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Патент USA US3034546

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May 15, 1962
H. F. KENNISON
3,034,536
PRESTRESSED CONCRETE PIPES
Filed Feb. 19, 1958
2 Sheejzs-Sheet 1
I'l
An---
M/l/ENTOE
HUGH F: KEN/V/SO/V
A TI'OR/VEY
May 15, 1962
H. F. KENNISON
3,034,536
PRESTRESSED CONCRETE PIPES
Filed Feb. 19, 1958
2 Sheets-Sheet 2
$32.3)
0-?’ I
United States Patent 0
3,034,536
Patented May 15, 1962
2
1
tensile capacity of longitudinal wires for effecting the de
gree of compression required in the ends of prestressed
pipes and to thereby accomplish greater economy in the
3,034,536
PRESTRESSED CONCRETE PIPES
Hugh F. Kennison, Essex Fells, N.J., assignor to Lock
Joint Pipe Company, East Orange, N.J., a corporation
of New Jersey
Filed Feb. 19, 1958, Ser. No. 716,135
5 Claims. (Cl. 138—176)
manufacture of such pipes. It is also a purpose to pro
vide adequate end anchorages which are embedded in
and protected by the concrete and to thereby attain equal
ly strong pipe with less longitudinal steel, or a pipe ca
pable of withstanding a higher working pressure with the
same quantity of longitudinal steel.
This invention relates to the manufacture of prestressed
The improved stress conditions and savings sought by
concrete, and more particularly to pipes, tubes, conduits 10
the present invention are attained by means for anchor
and other tubular bodies of originally plastic and subse
ing the ends of the longitudinal wires in a manner to es
quently hardened materials for con?ning ?uids and in
tablish an optimum condition of compressive stress of the
which the ?uid-con?ning conduit portion thereof com
concrete in the ends of a prestressed concrete pipe. In
prises a hollow monolithic core or barrel which is pre
loaded in compression by a prestressed wire wrapping 15 its more general form the anchorage comprises a coil or
loop in a wire which is formed by curling the wire over
around the outside of the core and by a plurality of lon
a pin before the wire is tensioned. The wire is curled
gitudinally extending prestressed wires embedded in and
over the pin at at point along the wire which is to be 10
reacting on the core.
cated as close to the end of a completed pipe as is prac
In prestressed tubular bodies of this character, such as
tical. Similar anchorages are made in each wire for
concrete pipe, the force of the tensioned wire wrapping
both ends of a pipe. One or more wires may be curled
over a single pin or all of the wires may be curled over
the band of a ring, and the wires are tensioned either
is a function of the hydrostatic head to which the pipe
is to be subjected when in use. The prestressed longi
tudinal reinforcing inhibits cracking of the concrete which
singly or in groups, depending upon the number of wires
otherwise would occur because of the shear and bend
ing stresses effected by the tensioned wire wrapping. The 25 which are curled around a common member or pin at
either end of the mould in which the concrete core is to
longitudinal reinforcing also supplies the beam strength
for the bending resistance required during manufacture
be cast.
When a plurality of pins are employed at one end of
a mould, the pins are of such length as to subtend equal
sile stresses involved (upwards of 120,000 pounds per 30 arcs without overlapping one another circumferentially
around the mould. Particularly when the invention is to
square inch, for example), the prestressing technique re
and for resisting live and dead loads that may be placed
on the pipe when it is in use. Because of the high ten
quires that high tensile steel be used.
Since wires of
this material are costly it is desirable that full use be
made of their strength in order to avoid an uneconomi
cal construction.
'
be utilized in making pipes for withstanding very high
working pressures a continuous hoop may be included as
apart of the anchoring means for increasing the area of
35 stress distribution and thereby reducing the stress concen
The compressive stress in the concrete in the length
wise direction of a pipe should be su?iciently high to
tration in the concrete.
located in the general vicinity of the transverse planes
proper positions in a mould. The pins and the coils may
be located outwardly from the circle of wires or inwardly
'
The ends of a wire running from a coil extend tan
gentially from the encircled pin in opposite directionsias
prevent cracking of the concrete in zones which are sub
the wires are tensioned around the pins by'forces apa
jected to the most severe conditions of shear and of
bending stress. These zones of potential cracking are 40 plied to their opposite ends while the wires are in their‘
in which the tensioned wire winding terminates and also
inward from the open end of the bell of a bell and spigot
pipe where an abrupt change in the wall thickness of the
45
pipe occurs.
The prestressed longitudinal wires usually extend into
from the circle of wires, as desired, and a wire may be
curled more than once around an engaged pin. A coil
forms an effective hook for added purchase on the con
crete and it supplies an additional length of the wire in
the shorter lineal distance from the beginning of the coil
to the nearest end of the wire and so greatly improves
or through the zones of potential cracking and are avail
able to exert the amount of compression of the concrete
the development of the bond between the wire and the
necessary to prevent cracking, but an excessive amount
of steel must be used unless the ends of the wires are 50 concrete. The encircled pins enlarge the anchorage and
distribute the pull of the wires over a greater area of the
adequately anchored. This is because the longitudinal
compression imparted by a prestressed wire embedded in
concrete is less along a limited distance from an unan
concrete.
Greatly improved results have ensued in pipes which
are ?nished with spigots having exterior jointing surfaces
chored end of the wire than the maximum compression
reached further inwards along the Wire where the bond 55 and in which the wire wrapping does not overlay that
portion of the pipe which has the jointing surfaces. Simi
between the wire and the concrete has built up to its
lar results are gained in the bells of pipes which are
maximum value. Owing to this phenomenon more steel
formed integrally with the pipe barrel and are therefore
is called for to effect the degree of compression required
subject to very high shearing stresses due to abrupt
in the ends of a pipe than is necessary for attaining the
compression required along the mid-length of the pipe 60 changes in the cross-section of the pipes. The resultant
maximum tension in the longitudinal wires is made ef
unless the ends of the wires are positively ?xed as ‘by
fective to produce optimum conditions of compressive
attachment to steel or iron rings supported on the end
stress throughout the areas of the concrete adjacent the
faces of the pipe.
pipe ends.
.
If ring anchorages located externally of the concrete
Although the novel features which are believed to be
are not to be employed, more longitudinal steel (heavier 65
characteristic of this invention will be particularly pointed
wires or a greater number of wires) is indicated to be
necessary than should be required to provide the proper
amount of compression to prevent cracking in the ends
out in the claims appended hereto, the invention itself,
- as to its objects and advantages, and the manner in which
it may be carried out, may be better understood by refer
of the pipes where the shear and bending stress are se
verest. It is a principal purpose of the invention to 70 ring to the following description taken in connection with
avoid the use of external anchorages for the longitudinal
the accompanying drawing forming a part hereof, in
wires and to enable more e?icient use to be made of the
which:
3,034,536
4
FIG. 1 is illustrative of a pipe embodying the'principle
together with the pin provides a relatively extensive area
normal to the longitudinal direction of the wire. The
other end of each wire is curled around a similar pin 24
of the invention;
FIG. 2 is a longitudinal section through a portion of
(FIG. 2) and forms a coil 25 close to the end face 26 of
the bell. The pins are of sufficient diameter and hard
ness to resist shearing by the wires as, the wires are ini
tially tensioned in the mould before the concrete is cast.
For a quarter-inch wire a pin having a diameter of ?ve
eighths of an inch has proven satisfactory.
the bell or socket end of ‘the pipe of FIG. 1;
FIG. 3. is a longitudinal section through the spigot end
' of the pipe of FIG.’ 1;
FIG._ 4 is a transverse section on line 4-4 of FIG. 5;‘
FIG. 5 is a, plan of a pipe end with the concrete broken
away to expose and thereby illustrate an anchoring ar
rangement for longitudinal wires;
FIG. 6 is a plan of the. same nature as that of FIG. 5
but showing the coils on the wires encircling a hoop or
ring;
10
In pipes designed to contain very high working pres
sures, steel hoops or rings 27 and 28v are located in abut
ting relationship to the coils at either end of the core
in order to increase the area of stress distribution and
reduce’ the stress concentration on the concrete, but these
FIG. 7 is a longitudinal sectional, view of a portion
of the spigot of a pipe in which the anchorage includes 15 rings may be omitted in pipes designed to contain lower
working pressures.
only a pin or a single ring;
A form of anchorage including only a coil 29 and a
FIGS. 8 and 9 are views at right angles to one another
pin 30 is shown in FIG. 7.
of a modi?cation by which a wire is tied to a single pin;
As more clearly shown in FIGS. 4 and 5, two of the
FIGS. 10 and 11 show another modi?cation by which
‘longitudinally extending wires 11 are engaged 'with a
a wire is tied to a single pin in another form;
FIGS. 12 and 13 show still another modi?cation in
which a wire is provided with two coils in engagement
with a single pin; 5
FIG. 14 diagrammatically represents a portion of a
V mould with part of its outside wall broken away;
single pin 22 at an end of the core. While the wires
of each pair of wires are curled around a common pin
in a manner to provide coils of opposite pitch or hand,
the two coils may be formed with the same pitch. The
25 pins are preferably of such length as not to interfere with
cludes a' main conduit portion 10 consisting of a hollow
one another when the respective pairs of wires are
stretched as they are stressed’ in tension, but each pin is
su?‘iciently long to effect uniform compression of the con
monolithic concrete core which extends for the full length
crete.
’ FIG. 15 is a detail of an end of a mould.
The pipe illustrated in the accompanying drawing in
of the pipe and, includes a plurality of prestressed wires 30 As an alternative arrangement, the several longitudinal
wires 32 (FIG. 6) may be coiled around a single hoop or
11 embedded therein in bonded relationship to the con
ring 33 extending entirely around the core. If the an
crete.
The core 10 is subjected to circumferential compres
chorages at both ends of a mould are formed in this
manner all of the wires should be stretched and tensioned
sion by a highly stressed wire 12 of high tensile steel
which is wound around the core and secured in place. 35 at one time, but they can be separately tensioned when
the pulled ends of the wires are individually curled around
In a finished pipe the wire winding is usually protected
different pin members.
by a self-hardening covering 13 of suitable thickness,
such as cement mortar, but the covering is not essential
to, the use of the present invention.
The ends of the core are ?nished to provide appro
In FIGS. 8 and 9 there is shown a form of anchorage
for a single wire. The anchorage includes a generally
L-shaped pin 34 having one leg 35 extending alongside
priate jointing surfaces for making joints with other pipes.
One end of the pipe illustrated in FIG. 1 is in the form
of a portion of a wire 36 which runs longitudinally of
a pipe and a leg 37 which is engaged by a coil 38 in the
of a socket or ball 14, which is complementary to the
wire.
The location and function of the leg 37 in a pipe
corresponds with that of a pin 22, or 24 as shown in
spigot 15 at the other end, and it is to be understood
that the invention is applicable to pipes, having both ends 45 FIGS. 2 and 3. The leg 35 is secured to the wire by a
lashing 39. The lashing prevents tipping or rotation of
?nished as spigots or as bells,‘ depending on the form ofv
the coil when tension is applied to the opposite ends of
the pipe desired. A steel hoop 16 (FIG. 2) engages the
the wire.
Wires 11 at a section from which they run into the en
The modi?cation illustrated in, FIGS. 10 and 11 in
larged end or<bell of the pipe. As is well understood,
the-bell 14 is provided with an inner cylindrical surface 50 cludes a generally U-shaped pin 40 with the legs of the
pin extending) across a wire 41'. The wire passes through
17 which surrounds a spigot of another pipe in making
an opening 42 in the leg 43 and the leg 44 is‘engaged by
a joint and engages a gasket by which the joint is sealed.
a coil 45.
The spigot end has a'relatively nan'ow circular surface
In the anchorage illustrated in FIGS. 12 and 13, a
18 (FIG. 3) between the end face 19 and a circumfer
ential groove 20. The groove is, formed in part by the 55 wire 46 is curled around two legs 47 and 48 of a U-shaped
member 49. The wire forms a coil 50 around the leg
concrete of the core and in part by the covering 13, al-.,
47 and a coil 51 around the leg 48.
V
though thegroove may be formed entirely.v in the concrete
The coils are placedv in a wire before the wire is ten
of the core in other forms of pipes without detracting
sioned by curling the wire around the pin members that
from. the effectiveness, of the present invention. In the
are to be used or around pins of'the ‘same diameter at
pipe illustrated. in the drawing, the jointing surfaces on
the spigot include the circular surface 18, the surfaces
de?ning the groove 20 and a cylindrical surface 21 on
the protective coating, and the wire winding 12 extends
well into the spigot of the pipe.
The longitudinal wires 11 are distributed at equal inter
vals in tubular arrangement around the core in such
number and under such stress as to exert the amount of
such a distance apart as to locate the coils close to the
ends of the core when the wires have been tensioned in
the amount required. The wires. with the pins extending
through the coils are placed in a mould.
65
A manner in which a pair of wires may be mounted
in a mould is exempli?ed in FIG. 14. The mould there
shown includes a mould form 53 and removable mould
ends 54 and 5,5 which abut the ends of the form and are
longitudinal compression required on the concrete of the
removable therefrom. At one end of the mould the wires
Wires
of
high
tensile
steel
are
used.
core.
70 56 pass through openings in the mould end 55 and are
Referring to FIG. 3, one end of each wire 11 extends
secured in place by clamping wedges 57 in such a man
into the spigot portion of the core and is curled around,
ner as to locate the coils 58 and the pin 59 close to the
a steel pin 22. disposed transversely of the wire. The
transverse moulding surface 60. The. other ends 61 of
pins for the several wires are preferably made from round
the wires extend- through openings in the mould end 54
stock. The curled end of the wire forms a coil 23 which 75 and are held in place by clampingwedges 62 after the
3,034,536
5
required amount of tension has been applied thereto by
conduit terminating adjacent the free end of the spigot,
a tensioning device 63. The tension in the wires e?ects
a very tight engagement with the pins 59 and 64 at either
end of the mould.
a tensioned wrapping around said conduit subjecting said
conduit to circumferential compression, said wrapping
ending short of said gasket-bearing surfaces, each of said
A section through the spigot end of a suitable pipe
anchors on the ends of said wires adjacent the free end
of the spigot comprising a pin member and a portion of
one of said pretensioned Wires engaged with said pin
member, said portion of said wire tensioned around said
pin member in a tight coil disposed on an axis crosswise
of said Wire and ended with a short straight length of the
mould is illustrated in FIG. 15. The mould includes a
split cylindrical shell 67 and a removable mould end ring
65 which axially abuts the mould shell at the circular
surface 68. While a stationary mould may be used, I
prefer to mould a hollow concrete core in a mould
adapted for use in a roller suspension machine or in a
centrifugal machine.
When rings such as the rings 16, 27 and 28 (FIGS. 2
and 3) are to be employed they are placed around the
wires before the wires are tensioned.
wire beyond the coil, said short length of wire extending
towards the free end of said spigot in a direction sub
stantimiy parallel to the length of the wire which con
tinues from the other side of the coil, each coil and pin
These rings are 15 member being completely encased by the concrete of
held in their respective positions during the moulding of
said conduit in bonding relationship therewith, whereby
the concrete by any suitable means such as light wire
the tension of each of said pretensioned wires is carried
into a coil and the coil together with the pin member dis
tribute the pull of the Wire onto the immediate concrete
lashings.
After the wires have been tensioned and secured, the
mould is rotated and ?lled with a rich concrete mix. The 20 of said spigot.
2. A prestressed pipe according to claim 1 wherein
concrete becomes bonded to the wires throughout their
said coils of only two of said longitudinal wires engage
a single one of said pin members.
3. A prestressed pipe according to claim 1 wherein
vices and the mould are removed and the reaction to the
tensioned wires which was previously provided by the 25 said pin member is generally L-shaped and the coiled
portion of a longitudinal wire is in engagement with one
mould is transferred to the concrete. The ends of the
leg of said member, and holding means is provided to
wires extending from the end faces of the concrete core
hold the other leg of said pin member substantially par
are severed close to the end faces of the core.
lengths as the hardening process develops. After the
concrete has thoroughly hardened, the wire-clamping de
allel to the wire.
As a consequence of the invention, savings in cost are
4. A prestressed pipe according to claim 1 wherein
effected because a less quantity of steel is required to be 30
said pin member is generally U-shaped and said coiled
used in the longitudinal wires than is required for a pipe
portion of a longitudinal wire is in engagement with one
of like design and of the same strength but in which ‘the
leg of the member and the wire is provided with another
ends of the wires are less securely anchored.
coiled portion in engagement with the other leg of said
A higher pressure classi?cation is produced for pipes
having any given core-thickness and size and number of 35 member.
5. A prestrcssed pipe according to claim 1, wherein
longitudinal wires as a result of the elimination of dam
said pin member is generally U-shaped and said coiled
aging cracks in the concrete.
portion of a longitudinal Wire is in engagement with one
The foregoing is illustrative of the invention and it is
leg of said member and said Wire extends through an
self-evident that various changes may be made in the
details of construction without departing from the spirit 40 opening in the other leg of said member.
and scope of the invention as set forth in the appended
claims.
What is claimed is:
1. In a prestressed pipe, a monolithic concrete conduit
having a spigot at one end and gasket-bearing surfaces 45
formed from the concrete of said spigot, a plurality of
longitudinally disposed pretensioned high tensile steel
wires embedded in the conduit at intervals around said
conduit and extending substantially the entire length of
the conduit, each wire uniformly stretched between an 50
anchor adjacent each end of the wire, the ends of said
longitudinally disposed wires at the spigot end of the
References Cited in the ?le of this patent
UNITED STATES PATENTS
468,269
979,285
1,900,145
2,236,167
2,662,555
2,686,951
Stempel ______________ __ Feb. 2,
Gilligan _____________ __ Dec. 20,
Whiting ______________ __ Mar. 7,
Miller et al ___________ __ Mar. 25,
Hirsh ________________ __ Dec. 15,
Seaman _____________ __ Aug. 24,
1892
1910
1933
1941
1953
1954
FOREIGN PATENTS
707,447
Great Britain _________ __ Apr. 21, 1954
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