Prestressed/post-tensioned concrete bridges - Computational Analysis and Design of Bridge Structures - page 167

of the main causes for inclined cracks, which are harmful to long-term
deflections, and that these tendons are actually very effective in limit-
ing the principal tensile stress.
5.7.1 the continuous rigid frame of sutong Bridge
approach spans
Deflection is mainly a result of two opposite actions. The first action is the
dead loads and live loads, and the second one is the longitudinal tendons,
which usually produce the counterdeflections to the dead loads and live
loads. A lesson learned from the deflection problem in long-span cantilever
bridges is that the deflection control is as important as conventional stress
control in prestressing design. It is commonly known, that the cantilever
tendons are very efficient for balancing the dead loads in the cantilever con-
struction stage. Their effects on the deflections of the bridge would, how-
ever, be limited after the structural system transforms (like the closure of the
main span). Here, the focal point is to design the tendons applied after the
cantilevers are made continuous to avoid the excessive deflections.
The continuous rigid frame of Sutong Bridge approach spans (Pan et al.
2010) is a segmental, cast-in-place concrete cantilever bridge completed in
2007, and the span distribution is 140 + 268 + 140 m (460′ + 880′ + 460′),
among the longest spans in the world. Figure 5.47 shows the bridge in con-
struction. The width of the top slab of the box girder is 16.4 m (53.8′), and
the width of the bottom slab is 7.5 m (24.6′). The height of the box girder
varies from 15 m (50′) at the piers to 4.5 m (14.8′) at midspan. The thick-
ness of the bottom slab varies from 1700 mm (67″) at the piers to 320 mm
(12.6″) at midspan. The web thickness varies in steps from 1000 mm (40″)
at the piers to 450 mm (18″) at midspan. Figure 5.48 shows the arrangement
of the box girder in the bridge, and Figure 5.49 shows the segments and lay-
out of longitudinal tendons including the cantilever webs' bent-down ten-
dons. The central span consists of 63 segments, whereas the two side spans
consist of 33 segments each, and the entire span is constructed in balanced
cantilevers. A similar approach as shown in Section 5.6 is used, except that
MIDAS program (MIDAS 2007) is adopted for this analysis.
Figure 5.47 Construction of the continuous rigid frame of Sutong Bridge approach spans.