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Concrete Bridge

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Prestressing tendons


The following 7 sections are a part of ‘Concrete Bridge User’s Manual’ in ICDAS COB subscription

relating prestressing tendons in concrete bridge. It guides the users to design prestressing tendons

and reinforcement at the anchorage zones, for massive concrete deck and thin deck box as well.  


2. Number of cables


4. Multi_strand_tendon

5. Thin elements tendon

6. Reinforcement at anchorage zone for multistrand tendon

7. Stress limitation



1. Prestressing tendon types


Pre-tensioned/Post-tensioned & Unboned/Bonded tendons


The words ‘Pre-tensioned’ and ‘Post-tensioned’ in Danish ‘Forspædte’ (Førspædte) and ‘Efterspædte’

have been used in some time oppositely. Definition for these words in Eurocode 2 Design of concrete

structures are highlighted below. 









cf. /2/ Eurocode 2 Design of concrete structures DS/EN 1992-1-1+AC:2008, p. 16





cf. /2/ Eurocode 2 Design of concrete structures DS/EN 1992-1-1+AC:2008, p. 22



Keep in mind the above definitions for the following examples about prestressing tendons.

EN 10138 or European Technical Approval (ETA)

Prestressing tendons have to comply with the criteria specified in EN 10138 or given in an appropriate

European Technical Approval (ETA). Below is producers of prestressing tendons.


ETA 06-0226 Freyssinet Prestressing (France)

ETA 06-0006 VSL Post-Tensioning System (Vorspann System Losinger, Switzerland)

ETA 07-0035 Skandinavisk Spaendbeton (Denmark)


Freyssinet and VSL provide prestressing tendons for both of massive concrete deck and thin box deck with

many options of cables. Skandinavisk Spaendbeton focus on 15.7mm/1860 MPa strands - commonly used in

Scandinavia for massive concrete deck only.



Freyssinet 13C15 and VSL 6S-12


Freyssinet has designations C and F range for massive deck and thin box deck, respectively. VSL has Multistrand

System and Slab system, respectively.


Table below shows designations of typical cables for massive concrete deck with Freyssinet and VSL. 


Table: Freyssinet 13C15 and VSL 6S-12


Designation (1)

Freyssinet 13C15

13 strands C range of dia. 15.7mm, cf. /7/ p. 26

VSL 6S-12 (2)

strand dia. 0.6 inch (~15.7mm) – 12 strands, cf. /8/ p. 14

(1) Both assumed Nominal tensile strength 1860MPa, strand breaking strength Fpk=279kN, pr EN 10183-3.

(2) S stands for Super. Otherwise, VSL 6S-12 has strand dia. 15.2mm and Fpk=260kN.


Keep Freyssinet 13C15 as reference tendon, one gets


VSL 6S-12 / 13C15 = 12/13 = 0.92

VSL 6S-15 / 13C15 = 15/13 = 1.15


I.e. when we need 15% bigger prestressing forces than Freyssinet 13C15, then VSL 6S-15 can be considered
with the same cable number and layout. The next Freyssinet 19C15 is too big, and needed the FEM mesh of the
bridge deck redesigned if the number of cables is reduced.


2. Number of cables

As experience for internal prestressing cables, a compressive stress of 4-5MPa is needed over the entire concrete

cross section Area incl. the two wings for bridge span less than 20m. By expression ncab´Pmax/Area @ 4-5MPa,

one can find the number of cables ncab, where the prestressed force Pmax is calculated in example below.


The case the maximum compression needed, we need to find the minimum distance between the cables anchor as
example below with tendon 13C15. Here the area (0.760*0.300) is the associated area to the anchorage (0.250*0.210)
of tendon 13C15. We get a compressive stress of 11.9MPa which is less the 60% of the concrete fck=20MPa at the time
of tensioning, cf. /3/ Eurocode 2 for Concrete bridges (J.101).

Figure: Example of Freyssinet cable 13C15 in minimum distance in 760mm depth deck.





cf. /3/ Eurocode 2 Design of concrete structure - Concrete bridges BS EN 1992-2:2005, p. 61 





cf. /2/ Eurocode 2 Design of concrete structures DS/EN 1992-1-1+AC:2008, p. 76

3. Cable Curve

The cable curve is created in ICDAS Excel as input to both of Revit and Lusas models. Below shown an

example of the cable curve in three-spans concrete bridge deck.

Figure: Excel cable curve input to Revit and Lusas.


Remarks for Lusas model:

›  Refer /1/ for the 5-Steps input in Lusas > Bridge > Prestress Wizard > Multiple Tendon…

›  Graphical check (X, Y, Z) for location of cables in bridge deck. Check (X, Y) of the cable fictive beam on

   the mesh is also the (X, Y) of the Tendon profile entered in Multiple Tendon step 2. Note that all points

   distribute along the tendon curve in step 2 do not need to coincide with the points created the cable fictive

   beams on the mesh. The vertical distance dzBot from bottom of deck to center of cable can be checked as


dzBot = ZCab - ZMesh  ,   where

        ZMesh = Z-Coordinate at bottom of deck at a selected point below the cable in Lusas

        ZCab  = Z-Coordinate of the cable entered in Step2 Tendon Profile at that point


The vertical distance dzTop from top of deck to center of cable can be checked as

dzTop = Thick - dzBot    ,   where 


       Thick = thickness of deck box at the edge defined by the cable fictive beam on the mesh.

Remarks for Revit model:

›  Positions of the cables are relative to the deck when loaded the cable family into the bridge project.

   The absolute coordinate for the cable obtained automatically when assign the true coordinate and the

   true angle to the north at Project Base Point in Floor Plans Site view.

›  The cable setting-out can both be in relative to the deck, or as absolute coordinate (X,Y,Z).

Minimum radius of tendon curvature and tangent length for internal tendons


cf. /11/ VSL Post Tensioning Solutions, p. 25

Prestressing tendon Modulus of Elasticity & Density



cf. /2/ Eurocode 2 Design of concrete structures DS/EN 1992-1-1+AC:2008, p. 44

Updated 20-06-2018
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