Prestressed/post-tensioned concrete bridges - Computational Analysis and Design of Bridge Structures - page 144

5.4 3d illustrated exaMPle of a
douBle-cell Post-tensioning concrete
Bridge—Verzasca 2 Bridge, switzerland

In European practice, post-tensioning is more popular. A Swiss bridge with
cast-in-place double-cell concrete beam is taking as an example in this
section. The Bridge Verzasca 2, which locates on the main road between
Bellinzona and Locarno, in the south of Switzerland, was built in 1990-
1991 and consists of six spans between 25.24 and 39.70 m (82.8′ and
130.3′), with a total length of 203.6 m (668′). The pier supports are skewed
at an angle of 28.8°, whereas the abutments are placed perpendicular to the
bridge axis. The superstructure is a post-tensioned continuous girder with a
cast-in-place double-cell section (Schellenberg et al. 2005).
The cross section changes in the region over the piers where negative
moments are expected. In this region the three webs of the double-cell sec-
tion are widened. Also, the bottom flange is thickened continuously from
200 to 300 mm (8″ to 12″) in this region.
Diaphragms are placed over each pier, providing a higher torsional rigid-
ity. Accounting for the diaphragms as well as a cross section of the beam,
a total of three cross sections can be determined. The post-tensioning ten-
dons are anchored approximately at the section of dead load point of con-
traflexure, where the webs change their width, providing required spaces
for the tensioning procedure.
Each tendon stretches over one span including both neighboring piers in
such a way that the tendons overlap over a single pier. Their distribution
over the cross section is shown in Figure 5.17.

5.4.1 Visual Bridge design system
Visual bridge design system (VBDS) is an AutoCAD-based finite element
program (Wang and Fu 2005). VBDS was specially developed for the calcu-
lation of bridge structures including their construction processes. The basic
idea is to define construction stages and the incremental actions of each
stage that can be accumulated to obtain the final results.

CAVO 4.1
CAVO 3.1

CAVO 6.1

CAVO 5.1

CAVO 1.1

CAVO 8.1

CAVO 2.1 CAVO 7.1

Section A-A

Figure 5.17 Location of the tendons in the cross section.