U.S. patent application number 16/361533 was filed with the patent office on 2019-09-26 for method for connecting precast segments tendon ducts and resulting structure.
The applicant listed for this patent is SOLETANCHE FREYSSINET. Invention is credited to Paul Arthur Bottomley, Boris Cousin.
Application Number | 20190292785 16/361533 |
Document ID | / |
Family ID | 61868481 |
Filed Date | 2019-09-26 |
United States Patent
Application |
20190292785 |
Kind Code |
A1 |
Bottomley; Paul Arthur ; et
al. |
September 26, 2019 |
METHOD FOR CONNECTING PRECAST SEGMENTS TENDON DUCTS AND RESULTING
STRUCTURE
Abstract
A method for establishing an air-tight connection between
post-tensioning tendon ducts of two consecutive precast segments of
a structure, each segment being cast with a recess opening out on a
jointing face of the segment leaving an access to ends of the
ducts. The method including connecting pairs of respective duct
ends of the two consecutive segments together, and pouring a
sealing material into the recesses of the two consecutive segments
around the duct ends while preventing the material to enter the
internal space of the ducts, thus forming an air-tight connection
at the junction of ducts.
Inventors: |
Bottomley; Paul Arthur;
(Shrewsbury Shropshire, GB) ; Cousin; Boris;
(London, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SOLETANCHE FREYSSINET |
RUEIL-MALMAISON |
|
FR |
|
|
Family ID: |
61868481 |
Appl. No.: |
16/361533 |
Filed: |
March 22, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E04C 5/10 20130101; E04G
21/12 20130101; E01D 2101/28 20130101; E01D 2/04 20130101 |
International
Class: |
E04C 5/10 20060101
E04C005/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2018 |
EP |
18305330.5 |
Claims
1. A method for establishing an air-tight connection between
post-tensioning tendon ducts of two consecutive precast segments of
a structure, each segment being cast with a recess opening out on a
jointing face of the segment leaving an access to ends of the
ducts, the method comprising: a) connecting pairs of respective
duct ends of the two consecutive segments together, and b) pouring
a sealing material into the recesses of the two consecutive
segments around the duct ends while preventing the material to
enter the internal space of the ducts, thus forming an air-tight
connection at the junction of ducts.
2. The method according to claim 1, wherein the sealing material is
Ultra High Performance Fibre Reinforced Concrete (UHPFRC).
3. The method of claim 1, the segments being deprived of
reinforcement bars protruding out into the recesses.
4. The method of claim 1, wherein a thermo-retractable sleeve is
pre-fixed on one of the duct ends of a pair of ducts and then the
sleeve is slid over and sealed onto the pair of ducts.
5. The method of claim 1, wherein an inflatable tube or an
inflatable ball, is introduced into the ducts and inflated before
the sealing material is poured so as to seal the inner part of the
joint between ducts.
6. The method of claim 1, wherein step b) takes place concurrently
with tendon threading.
7. The method of claim 1, wherein the recesses are provided in a
lower or upper slab of the segments and open out into the top
surface of the said lower or upper slab.
8. The method of claim 7, wherein the recesses are adjacent the
lateral walls of the segments.
9. The method of claim 1, wherein the segments are made using match
casting.
10. The method of claim 1, wherein the segments are box
segments.
11. The method of claim 1, further comprising testing the
air-tightness of the connection of the ducts.
12. A method for casting a segment, comprising: c) Positioning in a
mould: ducts for the passage of tensioning tendons, inserts for
making recesses into which the ends of the ducts extend,
reinforcing bars, and d) pouring concrete in the mould.
13. The method according to claim 12, wherein the reinforcing bars
are curtailed so as not to extend within the recesses.
14. A method for building a segmental structure comprising
assembling precast segments in continuity of each other, each
segment comprising post-tensioning tendon ducts, the method
comprising implementing the method of claim 1 for connecting the
ducts.
15. A segmental structure made in accordance with claim 14, the
segmental structure comprising a bridge deck having at least two
precast segments incorporating ducts in which tensioning tendons
are threaded, the ducts being connected together at the joint of
the segments by at least one block of Ultra High Performance Fibre
Reinforced Concrete (UHPFRC) extending around duct ends of the two
adjacent segments, this block extending into adjacent recesses of
the segments opening out on a jointing face of the segments.
Description
TECHNICAL FIELD
[0001] The present invention relates to the assembly of precast
construction segments (PCS) for building pre-stressed structures
such as post-tensioned concrete segmental structures.
BACKGROUND
[0002] It applies in particular, but not exclusively, to decks of
cantilevered bridges built using precast concrete box segments.
These structures are frequently subjected to post-tensioning using
tendons (also called "strands") threaded inside corresponding ducts
embedded in the concrete of several successive segments.
[0003] These segments are preferably made in accordance with a
match cast method to ensure a very closely fitting joint.
[0004] The connection of ducts at the joint of two adjacent
segments is exposed to a risk of infiltrations of various corroding
substances such as deicing solutions and achieving a good seal at
the joint if required.
[0005] Furthermore, grout is often injected into the ducts to
create a mechanical bound between the tendons and the concrete of
the segments and help protect the tendons from corrosion. This
grout must not escape from the ducts during injection.
[0006] The joint between two consecutive segments can be made
according to a so-called "dry joint" process where the segments are
placed side by side without any interface product or according to a
so-called "glued joint" process where an adhesive such as epoxy
paste is introduced between the segments. In the latter case, the
sealing at the junction of ducts also needs to prevent the adhesive
from penetrating into the ducts and hinder the further introduction
of the tendons.
[0007] In general, pneumatic tests are carried out to check the
quality of the sealing before installing the tendons and injecting
the grout. If leaks are detected in some ducts, the injection of
grout is rendered more difficult and some extra work is needed to
guarantee the tendons will be preserved from corrosion.
[0008] One test defined by Appendix A1 of the Technical Report No
72 Durable Post-Tensioned Concrete Structures from the Concrete
Society requires in the case of PCS construction that the duct
assembly after concreting should resist an air pressure of 0.1 bar
and maintain this with no more than 10% loss of pressure for 5
minutes.
[0009] Various solutions relying on the use of specific couplers
have been proposed in the past to provide air tightness and grout
tightness at the joints.
[0010] Some existing duct couplers are formed of many components
and are expensive and complex to use.
[0011] Some other couplers are believed not to provide the required
sealing and would have difficulties in passing the air tightness
test defined above.
[0012] Furthermore, the use of some couplers is limited to the
situation where the ducts are nominally perpendicular to the joint,
which is not always the case as in some instances the tendons are
inclined in the concrete webs.
[0013] FR-A-2 596 439 discloses a device to insert between sections
of pre-stressing ducts, comprising a cylindrical sleeve engaged
between the openings of two adjacent sections to ensure the
continuity of the ducts, and an elastic seal surrounding the
cylindrical sleeve to ensure sealing and compensate for the
positioning variations and dimensional deviations of the adjacent
segments which are assembled against each other.
[0014] WO 99/043910 discloses a device to engage in the ducts to
connect the adjacent sections in a sealed manner.
[0015] These devices are believed to perform quite well in many
situations but there remains a need for further improving the
coupling of ducts at the joints to obtain a duct continuity that
could pass with repeatability the air-tightness test mentioned
above even when the tendons are inclined in the webs.
SUMMARY OF THE INVENTION
[0016] An object of the present invention is thus to propose a
simple and efficient solution to the problem of achieving a duct
continuity that would pass the air tightness test mentioned above
with repeatability and even in situations when the tendons are
inclined in the webs.
[0017] A further object of the invention is to provide a solution
that is reliable and easy to implement.
[0018] The invention achieves this goal thanks to a method for
establishing an air-tight connection between post-tensioning tendon
ducts of two consecutive precast segments of a structure, each
segment being cast with a recess (also called a "box-out") opening
out on a jointing face of the segment leaving an access to duct
ends, the method comprising:
[0019] a) Connecting pairs of respective duct ends of the two
consecutive segments together, and
[0020] b) pouring a sealing material into the recesses of the two
consecutive segments around the duct ends while preventing the
material to enter the internal space of the ducts, thus forming an
air-tight connection at the junction of ducts.
[0021] By "air tight connection" it is meant a connection that
passes a pneumatic test usually performed for testing the quality
of the connection for this type of structure and preferably a
connection that passes the 0.1 bar test referred to above.
[0022] The sealing material is preferably a High Performance
Concrete (HPC) and most preferably an Ultra High Performance Fibre
Reinforced Concrete (UHPFRC).
[0023] The use of UHPFRC provides an air-tight, long term durable
"coupling" between the ducts which will not crack nor allow ingress
of any contaminant due to its complete lack of porosity and extreme
durability.
[0024] The method provides a simple way to obtain the air tightness
connection at a similar or lower cost compared to the use of known
couplers.
[0025] The invention allows obtaining an air tightness connection
even for tendons that are significantly deviated at the joints.
[0026] It is accepted that a very small thickness of UHPFRC is
equivalent in durability terms to many times that thickness in
normal concrete. Its pore structure is non-continuous so therefore
it is not vulnerable to the environment.
[0027] Experiments have shown that a connection made in accordance
with the invention is able to repeatedly pass the air-tightness
test mentioned above.
[0028] The connection of the duct ends of a pair at step a) does
not need to provide air-tightness as if suffices it prevents
ingress of the UHPFRC into the ducts during filling of the recesses
with that material.
[0029] One easy way to make this connection is to use a
thermo-retractable sleeve that is pre-fixed on one of the duct ends
of a pair of ducts. The length of such sleeve ranges for example
from 70 mm to 130 mm. The sleeve is slid over and sealed onto the
pair of ducts before UHPFRC is poured. This sleeve is a
non-structural element that aims to prevent ingress of the UHPFRC
into the ducts when UHPFRC is poured into the recesses. The sliding
and sealing of the sleeve may take place or not after the tendons
are threaded into the ducts.
[0030] Other possibilities exist to make a connection between the
ducts that would prevent ingress of UHPFRC into the ducts such as
the use of an inflatable tube or an inflatable ball, introduced
into the ducts and inflated before UHPFRC is poured so as to seal
the inner part of the joint between ducts.
[0031] It is also possible to use a coupler such as a rigid or
flexible sleeve engaged on the ducts for the purpose of preventing
ingress of UHPFRC.
[0032] If the distance between the two duct ends of a pair is
small, an adhesive tape wounded around the duct ends may also be
used.
[0033] Preferably, the segments are deprived of reinforcement bars
protruding out into the recesses, as the use of UHPFRC negates the
need to reinforce the infill concrete connection.
[0034] The absence of reinforcement bars protruding into the recess
makes the casting of the recesses relatively straightforward and
the access to the ends of the ducts is unfettered. A reusable
insert may be used for such casting.
[0035] Step b) may take place concurrently with tendon
threading.
[0036] HPC concrete is a concrete with a compressive strength equal
or exceeding 70 MPa.
[0037] UHPRFC concrete is a concrete with a compressive strength
usually exceeding 150 MPa, and of at least 120 MPa.
[0038] The UHPRFC comprises fibres that ensure tensile strength
with a ductile behavior.
[0039] The UHPRFC has a relatively high content of binder, which
leads to the absence of capillary porosity.
[0040] Compared to conventional concrete mix, the UHPRFC has a
dense matrix. The water/binder ratio (w/b) of UHPFRC typically lies
between 0.16 and 0.2.
[0041] In some exemplary embodiments, the recesses are provided in
a lower slab and/or an upper slab of the segments and open out into
the top surface of the lower slab and/or upper slab. These recesses
may be adjacent the lateral walls (also called "webs") of the
segments.
[0042] Preferably, the segments are made using match casting
technique. The segments may be box segments, for example one-cell
box segments.
[0043] The method may comprise testing the air-tightness of the
connection of the ducts.
[0044] A further aspect of the invention is a method for casting a
segment, comprising:
[0045] a) Positioning in a mould:
[0046] ducts for the passage of tensioning tendons,
[0047] inserts for making recesses into which the ends of the ducts
extend,
[0048] reinforcing bars,
[0049] b) pouring concrete in the mould.
[0050] The reinforcing bars may be curtailed so as not to extend
within the recesses.
[0051] A further aspect of the invention is a method for building a
segmental structure comprising assembling precast segments,
preferably segments with match cast joints, in the continuity of
each other, each segment comprising post-tensioning tendon ducts,
the method comprising implementing the method as defined above for
connecting the ducts.
[0052] A further aspect of the invention is a segmental structure,
in particular a structure made in accordance with the method as
defined above, preferably a bridge deck, comprising at least two
precast segments incorporating ducts in which tensioning tendons
are threaded, the ducts being connected together at the joint of
the segments by at least one block of a sealing material,
preferably Ultra High Performance Fibre Reinforced Concrete
(UHPFRC), extending around duct ends of the two adjacent segments,
this block extending into adjacent recesses of the segments each
opening out on a jointing face of the segments.
[0053] The joint between the two consecutive segments preferably
comprise two such blocks. These blocks preferably each extend
inwardly of the adjacent lateral wall (or web) of the segments, in
the bottom slab. The blocks preferably open out on top of the
bottom slab, in the corner thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0054] FIG. 1 is a partial perspective view of a segmental
structure made in accordance with the present invention;
[0055] FIG. 2 is a front view along arrow II of FIG. 1;
[0056] FIG. 3 shows detail III of FIG. 2;
[0057] FIG. 4 represents a joint between two consecutive segments
with a bundle of tendon ducts shown in transparency;
[0058] FIG. 5 is a partial longitudinal section view of a joint
taken where the ducts connect;
[0059] FIG. 6 shows a jointing face of a precast segment before
assembly with a next segment; and
[0060] FIGS. 7A, 7B, and 7C each illustrate the formation of a
connection between a pair of ducts.
DETAILED DESCRIPTION
[0061] The invention is described below with reference to FIGS.
1-7C in its application to a segmental structure 1 such as a bridge
deck made of several precast segments 10 with match-cast coupling
surfaces.
[0062] Each segment 10 is in this example a one-cell box concrete
segment comprising a bottom slab 11, two symmetrically inclined
lateral walls (or webs) 12 and a top slab 13 extending in
cantilever fashion beyond the walls (or webs) 12 to define a width
of the bridge deck.
[0063] In the longitudinal direction, each segment 10 is delimited
by a rear face 14 and a front face 15. The rear face 14 is intended
to come into contact against the front face 15 of the previous
segment installed on the structure during construction. Likewise,
the front face 15 of each segment 10 is intended to receive the
rear face 14 of the next segment 10.
[0064] The jointing faces 14, 15 of the adjacent segments 10 are
provided with a number of interlocking reliefs 17 ensuring a good
shear resistance of the joint and helping relative positioning of
the segments as well when they are brought together. In the example
shown in FIG. 1, these reliefs 17 are located on the end faces of
the lateral walls (or webs) 12 of the segments 10.
[0065] The interlocking reliefs 17 may comprise raised keys each in
the shape of a rectangular prism with tapered sides to provide
mechanical interlock for accurate location and shear
resistance.
[0066] Preferably the segments 10 are match cast, which means that
when casting a segment, the jointing face is match cast against its
previously cast mating segment so that this segment can act as a
former or as part of the mould for this new segment.
[0067] Each segment 10 comprises a number of longitudinal tendon
ducts 20, intended to receive post tensioning tendons. These
tendons are anchored at their ends by means of any appropriate
anchoring devices (not shown).
[0068] It is important to ensure an air-tight connection of each
pair of corresponding ducts 20 at the joint of two consecutive
segments 10.
[0069] According to the invention, the ducts 20 are connected
through blocks 30 of a sealing material that prevents ingress of
corrosive substances and provides mechanical resistance.
Preferably, this sealing material is UHPFRC.
[0070] The blocks 30 extend at the joint of two consecutive
segments 10 on the bottom slab 11 near the lateral walls (or webs)
12.
[0071] Each segment 10 is cast with a recess 40 opening out in the
jointing face of the segment 10 and in the top face of the bottom
slab 11, as shown in FIG. 6.
[0072] To make the recess 40, an insert (not shown) with
appropriate shape is placed in the mould used to cast the segment
10. This insert is preferably reusable.
[0073] Preferably, the bottom slab 11 comprises reinforcing bars
(not shown) but these bars are curtailed not to extend into the
recess 40. This facilitates the casting thereof.
[0074] When the segments 10 are assembled in the continuity of each
other to make the structure, as shown in FIG. 7A, their jointing
faces 14, 15 being in contact, the recesses 40 of the two adjacent
segments 10 form together a space 47 into which pairs of
corresponding duct ends 20 protrude.
[0075] The rear face 43 of each recess 40 may taper inwardly going
upward as shown in FIG. 7A. This helps retain the block 30 in the
bottom slab 11, as the two rear faces 43 converge upward. The outer
side face 44 of the recess 40 may extend in the continuity and
alignment of the inner face of the adjacent wall (or web) 12, as
shown in FIG. 3.
[0076] One thermo-retractable sleeve 21 may be pre-fixed (for
example threaded or installed otherwise) on one duct end of each
pair, as shown, and slid over the other duct end as shown in FIG.
7B. Then the sleeve 21 is sealed on the ducts 20. This connection
prevents ingress of UHPFRC into the ducts 20.
[0077] UHPFRC is then poured into the space 47 to fill in the
recesses 40 and make the block 30 extending around the duct ends
20, as shown in FIG. 7C.
[0078] UHPFRC is expected to reach a strength of far more than 50
MPa in less than 24 hours and exhibit a stiffness at least equal to
that of equivalent strength normal concrete so the stressing
operation is not impacted. Preferably, the filling in of the
recesses 40 takes place concurrently with tendon threading inside
the ducts.
[0079] Each block 30 connects the incorporated ducts 20 in an
air-tight fashion and enables the connection to pass the 0.1 bar
pneumatic test defined above. Furthermore, each block 30 provides
the required mechanical resistance at the junction.
[0080] Each block 30 may have a depth d.sub.7 (measured along the
longitudinal axis of the structure) ranging between 150 and 350 mm,
for example of about 250 mm.
[0081] In the example shown, the thickness d.sub.1 of UHPFRC
extending below the ducts 20 may range from 40 to 60 mm, being for
example of about 50 mm.
[0082] The thickness d.sub.2 of the bottom slab 11 below each
recess 40 may range from 25 to 35 mm, being for example of about 30
mm.
[0083] The thickness d.sub.3 of UHPFRC above the ducts 20 where the
blocks 30 are thinner, i.e. at their inner side, may range from 75
to 85 mm, being for example of about 80 mm.
[0084] The width d.sub.4 of the blocks 30 may range from 750 to
1250 mm, being for example of about 1050 mm.
[0085] The blocks 30 may have a bottom face 41 that is inclined
downwards toward the jointing face. The upper edge of the face 41
may be spaced from the ducts 20 by a distance d.sub.6 as shown in
FIG. 5 that ranges from 15 to 25 mm, being for example of about 20
mm. The thickness d.sub.5 of UHPFRC at the lower edge of face 41
below the ducts 20 is higher and may range from 50 to 60 mm, being
for example of about 55 mm. The volume of infill UHPFRC may be
about 0.2 m.sup.3 per joint and may be prepared easily on site.
[0086] The invention is not limited to the illustrated
embodiment.
[0087] For example, the invention applies to other segmental
structures, for example to two-cell box segments 10.
[0088] Furthermore, the tendon ducts may be provided elsewhere on
the segments, for example in the top slab and/or in the lateral
walls (or webs).
[0089] The number of pairs of ducts 20 connected by each block 30
may vary.
* * * * *