Polygonal manhole cover support

This cover support provides a seat and lateral keeper for a manhole cover. A principal feature is a plurality of straight lateral segments that are joined near their ends and have corner spreaders acting in an essentially horizontal direction that is biased with respect to the longitudinal axes of the lateral segments whose ends they spread or draw in.

BACKGROUND OF THE INVENTION 
This invention relates to adjustable manhole cover supports for emplacing 
over and raising the 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 that cover or grating ordinarily is 
intended to bear vehicular traffic. 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 utility enclosure serving, e.g., an 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 otherwise is overlaid or repaved to 
establish a higher grade. It then is advantageous to mount the inventive 
cover support atop the existing manhole receiving structure. Relevant 
prior art on manhole cover supports and manhole cover frames can be found 
in U.S. Pat. Nos. 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. 
Axle loads up to 40,000 pounds 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 
permitting a hazardous dislocation of the cover support or its cover. 
Often it is desirable also to cushion the cover a bit for resisting wear 
or reducing noise, 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 
paramount concern and a most general one. The supports often contain some 
reasonably thin (0.1 inch 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 
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 be 
effective for economy and/or ease of manufacture, handling an 
installation. However, a relatively low weight of the cover support, as 
compared to the usually thick 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 
cover supports such as those in U.S. Pat. Nos. 4,281,944, 4,236,358, 
4,097,171 and 4,302,126, noted above. polygonal, e.g., quadrangular, cover 
supports can be especially prone to such displacement. 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 receiving 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) 
simply by friction alone, and this not necessarily (but often desirably) 
with the use of any friction-enhancing retention member. 
Additionally, the present support is polygonal and adjustable. It can be 
adapted readily to sealing off against water infiltration and to 
cushioning the cover. Furthermore, its stiffness can be made unusually 
high while its weight can be kept low. 
No previously proposed manhole cover supports are known by the inventor to 
have these very desirable advantages, let alone the capability of 
combining several or all of them in a cover support in a practical manner. 
BROAD STATEMENT OF THE INVENTION 
The present adjustable manhole cover support is a polygonal one, often 
generally oblong or square in plan. It is designed to raise the grade of 
an existing manhole cover receiving structure. It can be, however, 
hexagonal, pentagonal, octagonal, triangular, and so on. 
It comprises a plurality of straight lateral segments joined near their 
ends for forming a polygonal perimeter. Each lateral segment has a base 
with an exterior wall and a collar element that extends upwardly from an 
essentially flat ledge element. The collar and ledge elements form a 
lateral keeper and a seat, respectively, for a manhole cover when the 
lateral segments are assembled. The distance between the adjacent ends of 
the assembled lateral segments is adjustable by means of a spreader for 
each corner that is adapted to move the adjacent ends essentially 
horizontally in a direction which is biased with respect to the 
longitudinal axes of those segments.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring to FIG. 1, arrow 1 broadly indicates a preferred embodiment of 
the instant cover support made to accommodate a nominally 24".times.48" 
rectangular catch basin cover. Such cover normally is perforated or 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 with rods and 
spreader bolts. The surfaces 11a, 11b, 11c and 11d are the ledge elements, 
i.e., seat portions for the cover. The seat portions form the top of the 
body's base portions and are made of cast ductile iron, grade 60-45-12. 
Extending downwardly from the seat portions are the inner wall portions of 
the bases, specifically 9a, 9b, 9c and 9d. Extending upwardly from the seat 
portions are welded-on sheet steel collar element portions 16a, 16b, 16c 
and 16d acting together as a lateral keeper for the manhole cover. All 
sheet steel elements are 14 ga. (0.078125"). 
Tack welded to the outside of the upper rim of the collar element portions 
are wales (better seen as square cross section steel rods 17a, 17b, 17c 
and 17d in FIG. 3) just under the slight outward flanging 28a, 28b, 28c 
and 28d of the collar elements. These impart ruggedness to the cover 
support. The ends of these rods fit into sleeves of rectangular cross 
section at each end of a lateral member, these sleeves being noted as 18a, 
18a', 18b, 18b', 18c, 18c', 18d and 18d'. 
The adjustable corners are formed by pairs of opposing jaw surfaces 
66a'-66b, 66b'-66c, 66c'-66d and 66d'-66a that are at the ends of the 
bases of each segment, each pair being joined by corner spreader bolts 
12a, 12b, 12c and 12d, respectively. These bolts are threaded on each end 
with threads of opposite handedness and are driven by cranking their 
respective hexagonal-faced centers 13a, 13b, 13c and 13d. The bolts 12a, 
12b, 12c and 12d screw into and out of suitably tapped holes 14a, 14a', 
14b, 14b', 14c, 14c', 14d and 14d' in the chamfered end ("jaw") surfaces 
66a, 66a', 66b, 66b', 66c, 66c', 66d and 66d' 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.degree. 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 lateral member nearest it 
that presses outwardly against the existing frame or other receiving 
structure 15 is 11/2 inches. This distance "x" is significant, as will be 
shown hereinafter. It can be measured in the vertical plane marked as 
Section "X-X" through bolt 12d in the lower left corner of FIG. 1. 
Fitting into the sleeves are the ends of bent steel rods 19a, 19b, 19c and 
19d. The rods make snug slidable fits with the sleeves. 
The body also has holddown clamps 21a and 21c at the inside of the base 
portion of the two opposite end lateral segments of the cover support. 
These are spaced outwardly from the base portions by spacers 22a and 22c, 
respectively, and bolted the base portions using pairs of nuts 23a and 
23c, respectively. The nuts screw down on threaded lugs projecting from 
the inside of the base portions of these lateral segments. 
FIG. 2 looks at the right end elevation of the cover support of FIG. 1. 
Collar element portions 16b, 16c and 16d 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 27b and 27d; these are the terminals 
of right end surfaces of the two longer lateral segments. It is those 
chamfered surfaces that are joined to the corresponding end surfaces of 
base portion 27c. The collar elements portions 16b, 16c and 16d are welded 
to the base portions of the lateral segments to form seams with the base 
portions, these seams being shown as items 26b, 26c and 26d. The seam 
between the outer wall of the base portion 27c and collar portion 16c is 
particularly evident in this view and is noted as seam 26c. The cover seat 
portions 11b, 11c and 11d actually are the tops of solid base portions 27b, 
27c and 27d, respectively. The thinner collar element portions rise at a 
slight slope to form a small outward flange like that represented by item 
28c. These small flanges extend between the end sleeves, the sleeves being 
those represented by items 18b', 18c, 18c' and 18d. Bent steel corner rods 
19b and 19c, often slightly tapered at their ends, fit slidably into the 
sleeves 18b, 18c, 18c' and 18d, while steel rods tack welded to the upper 
rims of the several collar elements also fit into the sleeves, as 
indicated by item 17c fitting into sleeves 18c and 18c'. Both kinds of 
rods here are substantially square in cross section, although it can be of 
advantage in some cases to taper the bent one appreciably. 
Holddown clamp 21c projects downwardly from the inside of base portion 27c 
and can be forced against an underpart of an existing manhole cover frame 
with the pair of bolts 29c that are threaded through the bottom of the 
clamp 21c. 
FIG. 3 is a vertical cross sectional elevation of the cover support of FIG. 
1 taken through the central plane marked "A--A" thereon. It shows how the 
cover support is mounted on an existing manhole cover frame 31; the cross 
section of that frame is indicated entirely in broken lines; it is a 
single piece of cast iron. 
Base portion 27b of the cover support and the other base portions forming 
the bottom periphery of the support all rest on sill 33 of the frame, 
which itself rises from its bottom flange 32. These base portions provide 
the seat for the cover, the seat being indicated in this view by 11a, 11b 
and 11c. Collar element portions 16a, 16b and 16c, welded to the base 
portions, rise above retaining rim 34 of the frame and, for the middle of 
their length, possess a small outward flanging 28a, 28b and 28c. The 
flanging terminates in sleeves at the ends of the lateral members 
indicated by sleeves 18a', 18b, 18b' and 18c. Rods 16a, 16b and 16c are 
welded to fit under the flanging 28a, 28b and 28c, respectively, and 
project their ends into the sleeves 18a', 18b, 18b' and 18c, respectively. 
Also projecting into sleeves 18 a' and 18b is bent rod 19a, while 
projecting into sleeves 18b' and 18c is bent rod 19b, both these bent rods 
being unbonded to the sleeves. 
Holddown clamps 21a and 21c are fitted to the inner periphery of base 
portions 27a and 27c, respectively, with threaded studs 37a and 37c, 
respectively, projecting through spacers 22a and 22c, respectively, and 
fastened respectively, by nut pairs indicated by 23a and 23c. The clamps 
are forced against sloping under ring 36 of the manhole cover frame by use 
of the bolt pairs indicated by items 29a and 29c. 
FIG. 4 shows the vertical cross sectional view of a corner of the cover 
support of FIG. 1 through section B--B thereof. Base portions of the steel 
body of the cover support show as 27a and 27d below seam lines 26a and 26d. 
Projecting above the seam lines and welded to the base are collar element 
portions 16a and 16d. The middle rim sections of the collar supports 
terminate in short outward flangings 28a and 28b while at the ends of 
collar supports 24a and 24d are sleeves 18a and 18d, respectively. Welded 
below the short outward flanging are longitudinal rods 17a and 17d; the 
ends of these project into sleeves 18a and 18d, respectively. Also 
projecting into the sleeve ends are the ends of bent rod 19d. 
Bolt 12d is threaded on each end with threads of opposite handedness. The 
ends screw into and out of holes 14d and 14d' that are appropriately 
tapped to make bolt 12d, in effect, a turnbuckle bolt. The middle of bolt 
14 has a hexagonal portion suitable for a wrench grip to turn the bolt. 
Alternatively, the center of the bolt can be studded, notched or 
perforated for gripping with a lever-like turning tool. Also 
alternatively, the turnbuckle can be made as two oppositely threaded bolts 
each pivotally connected to the inside wall of a base portion and connected 
by a threaded sleeve, usually fairly open at its sides, to be manipulated 
like the more familiar turnbuckle. 
The metal body of the embodiment shown in the fragmentary view indicated 
broadly as cover support 2 in FIG. 5 is essentially the same as the metal 
body of FIG. 1 except for the following elements: the sleeves 58b, 58c and 
58d of FIG. 5 now extend the full length of each straight lateral member 
and totally encase square rods 17b, 17c and 17d. A rod is under the rim of 
the end that is not shown; it, too, like rod 17c, is encased by a 
full-length sleeve not shown, but corresponding to sleeve 58c. 
In a less expensive embodiment like the one in this FIG. 5, but not 
illustrated, the rods 17b, 17c, 17d and its there-invisible corresponding 
rod to the rear are totally dispensed with. Such rims, hollow or filled 
with resin, concrete, etc., are highly resistant to bending. The remainder 
of the metal body elements of FIG. 5 correspond substantially identically 
to those of FIG. 1; accordingly, they are numbered with the same numbers 
in both FIGS. 1 and 5. 
The other differences between the embodiments of FIGS. 1 and 5 have to do 
with tough flat, about 1/8" thick foamed elastomer elements that are 
bonded to the seat and the outer walls of the base and collar element 
portions of the straight lateral segments. Thus, in FIG. 5 the cover seat 
portions 52b, 52c and 52d constitute the flat upper surfaces of a coating 
of elastomer bonded to the flat metal surfaces 11b, 11c and 11d, 
respectively, which were the cover seat portions in the embodiment of FIG. 
1. A like elastomer coating surface forms a seat portion on the end not 
shown; it, too, corresponds to elastomeric seat portion 52c, bonded to 
flat steel surface 11c. 
FIG. 6 is the side elevation view of the cover support of FIG. 5. Sleeve 
58c totally encases rod 17c, and sleeves 58b and 58d encase like rods not 
visible. Bent rods 19b and 19c fit slidably into the ends of the sleeves. 
The outer walls of the collar elements 16b, 16c and 16d and base elements 
27a, 27b and 27c are coated with the same foamed elastomer as the seat 
portions described in connection with FIG. 5. Those seat portions also are 
seen in FIG. 6 as items 52b, 52c and 52d. The remainder of the metal body 
elements of FIG. 6 correspond substantially identically to those of FIG. 
5. Accordingly, they have the same numbers. 
Expansion of the outer periphery of the cover supports illustrated in FIGS. 
1, 2, 3 and 4 can bring tremendous retaining pressure from the outer wall 
portions, particularly the outer wall portions of the base, against the 
retaining rim of the existing manhole cover frame or an existing cover 
support into which the new cover support is fitted. This is due to the 
corner spreading (as opposed to lengthening the lateral members along 
their longitudinal axes, a conventional practice less effective for 
developing this pressure and, thus, the frictional grip of the new cover 
support in such existing manhole cover receiving structure). 
The new cover support embodiment shown in FIGS. 5 and 6 can increase the 
frictional grip of the cover support of FIG. 1 greatly. This is because 
the coefficient of static friction between the surface of selected 
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 in a polymer-to-metal instance should be at 
least about 0.4, and generally it can be as high as 0.6-0.7 or even more. 
In a steel-to-steel instance it is unlikely to be as high as 0.35. Shore A 
Durometer hardness of the polymer composition preferably is at least about 
20, and preferably is about 50-70. Usually the thickness of a retention 
component will be between about 0.4 and 400 mils. Oil resistance can be 
desirable for them and 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 corner spreaders supply a large measure of 
pressure, and the bonded elastomers heighten friction, thereby making a 
cover support that is unusually effective for resisting dislodgement or 
tilting in highway service. 
It should be understood that the retention component can be, instead of a 
full coating, merely a series of dots or lines or other patterns bonded to 
the exterior of the expandable base of the new cover support. Alternatively 
such component can be one or more O-rings, continuous bands, a sleeve or a 
sheet that can be interposed between the exterior of the base and the 
shoulder of the existing manhole cover receiving structure. The effective 
thickness of such component should be between about 0.4 and 400 mils. 
Similarly, the polymer component used to cushion a cover on the new seat 
can be bonded to or separate from the seat, and be of a continuous or 
interrupted pattern. 
FIGS. 7 and 8 depict a way that the cover support of FIGS. 5 and 6 can be 
further modified to substantially prevent the infiltration of surface 
water under the cover edges and around the outer perimeter of the new 
support. 
FIG. 7 is the plan view of the right corner of FIG. 5, 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 63 at the top of side wall 67 is to fit 
under the bent rod 19b. Seat pad 64 is to fit between the mitered jaws 66 
and the ends of seat portions 52b and 52c. The tip of pad 64 is 
projectable to just short of the turning path of hexagonal wrench grip 
13b, and the upper flat portion of such tip is approximately 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. 
FIG. 8 is a vertical cross section of the fitment taken through plane Z--Z. 
Upper surface 63 of slightly flaring sidewall 67 is unitary with seat pad 
64. 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 FIG. 7 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 place. 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 67 and/or the seat pad 64 which seal 
against water leakage around the outer perimeter of the cover support 
and/or under the cover rim, respectively; (b) stuffing in, and 
advantageously 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. 
In FIG. 9 the seat, the rise of the collar, the box flanging at the collar 
top, and the base portions of a straight segment all are formed from a 
single piece of 18 gauge mild carbon steel to leave an almost squarish 
hollow channel 79 in the base and a rounded one at top. One edge of the 
bent steel piece is at the junction 76 and the other at the junction 77, 
both of which junctions are shown in FIG. 10. 
The collar top terminates in rolled box flange 71 extending from the 
lateral keeper wall 72 of the cover support. Seat 73 is a flattened 
portion, and the steel continues down to flattened bottom 74. Bottom 74 is 
to rest on the sill of an existing manhole cover frame. Then it bends 
upward to form the contact surface against the shoulder of such frame. 
Projecting leftward and out from channel 70 is corner reaction member 71. 
That member is of square cross section with rounded corners to fit snugly 
into channel 70. There it is fastened securely. This usually includes, for 
example, resistance welding and/or bolts coming from the inner side wall of 
the channel as that wall does not have to fit against a frame shoulder or 
manhole cover. It has a beveled face 78 like face 66b of FIG. 1. Into the 
face 78 is tapped a hole 79 for accepting one end of a turnbuckle bolt 
like an end of bolt 12a of FIG. 1. 
The sheet metal edge junctures 76 and 77 are evident in FIG. 10 (Section 
"Q--Q" of the segment portion shown in FIG. 9). These junctures can be 
seam-welded or tack-welded; if that is done it is desirable to fabricate 
juncture 76 without lumps etc., using grinding if necessary. 
The seat of the segment of the all-cast ductile iron cover support depicted 
in FIG. 11 has corner seat 81 and rising lateral cover keeper 82 as its 
upper piece. This piece also includes a skirt running downwardly from the 
seat and terminating in an enlarged lower rim 83 of trapezoidal cross 
section. These cover supports rarely are made with stiffening flanges or 
wales. 
The rim 83 and skirt fit slidably into complementary cavities in base 
(lower) piece 84. The lower cavity 86 is shown as being empty and the 
other one shown as supporting enlarged rim 83. To lower the seat level, 
the pieces are disengaged and then reengaged using the lower cavity 86 
instead of the upper one. More than two such cavities can be superimposed 
for greater seat elevation adjustment range as is shown in applicant's 
U.S. Pat. No. 4,281,944. This sort of cover support segment usually is 
made of cast ductile iron except for any seal and friction-enhancing 
elements, the cover seat padding, and the bolt, screw and/or rivet 
elements. 
FIG. -2 shows a fragment of a segment of a cover support having a cast 
malleable iron base 91 onto which is welded collar 96. Topping the collar 
is a short outward flanging 97. Notch 93 in base 91 has a vertical hole 
tapped upwardly from the center of its top to accept all the threads and 
the length to the bolt head of bolt 94 so that the bolt top can be made 
flush with the rest of the bottom of base 91 if necessary. Unscrewing the 
bolt adds elevation to the seat. Usually there are at least two and often 
more such height-adjusting bolts in each segment of a cover support if any 
are to be used at all. Quite often no elevating means are used at all with 
a new cover support. Separate shim or gasket-type elements also can be 
used for elevating the support or for leveling it up. 
FIG. 13, the cross section of FIG. 12 through Section "Y--Y" shows the 
profile of the segment fragment with the adjustable bolt protruding from 
the bottom of base 91. 
The turnbuckle bolts biased at the corners in accordance with the invention 
principles 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.degree. relative to the longitudinal axes of 
the lateral segments as illustrated in FIG. 1, 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 angle oblique to the corner it 
connects, i.e., biasing the bolt, is, of course, possible and practical in 
accordance with this invention. The perpendicular component of force holds 
the lateral 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 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 the instant invention makes the bending moment on the 
bolt work for better retention in the existing frame (or other existing 
receiving structure) instead of being useless or possibly even deleterious 
to the cover support. 
For the cover support depicted in FIG. 1 the holding force has been 
calculated to be 26,600 pounds on each side, or a total of 106,400 pounds 
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 lateral segments) design where both cover supports used the same 
kind of 1/2" turnbuckle bolts; in such conventional instance the holding 
force was only 25,000 pounds on each side or 100,000 pounds for the whole 
support. 
The holding forces here for one side of a rectangular cover support can be 
calculated in accordance with the following formula "F", below, employing 
inch, pound and degrees of arc units: 
##EQU1## 
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 
A.sub.t =tensile area of the bolt in square inches 
B.sub.T =the number of bolt turns after the cover support is seated 
l=the lead (inches) of the bolt threads 
l.sub.B =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 
.theta.=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 .theta. is 
45.degree. as it is in the embodiment shown in FIG. 1. The equation 
becomes: 
##EQU2## 
Relative to the foregoing force considerations is the realization that the 
placing of the turnbuckle bolt can be 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 point of entry of a 
screw protruding obliquely from a side of the cover support into a 
female-threaded end of a center turning member of the 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 perpendicular distance from the contact periphery of the cover 
support to center point where the spreader means starts to shorten or 
lengthen should be at least about one inch and preferably is more, e.g., 
one and a half inches. Stated another way, as the force is being applied 
by the spreader to a zone near the end of a segment, that zone can be 
treated as having a practical center point, and the perpendicular distance 
from that center point to the contact periphery of the segment should be at 
least about an inch. The 45.degree. angle biasing tends to develop about 
equal force in two directions, and this generally is desirable. 
Reference is made again to FIG. 6, which displays the bonded elastomer 
retention component (items 52b, 52c, 52d and has one corresponding to 52c 
on the side not seen). In tests on related four-segmented manhole cover 
supports of a different overall shape, but also joined with turnbuckle 
bolts and having the same kind of adhering foamed elastomer retention 
component, actually a heat-cured vinyl plastisol retention component, the 
following interesting fact was revealed: pulling directly upward on the 
expansible cover support that was held in a ring of steel by only the 
friction between its elastomer-coated periphery and the ring and its own 
weight (which was only an inconsequential few percent of the whole load to 
be pulled) took much more force to remove than a like cover support held 
the same way in the ring with the same hoop stress exerted, but having no 
such retention member interposed. The force factor was about 1.38 times as 
much for the coated support as for the uncoated one. 
Suitable polymers that can be formulated for use in the compressible 
retention component and water seals herein include natural and synthetic 
rubbers, various vinyl polymers and copolymers such as polyvinyl 
acetate-polyethylene-acrylic copolymers and polyvinyl chloride 
homopolymers, polyurethanes, polyesters resins, epoxy resins, 
styrene-containing copolymers such as ABS and butadiene-or 
isoprene-styrene copolymers, 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. The best retention components appear to be elastomeric. Many of 
them can be foamed and preferably are foamed only very slightly; this can 
soften them a bit, and it makes them slightly less dense than without 
foaming. Latent foaming agents reactive upon warming a film of an uncured 
polymer-providing material coated on a cover support are preferred. 
Customarily it is of advantage to prime a metal with a bonding agent or use 
a bonding treatment to secure the best bond of the retention component or a 
water seal to metal. Some polymers 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 of 
Shore A Durometer hardness about 45-70, and preferably about 50-65, and at 
least some of the water seals (sprayed on, then heat cured on the metal 
cover support) 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 rubbery urethane-polyol 
foam. Some need heat to cure and foam at about room temperature 
(78.degree. F.). The degree of foaming in both these formulations is very, 
very small; the bubbles are closed-cell and tiny. In some cases, especially 
where sealing is to be maximized and strength considerations are secondary, 
a fair amount of foaming and resulting softened and less dense foamy 
structure can be tolerated, e.g., Shore A Durometer hardness of 45-55. 
In the case of the preferred foamed plastisol that is sprayed on the area 
to be coated, it is advantageous to spray it onto the hot metal cover 
support body (370.degree.-380.degree. F.) and let it cure and foam a bit. 
If extra foaming and/or curing is desired, the coated part can be further 
warmed at 380.degree.-400.degree. F. for up to a few minutes. 
Metal surfaces should be cleaned to accept the polymeric material if it is 
to be bonded. Then a customary bonding agent such as Chemlok #218 
(Manufactured by Lord Corporation, Erie, Pa.) is applied, dried and 
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 is ferrous metal, e.g., steel and/or cast iron, particularly 
cast malleable 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 are cover support parts and even much of the main 
structure fabricated from glass fiber-, aramid fiber-, or graphite 
fiber-reenforced resin, e.g., a thermosetting polyester or epoxy resin. 
Means for locking down the cover support to a manhole flange, like the 
means shown in U.S. Pat. No. 3,773,428, often are desirable in addition to 
a frictional grip. 
Many 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 be understood that, within the scope of 
the appended claims, the invention can be practiced otherwise than as 
shown and described.