Prestressed/post-tensioned concrete bridges - Computational Analysis and Design of Bridge Structures - page 149

Z XX X Z XX Z XX Z XX

X Y Z XX YY ZZ X Y Z XX YY ZZ X Y Z XX YY ZZ X Y Z XX YY ZZ

Figure 5.22 Boundary conditions of Verzasca 2 Bridge model 3.

between spans 4 and 5 is fixed in the longitudinal direction of the bridge.
This point is marked with an additional X as X Z XX.
Besides the structural weight, Model 3 also takes into account the post-
tensioning forces. Although this model considers the bridge built all at
once, the definition of the loads already includes the incremental loads.
Therefore, instead of defining the structural weight of the whole model,
the weights are divided into six construction stages. The tendon forces
are also defined as they are applied on the structure during construction.
These forces will be discussed in Model 4 for the construction stages. For
this model, it is assumed that all these loads are applied at the same time.

5.4.2.4 Model 4: Girder built with actual construction stages
Model 4 is exactly the same as Model 3, but with the added consideration
of the construction stages. Span 5 is built in stage 1. These construction
stages include part of the neighboring span, ending where the post-tension
tendon is anchored (in the section of dead load point of contraflexure).
Then, in stage 2, the rest of short span 6 is built. Spans 4 to 1 are built
consecutively in stages 3 to 6.
Each stage also has a fixed sequence:

• Cast the concrete
• Stretch the tendon to 30% of the inal stress after ive days
• Stretch the tendon to 70% of the inal stress after 14 days
• Remove the falsework and formwork
• Stretch the tendon to the inal stress, as soon as the next stage's ten-
don is stressed to 70% of the final stress

The time sequence of the construction stages has been assumed according
to the dates that the plan for each stage was checked. Table 5.2 shows the
dates and the assumed construction time.

5.4.2.5 Model 5: Three girders skew supported
Model 5 (Figure 5.23) is the most complicated model of the Swiss bridge in
this series. In regard to the creep and shrinkage effects, there should not be