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.
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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.
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Figure: Figure: 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
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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.
