Prestressed/post-tensioned concrete bridges - Computational Analysis and Design of Bridge Structures - page 169

there are three external tendons (W1-W3) in the middle of the main span,
with each consisting of 25Φ j 15.24.

5.7.2 results of webs' bent-down tendons
If the cantilever bent-down tendons in the webs as shown in Figure 5.49
are changed into the straight layout of tendons (shown in Figure 5.45), the
shear force provided by the cantilever tendons can be calculated, and the
comparison with the straight layout of tendons is shown in Figure 5.51.
Figure 5.51 shows that the webs' bent-down tendons can provide more
shear force, which can balance the shear force induced by the dead loads.
Therefore, the shear stress in the web will be reduced, and the principal
tensile stress can be effectively limited.

5.7.3 results of two approaches on deflections
Obviously, the preset additional internal tendons in the bottom slabs can
effectively improve the stress deflection. Using the CEB-FIP78 creep and
shrinkage prediction models, which are adopted in the previous bridge code
(JTG D62-85 1985), the increments of deflections of the bridge after the
completion were analyzed, and the increments with and without the preset-
ting internal tendons in the bottom slabs are shown in Figures 5.52 and 5.53,
respectively. Figure 5.52 shows that tensioning the presetting tendons would
induce a camber of about 3 cm at midspan.

80000

70000

Designed layout of cantilever tendons
Straight layout of cantilever tendons

60000

50000

40000

30000

20000

10000

0

0 20 40 60 80 100 120

Center of main piers Midspan

Distance from the center of the main piers (m)

Figure 5.51 Shear force provided by cantilever tendons.