Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to adjustable manhole cover
supports for emplacing over and raising the effective
grade of an existing manhole cover receiving structure.
For simplicity the terms ~existing manhole cover
receiving structure~ and ~manhole cover~ herein are used
to refer to the existing, i.e., fixed in-place frame or
other existing seating receptacle for a removable cover
or grating that covers an access hole (i.e., hand hole,
tool hole, manhole, catch basin or the like), and to
that cover or grating. The resulting assembly of a
receiving strUctUre and a manhole cover ordinarily is
intended to bear vehicular tra~ic. The term "manhole
cover support~ or simply ~cover support~ here means a
structure that fits over the existing manhole cover
receiving structure, raises its grade, and thereby
accommodates a cover or grating at the new grade.
Advantageously, the cover or grating is the same one
that was used at the lower grade. The access hole
covered is a utiIity enclosure serving, e.g., an
~0 electric, gas, water, sewer or storm drainage system.
Ordinarily the instant cover support finds its use
when a roadway such as a street or highway is resurfaced
with an added layer of paving material, typically
asphalt concrete or sheet asphalt, to establish a higher
qrade. It then is advantageous to mount the inventive
cover support atop the~existing manhole receiving
structure. Prior art on manhole cover supports and
manhole cover frames can be found in U.S. patents
4,281,944, 4,236,358, 3,968,600, 3,773,428, 4,097,171,
4,302,126, 3,891,337 and 1,987,502. The first four of
these are for inventions of the applicant.
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Axle loads up to 18,182 kg. must be resisted by
many of these cover supports as well as serious impact
loads from vehicles and snow plows, a variety of
temperature effects, steam leaks, spillage, etc.,
without permiitting a hazardous dislocation of the cover
support or its cover. Often it is desirable also to
cushion the cover for resisting wear or reducing noise,
and/or to seal the cover and its cover support against a
substantial and possibly overloading infiltration of
surface water, e.g., storm drainage that otherwise would
enter a sanitary sewer system at various manhole
locations. Adjustability of the cover support in
peripheral dimension and height also is important for
accommodating the wide range of specifications to be
met.
Clearly the resistance to displacement from traffic
loading and impact is a para~ount concern and a most
general one. The supports often contain some reasonably
thin (0.254 cm. or less) elements such as sheet steel
elements. These can include upwardly projecting cover
keeper wall portions, flanging, and bases. Such thin
keeper portions can be fitted into an existing manhole
cover frame and, normally, still leave a large enough
i opening at the new grade to accommodate the same old
cover or lid which was used on the existing frame. The
lighter weight elements also can ~e effective for
economy and/or ease of manufacture, handling and
installation. However, a relatively low weight of the
cover support, as compared to the usually thick solid
cast iron fixture on which it is to rest, makes it a
candidate for displacement in service. This is true
even when a cover support can be expanded against the
rising shoulder of a receiving structure such as a
manhole cover frame in the manner of various prior art
3s cover supports such as those in U.S. patents 4,281,944,
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4,23~,358, 4,097,171 and 4,302,126, noted above. Where
the retention is mainly due to the weight of a cover and
its support, displacement is even more of a risk.
The instant support can be made especially highly
resistant to displacement and dislodgement in service
without being made ponderous in weight, even when it has
no mechanical fastening to the receivinq structure.
Thus, while the present cover support can be made to
incorporate conventional structural or mechanical
holddown means that are integral with it or easily
attached, the cover support also can do a good job of
holding in (being retained in the existing receiving
structure while in service) by friction alone.
Installing, adjusting, loading and unloading and
otherwise handling manhole cover supports and removing
manhole covers usually is done with powerful and
indelicate tools such as picks, pinch bars, crowbars,
tongs, heavy hooks and the like. Deformation of the
cover support can occur, particularly about its upper
edge which is nearest the road surface. The upper edge
usually is the handiest fulcrum area for applying
lifting and other tools. Deformations of the edge never
are good, and they can render the opening of the support
unfit for service. Hence, overall ruggedness and
stiffness against deformation, especially at or near the
top rim, and resistance to displacement are major
concerns about manhole cover supports.
On the other hand, a relatively light construction
of the cover support, in comparison to the ponderous
cast iron frame that usually initially supports the
manhole cover when the first paving is laid, can be very
desirable, provided, however, that an inordinate amount
of the ruggedness, stiffness, and resistance to
displacement or dislodgement is not sacrificed. Usually
3s a main place for weiqht reduction is in the lateral
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keeper for the cover. Another place is in the base
of the cover support. Clearly the economics of manufac-
ture, handling and installation all are generally in
favor of lower weight. A relatively thin wall keeper
would normally be of steel, the wall rarely being more
than about 0.254 cm. (12 ga.) thick, usually less.
The present adjustable support lends itself to being
sealed off against water infiltration and to cushioning
the cover. Furthermore, it can be made very stiff or
especially durable even when employing relatively thin
metal for some or all of the various body elements.
No previously proposed manhole cover supports a;e
known by the inventor to be able to develop the retentional
friction that this one can develop, let alone to include
as well at least another of the additionally desirable
features such as sealing off water infiltration, modest
weight coupled with high stiffness and/or special durability.
The instant manhole cover support is for emplacing
over and raising the effective grade of an existing
manhole cover receiving structure where that structure
has an upwardly-extending shoulder surface extending
from a sill that was made-to accomodate a manhole cover.
The new cover support has excellent retainability charac-
teristics in service without its necessarily being ponderous
and extremely heavy, comprising a manhole cover support
having improved retainability in service and resistance
to dislocation from vehicular traffic running over it,
the cover support being adapted for emplacing over and
raising the effective grade of an existing manhole cover
receiving structure which has an upwardly-extending
shoulder surface and a sill therebelow for accomodating
a manhole cover, the cover support comprising:
a body that is adjustable in outex perimeter dimension
and has a seat with a lateral keeper for a manhole cover
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and a base with an outer wall that is reactable against
the shoulder surface of the receiving structure, the
body being equipped with at least one spreader that
provides a gap in the base and seat; and
a flexible, compressible frictional retention component
therefor that is interposable between the outer wall
of the base and the shoulder surface of the receiving
structure,
said retention component comprising a synthetic
or natural resin-containing material, being not less
than 8 mils nor more than about 600 mils thick, and
having a coefficient of static friction with respect
to said wall and said shoulder surface that substantially
exceeds the coefficient of static friction obtainable
directly between said wall and shoulder surface,
said retention component being disposed to interact
with an expansion of the body for substantially enhancing
the grip between the body and the existing receiving
structure.
A further aspect of this invention is a process
for the installation of the foregoing manhole cover
support in a process for retaining a manhole cover support
in an existing receiving structure for a manhole cover
wherein the receiving structure has an upwardly-extending
shoulder surface and a sill therebelow, and the manhole
cover support has a body that is adjustable in outer
perimeter dimension and has a seat with a lateral keeper
for a manhole cover and a base with an outer wall that
is reactable against the shoulder surface of the receiving
structure upon expansion of the body, the body being
equipped with a spreader that provides a gap in the
base and seat, the base being emplaced with its outer
wall facing the upwardly-extending shoulder surface
of the receiving structure, the improvement which comprises:
interposing between said sholder surface and outer wall
area opposed thereto a flexible, compressible frictional
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retention component comprising a synthetic or natural
resin-containing material, being not less than 8 mils
thick nor more than about 600 mils thick, and having
a coefficient of static friction with respect to said
5 wall and shoulder surfaces that substantially exceeds
the coefficient of static friction obtainable directly
between said surfaces; and expanding the body against
the constraint of the receiving structure.
A still further aspect of this invention is an
10 improvement in process for manufacturing the foregoing
manhole cover support. The improvement comprises depositing
over at least a portion of the outer wall surface of
the cover support base or forming at least a part of
that outer wall surface from a composition that is curable
15 to leave a compressible and flexible solid surface which
is capable of enhancing substantially the frictional
grip between the cover support and the shoulder surface
of the existing receiving structure, and curing the
composition until said compressible and flexible surface
20 is formed.
Figures 1-4 illustrate an adjustable cover support
with a practically vertically rising cover keeper wall.
Such keepers necessarily must be thin-walled to fit
into an existing frame and still accomodate the original
25 cover. In other words, that cover must lie flat on
; the new seat that is bounded by the walls of such keeper.
In various other embodiments of the invention the keeper
walls can rise with a slight outward slant.
Figure 1 is a top plan view of a preferred nominally
30 91 cm. diameter split-ring embodiment of the instant
cover support adapted to fit a circular manhole and
having a bonded-on outer seal element and retention
component and a bonded-on polymer seat and seal element.
The outer surfaces of this retention component will
35 be in frictional contact with the shoulder of the existing
B receiving structure when this cover support is installed;
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Figure 2 is a vertical cross section of Figure 1
taken through Section A-A;
Figure 3 is a vertical cross section of Figure 1
taken through Section B-B;
Figure 4 is a side elevation view of the cover support
of Figure 1;
Figure 5 is a fragmentar~ perspective view of the
joint area of a split ring cover support embodiment
of the invention with the sealing plug for its joint
gap shown detached from that gap. The right side of
the ring is shown broken off, and the left side is drawn
as being cut off (for simplicity); and
Figure 6 is a cross sectional elevation of a four-
segment circular cover support of this invention
installed in a resurfaced street, the exposed part of
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the body being mainly flexible polymer stressed from the
inboard side with a metal body frame. The section is
taken in the center of a segment between turnbuckle bolt
expanders.
Figure 7 shows a simplified perspective view of a
four-segmented cover support being adjusted in exterior
diameter by a wrench preparatory to installation on a
manhole cover frame. The cover support differs from
that of Figures l, 2, 3 and 4 by having only very short
outward flange portions at the top of the keeper
portions and no connections between the tops of the
keeper portions;
Figure 8 shows in vertical cross section the
installation in a roadway of an embodiment of the cover
support like that of Figure 7. The section is taken on
a vertical plane through the middles of diametrically
opposite segments of the four-segment cover support;
Figure 9 shows a vertical cross section of an
alternative cover support fitted with an elastomeric 0-
ring stretched around the outer periphery of its manhole
cover supporting base and another resting in a notch on
the top of the base. The peripheral O-ring will be in
frictional contact with both the shoulder of the
existing receiving structure and the outer wall of the
base when this cover support is installed. The section
is taken in a vertical plane through the middle of the
pair of 180~ segments making a two-segment circular
cover support;
Figure 10 shows a vertical cross section of a all
cast ductile iron-bodied circular cover support. The
section is taken in a vertical plane through the ~iddles
of diametrically opposed segments of a four-segment
circular cover support; and
Figure 11 shows a vertical cross section of a
circular cover support fitted with an elevating screw,
several elastomeric band-like retention components
stretched around it and with an elastomeric seat for
the cover. The retention components and the seat need
not be bonded to the metal body of the cover support,
but that is preferable. The section is taken through
the middle of a split ring cover support opposite the
adjustable joint.
Figure 12 is a fragmentary top plan view of a preferred
form of a rectangular manhole cover support with box
flanging running the length of tops of the straight
lateral segments and water sealing elements bonded to
cover seat portions and outside wall portions of those
lateral segments. The sealing elements on the outer
wall also act as a cover support frictional retention
component when the cover support is expanded against
the upwardly extending shoulder surfaces of the existing
manhole cover receiving structure such as a manhole
cover frame.
Figure 13 is a side elevational view of the cover
support of Figure 12.
Figure 14 is a fragmentary plan view of the corner
of the cover support of Figure 12 with its corner joint-
sealing fitment removed. The fitment is of foamed elastomer
that acts to plug the corner and stop surface water
leakage at that point.
Figure 15 is a vertical cross-sectional elevation
of the fitment taken through section Z-Z of Figure 14.
Reference is made to Figure 1. The cover support
broadly is indicated by arrow 1. Seat 2 for the cover
is a polymeric seal and cushioning element on the top
of the cast ductile iron (ASTM type 536, Grade 60-45-12)
base of this cover support. Its inner vertical wall
is 2.54 cm. in height, item 3. Welded to and rising
up from the outside top edge of the base is a lateral
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keeper 4 for the cover. The keeper is of 13 ga. (0.~4
cm.) steel. The top 6 of the keeper is formed into a
hollow (1.91 cm. x 1.91 cm. inside dimensions) wale
having outside wall 7.
The base and keeper, including the wale, form an
almost complete circular pattern which is interrupted
only by a joint that is connected with a turnbuckle
bolt 9 and is bridged with tapered steel shaft 8.
The right end of the shaft is of essentially square
cross section, and it makes a snug fit into, and is
welded into the hollow channel part of the wale. The
left end of the shaft 8 is somewhat tapered, and it
makes a slidable fit into the other end of the hollow
channel part of the wale. Thus the entire wale can be
considered to be the box flanging around the upper
periphery of the keeper and the shaft 8 across the
joint.
The ends of the turnbuckle bolt 9 are threaded with
opposite handedness to open up the gap of the joint when
turned one way, and to close the gap when turned the
other way with a wrench acting on wrench grip 11. For
security in service, a nylon locking patch is applied to
the bolt threads. The bolt 9 is of A.l~S.1 type 302
stainless steel; each end of it runs into a horizontal
tapped hole in the base. The holes are tapped ap-
propriately for bolt adjustment and extend to reach the
notches 12a and 12b. The notches accept the protruding
ends of bolt 9 when the gap is shortened.
If a greater amount of peripheral adjustment and
greater frictional grip of the base into a manhole frame
or the like is desired, a pair or two pairs (or more)
of diametrically opposed joints of the type connected by
bolt 9 can be used in the cover support. Thus, the
cover support will be made of two or four (or more)
segments, usually of equal size if the cover is
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circular. However, if the cover support is rectangular
or otherwise polygonal or oval in plan, the joints can
be at corners or on the sides; the resulting connected
segments, while usually making a generally symmetrical
whole in p'an, will not necessarily be of equal size.
The elements of the cross section shown in Figure 2
include those with the same numbers as used in Figure 1
plus these: 17, the cast ducti~e iron base; lo, the top
of the base; 19, the hollow channel of the wale; 14, the
bottom of the wale which can be tack-welded along the
outside of keeper 4; cover seat 2, a 0.32 cm. thick
slightly foamed elastomer bonded to the top of the base;
bottom 18 of the base which is to rest on the existing
manhole cover receiving element; and a frictional
retention member 16 which is about 0.32 cm. thick of
slightly foamed elastomer bonded to the base all around
its outer perimeter. Sheet steel keeper 4 is welded to
base 17 and any lumps, spatter, etc. are removed, e.g.,
ground off the outer and inner seams that it makes with
the base.
The elements of Figure 3 are the same as those of
Figure 2 except that the wale at this zone includes
shaft 8 as an integral (e.g., welded-in) part.
The elements of Figure 4 that also are shown in
Figures 1, 2 and 3 have the same numbers as in those
figures. Thus, item 16 is the retention component, 8
the shaft and 19 the hollow channel of the wale, 9 the
turnbuckle bolt, 17 the wrench grip of the bolt, and 12a
and 12b the left and right notches, respectively, for
permitting protrusion thereinto of the bolt ends. If
desired, the retention component can be a separate
strip or strips of flexible, compressible polymer
interposed between the base and the existing manhole
cover receiving structure instead of such polymer being
bonded on. Furthermore, it can be in the form of one or
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more bands or O-rings surrounding and even elastically
gripping the base, e.g., in grooves therein. Likewise,
the seal element that makes the seat for the manhole
cover can be in the form of a washer or gasket or one or
more (concentric) rings, e.g., O-rings, and that element
need not be bonded to the cover support.
The cover support embodiment shown in Figures 1, 2,
3 and 4 has a good frictional grip to an existing
manhole cover frame. This is because the coefficient of
static friction between the surface of many conventional
flexible deformable polymers, including many foamed
elastomers, and metal surfaces can be much greater than
that between two metal surfaces. Thus, the coefficient
of static friction for the contact of a desirable
polymer to a metal should be at least about 0.4, and
generally it can be as high as 0.6-0.7 or even higher.
In a steel-to-steel instance it is unlikely to be as
high as 0.35. Shore A Durometer hardness of the polymer
composition for the frictional retention component
preferably is at least about 20, an~ preferably it is
about 50-70. Usually the thickness of a retention
component will be between about 0.01 mm. and 10 mm.
Oil resistance can be desirable for it and the other
water-sealing elements in some installations.
The coefficient of static friction is the ratio of
the maximum force parallel to the surface of contact
which acts to prevent motion between two bodies at rest
in contact with each other from sliding over each other,
to the force normal to the surface of contact which
presses the bodies together. Thus, the turnbuckle or
other conventional spreader means, usually screwed
types, at the joints supply a large measure of pressure,
and the bonded elastomer heightens friction, thereby
making a cover support that is unusually effective for
resisting dislodgement or tilting in highway service.
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Means for locking down the cover support to an existing
manhole cover flange, e.g., like the means shown in U.S.
Patent 3,773,428, often are desirable in addition to
simply a frictional grip.
In Figure 5 the 0.32 cm. thick slightly foamed
elastomer (a cured vinyl plastisol) seat 32 for the
manhole cover is bonded to the top of the cast ductile
iron base 22. A like layer 33 is bonded on the outside
of the base and runs a short way up the lower outside of
keeper 24. The keeper rises with a slight outward slant
and has a short lip or flanging 26 at its top.
Solid reaction post 28 projects inwardly from the
base near the left side of the joint gap. Post 27 has a
hole with tapped threads, and it projects in a similar
way at the right side of the gap. Both are of cast
ductile iron molded integrally with the rest of the
base ring. The head 31 of the spreader bolt 29 rests
against the reaction post 28; the bolt 29 screws into
the threaded hole of the post 27. Lengthening of the
bolt between the posts springs the base ends farther
apart, i.e., the base end 23 makes a larger gap with its
opposing end (that is not visible in this view).
Softer flexible polymer foam plug 36 fits into the
gap with a very slight compression. The plug can be
cemented into place, e.g., with suitable rubber cement
on side 34 of the plug to adhere to the unseen side of
; the base and the keeper at the gap.
In Figure 6, tough, dense, slightly elastic
composition compounded with Neoprene (a trademark of
E.I. duPont de Nemours and Company) polymer forms most
of the flexible, compressible cover support body visible
in this view. Thus, the seat 42 receives the cover.
The cover support rests on sill 47 of existing cast iron
manhole cover frame 48. The lower or base portion 46 of
the cover support body is forced against the inner
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surface of the shoulder of the manhole cover frame 48 by
stress from expanded steel body frame (ring) segment 41.
The pressure makes a slight bulge (exaggerated in the
drawings) at the top of the shoulder. Subsequently
asphalt concrete is forced against the outer wall 44 of
the cover keeper and brought flush with the keeper top
43. Under the asphalt paving layer is the original
portland cement concrete paving 51.
Turnbuckle bolts (not shown but each like stainless
steel bolt 9 of Figure 1) are disposed inboard of the
flat side of the four equal-sized body frame segments
such as the segment 41. The bolts have nylon locking
patches and are threaded on each end. Each bolt screws
into a pair of appropriately tapped steel lugs (not
shown) that project inwardly from a segment near the
opposing ends of a joint gap, The lugs on a segment are
formed integrally with that ~egment. Where hold-dGwn
means, such as screw clamps running from the base down
and under the existing sill are to be used, they can be
fastened to the steel segments. The joints can be
sealed in a manner set forth hereinafter.
For simplicity Figure 6 the rubber part of the body
of the cover support was shown without any reenforcing
cloth, wire, or cord embedded in it, although this is
often desirable, as is the compounding of the rubber
material with special fillers such as carbon black.
In the embodiment shown in Figure 6 the main seal
elements and retention component part shown are the seat
portion 42 and the outer wall portion 46 of the segment
of the base of the cover support. These surfaces are
integral with the rest of the segment except the steel
frame segment 41. These s`eal and retention component
elements can be made softer or harder than the main
depth of the rubbery part of the body, usually softer
for sealing, e.g., by building up layers with the
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softest on the outside. Alternatively, a separate
sealing and/or special retention component material
(usually softer than the core, e.g., a foamed elas-
tomer), can be used over them, either bonded to the
rubbery body surfaces or simply interposed as separate
elements where sealing and friction is particularly
desired.
It is possible to use various conventi~nal
elevating means to adjust the level of the cover
support. Thus, lifting bolts may be threaded into the
bottoms of metal bases, or shims or gaskets can be put
under the bottom of the base.
The simplified perspective view of Figure 7 shows a
preferred four-segment cover support with an open-ended
box wrench 62 fitted on the most distant wrench grip of
a turnbuckle bolt, a grip that otherwise would be seen
and numbered as 61c. Clockwise turns reduce the outside
diameter of the assembled segments when one is preparing
to slide the new cover support into an existing manhole
frame. The other such adjusting bolts shown are bolts
59a, b and d with their respective wrench grips 61a, c
and d. The bolts are of A.I.S.I. type 302 stainless
steel.
The top of the base portion of each segment has
deformable polymer seat portions, 56a, b, c and d, each
about 6.4 mm. thick, bonded thereto to cushion the
cover. The seat portions also act as part of the water
seal under the manhole cover. The bottoms 57a, b, c and
d of the base portions will rest on the sill of an
existing manhole frame when the cover support is
installed.
The outside wall portions of the base portions, and
the lower parts of keeper portions, terminating in
slight outward flanges or lips 58a, b, c and d, are
coated with about 3.2 mm. thick bonded-on polymer
layers, 63a, b, c and d, like that making the covPr
seat, specifically a tough, heat-cured slightly foamed,
elastomeric vinyl plastisol. These coatings act to grip
the shoulder of the existing manhole frame as well as to
form part of the water seal around the new cover
support.
The gaps between base portion ends such as those
marked ~64a~ and ~64dn (corresponding ones at the end of
each segment are not marked to avoid clutter) can be
sealed or plugged as will be taught hereinafter to
resist infiltration of much surface water.
The bolts joining the segments, and all other
threaded bolts and screws in the cover support, have
nylon locking patches on their threads for security in
service. Conventional hold-down means such as screwed-
on clamps running from the base down and under the sill
of the existing manhole frame are not shown; they can be
included when desired or needed.
In Figure 8 new paving layer 82 of asphalt concrete
surrounds the upper part of the installed manhole cover
support, while the outside of the existing manhole frame
78 is surrounded by the original portland cement
concrete paving 81. Resilient polymer cushion-seal 73
lies under manhole cover 71 and is bonded to the top of
cast iron cover support base 74. Welded onto and rising
from the base is 13 ga. (U.S. Std.) steel keeper 76.
Resilient polymer gripper-seal 77 is bonded to the
outside wall of the base and the lower part of the
keeper.
The cover support rests on the sill 79 o cast iron
manhole frame 78. The bottom of the cast iron cover 71
is reenforced with integral bracing 72 that projects
down into the manhole.
In Figure 9, both parts of the cast iron base 85
have an inner wall 87, a bottom 88, a top 86, and two
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grooves running for their full lengths. The welded-on
strip steel keepers 92 have outward flanging 92 at their
tops. Residing in groove 91 is an O-ring 93 to seal and
cushion a cover. ~o seal most of the outer wall of the
base and p~ovide extra friction with the rising shoulder
of an existing manhole cover receiving structure is an
O-ring 94 fitting into groove 89 that runs around the
outside of the base. Joint sealing will be dealt with
later. The O-rings are not bonded to the metal.
In Figure 10, the cast ductile iron, type 60-45-
12, segment has base 101 has bonded-on deformable
polymeric retention component 103 and a pair of
cavities, the presently empty lower one being denoted as
102. Projecting up from seat 96 is keeper 97.
Projecting down from seat 96 is skirt 98 terminating in
an enlarged lower rim 99. The rim can fit slidably into
each of the cavities of the base. The cavities and rim
have a trapezoidal cross section, and either cavity can
support the upper seat portion of a segment for
adjusting the seat elevation. More than two such
cavities can be superimposed in the stack of them for
greater adjustment, as is shown in Applicant's U.S.
Patent 4,281,944.
In Figure 11, cast ductile iron base 106 has top
107, bottom 108, and a 302 stainless steel elevating
screw 109 tapped into the base. The screw is one of
thirty. Projecting up from the base is welded-on strip
steel keeper 111 terminating in flange 112. Around the
outer perimeter of the base are thick narrow bands of
deformable polymer 114 and 116, fitting into peripheral
grooves in the base, and a wider band of like material
running around the outside of the keeper. The bottom of
the wider band fits into the slight peripheral edge that
the keeper makes with the base. On the top of the base
is bonded seal-cushion element 113 of a tough, flexible
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water-resistant ionomer. The ionomer is bonded to the
base. The other polymeric materials are not, although
some or all of them can be so bonded, e.g., directly to
the metal that has been cleaned and usually treated for
bonding, or with the use of a permanent or even a
temporary adhesive.
Referring to Figure 12, arrow 2 broadly indicates
fragmentary view of one end of a preferred embodiment of
a cover support made to accommodate a nominally 61 cm. x
122 cm. rectangular catch basin cover. The manhole
cover here normally is perforated, often in the form of
a grill. The body of the support is made of four
straight-sided lateral segments (lateral members)
joined at the corners witn rods and spreader bolts. The
surfaces 134a, 134b, and 134c are flat tough foamed
elastomeric surfaces on the ledge elements thereunder;
they are about 0.32 cm. thick and act as seat portions
for the cover. The ledge elements form the top of the
body's base portions. The base portions made of cast
ductile i-on, ASTM type 536, grade 60-45-12. Extending
downwardly from the inside of the ledge elements are the
inner wall portions of the bases. Extending upwardly
from each ledge portion is a welded-on sheet mild steel '
collar element portion indicated as 131a, 131b, and 131c
acting together as parts of a lateral keeper for the
manhole cover. All sheet steel elements are 14 ga.
(1.98 mm).
On the upper rim of the collar element portions are
box member wales 129a, 129b and 129c. These impart
ruggedness to the cover support. Welded inside the
wales are rods 132a, 132b and 132c of rectangular cross
section.
The adjustable corners are formed by pairs of
opposing jaw surfaces 133a-133b and 133c-133d th~t are
at the ends of the bases of each`segment, each pair
18
being joined by corner spreader bolts 127 and 127',
respectively. These bolts are threaded on each end
with threads of opposite handedness and are driven by
cranking their respective hexagonal-faced centers 126
and 126'. Bolt 127 screws into and out of suitably
tapped holes 124a and 124b; bolt 127' screws into and
out of like tapped holes 124c and 124d in the chamfered
end (~jawn) surfaces 133a, 133b, 133c and 133d of the
base portions of the lateral members. The longitudinal
axes of the bolts are substantially horizontal and enter
normal to the chamfered ends, which are mitered to make
a 45 angle with the longitudinal axes of the lateral
members. The perpendicular distance between the center
of the hole tapped for spreader bolt and the contact
periphery of the coating of the lateral member nearest
it that presses outwardly against the existing frame or
other receiving structure is 3.8 cm. This is the
distance ~X~, and it is significant, as will be shown
hereinafter.
Fitting into the wales are the ends of bent steel
rods 128 and 128'. The rods have square cross section
and make snug slidable fits with the sleeves.
The body also has a holddown clamp at each end.
Holddown clamp 121 is shown. It is spaced outwardly
from the base portion by spacer 122, and bolted the base
portions using pairs of nuts 123 and 123'. The nuts
screw down on threaded lugs projecting from the inside
of the base portions of these lateral segments.
Figure 13 looks at the right end elevation of the
cover support of Figure 12. Collar element portions
131a, 131b and 131c rise with a slight outward slant
from the base portions of the cover support. Squared-
off end parts of two longer base portions are indicated
as 137a and 137b; these are the terminals of right end
surfaces of the two longer lateral segments. The
~39~0~
19
collar element portions shown in end view are 131a and
131c. The collar element portions are welded to the
base portions of the lateral segments. They form seams
with the base portions, the seams being slightly above
the bottoms of the base portions. Elastomeric seat
portions 134a, b and c are evident in the view. The
thin collar element portions rise at a slight slope to
form box flanging at their tops as represented by items
129a, 129b and 129c. Bent steel corner rods represented
by 128 and 128', often slightly tapered at their ends,
fit slidably into the flanging. Straight steel rods are
tack welded inside the flanging. These rods are
represented by 132b. Both kinds of rods here are
substantially square in cross section, although it can
be of advantage in some cases to taper the corner ones
appreciably.
~olddown clamp 121 projects downwardly from the
inside of base portion facing the viewer and can be
forced against an underpart of an existing manhole cover
frame with the pair of bolts 138 and 138' that are
threaded through the bottom of the clamp 121.
Tough foamed elastomeric retention components and
sealing elements, about 0.32 cm. thick, are on the
outside of all collar portions. These elastomeric
elements are represented by 13~a, 136b and 136c in
Figure 13.
In a less expensive embodiment like the one in this
Figure 12, but not illustrated, the straight welded-in
rods like 132b are totally dispensed with. Such box
flanging rims, hollow or filled with resin, concrete,
etc., are highly resistant to bending.
Figures 14 and 15 depict a way that the cover
support of Figures 12 and 13 can be further modified to
substantially prevent the infiltration of surface water
~9~
under the cover edges and around the outer perimeter of
the new support.
Figure 14 is the plan view of the right corner of
Figure 12, and outboard of that, indicated by light
broken lines, is a water-sealing fitment. The arrow
labeled ~3~ indicates the molded fitment of moderately
soft, especially compressible foamed elastomer having
Shore A Durometer hardness of about 50-65. Its upper
surface 141 at the top of side wall 143 is to fit under
the bent rod 128. Seat pad 142 is to fit between the
mitered jaws 133a and 133b and the ends of seat portions
134a and 134b. The tip of pad 142 is projectable to
just short of the turning path of hexagonal wrench grip
126, and the upper flat portion of such tip is ap-
proximately flush with those seat portions; usually it
is slightly convexedly arcuate until the corner joint is
spread, at which time the cover support makes a tight
fit in the existing manhole cover receiving structure
and the manhole cover is emplaced on the new seat.
Figure 15 is a vertical cross section of the
fitment taken through plane Z-Z. Upper surface 141 of
slightly flaring sidewall 143 is unitary with seat pad
142. With a like fitment plugging each corner to seal
the gaps between the coatings of polymer bonded to the
seat and sidewall portions, an effective seal is formed
against appreciable ground water infiltration around the
cover seat and the outer periphery of the new support.
Optionally one side of the fitment of Figure 14 can
be attached to the end of the lateral segment it abuts,
e.g., with a water-resisting adhesive or mechanical
connection or both. Not shown, but also usable, are
one or more short flange or peg elements projecting from
the square and/or oblique ends of a pair of adjoining
lateral segments into corresponding holes or slot in the
vertical sides of fitment 3 or vice versa, going the
other way, to help anchor the fitment in placeO Also
not shown are the expedients of: (a) forming the deformable
sealing fitment around a stiffening steel core or armature
typically with the deformable material covering at least
those parts of the fitment side wall 143 and/or the
seat pad 142 which seal against water leakage around
the outer perimeter of the cover support and/or under
the cover rim, respectively; (b) stuffing in, and advan-
tageously adhering, a deformable plug-like corner seal
from the inside after the cover support is tightened
into place; and (c) spraying a sealant into the corner
after the cover support is tightened into place. Suitable
sealants for this usually are elastomeric. Advantageously
they should self-adhere or be adhered to most kinds
of surfaces, e.g., with a cement, and advantageously
also they can be self-expanding into a dense, closed
cell foam upon their emplacement, dispensing or shortly
after their in-situ deposition. Typical ones comprise
polyurethane or a modified styrene-containing polymer.
Suitable synthetic or natural resinous materials
that can be formulated for use in the compressible retention
component and water seals herein include rubber and
plastic materials such as natural and synthetic rubbers,
water-resistant ionomers, various vinyl polymexs and
copolymers such as polyvinyl acetate-polyethylene-acrylate
copolymers and polyvinyl cloride homopolymers, plastisols
such as a vinyl plastisol, polyurethanes, polyester
resins, epo~y resins, styrene-containing copolymers
such as ABS and butadiene-or isoprene-styrene copolymers,
rosin and rosin derivatives, thick tars and pitches,
polyolefins and copolymers containing olefin units,
and aminoplasts. Plasticizers, pigmentation, stains
and/or mineral fillers such as talc, carbon black, etc.
commonly are employed in their recipes. Cork particles
bonded with such resin material as a binder can be useful
also. The preferred retention components appear to
~J be elastomeric, i.e., resilient. Many of them can be
foamed and . . . . . . . . . . . . . . . . . . . .
~as~
preferably are foamed only very slightly; this can
soften them a bit without reducing their toughness too
greatly and it can help to allow for some thermal
expansion, and it makes them slightly less dense than
without the foaming. Latent foaming aqents reactive
upon warming and/or catalyzing, incorporated in a film
of an uncured polymer-providing material coated on a
cover support are preferred. Curing with heat,
ultraviolet or electron beam radiation and/or catalysis
can be practiced.
Customarily, it is of advantage to prime the metal
with a bonding agent or use a bonding treatment to
secure the best bond of the retention component or a
water sealing element to metal. Some polymers can bond
well without this, e.g., epoxy resins. However, the
bonds of most are improved by such priming and/or
treating.
A preferred foamed plastisol formulation for the
retention component is of Shore A Durometer hardness
about 20-70, and preferably about 50-65, as are the
water seals. The plastisol is compounded principally
from low molecular weight polyvinyl chloride resin
plasticized heavily with a conventional phthalate ester
plasticizer. It contains minute percentages of
stabilizer, red pigment and ozodicarbonamide blowing
agent. Another preferred formulation of about the same
Shore A Durometer hardness is a flexible polyol-
polyurethane foam, sIightly elastomeric and rubbery.
Some polymer recipes need heat to cure and foam, even
with catalysis, and others cure and even foam at about
room temperature (25C.). The degree of foaming in both
these plastisol and urethane formulations is very
small, and it could be called almost microscopic and
slight - the bubbles are closed-cell and tiny. In some
cases, especially where sealing is to be maximized and
. .
- - -,
12~0~
strength considerations are secondary, a large degree of
foaming and a resulting softened and less dense foamy
structure can be tolerated, e.g., Shore A Durometer
hardness of 20-55.
A recipe for a slightly-foamed polyurethane rubber
that has been found to be quite effective here is as
follows:
100 weight parts of Adiprene*#L167
polyurethane, a product of the Uniroyal
component of the F.G. Goodrich Company,
Naugatuck, connecticut
Compounded with these additives:
0.3 weight part of water:
0.3 weight part of Dabco-33LV* a product
of Air Products, Inc., Allentown, PA;
1.4 weight parts of DC-193* a product of
Dow-Corning Inc., Midland, Michigan; and
16.0 weight parts o~ ~BC~* a product of
Palmer, Sieka Inc., Port Washington, N.Y
This material can be applied to warmed, cleansed
and bonding agent-treated cast iron and steel, then
heated to 121- - 177- C. to develop the foam and full
cure of the polymeric material.
Some preferred heat-curable plastisol retention
component recipes for various Durometer hardness contain
100 parts of low molecular weight polyvinyl chloride
resin plasticized with 60-70 parts of a conventional
phthalate plasticizer such as dioctyl or dimethyl
phthalate. With this 1-3 weight parts of a conventional
stabilizer or polyvinyl chloride resin, e.g., a lead-
based stabilizer, is used along with 1-2 weight parts of
a red colorant (other pigments and colors, or none, can
be used, if desired) and O.S-3 weight parts of a
conventional ozodicarbonamide heat-and water-activated
blowing agent.
*Trade-mark
24
The preferred foamed plastisol usually i5 s~rayed
on the area to be coatedO It is advantageous to spray
it onto the hot metal cover suppcrt body (188-193-C.)
and let it cure and foam a bit. If extra foaming and/or
curing is desired, the coated part can be further warmed
at 193-204-C. for up to a few minutes.
The deformable retention component should be at
least about a 0.1 mm. thick for most effective gripping
to contact surfaces (which normally have irregular-
ities). Preferably it should not be more than about 10mm. thick for economy and durability, although thicker
retention components (or even portions of same) can be
especially useful for sealing on some occasions. The
same applies to cushioning components for cover seats,
although these usually are at least about 1.2 mm. thick
and easily can be as thick as 12 mm. or even more.
Metal surfaces should be cleaned to accept the
polymeric material if it is to be bonded thereto. Then
a customary bonding agent such a# Chemlok* #218 (Manu$ac-
~0 tured by Lord Corporation, Erie, Pa.) is applied, dr~edand warmed. Various other useful bonding agents are
available such as a Pliobond type (made by the Goodyear
Tire and Rubber Company).
As shown above, the preferred materials of
construction for most of the cover support, i.e., the
body and various elements of the body, are of a ferrous
metal, e.g., steel and/or cast iron, particularly cast
ductile iron. Other metals can be used where their
special properties are desirable and their cost can be
tolerated), e.g., stainless steel, high tensile strength
steel, wrought iron, bronze, brass, etc. Also, suitable
in some cases cover support parts can be, and even much
of the main body structure can be fabricated from glass
fiber-, aramid fiber-, or graphite fiber-reenforced
~5 resin, e.g., a thermosetting (curable) resin such as a
*Trade-mark
~>
polyester or epoxy resin. Also highly filled polymers
including elastomers, or ABS plastic and the like, i.e.,
tough structural polymeric materials can be used in the
invention. In some instances, it is possible to fit an
expansible metal shape, e.g., a body frame such as an
expansible steel hoop, to the inside part of a manhole
cover support body. The body is otherwise almost
entirely a tough, flexible polymeric material, optional-
ly pigmented (filled) with, e.g., carbon black. Also,
lo it may optionally be built up in plies with glass,
nylon, cotton and/or steel cloth, wire and/or cords
(like a truck tire carcass). In such instances, the
outer part of the body can act as the retention
component, although softer polymer-containing films
often can be used with advantage as special retention
components over or bonded onto a harder cover support
body.
Reference is made again to Figures 2, 3 and 4
which display a split-ring cover support with the bonded
polymer retention component 16 and to Figure 7 which
shows a four-segmented circular manhole cover support.
In tests on related nominally 58 cm. diameter circular
four-segmented manhole cover supports also joined with
turnbuckle bolts and having a bonded-on slightly foamed
elastomer retention component (actually a heat-cured
vinyl plastisol retention component) the following
significant fact was revealed: pulling directly upward
on an expansible cover support that was held in a ring
of steel by only the friction between its elastomer-
coated (bonded on) periphery and the ring and its ownweight (which was only an inconsequential minute
percentage of the whole load to be pulled) took much
more force (1477 kg.) to remove than a like four-
segmented cover support held the same way in the ring
with the same hoop stress exerted, but having no such
26
retention member interposed. The force factor was about
1.38 times as much for the coated support as for the
_ncoated one.
This series of tests also showed that the force
factor for the four-segmented, 58 cm. diameter cover
support with the polymeric retention component was 1.41
times that of its split-ring counterpart which also
had the same sort of retention component. Further,
it was found that the force factor for that so-coated
split-ring counterpart was roughly double that of a
like steel split-ring cover support that had no such
polymer retention component at all. Additionally, the
tests indicated that the strain distribution around
the four-segmented cover support was far more even than
that around the split-ring cover support. In a further
test, a nominally 61 cm. diameter four-segment cover
support, like that of Figure 7 and having the preferred
cured plastisol retention component, required 2159 kg.
of vertical pull to pull it out of the steel test ring.
This testing of an expandable, nominally 23-inch
(outside diamter) split ring 1 inch high by 3/4 inch
thick and equipped with strain gauges, the ring being
held in a manhole frame, further indicated that there
was ap~preciable nonuniform bending in the ring as the
gap therein was widened only slightly to force the ring
strongly against the frame.
Accordingly, a finite element analysis of a 1 inch
by 1 inch split ring (23~ inches in outside diameter)
held in a 1 inch by 1 inch cast iron frame (having a
23 3/4 inch internal diameter) was undertaken by computer.
The mat:erial properties listed below were used, the
force was reckoned in increasing finite increments,
and the materials were assumed to be elastic with large
deformations.
ComponentYoung's Modulus Poisson's
Ratio
Frame (cast iron)2.9 x 107 psi 0.3
B Split Ring (steel) 2.9 x 107 psi 0.3
39~
26a
At expansion forces of 2400 to 3000 pounds localized
ring-to-frame contact was found. This was consistent
with the previous ring-with-strain-gauge tests. From
the previous tests about 3000 pounds appeared to be
a high practical loading for a ring equipped with a
~-inch diameter threaded bolt for expansion. At the
3000 pound force the gaps between the ring and the frame
(calling for fill, eg. with a frictional retention component,
to complete the compressive contact between ring and
frame) ranged from 8 to 9 mils with an average of 11
mils. Based on this analysis the thickness of a frictional
retention component would need to be at least 11 mils
thick for the fill. In order to have about 75% of the
gaps filled 8~ mils would be required. To put this
into perspective, architectural paint coatings and primers
for steel work on bridges normally are about 1~ to 2
mils thick; the usual heavy industrial and maintenance
protective paint coatings can reach about 3 mils, and
occasionally they approach 5. Paint films in general
are expected to be less than 4 mils thick; thicker than
that, the films usually are termed "coatings" rather
than "paints". They often are referred to as coatings
of a special type, eg. coal tar epoxy finishes of 10
mils, and some other speciality coatings that can be
even thicker.
In connection with the present invention, however,
the frictional retention component is likely to be marginal
at best when such component is below 8-9 mils. One
must expect, also, asperities and irregularities in
surface and shape of the cover supports and frames as
well as wear, customary size variations in frames of
the same nominal sizes, the variability of the outward
flare in the keeper walls of the frame, the fact that
an expanding ring of a support, even a multisegmented
one with the superior gripping property as compared
to a split ring, deviates more and more from a true
circle as it is expanded (and maximum expansion must
..
26b
be expected in at least some few cases in any installation),
etc. Plus or minus an 1/8 inch per foot is the customary
tolerance for cast iron in this service. Hence, at
least a~out 20-25 mils is a preferable lower limit for
thickness of the retention component while 8-9 mils
is the extreme lower limit, and 11-20 mils is a bit
more comfortable lower limit in the typical service
situation.
On the other hand a thickness of as much as about
500-600 mils for such component often can be tolerated
in some cases, but beyond that this deformable, compressible
component is likely to be the main if not all of the
material in contact with the seat or sill of the manhole
cover frame and this can be undesirable. Furthermore,
especially where the keeper wall of the new cover support
being emplaced approaches being vertical, the original
manhole cover is unlikely to fit the new support. Accord-
ingly about 400 mils thickness is a preferred upper
limit for the frictional retention component.
For efficiency and economy and the broadest application
to general service situations, a thickness of the component
approximately about 1/16 to an 1/8 inch thickness (eg.
about, 60-130 mils) is the most highly preferred. Clearances
of about an 1/8 of an inch is generally all that can
be counted on consistently for existing covers. As
such retention components are new to the field of manhole
cover supports, the foregoing critically of their thick-
nesses appears not to have been considered by practitioners
of the art heretofore.
If the adjustable joints of such cover support are
plugged with deformable polymer (e.g., elastomeric
compositions like those discussed herein in connection
with retention componets and seats, and especially foamed
elastomer, so that complete water seals result under
the manhole co~er 81 and all around either the outer
perimeter of the cover support base or its cover keeper
rising there around, or both) then the cover support
~9~
26c
with an imperforate cover can be used to resist stray
surface water such as storm drainage.
Suitable sealing plug fitments to be used with the
cover support as it is being installed can be made of
polymer or with a core or armature, e.g., one of metal,
coated with polymer. Alternatively, the plug fitment
can be formed after the cover support is installed by
~-~r ~
~ ' . . :
~?~ O
27
stuffing in or spraying into the gap a flexible sealant,
preferably a foaming or foamable-in-place one.
Hollow box member flanging, i.e., peripheral
encircling wales as reenforcing rim portions and hollow
base portions can be filled or partly filled with a hard
or tough resin, optionally mixed with a mineral filler
such as mica or chopped glass fiber strand, to supply
desirable further resistance to crushing and other
deformation. Thermosetting resins such as polyester and
epoxy resins can be useful in this connection. Also,
thermoplastic ones such as ABS resin can be so used, or
even a concrete such as a Gunnite type.
The cross section of the sleeves and wales and
bases may be other than squarish or rectangular. They
can be made with many other fairly rigid conformations,
e.g., triangular or rounded, etc. The same applies to
the cross section of solid or tubular wale-forming and
base-forming members and joint-bridging rod or tube
élements. While only solid bases have been illustrated,
it should be clear that they can be made hollow, e.g.,
like the main part of the wale of Figure 1. They also
can be formed with at least part of the hollow wale
portion from a single piece of steel, e.g., 12-16
A.I.S.I gauge, and optionally with the whole keeper
portion, including the hollow wale portion, from a
single steel piece that includes the hollow-channeled
base.
Calculations have been made to estimate the
stiffness (resistance to bending from top loading) of
several conformations of the essentially horizontal
hollow wales of this invention and closely-related
wa1es. The results have indicated that the hollow steel
wale in the instant invention is significantly stiffer
than a solid steel bar wale having the same conformation
and cross section as the empty channel of the hollow
o~
28
wale. Thus, a straight 13 gauge hollow steel wale
enclosing a 1.91 cm. hollow square empty interior
channel is stiffer than a straight solid steel wale of
1.91 cm. x 1.91 cm. cross section by a factor of 1.35.
Additionally, the circular conformation of most wales
here renders them very rigid to horizontal loads.
While the cover support embodiments depicted are
for circular holes and a rectangle, other shapes such as
triangles, squares, ovals, etc. are usable in accordance
with invention principles, provided the cover supports
are rendered adjustable as to their perimeter, usually
with screw means.
It is especially desirable with polygonal (e.g.,
rectangular) manhole cover supports to have essentia}ly
horizontal turnbuckle bolts biased across the corners,
and these bolts set inboard as much as is permissible,
usually at least 2.54 cm., from the side of the cover
support to which they directly deliver a component of
their pressure.
The turnbuckle bolts biased at the corners in
impart components of force that are axial to and
perpendicular to the straight lateral segments of the
cover support that they connect. For the particular
bias of 45 relative to the longitudinal axes of the
straight sides of a rectangular or square cover support,
the magnitude of each such component is 0.707 times the
bolt force. Positioning these bolts in the same plane
as, but at virtually any other angle oblique to the
corner it connects, i.e., biasing the bolt, is, of
3~ course, possible and practical in accordance with this
invention. The perpendicular component of force holds
the lateral side (segment) directly against the existing
manhole frame. The axial component of force, being
located inboard from the outer edge of the cover
support, provides a bending moment on the lateral
,
29
segment that actually increases the holding force
between the periphery of the cover support and the
existing manhole frame.
The conventional positioning of an expansion
element such as a turnbuckle or spreading bolt somewhere
along the longitudinal axis of the lateral segment,
usually in the middle, exerts essentially only an axial
force. Also a deleterious bending moment can be
imparted to such bolt and segment. The bolt and its
segment are apt to bow-up, down, or in towards the
center of the manhole when especially heavily forced.
Accordingly, it can be said that corner-spreading makes
the bending moment on the bolt work for improved
retention in the existing manhole cover frame (or other
existing cover-receiving structure such as an existing
cover support) instead of being useless or possibly even
deleterious to the new cover support.
For a rectangular nominally 61 cm. x 122 cm. cover
support of this invention with turnbucXle bolts at the
corner, the holding force has been calculated to be
12,091 kg. on each side, or a total of 48,366 kg. for
the whole support. This compares quite favorably with
that estimated for the same size cover support of the
conventional (spread at the centers of the side lateral
segments) design where both cover supports used the same
kind of 12.7 mm. turnbuckle bolts. In the latter
conventional instance, the holding force was only 11,364
kg. on each side or 45,455 kg. for the whole support.
The holding forces in pounds (sidewise force) for
one side of a rectangular cover support with the corner
spreaders can be calculated in accordance with the
following formula ~Fn, below, employing inch, pound and
degrees of arc units:
Q~
Hc = 4EAtBTl Cos +
B
8 E At BT 1 X Sin , i.e., Formula nF~
lBS
where:
Hc ~ the holding force in pounds perpendicular to the
manhole cover frame (but limited in magnitude by
the yield strength of the bolt)
E = Young's modulus of the bolt in pounds per square
inch
At = tensile area of the bolt in square inches
BT = the number of bolt turns after the cover support is
seated
1 - the lead (inches) of the bolt threads
lB = the length of the exposed bolt in inches.
X = the perpendicular distance in inches from the
contact periphery of the cover support to the
center of the hole that is tapped therein for
accepting the turnbuckle bolt
S = the length of one side of the cover support in
inches
= the angle in degrees that longitudinal axis of
turnbuckle bolt makes with the longitudinal axis of
the side being held against the frame.
This equation, Formula F, can be simplified when
the angle is 45 as it is in the embodiment shown in
Figure 1. The equation becomes:
Hc = 2 2 E AtBT~ XS), i.e., Simplified
lB Formula ~F"
Relative to the foregoing force considerations is
the realization that the placing of the turnbuckle bolt
is significant for developing lateral force, the force
that is important for cover support retention in
highway service. Thus, keeping the bolt hole opening
(or the end pivot point of a turnbuckle having a screw
protruding obliquely into a female-threaded end of a
center turning member of a more common turnbuckle bolt)
far inboard makes for a higher force value than putting
it closer to the contact periphery of the cover support
(which contacts and presses against the existing cover
frame -- or other existing manhole cover receiving
structure). The inboard placement of any turnbuckle or
like spreader mechanism, of course, permits longer
threaded sections and allows for more peripheral
adjustment. However, while many manhole covers have a
reasonably flat top, they also can have a bottom that is
reenforced by ribs, bracing, or like structure hanging
down under; these cannot be interfered with, lest the
cover won't seat in the newly-installed cover support.
Accordingly, there can be a limit to the inboard
placement of the spreader.
Advantageously, then, for developing improved
retaining force and permitting substantial adjustment
with such biased turnbuckle spreader means, the
perpendic~lar distance from the contact periphery of the
cover support to center point where the spreader means
starts to shcrten or lengthen should be at least about
2.54 cm. and preferably it is more, e.g., 3.81 cm
Stated in another way, ~Xn in the above equations should
be at least 2.54 cm.; or, as the force is being applied
by the spreader to a zone near the end of a side
; segment, this zone can be treated as having a practical
center point, and the perpendicular distance from that
center point to the contact periphery of the straight-
sided segment should be at least about 2.54 cm. The 45-
angle biasing tends to develop about equal force in two
directions, and this generally is desirable.
Modifications and variations of the invention will
be apparent to those skilled in the art in the light of
the foregoing detailed disclosure. Therefore, it is to
.~ . .
32
be understood that, within the scope of the appended
claims, the invention can be practiced otherwise than as
shown and described.
. .
.: ~ , . ~ . ' . .
. .
