Prestressed/post-tensioned concrete bridges - Computational Analysis and Design of Bridge Structures - page 154

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Figure 5.30 Accumulated moments due to structural weight and post-tension, Verzasca 2
Bridge model 4.

the first stage, and not 0, because the first construction stage ends 3.75 m
over the support. Once span 6 is built continuously to span 5 in the second
stage, the negative moment over pier 5 increases to around 7800 kN-m.
Due to the structural weight of span 4, the moment over pier 5 decreases to
3700 kN-m and increases again with the structural weight of span 3, and so
on. In Figure 5.30, the distribution shows the addition of all moments due
to structural weight and post-tensioning, each in its corresponding static
system. Note that the cracking moment of the beam is around 12,600 kN-m
for section 1 and 16,380 kN-m for section 2 next to the diaphragms.

5.4.3.5 Model 5: Three girders skew supported
The results of Model 5 are similar to the results of Model 4, but now the
moments are distributed to three beams, whereas they were all on the same
beam in Model 4. The moments in the middle beam are 33% higher than
those in the beams at the sides. This can be explained by the fact that the
moment of inertia in the middle beam is 33% higher.
The skew supports that are not taken into account in Model 4 also affect
the distribution of the moments in the different beams. This effect is recog-
nizable in both end spans. The front beam has larger negative moments over
pier 5, because it is nearer to abutment B. Exactly the same effect occurs
over pier 1, where the back beam receives more negative moments, due to a
shorter first span.
Creep and shrinkage not only cause a redistribution of the internal forces
but are also essential factors whenever displacements are evaluated. For the
purpose of comparison, incremental displacements of all 19 stages in the con-
struction sequence are accumulated once for the elastic displacements and once
more for displacements due to creep and shrinkage, for AASHTO and for CEB-
FIP. Then displacements are divided into vertical and horizontal components.
From the vertical displacements shown in Figure 5.31, the construction
sequence can be reenacted. The peaks are located where the construction
stages changed. The sequence was from span 5 leftward to span 1.
The vertical displacements are mainly due to creep and the horizontal
due to shrinkage effects. The horizontal displacements due to shrinkage