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.

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

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.