Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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GUARDRAIL SAFETY SYSTEM FOR DISSIPATING ENERGY TO
DECELERATE THE IMPACTING VEHICLE
TECHNICAL FIELD
The present invention relates generally to safety treatment for the ends of W-
beam guardrails; and more particularly, to a tensioned guardrail terminal for
dissipating impact energy of a car colliding with the end of the W-beam
guardrail in
an end-on or re-directive impact.
BACKGROUND
Along most highways there are hazards that can be a substantial danger to
drivers of automobiles if the automobiles leave the highway. To reduce the
severity
of accidents due to vehicles leaving a highway, guardrails are provided. The
guardrails are installed such that the beam elements are in tension to aid in
re-
directive type impacts. Guardrails must be installed, however, such that the
terminal
end of the guardrail facing the flow of traffic is not a hazard. Early
guardrails had no
proper termination at the ends, and it was not uncommon for impacting vehicles
to
become impaled on the guardrail causing intense deceleration of the vehicle
and
severe injury to the occupants. In some reported cases, the guardrail
penetrated
directly, into the occupant compartment of the vehicle fatally injuring the
occupants.
Upon recognition of the problem of proper guardrail termination, guardrail
designs were developed that used box beams and W-beams that allow tapering of
the
end of the guardrail into the ground. Such designs eliminate any spearing
effect.
While these end treatments successfully removed the danger of the vehicle
being
penetrated in a head-on collision, it was discovered that these end treatments
operate
in a ramp-like fashion and may induce launching of the vehicle causing it to
become
airborne for a considerable distance with the possibility of roll over.
In search for better end treatments, improved energy absorbing end treatments
for W-beam guardrail elements were developed. For example, an extruder
terminal
was developed and typically includes a bending structure that squeezes the
guardrail
into a flat plate and then bends it about a circular arc directed away from
the
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impacting vehicle. Example extruder terminal products include the ET 2000TM
and the ET-
PLUSTm offered by Trinity Highway Products. Other extruder terminal products
include the
SKT 350TM and FLEAT 350TM offered by Road Systems, Inc.
All of these energy absorbing systems use a cable to connect the first w-beam
guardrail segment to the first post in the system. The cable provides tension
in the guardrail
beam element for a redirective hit along the length-of-need portion of the
guardrail. A
number of cable releasing posts have also been developed for use in these
terminals. The
cable release posts are intended to release the cable anchor and, thus,
release the tension in
the system when the post is impacted in either of a forward (end-on) or
reverse direction.
Such systems are not able to remain in tension during end-on and reverse-
direction type
impacts.
SUMMARY QF THE INVENTION
The present invention provides a new and improved end treatment for highway
guardrails.
In accordance with a particular embodiment of the present invention, there is
provided an end treatment of a guardrail safety system comprising: a terminal
portion of a
guardrail beam comprising a W-beam having a downstream end and an upstream
end, the
W-beam sloping from a first vertical height appropriate for redirecting an
errant vehicle to a
second vertical height proximate the surface of the ground at the upstream end
of the W-
beam, wherein the upstream end of the W-beam comprises a vertically flattened
W-beam
that is secured to a terminal support post proximate the surface of the
ground; a flattening
portion forming a channel through which the terminal portion of the guardrail
beam is
disposed, a vertical dimension of the channel being greater at a downstream
end of the
flattening portion than at an upstream end of the flattening portion; and an
impact plate
coupled to the flattening portion, the impact plate for engaging an impacting
vehicle at an
end of said guardrail beam; and wherein the upstream end of the W-beam is
vertically
flattened in an assembled state and prior to an end-on impact, and wherein the
impact plate
and the flattening portion are advanced longitudinally along the guardrail in
a downstream
direction by a vehicle during the end-on impact, the advancement of the impact
plate and
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flattening portion dissipating energy to decelerate the impacting vehicle and
flattening the
guardrail vertically as downstream portions of the guardrail beam are forced
into the
flattening portion.
Technical advantages of particular embodiments of the present invention
include a
guardrail end treatment that may dissipate impact energy through the
compression of the W-
beam guardrail element. Thus, one advantage may be that the guardrail end
treatment is
energy absorbing. Another advantage may be that the end treatment forces the W-
beam
guardrail element through a flattening structure that squeezes the guardrail
into a relatively
flat plate. Specifically, the guardrail end treatment may dissipate impact
energy of a vehicle
colliding with an end of a guardrail by flattening a portion of the guardrail.
Still another advantage may be that an end of the W-beam guardrail element
extends
through the flattening structure and tapers to the ground. The W-beam
guardrail element
may be secured to the ground in tension. The components of the system that
provide the
tensile connection of the guardrail beam to the terminal support post may
enable the
guardrail beam to remain secured after an end-on or re-directive impact. Thus,
the system
may remain in tension during both types of impacts. Still another advantage
may be that the
tension is released when the system is impacted in the reverse direction near
the terminal
end, however. The releasing of tension in the guardrail element for reverse
direction
impacts prevents vehicle instability and excessive deceleration.
Another exemplary embodiment provides a guardrail safety system comprising: a
guardrail beam comprising a W-beam having a downstream end and an upstream
end, a
terminal portion of the W-beam sloping from a first vertical height
appropriate for
redirecting an errant vehicle to a second vertical height proximate the
surface of the ground,
wherein an upstream end of the W-beam comprises a vertically flattened W-beam
that is
coupled to a terminal support post proximate the surface of the ground; a
plurality of support
posts installed adjacent a roadway in spaced apart relation to one another,
the plurality of
support posts coupled to the guardrail beam; and an end treatment releasably
coupled to at
least one of the plurality of support posts, the end treatment comprising: a
flattening portion
forming a channel through which the terminal portion of the guardrail beam is
disposed, a
vertical dimension of the channel greater at a downstream end of the
flattening portion than
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at an upstream end of the flattening portion; and an impact plate coupled to
the flattening
portion, the impact plate for engaging an impacting vehicle at an end of said
guardrail beam;
and wherein the upstream end of the W-beam is vertically flattened in an
assembled state
and prior to an end-on impact, and wherein the end treatment is advanced
longitudinally
along the guardrail in a downstream direction by a vehicle during the end-on
impact, the
advancement of the end treatment dissipating energy to decelerate the
impacting vehicle and
flattening the guardrail vertically as downstream portions of the guardrail
beam are forced
into the flattening portion.
A further exemplary embodiment provides a guardrail safety system comprising:
a
guardrail beam comprising a W-beam having a downstream end and an upstream
end, at
least a portion of the W-beam being positioned at a first vertical height
relative to the ground
for redirecting an errant vehicle, wherein an upstream end of the W-beam
comprises a
vertically flattened W-beam that is coupled to a terminal support post
proximate the surface
of the ground; a plurality of support posts installed adjacent a roadway in
spaced apart
relation to one another, the plurality of support posts coupled to the
guardrail beam; and an
end treatment releasably coupled to at least one of the plurality of support
posts, the end
treatment forming a channel through which a terminal portion of the guardrail
beam is
disposed, a vertical dimension of the channel greater at a downstream end of
the channel
than at an upstream end of the channel; and wherein the upstream end of the W-
beam is
vertically flattened in an assembled state and prior to an end-on impact, and
wherein the end
treatment is advanced longitudinally along the guardrail in a downstream
direction by a
vehicle during the end-on impact, the advancement of the end treatment
dissipating energy
to decelerate the impacting vehicle and flattening the guardrail vertically as
downstream
portions of the guardrail beam are forced into the flattening portion.
In accordance with a particular embodiment of the present invention, a
terminal
portion of a guardrail safety system includes a terminal portion of a
guardrail beam having a
downstream end and upstream end. The terminal portion of the guardrail beam
slopes from
a height appropriate for redirecting an errant vehicle to a height proximate
the surface of the
ground at an upstream end of the terminal portion. Support posts are installed
adjacent a
roadway in spaced apart relation to one another and are coupled to the
terminal portion of
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the guardrail beam. A terminal support post is installed adjacent the roadway
at an upstream
end of the end terminal. The terminal support post couples to an upstream end
of the
terminal portion of the guardrail beam by a resistive, tensile coupling that
maintains tension
in the terminal portion of the guardrail beam. The resistive, tensile coupling
is maintained
between the terminal support post and the guardrail beam during an end-on or
re-directive
impact by a vehicle. However, the resistive, tensile coupling between the
terminal support
post and the guardrail beam is released during a reverse-direction impact.
Technical advantages of particular embodiments of the present invention
include a
guardrail end treatment that dissipates impact energy through the compression
of a W-beam
guardrail element. Thus, one advantage may be that the guardrail end treatment
is energy
absorbing. Another advantage may be that the end treatment forces the W-beam
guardrail
element through a flattening structure that squeezes the guardrail into a
relatively flat plate.
Specifically, the guardrail end
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treatment may dissipate impact energy of a vehicle colliding with an end of a
guardrail by flattening a portion of the guardrail.
Still another advantage may be that an end of the W-beam guardrail element
extends through the flattening structure and tapers to the ground. The W-beam
guardrail element may be secured to the ground in tension. The components of
the
system that provide the tensile connection of the guardrail beam to the
terminal
support post may enable the guardrail beam to remain secured after an end-on
or re-
directive impact. Thus, the system may remain in tension during both types of
impacts. Still another advantage may be that the tension is released when the
system
is impacted in the reverse direction near the terminal end, however. The
releasing of
tension in the guardrail element for reverse direction impacts prevents
vehicle
instability and excessive deceleration.
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
FIGURE 1 illustrates a top view of an exemplary guardrail safety system that
incorporates certain aspects of the present invention;
FIGURE 2 illustrates a side view of a terminal portion of a guardrail system
that incorporates certain aspects of the present invention;
FIGURE 3 illustrates a side view of an exemplary embodiment of an end
treatment in the terminal portion of a guardrail system, in accordance with a
particular
embodiment of the present invention;
FIGURES 4A and 4B illustrate a side view and a profile view, respectively, of
a modified guardrail beam that incorporates certain aspects of the present
invention;
FIGURES 5A-5C illustrate an exemplary weakened support post suitable for
use in a guardrail safety system, in accordance with a particular embodiment
of the
present invention;
FIGURES 6A-6C illustrates another exemplary weakened support post
suitable for use in a guardrail safety system, in accordance with a particular
embodiment of the present invention;
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FIGURES 7A-7C illustrates an exemplary unmodified support post suitable
for use in a guardrail safety system, in accordance with a particular
embodiment of
the present invention;
FIGURES 8A and 8B illustrate an exemplary embodiment of a terminal
support post for use in a guardrail safety system, in accordance with a
particular
embodiment of the present invention;
FIGURES 9A-9C illustrate various components of a resistive, tensile
connection for connecting a guardrail beam to a terminal support post, in
accordance
with a particular embodiment of the present invention;
FIGURES 10A and 10B illustrate an exemplary resistive, tensile connection
for connecting a guardrail beam to a terminal support post, in accordance with
a
particular embodiment of the present invention;
FIGURES 11 A and 11B illustrate an exemplary strut for use in a guardrail
safety system, in accordance with a particular embodiment of the present
invention;
and
FIGURE 12 illustrates an alternative embodiment of a resistive, tensile
connection for connecting a guardrail beam to a terminal support post, in
accordance
with a particular embodiment of the present invention.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
Existing guardrail end treatments have proven to be unsafe for some collision
conditions that happen on the highway, sensitive to installation details,
and/or very
costly. However, the end treatment described below is a safety treatment for
the ends
of a W-beam guardrail that provides a higher level of performance over a wider
range
of collision conditions and reduces end treatment costs and the number of
injuries and
deaths associated with guardrail terminal accidents. The described system
maintains
the tension in the guardrail beam element during both end-on and re-directive
type
impacts. When the system is impacted in the reverse direction near the
terminal end,
however, the anchorage system may release to prevent vehicle instability or
excessive
deceleration.
FIGURE 1 illustrates a guardrail safety system 100 that incorporates certain
aspects of the present invention. Guardrail system 100 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
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other hazardous condition. Guardrail systems that incorporate 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 100 includes a guardrail beam 102 and support posts 104
that anchor guardrail beam 102 in place along the roadway. In a particular
embodiment, guardrail beam 102 may include multiple 12-gauge W-beam rail
elements of a length on the order of approximately 12.5 feet or 25 feet. The
guardrail
beam sections may be mounted at a height of on the order of approximately 27
to 31
inches with rail splices positioned mid-span between the support posts 104.
Guardrail
beam 102 and the terminal end of guardrail beam 102, specifically, are
illustrated in
more detail in FIGURES 4A and 4B and will be described below.
Guardrail beam 102 is attached to support posts 104 with connectors that may
include, in particular embodiments, slotted countersunk bolts such as, for
example, 16
mm (5/8-inch) diameter by 38 mm (1-1/2-inch) long flat slot machine screws.
Oversized guardrail nuts may be used on the back side of the support post 104.
Support posts 104 may be embedded in the ground, a concrete footing, or a
metal
socket. Support posts 104 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 104 within guardrail system 100 need not necessarily be made of
the
same material or include the same structural features. Furthermore, the cross-
section
of support posts 104 may be any engineered shape suitable for releasably
supporting
guardrail beam 102. Such cross-sectional shapes may include, but are not
limited to,
square, rectangular, round, elliptical, trapezoidal, solid, hollow, closed, or
open.
Guardrail system 100 is intended to keep errant vehicles from leaving the
roadway during a crash or other hazardous situation. In many instances,
guardrail 100
is installed between a roadway and a significant hazard to vehicles (e.g.,
another
roadway, a bridge, cliff, etc.). Therefore, guardrail system 100 should be
designed to
withstand a significant impact from a direction generally perpendicular to the
roadway, without substantial failure. It is this strength that allows
guardrail system
100 to withstand the impact, and still redirect the vehicle so that it is once
again
traveling generally in the direction of the roadway.
However, testing and experience has continuously shown 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
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system adjacent its terminal section, 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.
Patent 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.
Referring again to FIGURES 1 and 2, guardrail system 100 includes one
terminal post 106 and seven support posts 104. Collectively, this
configuration forms
a terminal section 108 of guardrail system 100. As shown, terminal section 108
is
employed in a preferred embodiment as an end terminal for a conventional
guardrail
assembly 100.
Although FIGURE 1 is illustrated with dimensions and depicts one exemplary
embodiment, it is understood that the dimensions of guardrail system 100 may
vary
depending on the nature of the roadside hazard being shielded. As illustrated,
each
terminal section 108 has a length on the order of approximately 35 feet.
However, the
dimensions of terminal section 108 may vary as needed. Additionally, the
length of
the length-of-need portion of the system may of any appropriate length
required by
the conditions of the roadway.
Terminal section 108 may be installed either parallel to the roadway or at an
angular departure from the roadway, as shown best in FIGURE 1. Additionally,
while
the terminal section 108 at one end of the guardrail safety system may be
flared, the
terminal section 108 at the opposite end of the system may not be flared, in
certain
embodiments. For example, in the embodiment depicted in FIGURE 1, an upstream
terminal section 108 is flared while a downstream terminal section 108 is not
flared.
Specifically, the upstream terminal sections 108 is flared away from the
roadway in a
substantially linear manner while the downstream terminal section 108 remains
substantially parallel to the roadway. In other embodiments, both terminal
sections
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108 may be flared or unflared in a similar manner. Additionally, it is
recognized that
other configurations may be used for terminal sections 108. For example, one
or both
of terminal sections 108 may be installed at a parabolic flare away from the
roadway.
A parabolic flare may be accomplished by increasing the offset of each support
post
in a generally parabolic progression as the terminal portion proceeds
upstream.
Where incorporated, positioning of one or more of terminal sections 108 at a
flared or
angular departure away from the roadway may permit the terminal sections 108
to
perform a gating function by facilitating movement of the impacting vehicle to
the
side of the rail opposite the roadway as the vehicle progresses.
In a particular embodiment where terminal section 108 is linearly flared,
terminal section 108 may be flared back at an angle of approximately 6 to 7
degrees
from the non-terminal portion of the guardrail. Where support posts 104 of
terminal
section 108 are spaced apart at intervals of approximately 75 inches, the most
downstream post 104 of terminal section 108 may be approximately 9 inches
offset
from a line tangent to the non-terminal portion of the guardrail, in a
particular
embodiment. Moving toward the upstream end of terminal section 108, the next
four
successive support posts 104 may be 19, 29.25, 39, and 48 inches offset from a
line
tangent to the non-terminal portion of the guardrail, in this embodiment.
Terminal
post 106, which may be positioned directly below guardrail beam 102, may be
approximately 47 inches offset from a line tangent to the non-terminal portion
of the
guardrail, in the described embodiment.
As shown better in FIGURE 2, terminal section 108 includes an end treatment
110. End treatment 110 includes a flattening chute 112 and a front striking
plate 114.
End treatment 110 and flattening chute 112, specifically, is mounted onto a
first post
104 by fasteners such as bolts. The purpose of end treatment 110 is to
dissipate
impact energy of the vehicle without creating a dangerous condition such as
causing
the vehicle to roll-over or allow the guardrail 102 to spear the vehicle or
the occupant
compartment of the vehicle.
Guardrail beam element 102 feeds into an inlet 116 at a downstream end of
flattening chute 112. Guardrail beam element 102 is disposed within flattening
chute
112 and extends the length of flattening chute 112. Guardrail beam element 102
exits
an outlet 118 at an upstream end of flattening chute 112. As will be described
in more
detail with regard to FIGURE 3, the dimensions of flattening chute 112 results
in a
terminal portion of the guardrail beam 102 tapering to the ground. The portion
of
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guardrail beam element 102 exiting outlet 118 is flattened vertically such
that the
terminal portion of guardrail beam element 102 resembles a stack of four flat
plates.
A terminal post 106 secures the terminal end of guardrail beam element 102 to
the ground and places guardrail beam element 102 in tension. As will be
described in
more detail with regard to FIGURES 8A and 8B and 10A and 10B, the coupling of
guardrail beam element 102 to terminal post 106 enables guardrail beam element
102
to remain secured in tension to terminal post 106 after either of an end-on or
re-
directive impact by a vehicle leaving the roadway. However, the components
effecting the tensile coupling enables the tension in guardrail beam element
102 to be
released when the system is impacted in the reverse direction near the
terminal end.
The releasing of tension in the guardrail element for reverse direction
impacts
prevents vehicle instability and excessive deceleration.
FIGURE 3 illustrates an exemplary embodiment of end treatment 110 in
greater detail. As described above, end treatment 110 includes a flattening
chute 112
and a front striking plate 114. Flattening chute 112 and front striking plate
114 are
coupled to an extruder 120. Extruder 120 surrounds the upstream portion of
guardrail
beam member 102 and is made up of an upper, U-shaped channel member 122 and a
lower, U-shaped channel member 124, which are secured in a spaced relation to
one
another by strap plates 126.
The vertical distance between channel members 122 and 124 is an appropriate
distance such that guardrail beam 102 is inserted into the channel created by
extruder
120. For example, where guardrail beam 102 comprises a 12-gauge W-beam rail
element having a vertical dimension of approximately 12.25 inches, the
distance
between the top of channel member 122 and the bottom of channel 124 may be
approximately 14 inches, in a particular embodiment.
Front striking plate 114 is secured by welding to extruder 120 of end
treatment
110. Front striking plate 114 may be vertically elongated, in particular
embodiments.
Thus, front striking plate 114 may extend both above and below extruder 120 to
permit front striking plate 114 to be easily engaged by either the high bumper
of
trucks, SUV's, and other taller vehicles and the low set bumpers of smaller
cars
impacting in a frontal manner. Front striking plate 114 is also positioned so
as to
engage the vehicle frame or rocker panel to reduce vehicle intrusion when the
upstream end of end treatment 110 is impacted by a vehicle in a sideways
manner.
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Flattening portion 112, which is mounted to extruder 120, may be constructed
from four metal plates, in a particular embodiment. The four metal plates may
be cut
and/or bent and then welded together to form the desired configuration.
Alternatively,
flattening portion 112 may be formed from more than four pieces or from a
single
piece of metal that is cut and bent into the desired configuration. When
flattening
portion 112 is assembled, flattening portion 112 may form an enclosed
structure that
houses a terminal portion of guardrail beam 102.
In the illustrated embodiment, flattening portion 112 includes three sections.
The most downstream portion of flattening portion 112 includes a throat 128.
The
vertical dimension of throat 128 is greater at the downstream end and
decreases as it
approaches the upstream end of end treatment 110. For example, in a particular
embodiment, the vertical dimension of throat 128 may be approximately 14
inches
wide at the downstream end and approximately 4.5 inches wide at the upstream
end.
The horizontal length of throat 128 may be within a range of approximately 11
to 13
inches.
In a particular embodiment, the slope of a lower edge 132 may be greater than
the slope of an upper edge 130. The increased slope of lower edge 132 may aid
in the
flattening of guardrail beam 102 during an impact. For example, in a
particular
embodiment, upper edge 130 may slope upward at an angle of approximately 11
degrees from the horizontal, and lower edge 132 may slope downward at an angle
of
approximately 13 degrees from the horizontal. In still other embodiments, the
slope
of upper edge 130 and lower edge 132 may be substantially the same. Thus, in a
particular embodiment, upper edge 130 and lower edge 132 may symmetrically
mirror
one another. In still other embodiments, one of top edge 130 and lower edge
132 may
be aligned with the horizontal (substantially parallel with the roadway) while
the other
of top edge 130 and lower edge 132 slopes upward or downward, respectively.
A mid portion 134 extends from the upstream end of throat 128 and slopes
toward the ground. Specifically, mid portion 134 is configured to transition
guardrail
beam element 102 from a height above the ground level that is appropriate for
redirecting an impacting vehicle (31 inches, in a particular embodiment) to a
height
that is proximate the ground's surface. Thus, mid portion 134 extends from a
vertical
distance associated with throat 128 at a downstream end to approximately
ground
level at an upstream end. In a particular embodiment, where the horizontal
length of
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mid portion 134 is approximately 18.75 inches, mid portion 134 may slope at an
angle
of approximately 38 degrees from the horizontal.
Mid portion 134 also provides a channel through which a terminal portion of
guardrail beam element 102 is disposed. In a particular embodiment, the
vertical
dimension of the channel within mid portion 134 may be approximately 4.5
inches
(similar to the width of throat 128 at the upstream end). The dimensions of
the
channel within mid portion 134 may remain substantially constant such that the
vertical dimension of the channel within mid portion 134 at the downstream end
is the
substantially the same as the vertical dimension of the channel within mid
portion 134
at the upstream end.
A third portion of flattening portion 112 includes outlet portion 136. Outlet
portion 136 extends from the upstream end of mid portion 134. Outlet portion
136 is
disposed proximate the grounds' surface and is in substantial alignment with
the
grounds' surface. Outlet portion 136 also forms a channel through which the
terminal
end of guardrail beam element 102 exits the flattening chute 112. In a
particular
embodiment, the vertical dimension of the channel within outlet portion 136
may be
approximately 4.5 inches (similar to the vertical dimension of the channel
within mid
portion 134). The dimensions of the channel within outlet portion 136 may
remain
substantially constant such that the vertical dimension of the channel at the
downstream end of outlet portion 136 is substantially the same as the vertical
dimension of the channel at the upstream end of outlet portion 136. In a
particular
embodiment, the horizontal length of outlet portion 136 may be approximately 5-
7
inches.
As stated above with regard to Figure 2, guardrail beam member 102 is
disposed within and extends throughout the length of flattening portion 112.
Specifically, guardrail beam member feeds into an inlet 116 at a downstream
end of
flattening chute 112. Guardrail beam element 102 traverses the length of
flattening
chute 112 and exits an outlet 118 at an upstream end of flattening chute 112.
Thus, a
terminal end of the W-beam guardrail element extends through the flattening
structure. The slope of mid portion 134 toward the ground in the upstream
direction
results in guardrail beam element 102 being gradually transitioned toward the
ground
over the length of flattening portion 112. After exiting the outlet 118,
guardrail beam
element 102 is secured to a terminal post 106 at ground level.
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During an end-on or oblique end-on collision of a vehicle with front striking
plate 114, end treatment 110 may be displaced in a downstream direction and
downstream portions of guardrail beam element 102 may be forced into the
displaced
end treatment 110. During such a collision, extruder 120 functions as a guide
to guide
guardrail beam element into flattening portion 112. Extruder 120 includes
guides 138
that prevent shaving of the W-beam guardrail element 102 by ends of extruder
120 as
extruder 120 moves along the length of the guardrail beam element 102 during a
collision. The guides 138 accommodate any irregularities or bumps in guardrail
beam
element 102 to ensure proper feeding of guardrail beam element 102 into
flattening
portion 112.
As end treatment 110 moves along guardrail beam element 102 and
downstream portions of guardrail beam element 102 are forced into flattening
portion
112, guardrail beam element 102 is flattened vertically. Portions of guardrail
beam
element 102 exiting outlet 118 of flattening portion 112 are flattened into
what may
appear to be four vertically stacked plates. For example, where the vertical
dimension
of guardrail beam element 102 is approximately 12.25 inches and throat portion
134
of flattening portion 112 is approximately 4.5 inches, the vertical dimension
of the
flattened portion of guardrail beam element 102 may be less than approximately
4.5
inches. As this flattening process occurs, substantial energy is dissipated
slowing the
impacting vehicle.
To aid in initial flattening of guardrail beam element 102 for coupling to
terminal support post 106, a terminal end of guardrail beam element 102 may be
modified. FIGURES 4A and 4B illustrate a modified guardrail beam element 200
in
accordance with one embodiment. As shown in FIGURE 4A, the guardrail beam
element 200 includes a slotted zone 202 at the upstream end of the terminal
portion of
guardrail beam element 200. In a particular embodiment, slotted zone 202
comprises
a series of slots longitudinally disposed in the guardrail beam element 200.
The use
of three slots has proven effective in testing models of guardrails
constructed similar
to guardrail safety system 100.
Slotted zone 202 may initiate at a terminal end 203 of guardrail beam element
200 and extend a desired distance downstream. The horizontal length of slotted
zone
202 may vary depending on the horizontal length of end treatment 110. It may
be
desirable for slotted zone 202 to include the portion of guardrail beam
element 200
that is coupled to terminal post 106 and the portion of guardrail beam element
200
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that traverses through flattening portion 112. Generally, slotted zone 202 may
extend
from the terminal, upstream end of guardrail beam element 200 to some distance
between the first and second support posts 104. Where, for example, the
dimensions
of the terminal section 108 of guardrail system 100 are similar to those
illustrated in
FIGURE 1, slotted zone 202 may extend approximately 80-85 inches from the
terminal end of guardrail beam element 200.
The placement of the slots in slotted zone 202, according to a particular
embodiment, may be better understood with reference to the cross-section for a
typical W-beam guardrail 200 as shown in FIGURE 4B. A valley 204 is positioned
between upper and lower peaks 206 and is formed at the intersections of
inclined web
portions 208. Edge members 210 laterally out lie each peak 206. Highly
preferred
placement for the slots is proximate each peak 206 and the valley 204. Thus,
in the
illustrated embodiment of FIGURE 4A, first and second slots 212 are placed in
the
first and second peaks 206, respectively. A third slot 214 is placed in valley
204.
Slots 212 and 214 should be of a size sufficient to enhance the ability of the
terminal end of guardrail beam element 200 to be flattened. In a preferred
embodiment, the entire vertical dimension of each peak 206 and valley 204 may
be
removed. Effective sizes for slots 212 have been found to be approximately 0.5
inches, as measured vertically. An effective size for slot 214 has been found
to be
approximately 0.75 inches, as measured vertically. Thus, in a particular
embodiment,
slots 212 may have a width on the order of 0.5 inches and extend approximately
81-82
inches. Slot 214 may have a width on the order of approximately 0.75 inches
and
extend approximately 81-82 inches. The provided dimensions are for example
purposes only, however. Any dimensions may be used for slots 212 and 214 to
enhance the ability of guardrail beam 200 to be flattened into four vertically
stacked
plates throughout the terminal end of guardrail beam element 200.
While guardrail beam 102 may include W-beam rail elements, it is generally
recognized that the illustrated guardrail beam 102 is merely an example of a
beam that
may be used in a guardrail system. Guardrail beams 102 or portions of
guardrail
beams 102 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 100 may vary as
desired.
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Returning to FIGURES 1 and 2, following the initial end-on impact of a
vehicle with end treatment 110 and the initiation of the displacement of end
treatment
110 in a downstream direction, the impacting vehicle and end treatment 110 may
engage one or more support posts 104. Where the support posts 104 comprises
steel
yielding support posts that are modified at ground level, the impacted support
posts
104 may release guardrail beam element 102 as they are impacted and bent
toward the
ground. Thus, support posts 104 that are impacted during the collision may be
displaced, in certain embodiments, such that they do not pose a hazard to the
impacting vehicle. Although guardrail beam 102 may be released from impacted
support posts 104, portions of guardrail beam element 102 downstream from the
impact may remain in substantially their original position relative to the
ground's
surface. Further, because guardrail beam 102 remains coupled to terminal post
106
during an end-on or re-directive impact, guardrail beam 102 remains in
tension. This
extends the range of acceptable performance of guardrail safety system 100.
The tension in guardrail beam 102 may also be retained in this manner when
guardrail system 100 is subject to a re-directive impact in the length of need
portion
of guardrail system 100. For example, when an impacting vehicle traveling in a
direction substantially parallel to the downstream direction of guardrail
system 100
leaves the roadway and impacts guardrail system 100, any support posts 104
impacted
by the vehicle may operate to release guardrail beam element 102 as they are
impacted. Modified support posts 104 may be bent toward the ground such that
the
support posts 104 are displaced and do not pose a hazard to the impacting
vehicle.
Because the tension in guardrail beam 102 is maintained, guardrail beam
element 102
continues to operate to redirect the vehicle back onto the roadway even after
one or
more support posts are released from guardrail beam element 102.
FIGURES 5A-5C, 6A-6C, and 7A-7C illustrate example embodiments of
support posts that may be used in conjunction with guardrail system 100 of
FIGURE
1. Specifically, FIGURES 5A-5C illustrate an exemplary weakened support post
that
may be used as a first support post 500 (after the terminal support post 106)
in the
terminal section 108 of guardrail safety system 100. FIGURES 6A-6C illustrate
an
exemplary weakened support post 600 that may be used throughout terminal
section
108 and other portions of guardrail safety system 100. FIGURES 7A-7C
illustrate a
standard line post 700 that may be used in certain portions of guardrail
safety system
100. Although FIGURES 5A-5C, 6A-6C, and 7A-7C illustrate three distinct
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embodiments, respectively, like reference numerals have been used to identify
parts
common to the three embodiments.
As illustrated, support posts 500, 600, and 700 include elongate, continuous
structural members and are each of a standard wide flange configuration. Each
support post includes two flanges 502, that are generally parallel with one
another,
and in spaced apart relation from one another. A web 504 forms the coupling
between flanges 502. In a preferred embodiment, flanges 502 include a
generally
identical configuration of boltholes 506 and cutouts 508, therein.
With regard to the 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.
In the illustrated embodiment of FIGURES 5A-5C, 6A-6C, and 7A-7C the
=
wide flange is a standard W6x8.5, which is commonly used in fabricating
support
posts for guardrail installations. A standard W6x8.5 wide flange may have a
nominal
six-inch depth and weigh eight and one-half pounds per foot. In fact, one
advantage
of the present invention is the ability to re-use existing, standard equipment
to
fabricate, modify, and install support post 500, 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 wide flange having a
six-
inch depth and weighing nine pounds per foot may also be used. Such a wide
flange
is referred to as a W6x9 wide flange. However, a W6x9 wide flange and a W6x8.5
wide flange are considered equivalent in the trade. The terms "W6x8.5 wide
flange"
and "W6x9 wide flange" are intended to refer to all sizes and configurations
of
guardrail posts that may be referred to as "W6x9" 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 posts 500, 600, and 700 have a length in a range of approximately 72
and 73 3/8 inches, in particular embodiments, and include an upper portion 510
and a
lower portion 512. A mid portion 514 couples upper portion 510 with lower
portion
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512. Upper portion 510 includes two boltholes 506 that are adapted to receive
connectors for the installation of a guardrail beam (e.g., guardrail beam 102)
upon the
support post. Lower portion 512 is suitable for installation below grade, as
part of a
guardrail support system.
Bolt holes 506 include a standard configuration that allow for the
installation
of widely used guardrail beams, upon the respective support post. In general,
bolt
holes 506 align with the center of the guardrail beam, and maintain the center
of the
guardrail beam approximately 30 inches above grade. However, the number, size,
location and configuration of boltholes 506 may be significantly modified,
within the
teachings of the present invention.
Support posts 500 and 600 are each modified to include a relatively "weak"
axis W, and a relatively "strong" axis S. Support posts 500 and 600 are
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 posts 500 and 600 are 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 posts 500 and 600 are
intentionally
designed such that failure will more readily occur in response to an impact
about the
weak axis W. Stated differently, support posts 500 and 600 exhibit adequate
strength
in the lateral direction but sufficiently low strength in the longitudinal
direction.
Accordingly, if a vehicle impacts end treatment 110 "end-on", support posts
500 and
600 will tend to fail (e.g., buckle), while allowing the vehicle to decelerate
as it
impacts consecutive support posts. However, if a vehicle strikes guardrail
system 100
along the face of and at an angle to guardrail beam 102, support posts 500 and
600
will provide sufficient resistance (strength) to redirect the vehicle along a
path
generally parallel with guardrail beam 102.
Mid portions 514 of support posts 500 and 600 include two cutouts 508, which
are configured to further weaken the support posts about the weak axis W, to
more
readily allow for failure due to impact from a vehicle along that direction.
Cutouts
508 are positioned within mid portion 514 to weaken the support posts about
weak
axis W, adjacent grade (when installed). This will accommodate failure of the
support posts approximately at grade, allowing support posts 500 and 600 to
"fold"
over from the point of failure, upward. Since lower portion 512 is below
grade, it is
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not expected that the ground, or lower portion 512 of the support post will
appreciably
deflect during an impact.
Since cutouts 508 are intended to occur approximately at grade, and the center
of bolt holes 506 are intended to occur 30 inches above grade, bolt holes 506
occur 30
inches above cutouts 508, in the illustrated embodiment. It will be recognized
by
those of ordinary skill in the art 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. The overall length of the
support posts,
and their respective upper, lower and mid portions may vary significantly,
within the
teachings of the present invention. For example, in other embodiments, cutouts
508
may occur below grade or above grade. The depth of cutouts 508 below grade
should
not exceed an amount that will prevent the support posts from failing at or
near the
location of cutouts 508. At some depth below grade, the surrounding earthen
(or
other) material will reinforce lower portion 512 of the support posts to an
extent that
will no longer accommodate such failure to occur.
The height of cutouts 508 above grade should not exceed a point at which the
support post will fail at cutouts 508, and leave a "stub" above grade which
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 the
support post is operating.
The vertical dimension of a cutout 508 is limited based upon the horizontal
dimension of cutout 508. 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 embodiments, the ratio is 1:1, since cutout 508 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 failure along the
vertical length
of support posts 500 and 600.
Various configurations of cutouts 508 are available to a designer of support
posts 500 and 600, in accordance with the teachings of the present invention.
For
example, rather than circular openings, cutouts 508 may comprise square,
rectangular,
triangular, oval, diamond shaped, or practically any other geometric
configuration,
and still obtain some or all of the benefits described herein.
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The horizontal orientation of cutouts 508 within flanges 502 may also be
altered significantly, within the teachings of the present invention. In the
illustrated
embodiments of FIGURES 5A-5C and 6A-6C, the centerline of cutouts 508 is
located
approximately one inch from the centerline of flanges 508. However, in
alternative
embodiments, cutouts 508 may be located closer to such edges, or further from
such
edges. In one embodiment, cutouts 508 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.
Alternatively, a sawcut could be employed from the outer edge of the flange,
and extending inward, to form cutouts 508. In this manner, the sawcut would
form
the starting point of the likely point of failure 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.
As stated above, FIGURES 5A-5C specifically illustrate a guardrail support
post 500 that may be used as the first support post (after the terminal
support post
106) in a guardrail system 100. Where an end treatment such as end treatment
110 is
incorporated into guardrail safety system 100, support post 500 may be
modified to
support an end treatment 110. Specifically, support post 500 includes
additional
boltholes 520 and 522 for coupling end treatment 110 to support post 500. In
the
particular illustrated embodiment, boltholes 520 and 522 are slightly smaller
than
boltholes 506 and cutouts 508. It is recognized, however, that the provided
dimensions of boltholes 520 and 522 are provided for example purposes only and
may
vary as appropriate for coupling the end treatment 110 to support post 500. In
contrast to support post 500, support posts 600 and 700 do not include
additional
boltholes 520 and 522 and, thus, are more appropriately used in portions of
the
guardrail system 100 that are not directly supporting end treatment 110.
Although W6x8.5 wide flanges are described above and illustrated within this
specification, it should be recognized by those of ordinary skill in the art
that
practically any size guardrail support post may be weakened as described
above. 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
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the weak axis while maintaining sufficient strength along the strong axis to
redirect
impacting vehicles. Further, although it may be desirable for at least a
portion of the
support posts in the guardrail safety system 100 to include weakened support
posts
such as support posts 500 and 600 of FIGURES 5A-5C, supports posts may also
include conventional, unmodified support posts or other structural members
suitable
for supporting a guardrail beam. FIGURES 7A-7C illustrate such an unmodified
support post. Support post 700 does not include cutouts 508 and may comprise
standard line posts such as unmodified W6x8.5 posts or any other support post
of an
appropriate size, weight and configuration.
Although certain of the support posts may be configured to release the
guardrail beam element upon vehicular impact, it may be desirable for a
terminal
support post to remain coupled to guardrail beam even after an end-on or re-
directive
impact. FIGURES 8A and 8B illustrate an example embodiment of a terminal
support post 800 that may be used in conjunction with guardrail system 100 of
FIGURE 1. Referring to FIGURE 1, terminal support post 800 is the first
terminal
support post at the upstream end of terminal section 108. FIGURE 8A is a side
view
of terminal support post 800, and FIGURE 8B is a front view of the same
terminal
support post 800.
In particular embodiments, terminal support post 800 is releasably coupled to
guardrail beam 102 such that guardrail beam 102 and provides positive
anchorage of
guardrail beam 102 to react to tensile loads on guardrail beam 102 to redirect
a
vehicle impacting laterally along the length of guardrail beam 102. Various
components are used to effect the coupling of guardrail beam 102 to terminal
support
post 800 such that guardrail beam 102 remains coupled to terminal support post
800
when guardrail system 100 is struck by an impacting vehicle in an end-on or re-
directive type impact. As a result, guardrail beam element remains supported
in
tension even after such an impact. However, when guardrail system 100 is
struck by
an impacting vehicle in the reverse direction, the tensile coupling of
guardrail beam
102 will be released from terminal support post 800 to prevent vehicle
instability and
excessive vehicular deceleration.
In the illustrated embodiment, terminal support post 800 includes a structural
member 802 of an I-beam configuration. Structural member 802 includes a pair
of
flanges 804 interconnected by a central web 806. In a currently preferred
embodiment, the beam member 802 comprises a W 6x15 steel post member. A pair
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of rectangular side plates 808 are affixed opposite sides of structural member
802.
Preferably, side plates 808 are secured by welding to each of flanges 804.
A connector assembly is used to couple structural member 802 to the guardrail
beam member. The connector assembly is configured such that the coupling of
the
structural member and the terminal portion of the guardrail beam is maintained
during
an end-on or re-directive impact by a vehicle. However, the connector assembly
is
configured to release the coupling during a reverse-direction impact. In a
particular
embodiment, the connector assembly comprises a plurality of stacked
rectangular
plates that are aligned to receive the terminal portion of the guardrail beam.
For
example, the connector assembly may include a stack of three plates: a flange
plate
810, a keeper plate 816, and a washer plate 824.
A flange plate 810 is secured between side plates 808. Flange plate 810 is
preferably a unitarily formed piece that is secured by welding to structural
member
802 and each side plate 808. Flange plate 810, as best shown in FIGURE 9A,
includes a rectangular plate with a V-shaped cut-out 812 at the center of an
upper
edge 813 of flange plate 810. In the illustrated embodiment, flange plate 810
has a
length of approximately 5 inches and a width of approximately 6 inches. The
thickness of flange plate 810, as best shown in FIGURE 8B, may be
approximately 1
inch.
V-shaped slot 812 is centered along the horizontal width of flange plate 810
and has a vertical length of approximately 1 inch and a horizontal width of
approximately 1 3/4 inches. The rounded bottom 814 of V-shaped slot 812 has a
diameter of approximately 1 1/4 inches. However, the described and depicted
dimensions of flange plate 810 are provided for example purposes only.
Although the
depicted dimensions may be appropriate where structural member 802 includes a
W
6x15 steel post member, the dimensions of flange plate 810 may vary and may
depend on size and dimensions of structural member 802.
Returning to FIGURE 8B, a keeper plate 816 is disposed adjacent to flange
plate 810. Similar to flange plate 810, keeper plate 816 is preferably a
unitarily
formed piece. As best shown in FIGURE 9B, keep plate 816 includes a
rectangular
plate with a circular shaped opening 818 proximate an upper edge 820 of keeper
plate
816. In the illustrated embodiment, keeper plate 816 has a vertical length of
approximately 3 1/8 inches and a horizontal width of approximately 5 3/8
inches.
Opening 818 is centered along the horizontal width of keeper plate 816 and has
a
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center that is approximately 7/8 inch from upper edge 820 of keeper plate 816.
U-
shaped opening 818 may have a diameter of approximately 1 1/4 inches. However,
the described and depicted dimensions of keeper plate 816 are provided for
example
purposes only. Although the depicted dimensions may be appropriate where
structural member 802 includes a W 6x15 steel post member, the dimensions of
keeper plate 816 may vary and may depend on size and dimensions of structural
member 802 and flange plate 810.
Returning to FIGURE 8B, a washer plate 824 is disposed adjacent to keeper
plate 816. Similar to flange plate 810 and keeper plate 816, washer plate 824
is
preferably a unitarily formed piece. As best shown in FIGURE 9C, washer plate
824
includes a rectangular plate with a U-shaped slot 826 at the center of the
upper edge
828 of washer plate 824. In the illustrated embodiment, washer plate 824 has a
vertical length of approximately 4 1/8 inches and a horizontal width of
approximately
5 1/2 inches. The thickness of washer plate 824, as best shown in FIGURE 8B,
may
be approximately 1/2 inch.
U-shaped slot 826 is centered along the horizontal width of washer plate 824
and has a vertical length of approximately 1 1/4 inches and a horizontal width
of
approximately 1 1/8 inches. The rounded bottom slot 826 has a diameter of
approximately 1 1/4 inches. However, the described and depicted dimensions of
washer plate 824 are provided for example purposes only. Although the depicted
dimensions may be appropriate where structural member 802 includes a W 6x15
steel
post member, the dimensions of washer plate 824 may vary and may depend on
size
and dimensions of structural member 802.
Each of flange plate 810, keeper plate 816, and washer plate 824 include a
pair
of boltholes 830. In the illustrated embodiments, boltholes 830 are
approximately 3/8
inches in diameter. When assembled together, a bolthole 830 of each of flange
plate
810, keeper plate 816, and washer plate 824 are in general alignment with one
another. A pair of threaded bolts 832 may be secured through boltholes 830 to
secure
flange plate 810, keeper plate 816, and washer plate 824 together. A washer
834 may
be threaded onto the end of each of the threaded bolts 832 to hold the plates
relative to
each other.
As described above, the purpose of terminal support post 800 is to secure
guardrail beam 102 in tension. FIGURES 10A and 10B illustrate an exemplary
tensile
connection of a guardrail beam 1000 to a terminal support post such as
terminal
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support post 800 depicted in FIGURES 8A and 8B. Specifically, a compressed
slotted guardrail beam 1000 similar to those described above with regard to
FIGURES
1, 2, and 4A-4B is coupled to a connection plate 1002.
In the illustrated embodiment, connection plate 1002 includes a pair of
boltholes 1004, which may be aligned with a pair of similar boltholes (not
shown) in
the terminal end of the compressed slotted guardrail beam 1000. A pair of
threaded
bolts 1006 may be threaded through boltholes 1004 and similarly sized
boltholes of
guardrail beam 1000 (not shown) that are aligned with boltholes 1004. A
threaded
nut 1008 may secure each connection of bolts 1006 through connection plate
1002
and guardrail beam 1000. In a particular embodiment, the boltholes 1004 and
boltholes in guardrail beam 1000 may have a diameter on the order of
approximately
7/8 inch. In such an embodiment, threaded bolts 1006 may include 2 1/2 x 3/4"
GR. 5
bolts. However, it is recognized that these sizes are provided as examples
only. Any
appropriate size of boltholes and bolts may used to secure guardrail beam 1000
to
connection plate 1002.
Connection plate 1002 is coupled to a threaded rod 1010. In a particular
embodiment, threaded rod 1010 may be welded to connection plate 1002. As best
shown in FIGURE 8B, threaded rod 1010 is threaded through V-shaped cutout 814
of
flange plate 810, circular opening 818 of keeper plate 816, and U-shaped
cutout 826
of washer plate 824. A nut 836 is threaded on the end of threaded rod 101 to
secure
guardrail beam 1000 in tension to terminal support post 800.
The presence of nut 836 prevents withdrawal of cable 1010 from the openings
formed by V-shaped cutout 814 of flange plate 810 and U-shaped cutout 826 of
washer plate 824. Since the opening of keeper plate 816 includes an enclosed
circular
opening 818 rather than an open cutout in the edge of the keeper plate 816,
keeper
plate 816 ensures that threaded rod 1010 is properly in place. Keeper plate
816 also
adds strength to the tensile connection of threaded rod 1010 to terminal post
800.
Washer plate 824, which functions as a washer between bolt 834 and keeper
plate
816, also adds strength to the connection.
During an end-on or redirective impact to a guardrail system incorporating the
above-described features, the assembly described in FIGURES 8A-8B, 9A-9C, and
10A-10B enables the tensile connection of guardrail beam 1010 to terminal
support
post 800 to remain intact. Because the guardrail beam 1010 remains in tension,
guardrail beam 1010 is able to redirect the impacting vehicle. Column buckling
of the
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system may be eliminated and an eccentric impacting vehicle may remain in the
system longer during deceleration.
In contrast, when a vehicle impacts the guardrail system in a reverse
direction,
the tensile connection of guardrail beam 1010 may be released. For example,
the
reverse-direction impact may cause the upper edge 820 of keeper plate 816
directly
above circular opening 818 to be sheared. Threaded rod 1010 is then freed from
the
openings formed by V-shaped cutout 812, U-shaped cutout 826, and circular
opening
818. Because the tensile connection in guardrail beam 1000 is released,
guardrail
beam 1000 may be controllably collapsed to prevent vehicle instability or
excessive
deceleration.
To further aid in the release of the tensile connection during a reverse-
direction impact, a modified strut may be used to couple the terminal support
post to
the first adjacent support post. Such a strut is indicated as reference
numeral 140 in
FIGURE 2 and is illustrated in more detail in FIGURES 11 A and 11B. In the
illustrated embodiment, strut 140 includes a longitudinal beam member 1112
that has
been modified to include a strut plate 1114. Longitudinal beam member 1112 may
include have any appropriate cross-sectional shape. The length of longitudinal
beam
member 1112 is appropriate for coupling terminal support post 106 and the next
adjacent support post 104. In a particular embodiment, longitudinal beam
member
1112 may include a C-channel member having a width on the order of
approximately
6 inches and a depth on the order of approximately 2 inches.
As best shown in FIGURE 11B, strut plate 1114 is preferably a unitarily
formed piece that is secured by welding to longitudinal beam member 1112.
Strut
plate 1114 includes a rectangular plate with a U-shaped cut-out 1116 at the
center of
the upper edge 1118 of strut plate 1114. In the illustrated embodiment, strut
plate
1114 has a horizontal dimension of approximately 10 inches and a vertical
dimension
of approximately 8 inches. The thickness of strut plate 1114 may be
approximately
1/4 inch. U-shaped slot 1116 is centered along the vertical dimension of strut
plate
1114 and has a vertical dimension of approximately 1 1/2 inch and a horizontal
dimension of approximately 5 1/2 inches. The rounded bottom 1120 of U-shaped
slot
1116 has a diameter of approximately 1 1/2 inches. However, the described and
depicted dimensions of strut plate 1114 are provided for example purposes
only. The
dimensions of strut plate 1114 and longitudinal beam member 1112 may vary.
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When a vehicle impacts the guardrail system in a reverse direction, strut 1112
and strut plate 1114 may facilitate the release of the tensile connection
between the
guardrail beam and the terminal support post. Strut plate 1114 is positioned
proximate the outlet end of flattening portion 112. Strut plate 1114 operates
as a ramp
to facilitate the lifting of the threaded rod coupled to the guardrail beam
from the V-
shaped cutout 814 of flange plate 810, circular opening 818 of keeper plate
816, and
U-shaped cutout 826 of washer plate 824. Because the tensile connection in
guardrail
beam 1000 is released, strut 1112 and strut plate 1114 prevent instability or
excessive
deceleration of the impacting vehicle.
As described above, FIGURES 10A and 10B illustrate an exemplary tensile
connection of a guardrail beam to a threaded rod. FIGURE 12 illustrates an
alternative embodiment of a tensile connection that may be used to couple a
guardrail
beam to a terminal post. In the illustrated embodiment, a slotted guardrail
beam 1200
may be modified similar to guardrail beam 200 of FIGURE 4A. Slotted guardrail
beam 1200 is modified at the terminal end 1202 and is coupled to a cable rod
1204.
In a particular embodiment, slotted guardrail beam 1200 may be coupled to a
pair of
cable rods 1204.
Cable rods 1204 may traverse through a flattening portion 1206. Flattening
portion 1206 may be similar to flattening portion 110 of FIGURES 1-3.
Accordingly,
at least a portion of cable rods 1204 may traverse the length of flattening
portion 1206
and exit an outlet 1206 at an upstream end of flattening portion 1206. After
exiting
the outlet 1206, cable rods 1204 may be secured to a terminal post 106 at
ground level
using a mechanism similar to that described above with regard to FIGURES 8A-
8B,
9A-9C, and 10A-10B.
Technical advantages of particular embodiments of the present invention
include a guardrail end treatment that dissipates impact energy through the
compression of a W-beam guardrail element. Specifically, the guardrail end
treatment may dissipate impact energy of a vehicle colliding with an end of a
guardrail by flattening a portion of the guardrail required for deceleration
of the
impacting vehicle. Another advantage may be that the end treatment forces the
W-
beam guardrail element through a flattening structure that squeezes the
guardrail into
a relatively flat plate. In contrast to prior systems, the W-beam guardrail
element may
be flattened vertically rather than horizontally.
CA 02725225 2010-11-05
WO 2009/137483 25 PCT/US2009/042850
Still another advantage may be that a tensile and resistive coupling may be
provided for connecting an end of the W-beam guardrail element to a terminal
support
post. The components of the system that provide the tensile connection of the
guardrail beam to the terminal support post may enable the guardrail beam to
remain
secured after an end-on or re-directive impact. Thus, the system may remain in
tension during both types of impacts. Still another advantage may be that the
tension
is released when the system is impacted in the reverse direction near the
terminal end,
however. The releasing of tension in the guardrail element for reverse
direction
impacts prevents vehicle instability and excessive deceleration
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.
