
plastic, rubber elastomer, or composite materials. When used in
conjunction with a corrugated rail element, such as a W-beam or
thrie beam, the plate may be fabricated to conform to the shape of
the rail element such that it can nest inside the rail element. The
dimensions of the plate are such that the edges of the plate extend
to or beyond the edges of the support post.
[0070] FIGS. 8A and 8B illustrate a flange protector 250 for
attachment to a support post 252. Flange protector 250 is a
modification of standard offset blocks and serves to prevent
tearing of the guardrail beam during impact. Because flange
protector 250 is a much smaller spacer than standard offset blocks,
flange protector 250 may be incorporated into a guardrail system at
a lower cost than a standard offset block. Although flange
protector 250 may be comprised of plastic, in preferred
embodiments, it is generally recognized that flange protector 250
may be alternatively made of wood, metal, rubber elastomer,
composite materials, or any combination of these or other suitable
materials.
[0071] Flange protector 250 includes a body portion that is
substantially rectangular. In particular embodiments, flange
protector 250 may comprise a substantially flat plate. In other
embodiments and in the illustrated embodiment, flange protector 250
includes an indentation 254 in the a first surface 256 that is
proximate to support post 252 when the flange protector 250 and
support post 252 are assembled together. Specifically, when
assembled together, a flange 258 of support post 252 that is
proximate flange protector 250 fits into indentation 254.
Accordingly, the dimensions of flange protector 250 and the size of
indentation 254 may vary as is appropriate for the particular size
and shape of support post 252. It is generally recognized, however,
that indentation 254 is optional, and flange protector 250 may or
may not include such an indentation.
[0072] In various embodiments, the depth of flange protector 250
may be selected based on the depth of support post 252. For
example, in a particular embodiment, the depth of flange protector
250 may be selected to be less than the predetermined depth of the
support post and may be selected to be less than half of the
predetermined depth of the support post. As another example, the
depth of flange protector 252 may be selected to be less than three
inches.
[0073] In particular embodiments, for example, where support post
252 includes a W6.times.8.5 Wide flange, flange protector 250 has a
length on the order of approximately 360 millimeters (14.17 inches)
and a width on the order of approximately 131 millimeters (5.16
inches). The depth of flange protector 250 may vary within a range
on the order of approximately 13 to 62 millimeters (0.5 to 2.4
inches). Indentation 254 in first surface 256 may have a depth of
approximately 10 millimeters (0.39 inches), in a particular
embodiment. Thus, lips on either side of flange protector 250 may
be raised approximately 10 millimeters (0.39 inches) to protect the
guardrail beam from the edges of the abutted flange 258 of support
post 252 and to keep flange protector 250 from rotating once
connected to support post 252. The width of the lips on either side
of indentation 254 may be on the order of approximately 13 mm (0.5
inches). For connection between support post 252 and the guardrail
beam (not shown), flange protector 250 includes one or more
boltholes 260 that are approximately 21 millimeters (0.82 inches)
in diameter, in the illustrated embodiment.
[0074] The dimensions of flange protector 250 may also be varied.
The combination of flange protector 250 with the frangibility of
support post 252 in a LON section of guardrail system 10 may
provide enhanced impact performance and reduced installation cost.
Specifically, a flange protector 250, as an alternative to the
standard offset block, may cost much less than the cost of a deep
offset block and may be attractive to a number of highways and
roads agencies where it is anticipated that the omission of both
may result in a system with an increased potential for incidence of
rupture of the guardrail beam when contacted with flange 258 of
support post 252.
[0075] As described above, flange protector 250 shields the
guardrail beam from the sharp edges of support post 252 to prevent
rupturing of the guardrail beam. Furthermore, a structure such as
flange protector 250 may be used as a retrofit spacer block when
steel-yielding support post 252 is placed in a foundation tube as
an alternative to a wood post. Thus, anywhere it is desirable to
protect the guardrail beam from the flanges of support posts, a
flange protector 250 may be used. As an additional variation, it is
recognized that support post may in particular embodiments include
a structural member that of a different cross-sectional shape than
that described. For example, and as discussed above, support post
may comprise a rectangular, a tubular member, or any other
appropriate shape. Where support post does not include flanges such
as flanges 258, it is recognized that flange protector may be
selected to accommodate the selected cross-sectional shape of the
support post and may be termed "a guardrail beam protector."
Returning to FIG. 1, guardrail beam 12 is attached to support posts
14 with connectors (not shown). The connectors may be threaded or
inserted through bolt holes formed through support posts 14 and
corresponding bolt holes formed through guardrail beam 12.
Oversized guardrail nuts may be used on the back side of the
support post 14 flange. Bolt holes formed through support posts 14
were illustrated and described above with respect to FIGS. 2A-2C,
3A-3C, 4A-4C, 5A-5C, 6A-6B, and 7 and were identified by reference
numerals 48, 74, 110, 184, and 188, respectively.
[0076] It is desirable for the connectors to sufficiently support
guardrail beam 12 but to be readily released upon load being
directly applied to support post 14 or upon deflection of the rail
element and rotation of the support post in surrounding soil. For
example, the connectors may enable support posts 14 to readily
release from guardrail beam 12 when support post 14 is contacted by
a vehicle. FIG. 9 illustrates an example of a connector 300 for
coupling a guardrail beam 12 with a yielding support post 14, such
as a terminal support post 14a or a LON support post 14b. The
configuration of connector 300 is such as to provide sufficiently
weak connection between guardrail beam 12 and support post 14 so
that support post 14 detaches from guardrail beam 12 when struck by
an errant vehicle. As a result, guardrail beam 12 remains
substantially at its original height after impact and the errant
vehicle may be prevented from driving over the guardrail beam 12
and further leaving the roadway or becoming unstable.
[0077] In particular embodiments, connector 300 includes a bolt
with a tapered or wedge-shaped head 302, such as a countersunk
bolt. Connector 300 provides sufficiently low force against
guardrail beam 12 to release support post 14 from guardrail beam 12
when an errant vehicle contacts and displaces support post 14.
Stated differently, the connection formed between guardrail beam 12
and support post 14 by connector 300 is strong in shear and weak in
tension. The shape of countersunk head 302 allows connector 300 to
pull through the mounting slot on the guardrail beam 12. Connector
300 may then be displaced with support post 14 upon impact.
[0078] Such a connector is improved over oval shoulder button head
bolts that provide adequate support for the guardrail beam but do
not provide sufficiently low release strength. Connector 300 is
also improved over small diameter bolts, which are typically used
with several washers. Small diameter bolt-washer combinations
provide only a limited ability to support the guardrail beam (not
strong in shear) and have variable release strengths.
[0079] In a particular embodiment, connector 300 may include
slotted countersunk bolts such as, for example, 16 mm (5/8-inch)
diameter by 38 mm (1-1/2-inch) long slotted flat countersunk head
machine screws. The countersunk head 302 of connector 300, in such
an embodiment, may have a diameter on the order of approximately 25
millimeters (1 inch) and have a length on the order of 13
millimeters (1/2 inch). Other embodiments may include a countersunk
head 302 having a diameter on the order of 25 millimeters (1 inch)
and a length on the order of 6.5 millimeters (1/4 inch). It is
generally recognized, however, that these are merely two examples
of connectors 300 that may be used to releasably engage guardrail
beam 12 with support post 14. Other connectors that may be used in
place of connector 300 include those specified by ANSI/ASME
B18.5.
[0080] Still other, alternative embodiments of possible connectors
may include appropriately sized standard bolts that will tear
through the guardrail beam without rupturing the guardrail beam.
For example, the standard bolts may be selected such that a head
portion of the bolt is of a size that overlaps an edge of the
aperture by a distance that generates a desired pullout resistance.
In particular embodiments, the size of the head portion selected as
a function of a thickness of the guardrail beam. Such bolts may
include 5/8-inch bolts, 1/4-inch bolts, or 3/16-inch bolts with or
without washers. A plow bolt may also be used where the resulting
connection is weak in tension such as to release when a lateral
load is applied. In still other embodiments, connector 300 may
release through fracture, shear, or tensile failure.
[0081] FIGS. 10A-10C illustrate another example of a connector 400
for coupling a guardrail beam 12 with a yielding support post 14,
such as a terminal support post 14a or a LON support post 14b. Like
connector 300, connector 400 includes a bolt with a countersunk
head 402 to provide adequate support of guardrail beam 12.
Connector 400 provides sufficiently low force against guardrail
beam 12, to release support post 14 from guardrail beam 12 when an
errant vehicle contacts and displaces support post 14. Stated
differently, connector 400 forms a connection between guardrail
beam 12 and support post 14 that is strong in shear and weak in
tension. The shape of countersunk head 402 allows connector 400 to
pull through the mounting slot on the guardrail beam 12. Connector
400 may then be displaced with support post 14 upon impact.
[0082] Additionally, the configuration of connector 400 prevents
connector 400 from rotating when connector 400 is used to couple
support post 14 with guardrail beam 12. Specifically, head 402 of
connector 400 includes a first surface 404 and a second surface
406. Whereas first surface 404 comprises the outer surface of
connector 400, second surface 406 is proximate threaded shaft 408.
In the illustrated embodiment, first surface 404 of head 402 is of
a substantially round configuration. By contrast, second surface
404 is of a substantially oval configuration. Thus a portion of
head 402 includes a shoulder 410. Where guardrail beam 12 includes
a slotted hole through which connector 400 is placed, the oval
shape of shoulder 404 prevents connector 400 from rotating in the
slotted hole. The shoulder 410 of connector 400 also limits the
horizontal movement of connector 400 within the slotted hole of
guardrail beam 12. This, in turn, limits the amount of overlap of
head 402 of connector 400 with the edge of the slotted hole of
guardrail beam 12. The result is that the pullout force required to
disengage connector 400 from guardrail beam 12 is further
reduced.
[0083] In a particular embodiment, connector 400 may include
slotted countersunk bolts such as, for example, 16 mm (5/8-inch)
diameter by 38 mm (1-1/2-inch) slotted flat countersunk head
machine screws. The countersunk head 402 of connector 400, in such
an embodiment, may have a diameter on the order of approximately 25
millimeters (1 inch) and have a length on the order of 13
millimeters (1/2 inch). The diameter of the longer dimension of
oval shoulder 406 may correspond generally with the diameter of
head 402 or approximately 1 inch, and the diameter of the shorter
dimension of oval shoulder 406 may correspond generally with the
diameter of the bolt shaft or approximately 5/8 inch. It is
generally recognized, however, that this merely one example of a
connectors 400 that may be used to releasably engage guardrail beam
12 with support post 14. Other connectors may be used in place of
connector 400.
[0084] Technical advantages of particular embodiments of the
present invention include a LON guardrail support post that has
sufficient strong axis strength to redirect vehicles that collide
along the length of the guardrail system at an angle to the flow of
traffic and substantially reduced weak axis strength to mitigate
the severity of the interaction (snagging) between an impacting
vehicle and the post without changing the deflection
characteristics of the guardrail system. For example, LON support
posts configured to include a weakened section may release from the
guardrail beam upon impact. As a result, the flanges of the LON
support posts may be prevented from tearing the guardrail beam and
the weakened section can readily yield to an impacting vehicle at
low force levels. Still another advantage may include, in
particular embodiments, the removal or reduction in size of an
offset block between the guardrail beam and the LON support post.
Accordingly, certain embodiments of a guardrail system of the
present invention may provide benefits in terms of space and cost
savings.
[0085] At least four types of guardrail support members are
described and illustrated within this specification: (I) W6.times.9
Wide flanges; (II) W8.times.10 Wide flanges; (III) W6.times.8.5
Wide flanges; and (IV) weakened wood posts. It should be recognized
by those of ordinary skill in the art that practically any size
guardrail support post may be enhanced by incorporating the
teachings of the present invention. 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.
[0086] 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 rail to the offset blocks or
flange protectors and support posts and the hole/slot pattern in
the rail through which these connecting bolts pass may be varied in
any manner suitable for enabling the post to release from the
guardrail element.
* * * * *