Technical Field of the Invention:
-
The present invention relates to the structure of a
tensioned end of a prestressed-concrete structure and also
relates to a method of constructing the tensioned end.
More particularly, the present invention relates to a
technique wherein a transparent material is employed for a
grout can to surely perform the construction of the
tensioned end.
Background Art:
-
According to a conventional prestressed-concrete
structure producing method (post-tensioning system),
prestressing steel and a sheath covering it, together with
reinforcing bars, are disposed in a form. Thereafter,
concrete is placed in the form. After, the concrete has
reached a predetermined strength, the prestressing steel
is tensioned from both horizontal ends or either of them,
and each end portion of the prestressing steel is anchored
with an anchoring device, thereby prestressing the
concrete.
-
Thereafter, a grout is externally injected into the
anchorage and its vicinities and also into the sheath at a
high pressure (0.5 to 1 MPa) to fill them for the purpose
of preventing corrosion of the tensioned prestressing
steel and for securing the prestressing steel in the
sheath under tension and further for fixing the interior
of the anchorage and its vicinities. At that time, a grout
can is secured to the anchorage to cover the whole
anchorage in a hermetically sealed state, and thereafter,
the grout is injected from an outer communicating hole
(grout hose fitting hole) to fill the inside of the grout
can.
-
Japanese Patent Application Unexamined Publication
(KOKAI) No. Hei 8-35331 discloses a method in which a
metallic grout can is used. In this case, however, the.
inside of the grout can cannot be seen. Therefore, it is
impossible to confirm the completeness of the filling of
grout at the tensioned end portion, which is particularly
important. Further, because the grout can is made of a
metal, an electric potential difference is produced
between the grout can and the prestressing steel or other
different kind of metal. Consequently, a corrosive current
flows, and this may cause corrosion of the prestressing
steel.
-
Further, when the grout is injected into the grout
can at a high pressure (0.5 to 1 MPa), if the grout can is
in the shape of a cylinder with a flat bottom as
illustrated in Japanese Patent Application Unexamined
Publication (KOKAI) No. Hei 8-35331, the pressure of the
injected grout is applied non-uniformly to the inner
surfaces of the grout can. This involves the danger that
the grout can may be deformed and hence the grout may leak.
-
In the case of internal cable construction, the
anchorage structure including the grout can and its
vicinities is covered with post-placed concrete. If the
adhesion between the post-placed concrete and the grout
can is incomplete, it is impossible to attain the primary
object, i.e. forming the anchorage and the post-placed
concrete into one integral structure. In the case of
external cable construction, the grout can is relatively
large in size. Therefore, the conventional metallic grout
can is heavy in weight and hence inconvenient to handle.
Disclosure of Invention:
-
As the result of conducting exhaustive studies to
solve the above-described problems with the prior art, the
present inventors succeeded in establishing a
substantially perfect grouting technique and thus came to
provide the present invention having the following
arrangements.
- (1) A tensioned end structure of a prestressed-concrete
structure wherein a grout can that is installed over an
anchorage in such a manner as to cover the whole anchorage
is filled with a grout as a cement or non-cement anti-corrosive
filler for anti-corrosive protection of a tendon
member and an anchoring device, which is characterized in
that the grout can is made of a transparent material.
- (2) A tensioned end structure of a prestressed-concrete
structure as stated in the foregoing paragraph (1), which
is characterized in that the transparent material
constituting the grout can is at least one selected from
the group consisting of polyethylenes and derivatives
thereof, polypropylenes, polystyrenes, polycarbonates,
polymethyl methacrylates, and polyvinyl chlorides.
- (3) A tensioned end structure of a prestressed-concrete
structure as stated in the foregoing paragraph (1) or (2),
which is characterized in that the transparent material
constituting the grout can consists essentially of an
ionomer resin, wherein the ionomer resin is an α-olefin-α,
β-unsaturated carboxylic acid copolymer having carboxyl
groups neutralized with metal ions.
- (4) A tensioned end structure of a prestressed-concrete
structure as stated in any one of the foregoing paragraphs
(1) to (3), which is characterized in that the grout can
is a half-cut hollow spherical member having a ring-shaped
rib at the upper edge thereof.
- (5) A tensioned end structure of a prestressed-concrete
structure as stated in any one of the foregoing paragraphs
(1) to (3), which is characterized in that the grout can
is a cylindrical member, one end of which is closed, the
cylindrical member having a ring-shaped rib at the upper
edge thereof and a half-cut hollow spherical portion at
the bottom thereof.
- (6) A tensioned end structure of a prestressed-concrete
structure as stated in any one of the foregoing paragraphs
(1) to (5), which is characterized in that the outer
surface of the grout can has been formed into an uneven
surface so as to be easily adherable to post-placed
concrete or mortar.
- (7) A tensioned end structure of a prestressed-concrete
structure as stated in any one of the foregoing paragraphs
(1) to (6), which is characterized in that the grout can
is made of an electrically insulating material.
- (8) A method of constructing a tensioned end of a
prestressed-concrete structure, which is characterized by
installing a grout can made of a transparent material over
an anchorage to cover the whole anchorage with the grout
can, and fully filling the grout can with a grout as a
cement or non-cement anti-corrosive filler for anti-corrosive
protection of a tendon member and an anchoring
device while visually observing the filling condition of
the grout in the grout can from the outside.
- (9) A method of constructing a tensioned end of a
prestressed-concrete structure as stated in the foregoing
paragraph (8), which is characterized in that the
transparent material constituting the grout can is at
least one selected from the group consisting of
polyethylenes and derivatives thereof, polypropylenes,
polystyrenes, polycarbonates, polymethyl methacrylates,
and polyvinyl chlorides.
- (10) A method of constructing a tensioned end of a
prestressed-concrete structure as stated in the foregoing
paragraph (8), which is characterized in that the
transparent material constituting the grout can consists
essentially of an ionomer resin, wherein the ionomer resin
is an α-olefin-α, β-unsaturated carboxylic acid copolymer
having carboxyl groups neutralized with metal ions.
- (11) A method of constructing a tensioned end of a
prestressed-concrete structure as stated in any one of the
foregoing paragraphs (8) to (10), which is characterized
in that the grout can is a half-cut hollow spherical
member having a ring-shaped rib at the upper edge thereof.
- (12) A method of constructing a tensioned end of a
prestressed-concrete structure as stated in any one of the
foregoing paragraphs (8) to (10), which is characterized
in that the grout can is a cylindrical member, one end of
which is closed, the cylindrical member having a ring-shaped
rib at the upper edge thereof and a half-cut hollow
spherical portion at the bottom thereof.
- (13) A method of constructing a tensioned end of a
prestressed-concrete structure as stated in any one of the
foregoing paragraphs (8) to (12), which is characterized
in that the outer surface of the grout can has been formed
into an uneven surface so as to be easily adherable to
post-placed concrete or mortar.
- (14) A method of constructing a tensioned end of a
prestressed-concrete structure as stated in any one of the
foregoing paragraphs (8) to (13), which is characterized
in that the grout can is made of an electrically
insulating material.
- (15) A grout can made of a transparent material as stated
in any one of the foregoing paragraphs (1) to (13), which
is used in a tensioned end structure of a prestressed-concrete
structure or a production thereof.
-
Brief Description of the Drawings:
-
- Fig. 1 is a sectional view of a tensioned end
structure of a prestressed-concrete structure of an
internal cable system according to Example 1 of the
present invention.
- Fig. 2 is a sectional view of a tensioned end
structure of a prestressed-concrete structure of an
external cable system according to Example 2 of the
present invention.
- Fig. 3 is a sectional view of a tensioned end
structure of a prestressed-concrete structure of an
external cable system according to Example 3 of the
present invention.
- Fig. 4 is a plan view and a sectional view of a
grout can in Fig. 1.
- Fig. 5 is a plan view and a sectional view of a
grout can in Fig. 2.
- Fig. 6 is a plan view and a sectional view of a
grout can in Fig. 3.
-
Explanation of Reference Signs:
-
- 1: prestressing steel cable
- 2: sheath
- 3: socket of anchoring device
- 4: plug of anchoring device
- 5, 5', 5": grout can
- 5a, 5a', 5a": rib of grout can
- 5b, 5b', 5b": grout discharge pipe
- 5c, 5c': grout discharge pipe
- 5d: bolt insertion hole
- 5e: grout injection pipe
- 6: grout hose
- 7: packing
- 8: grout can securing bolt
- 9: spiral reinforcement
- 10: differential-diameter joint
- 10a: grout injection pipe of differential-diameter joint
- 11: anchor plate
- 12: anchor head
- 13: wedge
- 14: inner trumpet
- 15: outer trumpet
- 16: caulking ring
- 17: resin sheath
- 18: steel pipe
- 50: half-cut hollow spherical portion
- 51: cylindrical portion
- C: concrete
- G: grout
- M: post-placed concrete or mortar
- V: void
-
Best Mode for Carrying Out the Invention:
-
Embodiments of the present invention will be
described below with reference to the accompanying
drawings.
-
Fig. 1 is a sectional view of a tensioned end
structure of a prestressed-concrete structure of an
internal cable system according to Example 1 of the
present invention. Fig. 2 is a sectional view of a
tensioned end structure of a prestressed-concrete
structure of an external cable system according to Example
2 of the present invention. Fig. 3 is a sectional view of
a tensioned end structure of a prestressed-concrete
structure of an external cable system according to Example
3 of the present invention.
-
Fig. 4 is a plan view and a sectional view of a
grout can in Fig. 1. Fig. 5 is a plan view and a sectional
view of a grout can in Fig. 2. Fig. 6 is a plan view and a
sectional view of a grout can in Fig. 3.
-
In the drawing: C denotes concrete; G denotes grout;
M denotes post-placed concrete or mortar; 1 denotes
prestressing steel cables; 2 denotes a sheath; 3 denotes a
socket of anchoring device; 4 denotes a plug of anchoring
device; 5, 5', 5" denote grout cans; 5a, 5a', 5a" denote
ribs of grout cans; 5b, 5b', 5b" and 5c, 5c' denote grout
discharge pipes; 5d, 5d', 5d" denote bolt insertion holes;
5e denotes a grout injection pipe; 6 denotes a grout hose;
7 denotes a packing; 8 denotes grout can securing bolts; 9
denotes spiral reinforcement; 10 denotes a differential-diameter
joint; 10a denotes a grout injection pipe of
differential-diameter joint; 11 denotes an anchor plate;
12 denotes an anchor head; 13 denotes wedges; 14 denotes
an inner trumpet; 15 denotes an outer trumpet; 16 denotes
a caulking ring; 17 denotes a resin sheath; and 18 denotes
a steel pipe.
-
First, as shown in Fig. 1, which is a sectional
explanatory view of a tensioned end structure in the
vicinity of an anchorage of an internal cable system, end
portions of prestressing steel cables 1 are anchored under
tension by using a socket 3 and a plug 4, which constitute
an anchoring device, buried in an end portion of concrete
C. A sheath 2 is connected to a projecting portion 3a of
the socket 3 through a differential-diameter joint 10 to
enclose a bundle of 6 to 12 prestressing steel cables 1. A
grout can 5 is secured over the anchorage of the tensioned
end with grout can securing bolts 8.
-
It should be noted that as the grout can those as
shown in Figs. 4 to 6 can be used.
-
The grout can 5 shown in Figs. 4(a) and (b) is a
half-cut hollow spherical member having a ring-shaped rib
5a at the upper edge thereof. The grout can 5' shown in
Figs. 5(a) and (b) is a cylindrical member, one end of
which is closed. The cylindrical member has a ring-shaped
rib 5a' at the upper edge thereof and a half-cut hollow
spherical portion 50 at the bottom thereof. The grout can
5" shown in Figs. 6(a) and (b) is a cylindrical member,
one end of which is closed. The cylindrical member has a
ring-shaped rib 5a" at the upper edge thereof and a
slightly curved bottom portion.
-
As shown in Figs. 1 and 4, the belly portion of the
grout can 5 is provided with connecting openings, and
grout discharge pipes 5b and 5c are attached to the
connecting openings to fit grout hoses 6 thereto,
respectively.
-
As shown in Fig. 1, grout G is introduced into the
sheath 2 at a high pressure (0.5 to 1 MPa) from a grout
injection pipe 10a of the differential-diameter joint to
fill the grout can 5 through through-holes (not shown)
provided in the plug 4 in the anchorage. Excess grout is
discharged to the outside through the grout discharge
pipes 5b and 5c and the grout hoses 6.
-
At this time, because the grout can 5 is made of a
transparent material, the filling condition of the grout
can be visually observed easily from the outside, and it
is possible to readily find any void portion left unfilled
in the inner wall of the grout can 5. Therefore, if such a
void portion is found, additional grouting is carried out
to refill it, thereby attaining a completely filled
condition.
-
It should be noted that the grout G is a cement milk
mixed with an admixture, e.g. a dispersing agent. Then,
concrete or mortar M for post placement is placed and
hardened by using a form so as to cover the surface of the
concrete C in the vicinity of the anchorage and also cover
the outer peripheral surface of the grout can 5.
-
It is preferable that the post-placed concrete or
mortar M should be a material identical or similar to the
concrete C so as to be integrated with the latter.
-
Next, the construction of a tensioned end in the
vicinity of an anchorage of an external cable system will
be described. As shown in Fig. 2, which is a sectional
view of a tensioned end structure in the vicinity of the
anchorage, end portions of prestressing steel cables 1 are
anchored under tension by using an anchor head 12 attached
to the outer surface of an end portion of concrete C,
together with wedges 13. An anchor plate 11 is embedded in
the inner surface of the concrete C inside the anchor head
12.
-
Further, an outer trumpet 15, together with an inner
trumpet 14 inserted therein, is installed in the vicinity
of the anchorage. A steel pipe 18 is fitted into the
forward end portion of the outer trumpet 15. The forward
end portion of the inner trumpet 14 is fitted into a resin
sheath 17. In addition, a caulking ring 16 is fitted
around the outer peripheral surface of the overlap of the
inner trumpet 14 and the resin sheath 17.
-
A bundle of 12 to 27 prestressing steel cables 1 is
inserted to extend through the inner trumpet 14 and the
resin sheath 17.
-
It should be noted that a grout can 5' is secured to
the surface of the anchor plate 11 with grout can securing
bolts 8.
-
The grout can 5' used in this case is, as shown in
Fig. 5, a cylindrical member, one end of which is closed.
The cylindrical member has a ring-shaped rib 5a' at the
upper edge thereof and a half-cut hollow spherical portion
50 at the bottom thereof. Because it has the cylindrical
portion 51, the grout can 5' is correspondingly increased
in height.
-
The belly portion of the grout can 5' is provided
with connecting openings, and grout discharge pipes 5b'
and 5c' are attached to the connecting openings to fit
grout hoses 6 thereto, respectively.
-
As shown in Fig. 2, which is a sectional view of the
anchorage and its vicinities, grout G is introduced into
the grout can 5' at a high pressure (0.5 to 1 MPa) from
the right-hand side through the sheath 17 to fill the
grout can 5'.
-
The grout G is filled into the grout can 5' through
through-holes (not shown) provided in the anchor head 12.
Excess grout is discharged to the outside through the
grout discharge pipes 5b' and 5c' and the grout hoses 6.
-
At this time, because the grout can 5' is made of a
transparent material, the filling condition of the grout
can be visually observed easily from the outside, and it
is possible to readily find any void portion V left
unfilled in the inner wall of the grout can 5'. Therefore,
if such a void portion is found, additional grouting is
carried out to refill it, thereby attaining a completely
filled condition.
-
The term "transparent material for the grout can" as
used in the present invention means a material that allows
the filling condition of grout G in the grout can and the
presence of air bubbles, etc. to be visually checked from
the outside of the grout can. It is possible to use any
material that is transparent and mechanically strong to
some extent, for example, synthetic resins, high-strength
glass (including tempered glass coated with a transparent
resin), and ceramics.
-
Particularly, a transparent synthetic resin material
is preferably used. Because the material is required to
exhibit pressure resistance (during grouting), impact
resistance, and moderate flexibility and toughness (when
the rib portion is bolted), it is particularly preferable
to use an ionomer resin consisting essentially of an α-olefin-α,
β-unsaturated carboxylic acid copolymer having
carboxyl groups neutralized with metal ions, which is a
polyethylene derivative.
-
The polyethylene derivative-base ionomer resin is
prepared by copolymerization of ethylene with a small
amount of (meth)acrylic acid metal salt, and also known as
an ethylene-base ionomer (EBI). The ionomer resin is
excellent in transparency and also excellent in pressure
resistance, flexibility and toughness.
-
The above-described transparent materials are
generally not electrically conductive (i.e. they are
electrically insulative) and hence unlikely to cause a
corrosive electric current. It should be noted that
polyethylenes (or polyethylene derivative-base ionomer
resins) are also preferable from the viewpoint that they
are free from leakage of harmful substances (e.g.
environmental hormones) into the environment.
-
Further, in the present invention, the grout can is
transparent and hence allows any portion left unfilled
with grout to be visually recognized easily from the
outside of the grout can. Therefore, if an unfilled
portion is found after the grout has hardened, the grout
can is bored to provide injection and discharge openings
to regrout the unfilled portion, thereby enabling the
grout to be completely filled in the grout can (easiness
and reliability of filling condition inspection and
repairing).
Examples:
-
The present invention will be described below more
specifically by way of examples.
Example 1:
-
This is an example of an internal cable system as
shown in Fig. 1.
-
Molding of the grout can 5 was carried out by
injection molding of a transparent resin using a mold
having an inner surface processed into an embossing
negative mold configuration in advance.
-
As a transparent electrically insulating resin
material, "Himilan 1706" (trade name), which is a
polyethylene derivative-base ionomer resin available from
DuPont-Mitsui Polychemicals Co., Ltd., was used.
-
The grout can 5 has a configuration as shown in
Fig. 4. That is, the grout can 5 is a half-cut hollow
spherical member having a ring-shaped rib 5a at the upper
edge thereof. The inner diameter of the upper edge is
122 mm. The height of the grout can 5 is 60 mm. The rib
width is 17 mm. Grout discharge pipes 5b and 5c (outer
diameter: 19 mm) for fitting grout hoses are attached to
the grout can 5, and grout hoses 6 are connected thereto.
-
First, as shown in Fig. 1, grout G, which is a
cement milk mixed with an admixture, e.g. a dispersing
agent, is introduced into the grout can 5 from the grout
injection pipe 10a via the anchorage.
-
The thickness of the grout can 5 is 4 mm. The
pressure resistance of the grout can 5 satisfies the
required waterproof pressure of 1 MPa. Even when grout was
introduced into the grout can 5 at a high pressure (0.5 to
1 MPa), neither deformation of the grout can 5 nor leakage
of grout was observed.
-
The filling condition of the grout G was visually
observable from the outside through the grout can 5. Thus,
it was possible to easily confirm that neither air bubbles
nor voids were present. It should be noted that the
surface of the grout can 5 had been formed into an uneven
surface (not shown) by embossing. Accordingly, the
adhesion of the grout can 5 to post-placed concrete M was
good (it was confirmed by a test of embedding the grout
can into concrete, which was carried out separately, that
the grout can did not separate from concrete after it had
hardened).
Example 2:
-
This is an example of an external cable system as
shown in Fig. 2. The grout can 5' was produced by
injection molding using a material similar to that in
Example 1.
-
The grout can 5' has a configuration as shown in
Figs. 5(a) and (b). That is, the grout can 5' is a
cylindrical member, one end of which is closed. The
cylindrical member has a ring-shaped rib 5a' at the upper
edge thereof and a half-cut hollow spherical portion 50 at
the bottom thereof. The grout can 5' is provided with
grout hose fitting pipes (outer diameter: 19 mm) 5b' and
5c', and grout hoses 6 are connected thereto.
-
The cylindrical inner diameter of the upper edge of
the grout can 5' is 227 mm. The height of the grout can 5'
is 204 mm. The rib width is 21.5 mm.
-
As shown in Fig. 2, which is a sectional view of the
anchorage and its vicinities, grout G is introduced into
the grout can 5' at a high pressure (0.5 to 1 MPa) from
the right-hand side through the sheath 17 to fill the
grout can 5'.
-
The grout G is filled into the grout can 5' through
through-holes (not shown) provided in the anchor head 12.
Excess grout is discharged to the outside through the
grout discharge pipes 5b' and 5c' and the grout hoses 6.
-
It was visually observed from the outside during
filling the grout that a void portion V remained in the
inner wall surface of the grout can 5'. Therefore, the
grouting was continued. Consequently, the void portion V
became invisible. Thus, it was perceived that the grout G
had been completely filled.
-
It should be noted that the grout G used in this
example was also a cement milk similar to that in Example
1.
-
The thickness of the grout can 5' is 4 mm. The
pressure resistance of the grout can 5' satisfies the
required waterproof pressure of 1 MPa. Even when grout was
introduced into the grout can 5' at a high pressure (0.5
to 1 MPa), neither deformation of the grout can 5' nor
leakage of grout was observed.
-
Further, the resin grout can 5' used in this example
was light in weight in comparison to the conventional
metallic grout can and hence easy to handle. Moreover,
because the grout can 5' was not electrically conductive,
there is no fear of the prestressing steel being corroded
by a corrosive electric current that would otherwise be
generated.
Example 3:
-
This is an example of an external cable system as
shown in Fig. 3. The grout can 5" was produced by
injection molding using a material similar to that in
Example 1.
-
As shown in Figs. 6(a) and (b), the grout can 5" is
a cylindrical member, one end of which is closed. The
cylindrical member has a ring-shaped rib 5a" at the upper
edge thereof and a slightly curved bottom portion. The
grout can 5" is provided with grout hose fitting pipes
(outer diameter: 19 mm) 5b" and 5e, and grout hoses 6 are
connected thereto. The pipe 5b" is for grout discharge.
The pipe 5e is for grout injection.
-
The cylindrical inner diameter of the upper edge of
the grout can 5" is 108 mm. The height of the grout can 5"
is 150 mm. The rib width is 24 mm. The grout can 5" was
made of an acrylic resin.
-
As shown in Fig. 3, grout G is introduced into the
grout can 5" through the grout injection pipe 5e to fill
the grout can 5". At this time, additional grouting is
carried out satisfactorily so that no void portion will be
left inside the grout can 5". Excess grout is discharged
to the outside through the grout discharge pipe 5b".
-
It should be noted that if there is some fear of the
presence of a void continuously extending to the inside of
the structure along the tendon member, a hole is bored in
the grout can, and a fiberscope or the like is inserted
into the grout can through the hole, thereby allowing
investigation of the void.
Industrial Applicability:
-
As has been stated above, according to the present
invention, the grout can is made of a transparent material.
Therefore, during the construction of a tensioned end of a
prestressed-concrete structure, the filling condition of
grout in the grout can can be visually observed easily
from the outside and grasped reliably.
-
If the material constituting the grout can is a
transparent and electrically insulating material, no
electric potential difference is produced between the
grout can and the prestressing steel or other different
kind of metal, which would otherwise occur due to water
present in a void or the like that is not visually
observable. Consequently, there is no danger of the
prestressing steel being corroded by a corrosive electric
current as in the prior art.
-
Further, the grout can is formed in the shape of a
half-cut hollow spherical member or a cylindrical member,
one end of which is closed, and which has a half-cut
hollow spherical portion at the bottom thereof, whereby it
is possible to prevent deformation of the grout can and
leakage of grout during grouting at high pressure. In the
case of internal cable construction, if the outer surface
of the grout can is processed into an uneven surface in
advance, the adhesion of the grout can to post-placed
concrete becomes good.
-
Further, in the case of using a grout can made of a
transparent resin, even if it is relatively large in size,
the grout can is easy to handle because it is light in
weight.
-
It should be noted that it was possible to fill the
grout completely in the examples using transparent grout
cans. However, even if a void is present in the grout can
for some reason after the grout has hardened in an
external cable system, the void can be visually recognized
easily from the outside of the grout can. Therefore,
repair can be executed by boring grout injection and
discharge openings in the grout can and refilling the
grout into the void.