Prestressed/post-tensioned concrete bridges - Computational Analysis and Design of Bridge Structures - page 158

Figure 5.35 Section of the AASHTO beams with strands.
The precast and prestressed AASHTO type V beams contain different
numbers of strands, depending on the span length. Figure 5.35 shows the
cross sections with the reinforcement for spans 1 and 2. The I-beam section
on the left is at midspan, and the one on the right is over the supports. In
the first two spans, 71 12,7-mm (1/2″) diameter strands are placed; 27 of
these are draped.
In the model, the prestressing truss is situated at the centroid of strands.
And, while spans 3 and 4 are shorter than spans 1 and 2, the number
of placed strands is smaller, which results in a different geometry of the
trusses.
While spans 1 and 2 are prestressed with 71 strands and spans 3 and 4 with
43, the resulting forces applied on the truss elements are (1) F 1,2 = 9123.5 kN
and (2) F 3,4 = 5525.5 kN.
The construction sequence of the bridge US23043 has six stages:
• Stage 1 —Place precast I-beams from pier to pier.
• Stage 2 —Cast midspan diaphragms, leaving a gap in the middle of
the cross section.
• Stage 3 —Pour the slab, except in the region of piers and in a gap in
the middle of the cross section.
• Stage 4 —Cast the gaps of the midspan diaphragms and the slab.
• Stage 5 —Cast the pier diaphragms.
• Stage 6 —Pour the slab in the regions of the piers.