BBR EURO PT Slabs...BBR Systems Ltd. Tel: +41 - 1 - 806 80 60 Bahnstrasse 23 Fax: +41 - 1 - 806 80...

BBR Systems Ltd. Tel: +41 - 1 - 806 80 60 Bahnstrasse 23 Fax: +41 - 1 - 806 80 50 CH-8603 Schwerzenbach / Zürich Email: [email protected] Switzerland Web: www.bbrsystems.ch

06.08.04 Monostrand field manual #16 – Post tensioned slabs 1/12

BBR EURO PT Slabs

General tasks description

Version 1.0

Approval: Version: Date: Name: Signature: Remark: Date: Name: Signature:

1.0


06.08.04 BBR EURO PT slabs Mono Field Manual.doc 2/12

Index

Index .................................................................................................................................................... 2

1 Constructive sequence........................................................................................................................ 3

2 Tasks sequences................................................................................................................................. 3

2.1 Installation .................................................................................................................................. 3

2.2 Shafts.......................................................................................................................................... 8

2.3 Stressing...................................................................................................................................... 8

2.4 Prefabrication of tendons............................................................................................................ 8



1 Constructive sequence The following assembly sequence is oriented to make a complete cycle (of formworks assembly to their release) in one working week. Thus, without the execution of special schedules, with one team of workers four cycles can be executed in one month with one set of formwork corresponding to the area of the largest concrete pour. Depending on the relation of the design live loads to the self-weight of the next level’s slab, a set of supporting props would be required to transfer the slab´ s weight difference to a lower level. This will also control its deflection during the construction. One of the main parameters driving the post-tensioned slab design is the balance between reinforcement and post-tensioning tendons densities. Thus, there will be no need of excess of labour to install reinforcement that is not compatible with the other tasks requirements. For the same reason, only the use of high performance formwork systems allows to maintain a good productivity and take profit of the fast formwork cycles. This cycle is valid for concrete pouring areas between 500 m2 and 1200 m2 with BBR-CONA Single mono-strand system, and can be extended, adjusting the resources up to maximum of 2000 m2 or 6.5 tons of strand. 2 Tasks sequences 2.1 Installation During the first day of the cycle, two post-tensioning workers are only necessary. While the formwork installation is underway, install the post-tensioned anchorages at the edge of the slab. Mark on the fenolic plywood formwork the position of the chairs (with an aerosol spray in the same color as in the executive drawing). The locations where the strands have covers below 5 cm must be clearly marked in the slab bottom (with water-color, double head nails, etc- Figure 1) to avoid latter damage of the tendons by fixing elements (nails, Hilti, etc) to support loads from the bottom of the slab.

Figure 1



According to the drawings, do not drill for fixations or perforate shafts in the slab for any service in that area.

Figure 2

At this stage, all post-tensioned recess boxes, shafts and intermediates joints’ formwork are installed. The holes for mono-strands are perforated in the lateral formwork. The live anchorages and their pocket formers are to be placed properly fixed. This task has to be done as early as possible, because having placed these anchorages simplifies the installation of all the reinforcement. Once approximately 25% of flywood formwork’s area is leveled, start placing the shear’s head reinforcement and bottom mesh, in the alignment of the distributed tendons. Immediately after each tributary has the mesh and the shear heads been placed, un-coil the corresponding tendons to the columns strip in the distributed direction (Figure 2).

Figure 3

For long cables with intermediate anchorages, the mono-strand coil must be tied in a way to maintain the section corresponding to the next pour without completely untie the coil, and with the intermediate anchorage in position and fixed with adhesive tape. Do not cut the PE cover in the intermediate anchorage at prefabrication’ stage. The uncoiling is done from the intermediate anchorage (leaving the length of strand for the next pour over the formwork extension Figure 3) towards the live/dead end.



Figure 4

If it is a live end, the mono-strand must be threaded through the anchorage and the pocket former. Make sure that a minimum of 60 cm of extra length of the strand has been left from the anchor plate and align the mono-strand between both anchorages, in tendons of no more than five mono-strands (as is shown in the drawings – Figure 5)

Figure 5

If it is a dead end and the the anchor is already pre-blocked over the monostrands, place it over the surveying the replacement mark and proceed as if it were a live end. Otherwise, tie the extreme end of the mono-strand to the bottom mesh, on the surveying mark and proceed as if it were a live end. With this tasks sequence, at the end of the net mesh installation, all columns strips’ tendons of the distributed direction (approximately 30% of total PT) and also all the active anchors will have been installed. Simultaneously, start with the placement of the edge reinforcement. Also, start installing bursting and stressing pockets reinforcement.

Figure 6



In case of not having made the dead end wedge blocking, this must be done simultaneously with the edge reinforcement placing. Then, all the tendons corresponding to the banded direction will be aligned and placed over the previously installed. Start installing banded tendons from the dead end. Once the cables have been well placed, proceed placing to install the chairs for the negative reinforcement over shear heads in the distributed direction, passing the rebars under the banded tendons, such to obtain the maximum cover.

Figure 7

Then, the negative reinforcement’s rebars in the banded direction will be placed over the previously placed rebars (between the packages of mono-strands), tying itself to the rebars and finally, rise distributed direction tendons until being tied to the passive reinforcement’s rebars. (Figure 8)

Figure 8



The remaining cables (span cables of the distributed direction are placed and aligned, all the tendons are tied to the bottom mesh control points, and the intermediate height’s chairs are placed are tied to the mesh The tendon’s layout should be checked. (Figure 9)

Figure 9

The negative “wedge” reinforcement between bands is installed. (Figure 10)

Figure 10

After that, the slab is ready to be concreted. At this stage, take care must be taken on not modifying the tendon heights and a careful compaction of the fresh concrete must be done in the anchorages zones. Just before pouring start, and over the formwork release agent, the tendons zones where cover is minimum (tied to bottom mesh) should be sprayed with paint, so the marks stays in the concrete once the formwork is stripped and easy location of tendon is possible.

Figure 11



Post-tension personnel must stay during the concreted pour with the objective to rectify any deviation in cables and/or obstructions in stressing reservations and pocket-formers, etc.(Figure 12)

Figure 12

2.2 Shafts In case of shafts or drillings in the slab, not anticipated in the project, but that appear at shop, the following must be considered:

• Circular or square shafts with dimension smaller than the slab’s thickness can be executed at any point of the slab, except within the perimeter defined by the column edge plus a thickness of a slab.

• Bigger shafts should provide edge reinforcements, according to the general detail. • Every shaft of more than 1’2 m dimension should be analyzed and approved by the designer. • In case of a shaft interference with a mono-strand tendon, this can be moved in plant without

requiring the designer’s approval whenever an angle of 1/12 with the original layout is not overcome.

• The tolerance for the mono-strands installation will be of 6 mm in the vertical

2.3 Stressing Before stressing, while the minimum resistance is reached, the following tasks are to be done, outside the critical path of the construction site.

• Remove the lateral formwork, stressing reservation’s formwork and clean them from obstructions.(Figure 13)

Figure 13



• Remove the plastic pocket-formers.(Figure 14)

Figure 14

• With a special tool (system dependent), cut the PE sheath inside the anchorage up to the wedge depth. Retire the PE sheath, clean the mono-strand extra length from sand and wax. For the intermediate anchorages, cut the sheath 35 cm behind the anchorage.

• Place the wedges, and take care to push them to an even level. • Paint the mono-strand extra length with aerosol spray from the wedge to about 10 cm

more.(Figure 15)

Figure 15

Once the concrete has reached the sufficient resistance (average of three samples, cured with the same conditions that the slabs) to carry out the stressing, start stressing the span cables from the distributed direction, following by strip cables from the distributed direction and finally the cables from the banded direction. Only qualified personnel, according to the manual and to the security instructions, could do the stressing operation. They will have to check that the elongations, measured from the wedge to the beginning of the painted mark, are between the maximum and the minimum values of the corresponding table. In any anchorage that shows displacement, cracking in the concrete, etc the stressing must be stopped at once and are marked for inspection. (Figure 16)

Figure 16



The strand’s tails will be cut only after the approval of the Site Manager is given in written, on the stressing/elongation tables.(Figure 17)

Figure 17

Install cap filled with non-corrosive grease and finish with non-shrink grout.(Figure 18)

Figure 18

The full formwork and propping can be removed immediately after stressing.(Figure 19)

Figure 19



2.4 Prefabrication of tendons It is strongly advised not to cut the strand on the formwork, as the external HDPE sheath is sensible to puncture and abrasion, and there is a congestion of workers doing different tasks. On the other hand, this will optimize the use of post-tensioned resources, since the tendon, prefabrication is done outside the job’s critical path when the post-tensioning personnel do not have any tasks to do. It also eliminates contamination of the tendon with the ground, cement grouts, etc… which are on the job site. If there is no automatic cutter line, the optimal procedure to prefabricate mono-strands is as follows:

• Secure an area with clean floor equal to the longest stand by 2 m width. • Place the Unbonded strand coils at the end of the area with the axis of the coil aligned with the

long side of the area. Put the un-coiler in the first coil.(Figure 20)

Figure 20

• At the mouth of the un-coiler, prepare the anchorages in boxes (live, dead and intermediate); place carpet or another smooth material on the mouth of the un-coiler to avoid any damage in the strand.(Figure 21)

Figure 21

• Install the cutting machine (grinding electrical 9”) at 1’5 m away from the un-coiler cone exit and install a workbench in that point.

• Prepare the cut list and the labels with the cable identification near the workbench. • Assemble the equipment (pump and jack) over the workbench.



• For each cable length of the cut list, mark on the floor with painting or chalk, the distance from the active anchorage to the first intermediate anchor and the overall length.

• In case of having to install an intermediate anchorage, thread the strand thorough the anchor cone, placed at the un-coiler’s mouth, and hold on to it with a tied wire.

• A worker takes the end of the strand and walks toward the first mark (intermediate anchorage), matching that with the end of the strand, under a small tension, just to remove slack. The second worker, at the workbench, will release the first intermediate anchorage from the un-coiler and fix it with a wire/adhesive tape to the strand in the corresponding point. Do no cut the HDPE sheath at the intermediate anchor at prefabrication stage.

• Once the intermediate anchorage has been fixed, the first worker keeps on pulling the strand, until the end matches with the total length. Then, with the strand tensioned to remove all slack, ; the second worker cuts the strand at the workbench. While the first worker walks back coiling the strand to form rings approximately 1.2 / 1.4 diameter, the second worker cuts the HDPE sheath in 20 cm, places the dead anchorage, the wedge, and then pre-blocks it, seals the anchorage, and puts a label on the cable.

• The first worker then coils the strand from the dead end toward the intermediate anchorage. The two rings are tied together.

• All the strands rings of each tendon are stacked together, grouping all the tendons corresponding to the same placement sequence over a pallet.

• A duplication of workers could be done to accelerate the cutting and coiling operation. • For big jobs, use a legend of four colors: 1) Slab Level, 2) pour, 3 and 4) placement order.

Colors are applied inside the stacks of rings over the pallet painted with aerosol.

Figure 22

BBR EURO PT Slabs...BBR Systems Ltd. Tel: +41 - 1 - 806 80 60 Bahnstrasse 23 Fax: +41 - 1 - 806 80...

Documents

Transcript of BBR EURO PT Slabs...BBR Systems Ltd. Tel: +41 - 1 - 806 80 60 Bahnstrasse 23 Fax: +41 - 1 - 806 80...