U.S. patent application number 10/082898 was filed with the patent office on 2002-06-27 for method, member, and tendon for constructing an anchoring device.
This patent application is currently assigned to VSL International AG. Invention is credited to Belbeoc'h, Herve.
Application Number | 20020078643 10/082898 |
Document ID | / |
Family ID | 8235928 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020078643 |
Kind Code |
A1 |
Belbeoc'h, Herve |
June 27, 2002 |
Method, member, and tendon for constructing an anchoring device
Abstract
An anchoring device not accessible from one of its sides can be
produced by making a cavity (11) of a particular shape and using
tendons (4), each of which has an end portion (41) of adapted
shape. The cavity may be made in different ways, especially by
concreting an anchor member (1) having an opening (12) at one end,
the anchor member and the cavity it contains each having an adapted
shape. After the anchor member has been concreted and the tendons
inserted in the cavity, the cavity is filled with an embedding
mortar in order to block the ends of the tendons therein.
Inventors: |
Belbeoc'h, Herve;
(Versailles, FR) |
Correspondence
Address: |
HAHN LOESER & PARKS, LLP
TWIN OAKS ESTATE
1225 W. MARKET STREET
AKRON
OH
44313
US
|
Assignee: |
VSL International AG
|
Family ID: |
8235928 |
Appl. No.: |
10/082898 |
Filed: |
February 26, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10082898 |
Feb 26, 2002 |
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09799283 |
Mar 5, 2001 |
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09799283 |
Mar 5, 2001 |
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09244938 |
Feb 4, 1999 |
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6216403 |
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Current U.S.
Class: |
52/223.13 ;
52/223.14; 52/295 |
Current CPC
Class: |
E04C 5/127 20130101;
E04C 5/125 20130101; E04G 21/12 20130101; E04C 5/12 20130101; E02D
5/58 20130101 |
Class at
Publication: |
52/223.13 ;
52/223.14; 52/295 |
International
Class: |
E04C 005/08; E04C
001/40 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 9, 1998 |
EP |
98810096.2 |
Claims
What is claimed is:
1. An anchoring device in a structure, the device having an opening
accessible from a single side of the structure, comprising: an
anchoring member secured in the structure, the anchor member
comprising a well member, bounding a cavity of a substantially
oblong, tapering shape with two ends, the first end comprising the
opening, a cross-sectional area of the first end being smaller than
a cross-sectional area of another portion of the anchor member, and
a bottom wall at the second end; and a plurality of tendons, each
said tendon comprising a traction rod having a first end and an
intermediate portion with a first cross-sectional area and a second
having an end portion with a second cross-sectional area larger
than said first cross-sectional area, N such tendons inserted into
the anchor member with the second ends in the cavity and the first
ends and intermediate portions extending outwardly therefrom,
wherein the first and second cross-sectional areas of the traction
rods and the cross-sectional area of the opening are related such
that when N traction rods are in place, the N traction rods cannot
be arranged at the opening to allow the second cross-sectional area
of one additional traction rod to pass through the opening
2. The anchoring device of claim 1, wherein the cavity has at least
one cross-sectional area that is greater than the sum of the
maximum cross-sectional areas of the N second ends.
3. The anchoring device of claim 1, wherein the cross-sectional
area of the opening of the cavity is less than the sum of the
cross-sectional areas of the second ends of the N tendons inserted
in said cavity.
Description
[0001] This application is a division of U.S. Ser. No. 09/799,283,
filed Mar. 5, 2001, and currently pending, which is in turn a
division of U.S. Ser. No. 09/244,938, filed Feb. 4, 1999, now U.S.
Pat. No. 6,216,403 B1, issued Apr. 17, 2001, which in turn claims
priority upon European patent application No. 98810096.2, which was
filed on Feb. 9, 1998. Each of these applications is incorporated
by reference as if fully recited herein.
[0002] This invention relates to anchoring apparatus used in civil
engineering, especially so-called blind anchoring devices
accessible from only one side, and more particularly to a method of
constructing such a device of the type having more than one tendon,
as well as to an anchor member for constructing such a device. The
invention further relates to a tendon of the type having one end
intended to be inserted into an anchoring cavity of such an
anchoring device.
BACKGROUND OF THE ART
[0003] For certain anchoring devices having an anchor head with a
tendon, prestressed or not, it is not possible to gain access to
the anchoring device from the rear. This situation is encountered
particularly in the case of a buried anchoring device where access
is possible only from the surface of the ground, or when
fluid-tightness or anticorrosion protection must be especially
meticulous, so that the rear side of the device must be closed.
This requirement prevents the use of a conventional anchor plate
where the attachment of the tendon to the plate, e.g., with the aid
of anchoring cones, calls for the development of new types of
anchoring.
[0004] U.S. Pat. No. 5,056,284 shows an anchoring device accessible
from only one side, the drawback of the device described there
being that each tendon, hence the tube in which they are inserted,
is held solely by longitudinal adhesion, thus greatly limiting the
tractive stress which such an anchoring device can withstand and
leading to a very great anchoring length to obtain a sufficient
adhesion surface.
[0005] Likewise, U.S. Pat. No. 4,043,133 provides a tendon
sheathing held solely by longitudinal adhesion to the surrounding
earth. The tendons extend from the bottom end of the sheathing and
are all attached to an anchor plate; the way in which this plate is
inserted in the cavity, and the way in which the tendons are
fastened to the plate, are not described. In case this embodiment
can be produced, the transmission of the anchor force to the ends
of the tendons in the surrounding earth through the injected
sheathing is produced solely by longitudinal adhesion, without
benefiting from the wedge effect as described below in connection
with the present invention.
SUMMARY OF THE INVENTION
[0006] It is an object of this invention to provide a method of
constructing an anchoring device accessible from only one side
which does not encounter the mentioned drawbacks of prior art
anchoring devices, i.e., an anchoring device wherein the tendons
are held so that the tractive stress on each of them at the level
of the anchoring device is taken over by adhesion, this adhesion
being appreciably favored by the confinement induced by the overall
shape of the anchoring device, and by longitudinal mechanical
blocking of the ends of the tendons due to the particular shape of
these ends and their arrangement in a cavity of substantially
tapering shape.
[0007] A further object of the invention is to provide an anchor
member of a particular shape which, associated with a plurality of
tendons also having a particular shape, makes it possible to
construct such an anchoring device.
[0008] Still another object of the invention is to enable the
construction of such an anchoring device without the direct use of
an anchor member.
[0009] To this end, the method of constructing an anchoring device
according to the present invention, of the type initially
mentioned, includes the steps of making a cavity in a surrounding
structure, this cavity having a substantially oblong, tapering
shape and having two ends, the area of the cross-section of the end
disposed on the accessible side of the anchoring device being less
than the area of the cross-section of another portion of the
cavity, the cavity comprising an opening on the accessible side of
the anchoring device; successively inserting through the opening of
one end of each of the tendons, each of these tendons being made up
of a traction rod having a first cross-sectional area and an end
portion having a second cross-sectional area larger than the first
cross-sectional area; and filling the cavity with an embedding
material.
[0010] The anchor member according to the present invention is of a
substantially oblong, tapering shape and has two ends, the area of
the cross-section of a first end being less than the area of the
cross-section of another portion of the anchor member, the anchor
member being made up substantially of a wall bounding a cavity of a
shape substantially similar to that of the anchor member and
provided with an opening having a first cross-sectional area at the
first end of the anchor member and comprising a bottom wall at the
second end, another cross-section of the cavity having another area
larger than the first area.
[0011] The tendon according to the present invention, of the type
initially mentioned, is made up of a traction rod provided at the
end thereof intended to be inserted in the cavity with an end
portion, the area of the cross-section of which is larger than the
area of the cross-section of the traction rod.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Preferred embodiments of the invention will now be described
in detail with reference to the accompanying drawings, in
which:
[0013] FIG. 1 is a sectional view of a preferred embodiment of an
anchor member according to the invention,
[0014] FIG. 2 is a series of sectional views (A-H, L) representing
steps in the method of constructing an anchoring device according
to the invention,
[0015] FIG. 3A is a diagrammatic elevation of part of a tendon in a
first embodiment of the invention,
[0016] FIG. 3B is a diagrammatic elevation of part of a tendon in a
second embodiment of the invention,
[0017] FIG. 3C is a diagrammatic elevation of part of a tendon in a
third embodiment of the invention, and
[0018] FIG. 3D is a diagrammatic view, partially in section, of
part of a tendon in a fourth embodiment of the invention.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0019] For carrying out the inventive method, an anchoring cavity
of a certain shape must first be obtained. The shape of this
anchoring cavity is substantially oblong and tapering, with a first
open end on the accessible side of the anchoring device and a
second closed end on the non-accessible side of the anchoring
device. Moreover, the cross-section of the first end of the
anchoring device must be smaller than another cross-section of the
cavity, whether this section corresponds to that of the second end
or to an intermediate section of the cavity.
[0020] Such a cavity may be obtained by several means or devices. A
first means consists in using an anchor member comprising a
prefabricated interior cavity having the required shape of the
anchoring cavity. A preferred embodiment of such an anchor member
is illustrated in FIG. 1. The anchor member 1 consists essentially
of a preferably thin wall 10 bounding an interior cavity 11. A
first end of the anchor member 1, i.e., the top end of the member
as viewed in the drawing, includes an opening 12, as well as means
13 for fastening a tubular sheath for protecting tendons, the use
of which will be described below. The other end of the anchor
member 1 is closed by a bottom wall 14. The outside shape of the
anchor member 1, hence of the interior cavity 11, is substantially
tapering, e.g., frustoconical or frustopyramidal, with the smallest
cross-section close to the opening 12 and the largest cross-section
close to the bottom wall 14. An inlet 15 is disposed close to the
bottom wall 14, an injection tube 16 being attached or attachable
to inlet 15. Similarly, an outlet 17 is disposed close to the
opening 12, an exhaust tube 18 being attached or attachable to the
outlet 17. The use of elements 15-18 will be described below.
[0021] The tapering, frustoconical, or frustopyramidal outside
surface of the anchor member 1 includes one or more anchor rings 19
disposed at the periphery of this surface, the purpose of which is
to improve the transmission and distribution of the anchoring force
to the surrounding structure. The embodiment shown in the drawing
includes two such rings 19. The anchor member 1 may be made of
synthetic material, of metal, or of concrete, its size depending
essentially upon the extent of the anchoring device being
considered.
[0022] FIG. 2A shows the first step in the inventive method of
constructing an anchoring device using such an anchor member. While
the surrounding concrete structure has not yet been made, an anchor
member 1 is placed at the exact location where the anchoring device
is to be constructed, the opening 12 being aimed in the direction
of the future tendons. The anchor member 1 is held in place by
temporary scaffolding or, preferably, by iron bars 20 of the
concrete reinforcement. Preferably, although this is not
indispensable to the invention, one or more circular iron bars 21,
forming one or more hoops, are disposed about the anchor member 1
in order to improve the cohesion of the concrete at that
location.
[0023] In FIG. 28, it is seen that the concrete structure 2
intended to support the anchoring device has been conventionally
poured about the anchor member 1. The anchor member 1 is thus
completely surrounded and held in the concrete structure 2 except
for its first end provided with the opening 12 which is flush with
the top surface of the concrete structure 2 or, as shown here,
projects slightly above that surface, and except for the ends of
the injection tube 16 and exhaust tube 18, which remain accessible
outside the concrete structure 2.
[0024] It will therefore be noted that in this second step of the
method, a 20 cavity 11 of a certain shape has been produced within
a concrete structure 2. As described until now, the cavity 11 has
been produced using an anchor member 1 provided with a
prefabricated cavity. A like cavity 11 in a concrete structure 2
may also be produced in other ways, e.g., by fabricating it in
situ. For instance, provision may be made for a form capable of
being dismantled, made of wood or some other material, having an
outside shape corresponding to the desired shape of the cavity 11,
and placed at the required location, about which form the concrete
structure 2 is subsequently poured. As soon as the concrete is
hardened, the form is dismantled through the opening 12 and
extracted from the cavity 11 through that same opening. In a rather
similar manner, a flexible, inflatable component may be used, which
after inflation has the desired shape of the cavity 11 and is
placed at the required location. After the concrete structure 2 has
been poured, the inflatable component is deflated, leaving a cavity
11 of the required shape in the structure 2. Another procedure
would be to produce the cavity 11 by drilling out such a cavity of
the required shape in an existing structure 2. This drilling
procedure would be reserved for anchoring directly in the earth or
else for the installation of a new anchoring device on an existing
structure 2. The cavity 11, produced in anyone of the ways
described, has two important dimensions, a passage area of the
opening 12 designated S12 and a maximum cross-sectional area
designated S11 (see FIG. 1).
[0025] During the third step of the method, shown in FIG. 2C, the
structural element 3 to be prestressed is placed or concreted, in a
manner 10 known per se, above the concrete structure 2, the
structural element 3 preferably comprising a conduit or a sheathing
tube 30, one end of which is situated opposite the opening 12 to be
attached to the fastening means 13 adjoining the opening 12. The
cross-section of the sheathing tube 30 or of the conduit contrived
in the structural element 3 for the tendons corresponds
substantially to the cross-section of the opening 12 of the cavity
11. The tube 30 or corresponding conduit includes at least one
injection port 31 connected to an injection tube 32, at least one
of the ports 31 preferably being disposed near the end of the tube
30 close to the opening 12, as well as at least one outlet
connected to an exhaust tube, at least one of the outlets being
disposed near 20 the other end (not visible in the drawing) of the
tube 30, hence near the structural element 3.
[0026] The fourth step, shown in FIG. 2D, consists in inserting the
tendons. Here reference is made to FIGS. 3A-3D showing, by way of
non-limiting examples, four designs of such a tendon 4. This tendon
is substantially made up of a traction rod 40 and an end portion
41. The end portion 41 on the rod 40 is so designed that it has a
cross-sectional area S41 larger than the cross-sectional area S40
of the traction rod 40, for reasons to be explained below. The
other end of the rod 40 has no end portion of this kind and is made
up for a normal anchoring device as known in the art.
[0027] The traction rod 40 may be of any known type, consisting
either of an undivided strand or of a plurality of strands
assembled helically in order to constitute a traction cable. The
undivided strand or the strands assembled into the traction rod 40
may be of steel, preferably of a steel having high resistance to
traction, or of synthetic material, e.g., carbon-fiber- or
Kevlar-based.
[0028] The end portion 41 may be an end piece 41 of metal or
synthetic material which is firmly fixed to the end of the traction
rod 40. The choice of material of which piece 41 is made, as well
as the way it is fixed to the traction rod 40, depend essentially
upon the material and the manner in which the traction rod 40 is
made. The end piece 41 essentially includes a central body 42
bounded by an upper portion 43 and a lower portion 44. The body 42
may have the shape of a right cylinder, with a circular
cross-section as in FIG. 3A or a polygonal cross-section, or else a
frustoconical or frustopyramidal tapering shape, with a circular
cross-section or a polygonal one as shown in FIG. 38. In the case
of a tapering shape, the part with the smaller cross-section is
that adjacent to the upper portion 43. The two portions 43 and 44
are preferably domed or formed of inclined planes so as to
facilitate the sliding of an end portion being installed on another
end portion already installed, as will be seen below.
[0029] In another design, the end portion 41 may be formed by
deformation or machining directly on the end of the traction rod
40. FIGS. 3C and 3D show examples of end portions of this type. In
FIG. 3C, the traction rod 40 is made up of an undivided strand, and
the end portion 41 is obtained by deformation, e.g., by forging,
dieing, or stamping, of the end of the traction rod 40. FIG. 3D
shows an example of an end portion 41 on a traction rod 40 made up
of assembled strands. In this example, the end of each strand has
been displaced from its normal position, it being possible to
provide a ring or a binding just before this displacement in order
to prevent the rest of the traction cable from untwisting. The
displaced ends of the strands may be held in position by a
supplementary holding part 45, e.g., a circular disk soldered or
fixed in any other way under the displaced strands, or they may be
left free. In a design not shown, the part for holding the
displaced strands may consist of an element having the shape of two
conical portions coupled at their bases, a first conical portion
being inserted between the strands to displace them, while the
second conical portion is used for the same purpose as the lower
portion 44 described above. Thus, in any design of the end portion
41, it may also have a circular or polygonal shape and include
upper and lower portions 43 and 44, as described previously.
[0030] The described examples of end pieces 41 or of deformed end
portions 41 are not limiting as regards either their shape or the
way in which they are produced; any means may be envisaged for
increasing the area of the cross-section of the end portion of the
traction rod 40. When the following description speaks of end piece
41, it shall be understood that this may also be an end portion as
described above.
[0031] Returning to FIG. 20, it will be seen that a first tendon 4
has been pushed into the guide tube 30, then into the cavity 11,
until its end piece 41 comes in contact with the bottom surface of
the cavity 11. A second tendon 4 is being installed in the same
way.
[0032] FIG. 2E shows the usefulness of the domed or inclined shape
which may be provided on the upper and lower portions 43, 44 of the
end piece 41. When a tendon 4 is being installed, it is quite
possible for its end piece 41 to come up against another end piece
of a tendon already installed. Owing to the domed or inclined shape
of these portions, the second end piece does not jam against the
first one but is moved away from it and slides against it until it
arrives at its final position beside the first piece.
[0033] FIG. 2F shows that after a number of tendons have been
installed, a new end piece to be installed may not have room at the
bottom of the cavity 11; in that case, in order for the tendon in
question to play its full part later on, it suffices if the end
piece is pushed down as far as possible in the cavity until it
comes up against one or more pieces already installed or against
the sidewall of the cavity.
[0034] In order to anchor the guying or the prestressed element, a
certain number N of tendons 4 must be inserted in the cavity 11.
Knowing that the cross-section of each traction rod 40 has an area
840 and that the maximum area of the cross-section of the end piece
41 equals 841 (see FIGS. 3A, 38, 3C, and 30), the following
relations should exist:
[0035] to allow the insertion of the last tendon 4, i.e., to allow
the last end piece 41 to pass into the guide tube 30 and into the
opening 12:
[(N-1).times.S40]+S41<S12
[0036] wherein S12 is the area of the cross-section of the opening
12 (FIG. 1 ).
[0037] to allow the end pieces 41 to be disposed properly on the
bottom of the cavity 11:
(N.times.S41)<S11
[0038] wherein S11 is the area of the cross-section of the cavity
11 having the largest area (FIG. 1 ).
[0039] When all the tendons 4 have been pushed through the conduit
of the tube 30 so that all their end pieces 41 are accommodated in
the cavity 11 as indicated above, the next step may be undertaken
as shown in FIG. 2G. During this step, a liquid embedding material
50 is inserted through the injection tube 16; this embedding
material enters the cavity 11 through the inlet 15 and fills the
empty spaces between the end pieces 41 and the ends of the traction
rods 40 in the cavity 11 until it fills the cavity 11 at least
partially. During this operation, the outlet 17 and the exhaust
tube 18 serve to exhaust the air contained in the cavity 11 during
its filling, as well as to check the filling level of the cavity
11. The cavity 11 is preferably filled until the liquid mass
inserted reaches the level of the outlet 17. The embedding material
contained in the cavity 11 then hardens into a rigid block 5 of
high mechanical strength in which the end pieces 41 and the ends of
the traction rods 40 are encased.
[0040] In the following step, shown in FIG. 2H, each of the tendons
4 is subjected to traction until the prescribed prestresssing
tension is reached. This application of traction takes place in a
conventional manner by acting on the other end of each tendon 4,
i.e. , of each traction rod 40, the tendons being pretightened
simultaneously or in sequence. As may be seen in the drawing, the
frustoconical or pyramidal tapering shape of the cavity 11, hence
of the hardened mass in which the end pieces 41 and the ends of the
rods 40 of the tendons 4 are encased, permits efficient
wedge-shaped anchoring in the surrounding concrete structure.
Contrary to the prior art devices mentioned earlier, this wedge
shape prevents any possible axial movement of the hardened mass 5
and causes transmission of the anchoring forces into the
surrounding structure 2 by axial compression and not by simple
adhesion. The length of this anchoring device is therefore
favorably reduced.
[0041] Additional anchoring security is ensured by the particular
arrangement of the end pieces 41 within the cavity 11. Considering
that the end pieces 41 are disposed in a bundle in the cavity 11,
the area of the cross-section generated by the casing of the bundle
of assembled end pieces 41 is greater than the area of the opening
12 of the cavity 11. The bundle of end pieces 41 is therefore
blocked in the cavity 11 .
[0042] Reverting to the expressions given above,
[0043] for enabling blockage of the tendons 4 in the cavity 11 by
preventing the mutually blocked end pieces 41 from coming out
through the opening 12, the relation should be:
(N.times.841)*>812
[0044] wherein (N.times.841)* represents generally the surface
generated by the casing of the bundle of the N assembled end
pieces, each having a cross-sectional area S41. In order to take
into account that one or two end pieces 41 may possibly not have
found their proper place, as indicated with respect to FIG. 2H, the
individual sections S41 and the passage section S12 must be of a
size to block the end pieces 41 when the tractive force is exerted
simultaneously on all the tendons 4.
[0045] It should be noted that the step of pretightening the
tendons 4 as just described may be carried out differently,
especially in the case of simple guying, not pretightened.
[0046] In a final step of the method, illustrated in FIG. 2L, the
empty space within the sheathing tube 30, or within the conduit
made in the structural element 3, may be filled with a sealant 60
through the injection tube or tubes 32 and the inlet or inlets 31
in order to preserve the fluid-tightness of the pretightened system
and to prevent corrosion of the pretightening elements. This last
step is also optional, depending upon whether such protection 6 is
required or necessary.
[0047] It will therefore be noted that a very effective anchoring
device is thus obtained, the longitudinal tractive force of each
tendon 4 being taken over mainly by its end piece or portion 41 and
transferred to the hardened block 5 of embedding material having
high mechanical strength. Efficient transmission of this force is
possible owing to the firm attachment of the end piece 41 on the
traction rod 40; since this attachment may take place in the
factory, its mechanical strength is very high. This force is then
transferred by the oblique walls of the cavity 11 to the
surrounding structure 2. By disposing one or more anchor rings on
the anchor member 11 it is even possible to improve the mentioned
anchoring effect in the surrounding structure 2. As mentioned,
hoops 21 may be provided in order further to improve the cohesion
of the surrounding structure 2 about the cavity 11. In addition to
the mentioned longitudinal strength--each end of a traction rod 40
being held in the block 5 of embedding material-each rod 40 is held
by radial compression as well.
[0048] This type of anchoring device lends itself particularly well
to prestressed anchoring of a prestressed structural element 3. It
may also lend itself to anchoring of non-prestressed tendons, e.g.,
guys for staying a mast or pylon, in which case the guys need not
be protected by a protective tube 30. Likewise, it is not
indispensable for the cavity 11 to be contrived in a surrounding
structure of concrete; a borehole in the earth or in rock whereby a
cavity as required may be obtained might be provided instead.
[0049] The foregoing description pertains to a cavity having a
substantially vertical longitudinal axis, with its opening 12 at
the top. Other geometric arrangements are also possible; the
dimensions of the cavity 11 are to be adapted in order to obtain
sufficient filling of the cavity 11 by the embedding material
50.
* * * * *