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Патент USA US3045315

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July 24, 1962
A. R. ANDERSON
3,045,305
CONCRETE PRESTRESSING CABLE GRIP
Filed Jan. 28, 1954
2 Sheets-Sheet 1
INVENTO
Q
.
ARTHUR R. ANDERS
July 24, 1962
3,045,305
A. R. ANDERSON
CONCRETE PRESTRESSING CABLE GRIP
2 Sheets-Sheet 2
Filed Jan. 28, 1954
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INVENTOR.
ARTHUR A’. ,4/v0ms0/v
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ZITTORNEYS
ice
United ‘States
3,045,305
Patented July 24, 1962
1
2
3,045,305
helically around the core Wire. In this case, when ten
sion is applied the‘helical pattern of the strands is im
.
CONCRETE PRESTRESSING CABLE GRW
pressed into the initially smooth surface of the grooves
in the member made of aluminum or other relatively
soft metal. However, the invention is useful also in grip
ping solid wires having any surface deformations which
will bite into the metal of the grooves. Such deforma
1 Claim. (Cl. 24-4216) ->
tions may be specially formed, or may comprise slight
The invention relates to apparatus'for prestressing con
bends or irregularities existing in the wire as manufac
crete, and more particularly to an improved form of 10 tured. Throughout the speci?cation and claim, I shall
grip for anchoring a group of wires under high tension
employ the term “wire” in its generic sense as including
in the casting of the prestressed concrete.
both a single wire and a wire made up of any number
‘One of the most troublesome problems ‘encountered in p
of single wire strands twisted together.
the engineering of prestressed concrete structures and
Description '
their fabrication, has been to provide a satisfactory way 15
Referring to the drawings, I shall now describe the best
of anchoring the high-tensile steel wires during casting
mode contemplated by me of carrying out my invention.
of the concrete. Under the extremely high tensions which
FIG. 1 is a general arrangement view illustrating my
must be imposed if the tensile strength of the wire is to
improved wire grip in use at one end of a prestressing
be utilized to full advantage, the wires frequently slip
or break, whereas lower tensions can only have the re 20 concrete testing ?oor, and a fragmentary plan view of
the prestressing apparatus, showing one end of the mold
sult of lowering the strength characteristics of the pre
stressed structures produced. Tests made with grips con
(in horizontal section), the distributor plate at that end,
and the hydraulic jack for tensioning the wires anchored
structed in accordance with this invention have demon
in the grip.
strated that ‘wires having a tensile strength of 265,000
FIG. 2 is a central longitudinal sectional view of my
p.s.i. (pounds per square inch) can be anchored in groups 25
preferred form of grip, taken as indicated at 2—2 in FIG.
of eight and pulled up to an average tension of as high
4, with the wires in place, before tensioning.
as 250,000 p.s.i. before the ?rst wire breaks.
FIG. 3 is a view similar to FIG. 2, after tensioning.
Summary
Arthur R. Anderson, Tacoma, Wash, assignor, by mesne
assignments, to Concrete Technology Corporation,
Tacoma, Wash, a corporation of Washington
Filed Jan. 28, 1954, ’Ser. No. 406,671
FIG. 4 is a transverse sectional view of the same grip,
According to my invention, there is provided a grip for 30 taken as indicated at 4-4 in FIG. 2.
anchoring a group of wires under high tension in the cast
FIG. 5 is an enlarged detail sectional view taken in the
ing of prestressed concrete, comprising a metal socket
same plane as FIG. 4, but illustrating the condition which
member having tapered inner Walls and a metal plug
exists after tensioning.
‘ .
member received within the socket member and having
FIG. 6 is an elevational view of the plug member of
tapered walls complementary to the tapered inner walls 35 the same grip, as it appears before use.
of the socket member, the tapered walls of one of the
FIG. 7 is a similar view of the plug, as it appears after
members having longitudinal grooves to receive the wires
to be tensioned, the metal of the grooved member in the
FIG. 8 is a central longitudinal sectional view of a plug
region of the grooves being of a hardness substantially
of modi?ed construction.
.
use.
less than that of the surface of the wires so that as the 40
wires are tensioned, portions of the surfaces of the wires
are pressed into the metal of the grooves, deforming the
.
FIG. 9 is a sectional view similar to FIG. 2, illustrat
ing a further modi?cation taken as shown at 9--9 in FIG.
10.
‘
FIG. 10 is a transverse sectional view, taken as shown
at 10-—10 in FIG. 9.
hardness at least equal to that of the surface of the wires,
FIG. 11 is a detail perspective view of a solid wire of
so that the wires slide over such hard tapered walls as 45
latter. The tapered walls of the other/.member are of a
the wires and grooved member are drawn into tight
a form adapted for anchoring by the use of my improved
wedging engagement with said other member.
grip.
In FIG. 1, I have shown one end of a mold 12 for
Thus in one form of my invention, I provide a wire
grip comprising a frusto-conical socket member and a
casting a prestressed concrete beam. A group of high
wires 13 extends through the mold length
beam, the position of the respective wires
being determined by distributor plates 14 at
complementary plug member received therein; the plug 50 tensile steel
wise of the
having grooves to receive the Wires to be tensioned, this
in the mold
grooved member being made of aluminum, and the other
the ends of
member being made of hardened steel. Upon tensioning,
the mold, these plates ‘being perforated to
receive the wires. From the distributor plate at one end
the wires “bite” into the aluminum grooves as they slide
over the hardened steel to wedge the wires tightly between 55 of the mold, the group of wires '13 are gathered into the
grip 15 by which they are to be anchored. Grip 15
the two members and lock them securely in the grooves.
‘bears against a cross-head plate 16 in which there is an
What happens is that the wires die-form their own pat
opening to permit the group‘ of wires to pass through.
tern into the relatively soft aluminum, keying them to '
For prestressing the wires, hydraulic jacks, one of which
the aluminum member. This action takes place as the
hardened steel member moves relatively to both the wires 60 is shown at 17, act against a heavy reinforced concrete
and the aluminum member, camming the wires into the
aluminum to produce the aforesaid die-forming opera
abutment 18, to apply tension through cross-head 19 and
rods 20 connecting cross-head 19 with cross-head 16.
Rods 20 extend through holes in the concrete abut
tion. Note that there is substantially no deformation of
ment 18.
the wire surfaces themselves and therefore no substan
tial tendency to weaken the wires at the grip, which is a 65 It will be understood that similar anchoring means are
common fault in certain types of grip used or proposed
provided at the other end of the mold (not shown) in
heretofore.
,
cluding another wire grip 15 and a cross-head or other
My invention is particularly advantageous as applied
device for holding it in place during the vapplication and
to the stressing of stranded wire, i.e. wire made up of a
maintenance of tension by the hydraulic jack 17, de
group of smaller wires, or strands twisted together as in 70 scribed. It'will also be understood that, depending upon
a wire “rope”, as where a center wire, or core, is sur
rounded by, say, six other wires of the same size twisted
the nature and design of the prestressed structure being
manufactured, there may be several groups of wires 13
3,045,305
3
4
arranged, for example, one above the other in engage
ment with cross-head plate 16, or attached to separate
plug need not be formed entirely of the relatively soft
tensioning means, as may be desired.
steel core 26 of the modi?ed plug construction shown in
FIG. 8.
.In FIGS. 9 and 10 I have illustrated a modi?ed ‘form
of grip in which the socket 27 and plug 28 are of rec
tangular form instead of round. As in the embodiment
Referring to FIGS. 2 and 4, the grip 15 comprises a
metal socket 21 having tapered inner wall portions 22
of frusto-conical form, and a metal plug 23 received
metal, but could if desired have a hard core such as the
within socket 21 and having tapered wall portions 24
previously described, the socket has tapered inner wall
(FIG. 6) complementary to the tapered inner wall por
portions 29 and the plug has tapered inner wall por
tions of the socket, the tapered wall portions of the
plug having longitudinal grooves 25 to receive the wires 10 tions 30 complementary to the tapered inner wall por
tions of the socket, the plug also having longitudinal
13 to be tensioned. The metal of the plug 23 in the re
gion of grooves 25 is of a hardness substantially less than
that of the surface of the vwires 13 so that as the wires
are tensioned, portions of the surfaces of the wires are
pressed into the metal of the plug, deforming the latter.
Further, the tapered inner wall portions 22 of the socket
grooves 31 to receive the wires 13 to be tensioned.
The
same relative hardness conditions are observed here as
in the previous embodiment. In all cases I have found
1 it helpful to have the socket entrance ?ared and rounded
(32, FIG. 2; 33, vFIG. 9). This is a point of high stress
out substantial deformation of the socket, as portions of
the surfaces of the wires are pressed into the metal of
concentration, and a carefully contoured curvature in
the socket entrance is important to relieve the stress
concentration.
The plugs may be grooved to accommodate two, three,
four, six or eight Wires, solid or stranded. In producing
the plug, deforming the latter while the socket is drawn
into tight wcdging engagement with the wires and plug.
large beams, I have used thirty-two wires with four grips
at each end of the mold, eight wires per grip. If desired,
has a hardness at least equal to that of the surface of
the wires, so that when tension is applied, the hard inner
wall portions 22 of the socket slides over the wires with
the grips could be designed to carry a greater number of
Thus, as the socket 21 slides relatively to the wires 13,
the pattern of the strands of the wires is impressed into ' wires, this being largely a matter of choice. While I have
the metal of plug 23 to lock the plug and wires against
illustrated in the drawing the use of multi-wire strands
relative longitudinal movement. Movement of the socket
(the strands shown having seven wires), my grip is useful
21 relatively to the wires 13 and plug 23 is indicated
also in anchoring solid wires having surface deformations
schematically in FIGS. 2 and 3. FIG. 2 shows the rela
which will bite into the metal of the grooves. Such de
tive positions of the members before tensioning, and FIG. 30 formations may be specially formed, such as the lugs 34
3 the relative positions after tensioning. The extent of
of wire 35 shown in FIG. 11, or may comprise slight
relative movement is indicated by comparing these two
bends or irregularities existing in the wires manufactured.
views and would be equal to a minus b. However, the
The terms and expressions which I have employed are
drawings have not been prepared to scale, and therefore
used in a descriptive and not a limiting sense, and I have
are not intended to indicate the extent of this movement 35 no intention of excluding such equivalents of the inven
quantitatively. In practice, this will vary and will de
tion described, or of portions thereof, as fall within the
pend to some extent upon the form of wires 13 and the
purview of the claim.
difference in relative hardness between the wires and the
I claim:
plug.
A grip for anchoring a group of wires under tension
FIGS. 2 and 4 represent the condition before tension
in stressed concrete work without requiring the use of
‘has been applied to the wires, when the grooves 25 are
auxiliary clamping devices or procedures to effect clamp
smooth. FIGS. 3 and 5 represent the condition after
ing, comprising a metal socket having tapered inner wall
tensioning, when the pattern of the strands of the wires
portions and a metal plug received within said socket
has been impressed into the metal of the plug to lock the
having tapered wall portions complementary to the
plug and wires against relative longitudinal movement.
The effect of the action described will further be under
stood by a comparison of FIGS. 6 and 7, FIG. 6 show
ing the plug before use, and FIG. 7 the same plug after
use.
Note that in FIG. 6 the grooves 25 are smooth
whereas in FIG. 7 they are impressed with the pattern
of the strands of wires 13.
tapered inner wall portions of the socket, said tapered
wall portions of the plug having longitudinal grooves to
receive the wires to be tensioned, the metal of said plug
in the region of said grooves being of a hardness substan~
tially less than that of the surface of the wires and the
tapered inner wall portions of the socket being smooth
and free of grooving at points opposite the longitudinal
In practice LI have generally made the socket 21 of
grooves of the plug and being of a hardness at least equal
steel, case hardened, and the plug 23 of an aluminum
to that of the surface of the wires.
alloy having a Brinell hardness of not substantially more
than about 70 (50.0 kg., 10 mm. ball), and preferably
References Cited in the ?le of this patent
having a Brinell hardness of between about 45 and 70.
UNITED STATES PATENTS
The tapered inner walls 22 of the socket may be case
1,297,187
Lamb _______________ __ Mar. 11, 1919
hardened to a Brinell hardness of between about 650 and
1,642,628
Philbrick ____________ __ Sept. 13, 1927
700 (3000 kg., 10 mm. ball). The tests which I have
Briggs _______________ __ Sept. 20, 1927
performed reveal that good results are obtainable with 60 1,643,110
plugs made of zinc and of copper, as well as of alumi
num. The essential point appears to be the use of a
1,706,805
1,758,312
De Right ____________ __ May 13, 1930
material which is deformable by the wires to ‘be tensioned
under normal wedging conditions produced by the ten
1,886,247
2,017,887
2,042,090
Cole _________________ __ Nov. 1, 1932
Blackburn ___________ __ Oct. 22, 1935
Cummins ____________ __ May 26, 1936
2,294,398
2,341,922
Ferguson _____________ __ Sept. 1, 1942
King ________________ __ Feb. 15, 1944
sioning itself.
7
The metal of the plug in the region of the grooves
should be relatively soft as compared with the hardness
of the tapered inner wall portions of the socket. The
2,686,963
Mof?tt ______________ __ Mar. 26, 1929
‘
Freyssinet ____________ __ Aug. 24, 1954
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