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123456789_123456789_1123456789Concrete Bridge Software 

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Prestressing tendons (continued)


4. Multi strand tendon

 

Internal prestressing

 

Internal bonded multistrand post-tensioning is the most applications in massive concrete deck.

 

Freyssinet provides bonded

and unbonded internal

prestressing as shown

to the right.

 

For bonded prestressing

tendons the bare strands

are located in a duct with

cement grout after

tensioning of the strands.


Unbonded prestressing

tendons (no cement grout)

are mainly used where the tension of the tendon needs

to be measured, retensioned, detensioned or replaced.

 

222222222222222222222222222222222222222222 

cf. /7/ Freyssinet Prestressing, p. 4




The components of the internal bonded multistrand post-tensioning are shown in figure below.



FigureInternal bonded VSL Multistrand post-tensioning, cf. /12/ VSL-Strand-post-tensioning, p. 10

 




















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The bare strands are protected with cementitious grout, providing a bond to the concrete surrounding.

At the live end (active) the prestressing force is transferred to the deck by a bearing plate of e.g. VSL

E-anchorage. At the dead end (passive) the prestressing force is transferred to the deck partially by

bond and partially by end bearing of e.g. VSL H-anchorage.

 

VSL also provides solutions with unbonded multistrand tendon for special applications


The next two figures show

example of internal prestressing

with Freyssinet C range tendons.

 

Figure to the right shows

hydraulic pumps which drives by electric motors typically for

stressing of the tendons.

 

See video example for internal stressing.

 

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Figure: Hydraulic pumps


Figure to the right shows 

the cables run in the center

box of the 6-bottom-lines

model.

 

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Figure: Internal prestressing with Freyssinet C range tendons. 

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Number of strands from 1 to 55 on basic of anchorages

Freyssinet C Range

VSL Multistrand System

3 - 4 - 7 - 9 - 12 - 13 - 19 - 22 - 25 - 27 - 31 - 37 - 55

2222222222222222222222222222222222222222222222222

1 - 2 - 3 - 4 - 7 - 12 - 15 - 19 - 22 - 27 - 31 - 37 - 43 - 55

22222222222222222222222222222222222222222222222

Anchorages type

Freyssinet C Range

VSL Multistrand System

 

Typical type: AnC15 for tendon 13C15, cf. /7/ p. 8





 

Typical type: E @23/28 MPa for tendon 6S-15, cf. /8/ 


Other: AnC15GI, ADnC15GI, ADnC15, ADnC15W


Other: CS, GC, NC and NC-U



Reinforcement at anchorage zone for multistrand tendons is outlined in a later separated section.



External prestressing

 

External prestressing applied to bridge deck for the following reasons:


› Bridges with deck box having thin concrete thickness.


 Bridges which require high degree of corrosion protection, the possibility to inspect

  the main run of the tendons during their service life and easy replacement.


› To increase the carrying capacity of the existing bridges.


The components of external multistrand post-tensioning are shown in figure below.


Figure: External VSL Multistrand post-tensioning, cf. /12/ VSL-Strand-post-tensioning, p. 12

 


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VSL apply PE duct having the strands placed inside, which are injected with cement grout after tendon tensioning, and the tendons are not bonded to the concrete structure.


Freyssinet provides two

options of the ducts for

external tendons.


› HDPE tube (High Density

  Polyethylene), the most used

  case where the strands placed

  inside sections of thick HDPE

  tube, which are injected with

  cement grout after tendon

  tensioning.


› LFC sheath (Factory

  lubrication of the corrugated

  metal sheath) used in special

  case. It lowers coefficient of

  friction, and it is possible to

  reduce the radius of curvature

  of sheaths bendable by hand,

  while maintaining correct

  transmission of the

  prestressing forces.

 222222222222222222222222222222222222222222222 

cf. /7/ Freyssinet Prestressing, p. 6


     

Figure: External tendon ducts with HDPE (left) and LFC (right)

 

Exemples below show unbonded external post-tensioning. The following remarks are for the FEM model:


› Unlike internal post-tensioning having the curved cables run, the external post-tensioning in bridge deck have

  rectilinear cables run between the anchoring points. It LUSAS analysis it must modelled as separated beam

  elements where the cable forces do not integrated with the concrete internal shell forces.


› Lusas Multiple Tendon Prestress Wizard can be used with cautions. The cable fictive beam must have correct
  material and dimensions since it stiffness is no longer represented by the concrete shell element in the case of
  internal prestressing. Higher concrete stress at transfer. Set ‘Duct friction coefficient’ to 0. Note that deformation
  of a point on the cable is different than the neighbour point on the concrete since the cable now is a separated
  steel element.

 

 

 

Figure: Example of unbonded external post-tensioning.


5. Thin elements tendon


The components of bonded slab post-tensioning are shown in figure below



Figure: Bonded slab post-tensioning, cf. /12/ VSL-Strand-post-tensioning, p. 8 


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VSL provides up to 5 strands

15.7mm contained in flat shaped

ducting and anchored in a single

anchorage as shown to the right.


222222222222222222222222222222222222222

 

FigureFigure: VSLab S 6-2 to 6-5 principle, cf. /8/, /9/. 


Tables below compare thin elements tendon from Freyssinet and VSL with typical set of anchorages.

  

Table: Thin elements tendon (thin box deck, slabs, etc.)


Number of strands from 1 to 5 on basic of anchorages

Freyssinet C Range

VSL Multistrand System

1 - 3 - 4 - 5

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1 - 2 - 3 - 4 - 5

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Anchorages type

Freyssinet C Range

VSL Multistrand System


 


Bonded internal prestressing

Typical type: A4 F15 to tendon 4 F15, cf. /7/

 

 

Bonded internal prestressing

Typical type: Si 6-4 for tendon 6S-4, cf. /9/ p. 47 


         Other: A3 F13/15, A4 F13, A5 F13/15, CI 1F13/15

                   CI 1F13/15, CI 3F13/15, CI 4F13/15

                   CI 5F13/15


       Other: Si 6-1, Si 6-1 PLUS, Si 6-1 STANDARD
                 SFi 6-1, SFi 6-1 PLUS, SFi 6-1 STANDARD
                 SKi 6-1 SL, H 6-1 & 6-4

Reinforcement at anchorage zones

Freyssinet C Range

VSL Multistrand System


 

                 

2222222222222222222222222222222222222222222222222

 

 

 

 

 

 

 



 

Vertical Section (top), Plan View (bottom)

Typical type: A4 F15 to tendon 4 F15, cf. /7/

 

Typical type: Si 6-4 for tendon 6S-4, cf. /9/ p. 48 


Example of small tendon Freyssinet F-Range

being used in transverse direction.

 

It is typical tensile forces on top of deck in
transversal direction (YTop), especially when a
big prestressing forces needed in longitudinal
direction.








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Figure: Freyssinet F-Range applied in transversal direction.



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Updated 20-06-2018

  
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ICDAS  •  Hans Erik Nielsens Vej 3  •  DK-3650 Ølstykke  •   
E-mail: th@icdas.dk   •  Tel.: +45 60 53 83 79  •  CVR no.: 34436169 
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