Note: Descriptions are shown in the official language in which they were submitted.
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CRASH IMPACT ATTENUATOR SYSTEMS AND METHODS
Background of the Invention
The present invention relates generally to crash impact attenuators, and
more particularly to motor vehicle and highway barrier crash impact
attenuators
comprising fixed systems protecting leading edges of abutments and other fixed
roadside hazards.
Vehicular accidents on the highway are a major worldwide problem and are
undoubtedly one of the largest causes of economic and human loss and suffering
inflicted on the developed world today. In an effort to alleviate, in
particular, the
human toll of these tragic accidents, guardrails, crash cushions, truck-
mounted
crash attenuators, crash barrels, and the like have been developed to
attenuate the
impact of the vehicle with a rigid immovable obstacle, such as a bridge
abutment.
A crash attenuator of the type described must absorb the vehicle impact
energy without exceeding limits on the vehicle deceleration. In addition, it
must
accommodate both heavy and light weight vehicles. The lightest vehicle will
set
the limit on the maximum force produced by the attenuator and the heavy
vehicle -
which will experience a lower deceleration, and thus will determine the total
impact
deformation required. The force cannot exceed the light vehicle limit and
therefore the initial force and deceleration is low, limiting the energy
absorption.
Increasing crash resistance as the vehicle "rides down" from its impact speed
to
zero is a vitally important feature of a crash attenuator system which meets
rigid
governmental safety standards. The present invention accomplishes this
objective
in an innovative, inexpensive, and very simple, but effective, manner.
The invention, together with additional features and advantages thereof,
may best be understood by reference to the following description taken in
conjunction with the accompanying illustrative drawing.
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Summary of the Invention
The present invention comprises, in one exemplary aspect, a crash
attenuator system for deployment in front of a fixed structure, such as a
bridge
abutment. The system comprises a rail extending along a length of the crash
attenuator system, a plurality of diaphragms initially disposed in spaced
relation
along the length of the rail, each of the plurality of diaphragms having a
base end
adapted to be movably engaged with the rail, so that when a front end of the
crash
attenuator system receives an impact force from an errant vehicle, a first one
of the
plurality of diaphragms moves rearwardly along the rail and impacts a second
one
of the plurality of diaphragms so that both the first and second ones of the
plurality
of diaphragms move further rearwardly along the rail, this process continuing
with
additional ones of the plurality of diaphragms until the impact forces have
been
fully attenuated. The system further comprises a tearing member on the crash
attenuator system which is adapted to engage material forming a tearable
member
of the crash attenuator system, the tearing member and the tearable member
being
relatively movable when an impact force strikes the crash attenuator system so
that
the tearing member tears the tearable member, thereby increasing attenuation
of the
impact force.
In exemplary embodiments, the tearing member comprises a bolt, and may
be disposed on one of the plurality of diaphragms, such as on a base end of
the first
one of the plurality of diaphragms. The tearing member may comprise a
plurality
of tearing members.
The tearable member extends along at least a portion of the length of the
crash attenuator and includes a plurality of holes disposed therein, the
plurality of
holes extending along a length of the tearable member and spaced lengthwise
from
one another. The tearing member is engaged with one of the plurality of holes
so
that when an impact force is applied to the crash attenuator, relative motion
occurs
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between the tearable member and the tearing member so that the relative motion
causes the tearing member to tear the material between adjacent ones of the
plurality of holes, thereby creating a continuous slot, the tearing of the
material
functioning to attenuate the impact force.
In some embodiments of the invention, the holes are not evenly spaced
along the length of the tearable member having the plurality of holes disposed
therein. For example, adjacent ones of the plurality of holes nearer to one of
the
front and back ends of the crash attenuator may be more closely spaced than
adjacent ones of the plurality of holes closer to the other of the front and
back ends
of the crash attenuator. In some circumstances, the plurality of holes are not
uniform in size, respective to one another. For example, in the illustrated
embodiment, the frontmost ones of the plurality of holes may be larger and
more
elongated than those of the plurality of holes which are located closer to the
back
end of the crash attenuator, though the directional orientation may be
reversed
depending upon application and desired attenuation characteristics.
In still other variants, the material forming the tearable member may be
thinner toward one of the front and back ends of the crash attenuator, and
thicker
toward the other of the front and back ends of the crash attenuator. In any or
all of
the embodiments and variants discussed above, which may be utilized singly or
in
various combinations, the tearable member may comprise a plurality of stages
as it
extends from one of the front and back ends of the crash attenuator toward the
other
end of the front and back ends of the crash attenuator, wherein a first stage
toward
one of the front and back ends of the crash attenuator is softer than a second
stage
toward the other of the front and back ends of the crash attenuator.
In illustrated embodiments, the one of the front and back ends of the crash
attenuator is the front end of the crash attenuator and the other of the first
and
second ends of the crash attenuator is the back end of the crash attenuator.
The first stage may be softer because the material forming the first stage is
thinner than the material forming the second stage. The first stage may also
be
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softer because the holes of the plurality of holes which are disposed in the
first
stage are closer together than the holes of the plurality of holes which are
disposed
in the second stage. The first stage may be softer, as well, because the holes
of the
plurality of holes which are disposed in the first stage are larger in size
than the
holes of the plurality of holes which are disposed in the second stage.
In particular embodiments of the present invention, the rail comprises first
and second outer rails spaced apart in a widthwise direction, and the tearable
member comprises a center rail. A plurality of fender panels are disposed
along
each side of the crash attenuator along its length, wherein frontmost ones of
the
plurality of fender panels are adapted to slide alongside of rearmost ones of
the
plurality of fender panels when the crash attenuator is impacted by a vehicle.
A
nose box is disposed at the frontmost end of the crash attenuator. The
tearable
member is stationary and the tearing member moves responsive to the impact
force,
in particular embodiments, though this may also vary, depending upon design
goals.
In still another aspect of the invention, there is provided a crash attenuator
system for deployment in front of a fixed structure, the system comprising a
base
portion having a first outer rail extending along a length of the base
portion, a
second outer rail spaced from the first outer rail and also extending along a
length
of the base portion, and a plurality of spaced cross-members extending across
a
width of the base portion and joining the first outer rail to the second outer
rail.
An upper attenuator portion comprises a plurality of diaphragms initially
disposed
in spaced relation along the length of the base portion. Each of the plurality
of
diaphragms has a base end adapted to be movably engaged with each of the first
outer rail and the second outer rail, so that when a front end of the upper
attenuator
portion receives an impact force from an errant vehicle, a first one of the
plurality
of diaphragms moves rearwardly along the first and second outer rails and
impacts
a second one of the plurality of diaphragms, so that both the first and second
ones
of the plurality of diaphragms move further rearwardly along the first and
second
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outer rails, this process continuing with additional ones of the plurality of
diaphragms until the impact forces have been fully attenuated. A tearing
member
is disposed on the upper attenuator portion, which is adapted to engage
material
forming a tearable member of the upper attenuator portion, the tearing member
and
the tearable member being relatively movable when an impact force strikes the
crash attenuator system so that the tearing member tears the tearable member,
thereby increasing attenuation of the impact force.
In yet another aspect of the invention, there is disclosed a method of
attenuating a crash impact force imposed by an errant vehicle which would
otherwise strike an immovable object. The method comprises steps of receiving
an impact force at a front end of a crash impact attenuator having a base
portion
and an upper attenuator portion and causing one or more members of the upper
attenuator portion to move rearwardly along the base portion responsive to the
impact force. A further step is one of causing a tearing member disposed on
the
crash impact attenuator to tear tearable material disposed on the crash impact
attenuator as the one or more members of the upper attenuator portion move
rearwardly, wherein tearing of the material acts to attenuate the impact
force.
In certain variants of the method, the tearing member is a projection
disposed on one of the one or more members of the upper attenuator portion,
which
is initially engaged with a hole formed in the tearable material. There are a
plurality of holes in the tearable material, arranged longitudinally in spaced
relation, and the tearing step comprises tearing the tearable material between
the
initially engaged hole and an adjacent one of the plurality of holes, to form
a slot.
The one or more members of the upper attenuator portion comprise one or more
diaphragms, and the tearable material comprises a rail forming a part of the
base
portion.
The invention, together with additional features and advantages thereof,
may best be understood by reference to the following description taken in
conjunction with the accompanying illustrative drawings.
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Brief Description of the Drawings
Fig. 1 is an isometric view of an exemplary embodiment of a crash
attenuator constructed in accordance with the principles of the present
invention,
disposed in a deployed orientation;
Fig. 2 is an isometric view similar to Fig. 1, wherein the crash attenuator is
in a partially compressed orientation, illustrating the crash attenuator with
an
inventive tearing member removed so tearing does not occur and the holes or
apertures in the center rail are visible;
Fig. 2a is an isometric view similar to Fig. 2 wherein the inventive tearing
member is present and tearing of the forward apertures 38 has occurred to
attenuate
the impact forces;
Fig. 3 is an isometric view similar to Figs. 1 and 2, wherein the crash
attenuator is in a fully compressed orientation, but the inventive tearing
member
has been removed so that tearing does not occur and the holes or apertures in
the
center rail are visible;
Fig. 3a is an isometric view similar to Fig. 3 wherein the inventive tearing
member is present and tearing of the forward apertures 38 has occurred to
attenuate
the impact forces; and
Fig. 4 is a rearward looking view from the front end of the crash attenuator.
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Description of the Preferred Embodiment
Referring now more particularly to the drawings, Figs. 1-4 illustrate an
exemplary embodiment of a fixed crash impact attenuator system 10 of the type
discussed above, wherein the design is sacrificial, in that it is intended for
a single
impact only, after which it is replaced. Thus, it is designed to be relatively
inexpensive and simple in design and construction, yet highly effective in
protecting the occupants of vehicles striking the attenuator.
Design considerations for the system 10 are that it meets U.S. federal TL
(Test Level) -3 crash attenuation specifications, that it is narrow in
profile, bi-
directional capable, MASH (Manual for Assessing Safety Hardware) compliant,
inexpensive, and free-standing (does not need to butt to rigid object,
although it
can, of course). The system is of a simple design and easy to manufacture
(materials are standard sizes and shapes and fender panels are standard Thrie
Beam-based), easy to assemble, and ships as a complete assembly. The base is
the
drill template, and anchor holes can be drilled with the unit 10 assembled.
The
length of the unit is designed, in an exemplary embodiment, is approximately
20-24
feet. Its width is 32 inches or less, which permits the units 10 to be shipped
three-
wide on a truck. The height is 32 to 36 inches. The unit 10 may be anchored to
concrete, asphalt, or a hybrid of both, and it is anchored using standard
anchors and
adhesives. It is suitable for use in temperatures ranging from -40 degrees to
150+
degrees F.
In the illustrated exemplary embodiment, the system 10 comprises a base
portion 12 having a ladder frame design, comprising a plurality of cross
members
14 supporting first and second outer rails 16 and 18, respectively, as well as
a
center rail 20. The cross members 14 include anchor holes 22 for anchoring the
base to the ground using bolt anchors or other suitable mechanical fasteners.
In
some instances, adhesive may be used instead or as well. The anchor holes 22,
in
the illustrated embodiment, are spaced along a length of each cross member 14,
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both outside of and within the first and second outer rails 16, 18.
The system 10 further includes an upper attenuator portion 24, which
comprises a nose box 26, a plurality of diaphragms 28, and a plurality of
fender
panels 30. The nose box 26 may comprise a notice sign 32, and may include a
crushable element in the front, behind the sign 32. The nose box 26 supports
loads
related to frontal, side, and angled nose impacts, and is supported on rollers
34,
which allow the nose panel to move rearwardly along the outer rails 16, 18.
The
rollers 34 are designed to prevent binding/locking in an angled nose impact.
As
the nose box 26 moves rearwardly after a vehicular impact, attenuation may be
activated.
The diaphragms 28 are disposed in spaced relation behind the nose box 26.
They are made from standard shapes and sizes and have cross braces sized for
loads. Each cross brace is positioned for ease of assembly of the fender
panels 30.
Each diaphragm 28 is slidably mounted at their base ends 36 on each side to
the
outer rails 16, 18, as illustrated.
The fender panels 30 are standard in construction, being a standard Thrie
beam panel, preferably fabricated of 10 or 12-gauge steel. When a vehicular
impact occurs, and the attenuator is compacted, as shown successively in Figs.
2,
2a and 3, 3a, the fender panels 30 are preferably designed to nest or double
over
one another in a sliding pattern, as illustrated in the drawings. The length
of the
fender panels 30 is determined by loads in side impacts, and panels are
preferably
designed to be common and interchangeable where possible. Bolts secure the
foremost fender panel 30 to the nose box 26, and also secure the fender panels
to
the diaphragms 28. The rear of the panels 30 are secured by clips, rather than
slots, in illustrated embodiments, though other attachment methods may be
used.
The system 10 is designed for standard Thrie beam transition pieces.
The steel forming the fender panels may be galvanized, and may be A36,
A513, or A517, for example.
Various approaches for attenuating the crash/impact forces are within the
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scope of the invention. For example, ripper plates may be used, with varied
and
staged thicknesses and shapes to stage attenuation, laser/plasma cut patterns
to
stage attenuation, or a cutter located on the nose box 26, for example.
Shearing
bolts may be used, comprising double shear approaches or a cutter on the nose
box
26, for example. Failing wire rope sections, comprising wire rope loops being
pulled to failure, kinking of tube arches, cartridges with honeycomb
(aluminum,
steel, or plastic), crushable foam-filled cartridges, sand-filled cartridges,
pea gravel
filled cartridges, water-filled cartridges, cartridges filled with glass beads
in oil,
drawing a metal strip through offset rollers, a friction brake on a wire rope,
a
friction brake on bar stock, or velocity magnetics (magnetic attenuation) are
all
potential possibilities.
An attenuation approach which is illustrated in Figs. 1-4 involves the center
rail 20. As illustrated, the rail 20 is fixedly mounted to the cross members
14 of
the base portion 12, in an upright orientation. As shown in Figs. 2a and 3a, a
plurality of holes or apertures 38 are disposed in spaced relation along a
length of
the rail 20.
Attenuation occurs as the upper attenuator portion 24 moves rearwardly
upon impact by a vehicle, thus absorbing impact energy from the crash, and
this
attenuation capability is greatly enhanced by the employment of one or more
inventive shear bolt or tearing member 40 (Figs. 2b, 3b, and 4), which extends
from
the attenuator portion 24, and engages the holes 38. It should be noted, at
this
point, that Figs. 2a, 3a are illustrated with the tearing member 40 removed,
so that
the holes 38 are shown, whereas Figs. 2b, 3b show the crash attenuator with
the
tearing member 40 in place, as would be the case in an actual installation. It
should also be noted that the terms "tear", "rip", "shear", "slice", "cut",
and the like
are used interchangeably throughout this application to identify any process
by
which a slit is created in material to dissipate and attenuate impact energy.
The
terms "tear", "tearing", "tearable" and the like are used herein and in the
appended
claims as stand-ins for any of the above mentioned terms for creating a
lengthwise
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slit in a crash attenuator component to attenuate impact energy, and are
intended to
be broad enough in scope to include any of these terms.
In the illustrated embodiment, the tearing member 40 is disposed on the
frontmost diaphragm 28, as shown, but it is within the scope of the invention
to
employ a plurality of tearing members 40, spaced widthwise on one diaphragm 28
to tear corresponding structural members like rail 20, or opposing sides of
the rail
20, or, alternatively, to employ one or more tearing members 40 on more than
one
of the plurality of diaphragms 28. As shown in Figs. 2b, 3b, as the attenuator
portion 24 moves rearwardly, the holes 38 are ripped by the tearing member 40,
thus absorbing much of the crash impact forces by ripping the material forming
the
rail 20, between the holes 38, creating a slot 42 in the rail 20. The holes 38
may be
tuned to optimize the tearing, and thus attenuation effect, by changing their
spacing
in different sections of the rail 20, and/or by changing the size of the holes
For
example, the holes 38 may be more closely spaced in front portions of the rail
20,
and may also be more elongated, to make the rail "softer" when crushed,
whereas
the holes 38 in more rearward portions of the rail 20 may be smaller and less
elongated, and farther spaced apart, in order to make these portions of the
attenuator "harder" when crushed, to attenuate higher forces. Additionally, if
desired, the rail 20 may be made of thinner material (gauge) in the forward
sections, and thicker material (gauge) in the rearward sections, for similar
reasons.
This adds to the "tuning" of the rail 20. Also, if desired, the material of
the rail
itself might be changed as the attenuator travels along the rail from front to
rear,
from one stage to the next. Of course, though in the illustrated embodiment it
is
desired that the softer portions be forward and the harder portions be
rearward,
differing design considerations may dictate a different orientation, such as
softer
portions being rearward and harder portions being forward.
The diaphragms 28 serve to transfer the load of a side impact from the
diaphragm to the pavement, through the cross members 14 and anchors 22. This
anchoring to the pavement makes the pavement itself a structural member for
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attenuator system 10.
Thus, important features of the present invention include, for example:
1) low cost;
2) free standing (not an end treatment ¨ not relying on the structure being
shielded
for structural support);
3) easy assembly ¨ a 20 ft. assembly may be trucked to the site and easily
bolted to
the ground ¨ standard material lengths make for easier shipping;
4) tunability may be altered to adapt to different crash standards and
applications.
Accordingly, although an exemplary embodiment of the invention has been
shown and described, it is to be understood that all the terms used herein are
descriptive rather than limiting, and that many changes, modifications, and
substitutions may be made by one having ordinary skill in the art without
departing
from the spirit and scope of the invention.
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