Prestressed/post-tensioned concrete bridges - Computational Analysis and Design of Bridge Structures - page 131

Raised tendons

(a)

All tendons

Partial tendons
sheathed

(b)

Figure 5.2 Prestressing strand profiles. (a) Harped strands. (b) Debonded strands.
The dashed lines indicate debonding material around prestressing strand.

tendons. In the most common technique of internal post-tensioning, cables
are threaded through ducts in the cured concrete and the stressed tendons
are locked with mechanical anchors. These cables are stressed to design
values by hydraulic jacks, and the ducts are thoroughly grouted up with
cement grout after stressing has occurred. Figures 5.4 and 5.5 show two
different types of post-tensioning. Figure 5.4 illustrates a post-tensioned
beam before concrete pouring and post-tensioning to show its rebar cages
and conduits. Figure 5.5 shows a perspective view of a typical precast bal-
anced cantilever segment with various types of tendons (FLDOT 2002).
Also illustrated in FLDOT (2002), Figure 5.6 shows a typical layout of
cantilever tendons that are anchored on the face of the precast segments,
which do not allow later inspection of the anchor head following ten-
don grouting. An alternate approach is to anchor the cantilever tendons
in blisters cast with the segments at the intersection of the top slab and
web where anchorages of these tendons can be inspected at any time. The
same arrangement can be made for bottom continuity tendons at midspan.
Figure 5.7 shows a typical layout of span-by-span tendons for an interior
span where all tendons deviate at a common deviation saddle.