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BACKGROUND OF THE INVENTION
The present invention relates to the field of gates, and more particularly
to the field of cantilivered sliding gates.
Gates, of course, have been known since extremely ancient times, but few
advances in their basic design have been made. A primary effort has been
directed toward reducing the space that must be allocated for the typical
swinging gate. A first-order solution to that problem substitutes a
sliding member for the conventional swinging member, but a difficulty
immediately arises in supporting the sliding member. Overhead support is
only suitable when an overhead obstruction is permissible; clearly,
roadways and the like where vehicles will pass are not amenable to this
solution. Support from below also is possible, either by a track mechanism
or a gate-mounted roller, but uneven surfaces and the possibility of
obstructions, such as ice and snow, subtract from the utility of that
approach.
As early as the beginning of this century, it was proposed to cantilever a
gate across an opening, permitting a sliding gate, able to span a gap yet
not requiring support either from above or below. U.S. Pat. No. 1,020,488,
to Friend, discloses the basic design for such a concept. There, it can be
seen that two vertical supports are provided, one immediately adjacent the
gap and another spaced a distance away from it, with the gate being
mounted to slide in a plane defined by the two vertical supports. The most
important problem associated with cantilever structures, i.e., preventing
downward deflection or sag in the far end of the cantilever beam, is
addressed by a guy wire assembly. A prior reference to Anderson, U.S. Pat.
No. 920,810, discloses much the same construction but without the guy wire
assembly. Even so, the disclosure states that the assembly would sag but
for provision of a triangular brace structure which absorbs much of the
stress transmitted through the structural members. In both disclosures,
the structural members are preferably iron pipe.
Over the years, improvements have been presented that eliminate some of the
operational problems of this type device. For example, a significant
problem relates to the use of exposed rollers as means for allowing the
gate to slide. Such devices are highly susceptible to adverse weather
conditions, particularly ice and snow, and over time they tend to become
clogged with dirt and debris, degrading their movement. Also, they tend to
move out of alignment over time, further impeding the easy movement of the
gate. A solution to that problem was included in U.S. Pat. No. 3,531,895,
which disclosed a vertical gate including a slide assembly riding in an
enclosed track on the gate member. Also, U.S. Pat. No. 4,336,670, to
Brutosky, suggested a telescoping mechanism that obviated the need for a
"counterweight" section of the gate extending beyond the secondary support
post when the gate was in the retracted position.
Notwithstanding these improvements, however, significant problems remain in
this field. Primarily, such gates normally are constructed as single-piece
units. That is, the upper and lower transverse members are fabricated as
single pieces of tubular steel or aluminum. Thus, state-of-the-art
devices, such as produced by the Anchor Post Company, of Baltimore, Md.,
and International Gate Devices, Inc., of Folsom, Pa., all see the
necessity of long, relatively heavy transverse members to cope with the
stress inherent in a cantilever device. The disadvantages of this approach
are manifest. For example, such long, cumbersome structures are difficult
and expensive to transport. Further, they require special care in
installation, and if damaged, they cannot be repaired easily in the field.
Moreover, another serious problem appears when one attempts to construct
such a wide gate, in that the downward-directed forces result in a
twisting moment, producing a camber at the end of the gate. The art's only
solution to this problem has been to add stiffening materials to the gate,
exacerbating the weight, installation and transportation problems. Indeed,
for relatively wide gates, the only solution has been to construct the
gate in a so-called "box-spring" design, employing two complete gate
structures in a side-by-side structure, connected by struts.
Thus, the time is ripe for a new approach to this problem, one that allows
for ease of use and maintenance, without sacrificing stability.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
cantilevered gate having light weight and significantly greater rigidity
than products available according to the prior art.
Another object of this invention is to produce a cantilevered gate having a
multi-panel form of construction, allowing users to assemble the gate
quickly and easily at the installation location.
A further object of this invention is to provide a cantilevered gate that
can be transported in relatively small vehicles, such as panel or pickup
trucks.
Yet another object of this invention is a cantilevered gate that can be
repaired at the user site by user personnel.
Still another object of the present invention is to provide a cantilevered
gate having sufficient stability to span a gap of up to 40 feet in width.
Also, it is an object of this invention to provide a cantilevered gate
which mitigates the tensile forces imposed during use by applying a
compressive force to the horizontal structural elements of the gate,
during its assembly.
A further object of the present invention is to provide a cantilevered gate
that avoids camber without adding material.
These and other objects are achieved by the present invention, which
includes a gate assembly carried by support means. In a preferred
embodiment, the support means includes two vertical posts adjacent to the
gap to be spanned and both located on the same side thereof, the two
supports defining a closure plane across the gap. The gate may be carried
on the support members by slidable means such as a truck assembly
including bearing wheels for allowing free sliding movement, with a guide
roller assembly for maintaining the gate oriented parallel to the closure
plane.
The gate member of the invention preferably includes panels, which are
assembled into a relatively long gate at the user site. By manufacturing
panels in standard sizes, a relatively small number of such standard
panels could allow a user to construct a gate in any one of a number of
different widths.
Structural rigidity is obtained by post-tensioning at least one horizontal
member of the gate. That is, means are provided for applying a compressive
force to these components before the gate is erected. In a preferred
embodiment of the invention, the post-tensioning means is a threaded,
tubular member carried in the upper and lower gate horizontal members,
which tubular member can exert compressive force by threading bolts on the
end of same, these bolts bearing on the ends of the horizontal members by
means such as an end plate. When the bolt is taken up, the tubular member
is placed in tension, which is transmitted to the horizontal member
through the end plate as a compressive force. So long as the applied
compressive force, plus any force imposed by loading, does not exceed the
failure strength of the material, then the upper portion of the horizontal
member cannot go into tension itself until the large compressive force is
overcome. Thus, the gate is greatly stiffened compared to gates
constructed according to the teaching of the prior art.
Although the preferred embodiment is a cantilever sliding gate, other gate
types can be constructed according to the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic representation of the principle upon which the
invention is based;
FIG. 2 is a perspective of a gate constructed according to the present
invention;
FIG. 3 is a front view of a gate constructed according to the present
invention;
FIG. 4 is a cross-section taken on plane IV--IV of FIG. 2;
FIG. 5 is a detail perspective of a portion of the embodiment seen in FIG.
1; and
FIG. 6 is a detail perspective of a portion of the embodiment of FIG. 1.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Understanding of the present invention will be facilitated by considering
some basic principles, illustrated in FIG. 1. Consider the cantilever beam
1, whose weight is graphically depicted as the downward-thrusting arrows
W. That beam will exhibit stress characteristics as shown in stress
diagram 2, with the neutral plane located approximately in the center of
the beam, with tensile stresses located above the neutral plane and
compressive stresses below it. Compare that beam with beam 3, whose weight
again is shown by arrows W, but with the addition of a compressive force C
bearing axially against the end of the beam. Stresses within that beam
will be as shown in diagram 4, with one set of stresses being identical to
those shown in diagram 2, plus a set of compressive stresses imposed by
the force C. Adding these stresses by superposition, the resultant stress
pattern shows a very small net tensile force, exerted only in the extreme
upper portion of the beam, the remainder of the stresses being
compressive. Clearly, the end of beam 3 will be subject to considerably
less downward deflection than is the end of beam 1.
These diagrams graphically illustrate the point that one can in effect add
a measure of stiffening to a beam by increasing the compressive forces
acting upon it. It will be familiar to those in the art, of course, that a
designer must insure that the aggregate compressive forces do not exceed
the yield strength of the material involved.
A preferred embodiment 10 of a cantilevered sliding gate constructed in
accordance with the present invention is shown in FIG. 2. As seen there,
the general environment for the invention includes a gap to be
spanned--typically, a roadway--and a perimeter fence 14, often of the
chain-link variety. The gate extends laterally from one side of the gap,
hereinafter referred to as the "gate side". Of course, one can span gaps
wider than the maximum length of the gates described herein by providing
one gate assembly on each side of a gap, operating in opposite directions.
The gate is carried by support means, preferably two vertical support
members, with a primary vertical support 18 located adjacent to the gap,
and a secondary vertical support member 20, spaced further back from the
gap and from the primary member. These two supports define a plane,
extending in one direction along a portion of the perimeter fence and in
the other direction across the gap. Construction and operation of the
support members will be discussed in greater detail below.
The gate assembly means itself can be described as including several
different types of panels, joined together in a manner described below, to
make up a complete gate, as seen in FIGS. 2 and 3. The types of panels can
be defined by their function and by their construction. Generally, any
complete gate will include a counterbalance panel 22, one or more spacer
panels 24, and an end panel 26. The counterbalance panel performs the
function of supporting the gate in its fully closed position. When the
gate is fully closed, the counterbalance panel extends approximately from
the location of the primary vertical support at least to and overlapping
the secondary vertical support.
The end panel is located at the opposite end of the gate, with spacer
panels placed between it and the counterbalance panel. It will be
appreciated that by supplying such panels in a relatively small number of
standard widths, a variety of gates can be fabricated for different size
gate openings. Note, for example, that the gate shown in FIG. 2 is longer
than that depicted in FIG. 3, the former including two spacer panels. This
fact presents an important advantage of the instant invention, in that the
prior art necessitates a choice between either custom-ordering a gate,
entailing long delays, or limiting the buyer to a few sizes.
A single type of horizontal member and several types of vertical members
are assembled in various combinations to produce the three panel types. In
cross-section, seen in FIG. 4, horizontal member 28 consists of two
portions. One portion generally has the form of a square box section,
having a central passage 30. A second portion is a mounting leg 32,
extending normal to one of the faces of the square and located at one end
of a face, so that one of its sides forms an extension of the square
portion. The member thus exhibits the general shape of the letter "P". A
receiver face 40 occupies the remainder of the face of the square section
from which the mounting leg extends. Horizontal members are located at the
top and bottom of each panel.
Vertical members can take the form of end members 34, support members 36,
or spacer end members 38 as seen in FIG. 3. End members are generally
formed having a square box section, compatible in appearance to the square
portion of the horizontal member. Support members are square in
cross-section, with each side of the square slightly smaller in length
than the receiver face 40 on the horizontal member. Spacer end members are
rectangular; their shorter sides have half the length of corresponding
sides of support members.
The various vertical members can be combined with horizontal members to
form the three panel types in the following manner. The counterbalance
section 22 shown in FIGS. 2 and 3 has an end member 34 at one end, a
spacer end member 38 at the opposite end, support members 36 spaced at
intervals therebetween, and an end member 34 adjacent to and inside the
spacer end member. For longer gates, of course, longer counterbalance
sections are fitted with differing arrangements of vertical members, such
as additional support members. Diagonal support members 44 may be added to
the counterbalance section for additional stability.
The end section 26 has an end member 34 at one end, a spacer end member 38
at the other end, and support members 36 disposed therebetween. Spacer
panels 24 have spacer end members 38 at both ends, with support members 36
between them. It will be appreciated that when spacer panels are abutted
either to another spacer panel, an end panel or a counterbalance panel,
the reduced thickness of the spacer end member allows the joined members
to present a visual impression identical to that of a support member;
thus, the completed gate does not give the appearance of an assembly of
panels, but rather of a unitary structure.
Any suitable material can be employed to fabricate the various horizontal
and vertical members, but it is preferred to employ extruded aluminum
sections. Aluminum offers advantages of light weight, high strength, and
good machinability, particularly compared to high-weight products such as
steel. It has proven convenient to produce the end members having two-inch
square sections, matching the square portion of the horizontal member.
Support members may have a one-inch square section, with spacer end
members a section 1/2 inch by 1 inch. All types of vertical members extend
between horizontal members mounted at the top and bottom of the gate
assembly, as shown. Preferably, all vertical members are located on
two-foot centers. It will be appreciated that a customer desiring a gate
having a "picket-fence" appearance could easily obtain additional support
members and could quickly and conveniently secure them in place, for
example, with rivets, on the spacer and end panels, producing a gate with
a denser concentration of vertical members in the area of the gate
extending across the gap.
In the embodiment shown, it is preferred to produce counterbalance panels
in 10 and 12 foot widths, end panels in 6 foot widths, and spacer panels
in 6 foot, 8 foot, and 10 foot widths. It has also been found convenient
to provide sections with nominal heights (the height from ground level) of
from four to twelve feet. Thus, one can combine these sections to obtain
gates having nominal widths (that is, the width of the gap to be spanned)
of from 8 feet to 40 feet, the latter being the outer structural limit of
the embodiment disclosed, but not necessarily the widest possible gate
that could be fabricated employing the present invention.
Initial assembly of the gate proceeds by selecting the particular panels to
be employed and securing the panels together. As will be seen, this
securing step is preliminary, and can proceed by any means suitable, such
as by bolting the various panels together.
A track assembly 44 is secured to the upper horizontal member, extending
the entire width of the gate assembly. This assembly, seen in FIGS. 4 and
5, is generally in the form of the letter "C", lying with the open side
facing downward. The interior of the track is a channel 46 with a slot 48
opening downwardly, defined by flanges 49, which extend inwardly from the
vertical sides of the track assembly. Horizontal and vertical mounting
flanges 50 and 52, respectively, extend from adjacent outer corners of the
track, dimensioned to overlap the mounting leg and upper face of the
horizontal member 28, secured thereto by suitable means, such as rivets.
An indexing groove 54 on the horizontal member and a corresponding
indexing land 56 on the mounting flange may be provided to assist in
positively engaging these parts during assembly.
It has been found advantageous to provide track assembly in lengths
different from the lengths of the various panel elements. This arrangement
allows points where two panel assemblies abut to be overlapped by solid
portions of track assembly, and vice versa, leading to greater structural
rigidity.
Vertical stability is enhanced by provision of cables 98, extending
diagonally between top and bottom horizontal members, preferably
criss-crossed as shown in FIGS. 2 and 3. For cables terminating at end
members, eyebolts 100, carried on struts 101 may be provided. At
intermediate points, pads 102 may be secured to the horizontal members,
preferably spaced between support members. If a gate is of sufficient
width that some cables have both ends terminated at pads, e.g., cables 99,
FIG. 2, turnbuckles (not shown) may be provided to allow the cables to be
tightened, as known to those in the art.
The ultimate structural rigidity provided by the present invention,
however, is obtained by employing post-tensioning assemblies, seen in FIG.
6. This assembly includes a tubular. member, such as rod 62, dimensioned
to fit snugly but slidable within the central passage 30 formed in a
horizontal member. The rod carries a threaded receiver 68 in its extreme
tips. Suitably, the rod may be formed from commonly-available thin-walled
tubing pipe; in the embodiment shown, a 15/8 inch O.D. pipe has been found
to provide excellent results, and offers the advantage of using
readily-available materials. A specially-constructed rod, utilizing a
material of exceptional strength/weight ratio, such as graphite, could
offer improved performance, albeit at higher cost. The threaded receiver
68 may be a nut and the 24 end section of the rod may be adapted to carry
the nut by providing a tip section 66 within the larger pipe 62. A 13/8
inch O.D. pipe, inserted into the larger pipe and welded in place, has
been found suitable. Similarly, the nut preferably is dimensioned to
accept a 3/4 inch bolt 64; the nut preferably is inserted in the end of
the tip and welded in place.
Clearly, the ease of transporting materials for gates according to the
present invention would be somewhat negated if the post-tension assembly
had to be fabricated in a single piece. Yet, this assembly must be an
integral unit in order to function. The solution to this dilemma is to
employ multiple, shorter sections of 15/8 inch O.D. pipe, joined by
sections of 13/8 O.D. inch pipe, all welded together to produce a single,
integral element.
Thus, rather than manufacturing and transporting a very long element, it is
possible quickly and readily to fabricate a very long post-tension
assembly (for example such an assembly to span a 30-foot gap, including
the length of the counterbalance panel, would be over 44 ft. wide), using
readily-available apparatus, at the installation location. Length of the
assembly should be controlled during fabrication so that each of the
threaded receivers is recessed a short distance, for example about 2
inches, from each end of the horizontal member.
Two post-tension assemblies are fabricated, and they are inserted into the
passages 30 in the upper and lower horizontal members 28. End plates 70,
dimensioned to fit over the ends of the horizontal members, are placed
over the openings, and bolts 64 are inserted through apertures in the end
plates and threaded onto the nuts 68. The end plates are preferably
aluminum, about 1/2 inch thick. The bolts are tightened to provide about
several hundred pounds of force. No need exists, however, to gauge the
force applied with precision; the bolt is tightened until the gate becomes
laterally straight. In this manner, the post-tension rod is placed in
tension, and that force is transmitted to the horizontal members through
the end plates as a compressive force. It has been found most effective to
perform final tightening of the post-tensioning bolts after the gate is
installed, to achieve the straightest possible assembly. This operation is
performed in conjunction with final tightening of the cables 98 and 99, to
achieve both lateral and vertical alignment.
It has been found that camber problems in relatively wide gates can be
avoided by pre-bending the horizontal members. After the initial assembly
of the horizontal members, each is bent slightly in the horizontal plane
(i.e., the plane parallel to the ground after installation) to form a
shallow arc. Post-tensioning straightens the horizontal members, and the
resulting balance of the stresses resists the twisting moment at the end
of the gate. Thus, difficulties with camber are eliminated without adding
stiffening material.
After assembly, the completed gate is mounted on the vertical support
means, as seen in FIG. 2. Each vertical support includes slide means 80,
best seen in FIG. 5, each of which engages the track assembly to permit
easy sliding movement. As shown, the slide means is a truck assembly 82,
one of which is carried on each vertical support, mounted on a bracket 84
secured to the top of same by bolts 85. The truck assembly is well-known
to the art, and includes a body 86, four vertical rollers 88, and two
horizontal rollers 90, all journaled to the body for rotation, and
preferably also includes sealed bearings for ease of maintenance. The
vertical rollers bear against the inner sides of flanges 49 or the inner
surface of the top face of the track 44, and the horizontal rollers bear
against the inner surfaces of the sides of the track. Of course,
sufficient clearance is provided so that each roller only bears against
one of these respective surfaces at a time. Thus, the gate assembly may
slideably move with great ease, yet substantial transverse motion, either
horizontal or vertical, is prevented.
A guide roller assembly 92, also mounted on each vertical support, bears
none of the weight of the gate assembly, but restrains horizontal movement
of the bottom of the gate by engaging the outer sides of the bottom
horizontal member with horizontal rollers 94.
As seen in FIG. 2, the panels may be provided with chain-link mesh 96 or
other suitable materials, if desired. Suitable gate accessories, seen in
FIGS. 2 and 3, may also be provided, such as a support roller 104, and a
latch 106, carried on the fence post at the far side of the gap, or on
other suitable means. Support rollers can be provided on the
counterbalance side of a gap and are particularly suitable for gates
spanning gaps over 20 feet in width. Also, a barbed wire assembly 108 can
be carried atop the gate member if required. These and other accessories
will be appreciated and can be implemented by those having skill in the
art.
Once mounted on the vertical supports, the gate operates by sliding between
open and closed positions, spanning the gap. Gate motion can be actuated
manually, or by a suitable motor mechanism, controlled either directly or
remotely, as known to the art. The entire weight of the gate, including
both the vector and moment components, is transmitted by the truck
assemblies to the vertical supports. The post-tensioning devices provide
an increased stiffness to the structure, permitting the use of very light
materials, capable of spanning relatively wide gaps.
The use of light-weight materials, heretofore unsuitable for long gates, is
but one of the advantages afforded by the present invention. In addition,
transportation problems associated with the prior art gates are avoided
completely. Moreover, repair of gates is greatly facilitated. Heretofore,
major repair of a long, cantilever gate required returning the gate to the
manufacturer. Not only does that process repeat the transportation
difficulties associated with such gates, but also the user lacks security
during the long period required in moving the gate back and forth and
repairing same. The present invention permits onsite repairs, at most
necessitating replacement of one or more panel sections. Also, heretofore
it has not been possible to adjust the camber of a wide gate without
adding stiffening members. By varying the amount of post-tensioning force,
misalignment can be corrected and camber eliminated. Moreover, manufacture
of such gates is facilitated, as the necessity for custom-manufactured
gates is eliminated. Thus, panel sections can be produced in a highly
efficient manner, and scheduling is greatly simplified.
It should particularly be noted that the present invention is adaptable to
a wide variety of gate types, notwithstanding the preferred cantilever
sliding gate depicted herein. Swing gates, vertical gates, telescoping
gates, and others may be constructed according to the present invention.
It will be understood by those in the art that various modifications can be
introduced without departing from the scope of this invention. For
example, in addition to the panel types described, a pedestrian door could
be provided as an attachment to the end panel. In this manner, pedestrians
could use this door to gain access without having to open the gate. These
and other modifications can be made without departing from the scope of
the present invention, which is defined solely by the claims appended
hereto.
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