Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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[MPROVEMENT IN ENERGY ABSORBING GUARD RAIL TERMINAL
Back~round of the Invention
Technical Field:
This invention relates to energy absorbing guard rail
terminals of the type which are used along the roadside and
in the median between limited access highways to deflect
vehicles from hazards which can be associated behind the
barriers. Guard rails are typically defined of a W-shaped
configuration mounted on a plurality of spaced posts so as to
function primaxily intension when redirecting the impact of
the vehicles.
Descri~tion of Prior Art:
Prior Art devices of this type have relied on a variety
of different structural configurations design to redirect, t
reflect and to absorb the kinetic energy of the vehicle upon
impact, see for example U.S. Patents 4,655,434, Patent 4,452,431,
Patent 4,678,166 and U.S. Patent 4,330,106.
In U.S. Patent 4,655,434 an absorbing guard rail terminal
~; is disclosed in which applicant's invention is an improvement
thereon.
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In U.S. Patent 4,452,431 a restorable fender panel is
disclosed wherein a reusable impact attenuation device is
provided to collapse under the impact of a vehicle in protecting
stationery structures from damage.
Buffer elements are interposed between the diaphram panel
members, thus absorbing the kinetic energy of the vehicle as
the successive buffer elements are compressed therebetween.
In U.S. Patent 4,678,166 an eccentric loader guard rail
terminal is disclosed for use at the upstream end of a con-
ventional guard rail utilizing a plurality of joined together
horizontally extending W~beam guard rails. The device is devised
so as to utilize an eccentric lever means whereby as the impacting
vehicle at the upstream end will facilitate buckling of the rails
allowing the vehicle to pass behind the terminal preventing
possible roll ovér or other destabillzing features associated
with vehicle impact on a barrier.
In U.S. Patent 4,330,106 a guard rail construction is
disclosed which utilizes a plurality o~ overlapping guard rail
sections with each of the rail elements attached to the ad~oining
Z0 or overlapping section by a bolt so that upon actual impact the
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rail sections will move axially with respect to one another,
but remain in full tensile strength and thus maintaining
their redirectional characteristics.
Development of terminal designs is complicated by the
need to minimize resistance for small car impacts while still
providing the necessary strength for full size car impacts
either on the end or downstream of the approach end.
The present invention is directed to improvements to an
energy absorbing guard rail terminal which functions essentially
as a crash cushion providing a series of spaced opening which
are in line with splice bolts when two beams are overlapped.
This provides an energy absorbing mechanism as the rails are
telescoped relative to each other by the æplice bolts shredding
out the metal stripæ between the openings. The shredding of the
material provides a unlform and controlled energy absorbtion
mechanism. In addition the sections of the guard rails are
staggered so that the upstream section will telescope first so as to
mlnimize resistance for the small car impacts while still providing
strength necessary to absorb full size car impacts.
Summarv_of the Invention
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An improvement to an energy absorbing guard rail terminal
utilizing oppositely disposed overlapping guard rail sections
on break away pDStS which will effectively absorb and dissipate
the kinetic energy of a vehicle upon impact. The improvement is
directed towards the improved break away post characteristics
and initial resistance encountered in the telescopic collapsing
action of the overlapping energy absorbing rail sections.
Descri~tion of the Drawin~s
Figure 1 is a top plan view of the energy absorbing rail
terminal of the present invention;
Figure 2 is a side elevational view of the structure of
Figure 1,
Figure 3 is a cross-sectional view taken along lines 3-3
of Figure 2;
Figure 4 is a cross-sectional view taken along lines 4-4
of Figure 2;
Figure 5 is a cross-sectional view taken along lines 5-5
of Figure 2;
Figure 6 is a cross-sectional view taken along lines 6-6
of Figure 2;
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Figure 7 is an enlarged perspective view of a portion of
the guard rail terminal showing the overlapping rail portions
and attachment to a break away post;
Figure 8 is a side elevational view of the nose portion
and associated post support; and
Figure 9 is a perspective view of an enlarged portion of
the guard rail terminal.
DescriDtion of the Preferred Embodiment
An improvement to an energy absorbing guard rail terminal
as illustrated in U.S. Patent 4,655,434 wherein the terminal
comprises multiple pairs of oppositely disposed horizontally
extending guard rails 10, 11 and 12 having overlapping ends
supported from a plurality of longitudinally spaced vertical
break away wooden posts 13 through 18. The guard rail pairs
may be of any suitable metal, but preferably are of a conventional
W-beam rail configuration.
An impact nose section 19 can best be seen in Figures
1, 2, and 3 of the drawings at the upstream vehicle approach
end of the terminal. The nose section 19 comprises a three-
part wrap around construction with a curved end piece 20
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secured to the post 13 by a fastener 21. Oppositely disposed
nose panels 22 and 23 overlap and are secured to the free ends
of the curved end piece 20 by a plurality of fasteners 24.
The remaining ends of the nose panels 22 and 23 are secured in
overlapping relationship to the respective ends of the guard
rail pairs 10 and the post 13, as best seen in Figure 4 of the
drawings.
The post 13 to which the nose curved piece 20 is secured
is comprised of a main body member 25 which is notched inwardly
of its upstanding free end at 26 reducing the effective cross-
sectional dimension of the post at the notch by approximately
one-half. A metal support sleeve 27 is positioned on the post
inwardly from the ~ree end o~ said post, acting as a reinforcement
and spacer for a pair of wooden spacer blocks 28 secured to the
support sleeve 27 and the post 13 by the fastener 21. Each of
the posts 13-18 is positioned within a metal post tube 29 with
a soil anchor plate 30 secured to the post and post tube below
ground level GL. A cable assembly 31, best seen in Figures 1,
2, and 8 of the drawings has a steel cable 32 e~tending through
an aperture in the notch portion of the post 13 with apertured
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retainer plate 33 positioned on the upstream side of the post 13
restingontha steel post tube 29 on the post main body member 25
and notch portion. Fastening nuts 34 are threadably engaged on
a stud S swag to the end of the cable 32 restricting cable
movement through the post. The other end of the cable 32 extends
through an aperture in the post 14 at 35 and a spacer channel 36
that extends between the guard rails 10 abutting the post assembly
14 as seen in Figures 1, 2, 8, and 9 of the drawings. ~ pair
of nuts 37 threadably secured to the end of a stud 38 swag
connected to the end of the cable 32 as is well known in the art.
A post connection strut 39 extends between the posts 13 and 14
~ust above the terminal end of steel post tubes 29 and ~ust below
the cable 32 on the post 13 only.
The overlapping ends of the guard rail pairs 10, 11, and
12 are secured to one another via land shearing bolts 40.
configurations 41 illustrated in Figure 7 of the drawings to provide
energy absorbing shredding of the metal strlps between a series of
openings or slots in the guard rails upon impact. The slot
configurations 41 are characterized by the first engagement slot
4Z in the rall 10 being of a substantially greater length than
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the next engageable slot 43 so that during impact as the rails
10 telescope over the rails 11 the initial movement will be
less restrictive providing a slight timing delay before shredding
begins. It will be seen that only the upstream ends of each
guard rail pairs are secured to the respective posts by fasteners
extending through the spacer blocks 28 and posts providing the
stabilization for the upstream rail ends for proper telescopic
and shredding to occur.
It is critical that as the first set of guard rails 10
telescope over the second set of rails 11 that the second rails
11 remain secured to their respective posts to insure that the
shredding action takes place and energy absorbtion of the shearing
i8 utillzed. Once the impact movement has fully engaged the
firæt set of rails 10 and the intermediate post 15 breaks away,
then the post 16 breaks away and the second rail set 11 telescopes
by shreddirg as hereinbefore described against the rail set 12
secured at its respective upstream end to the post 18. The kinetic
energy generated by the impact vehicle (not shown) is thus
dissipated by the successive energy absorbing nature of the
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nose piece, rail configuration and break away posts.
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Preferably the upstream rails 10 may be of a smaller gage
metal than the downstream or falling rails 11 for proper per-
formance .
Referring back to Figure 1 of the drawings, a connecting rods
44 will be seen extending transversely between the respective
rail pairs 10 and 11 adjacent posts 15 and 17 only. Each of
the rods 44 is fastened to the rail pairs via a keyhole opening
in the rail.
Downstream from each connecting rod 44 a box beam 45 is
mounted on the upstream side of each posts 16 and 18 respectively.
Each of the box beams engages, bends and releases the rod 44
upon impact as the rail pairs 10 and 11 telescope down over one
another as hereinbefore described.
Referring now to Figure 7 of the drawings and the slot
configurations 41, it will be seen that the spacing between
said next engageable slot 43 can be progressively increased
thereby gradually increasing the relative energy needed to shred
the space material between the slots 43 thus proportionally
dissipating the kinetic energy of the vehicle during impact.
~0 The progressive increase in spacing can be varied as well as the
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duration of the progressive increase so as to match the desired
energy absorbtion effect required during selected vehicle
impact.
It is evident from the above description that it is important
to utilize the combination of all the elements, that is the
break away posts, the telescopic rail and the shredding effect
between the rail pairs and the nose piece collapse and associated
cable assembly to dissipate the kinetic energy and to provide
a proper energy absorbing terminal as required. The connecting
rods, mentioned above, maintain the rails parallel to one another
during the initial telescopic action, but is removed upon impact
with the next succeeding post having the box beam 45 secured
thereto. This action allows for smooth transition of the
telescopic rail sections pass the next adjacent break away post,
thus instituting a further telescopic and shredding configuration
as described. The improvements to the energy absorbing terminal
as described in U.S. Patent 4,655,434 are characterized by
changing the slots for the shearing bolts 40, decrease
overall dimension of the first break away post 13,by the notch
portion above ground level and the positioning of the cable 32
from the post 13 to the post 14 in combination with the fixed
strut extending therebetween. Therefore I claim:
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