Civil Engineering Reference
In-Depth Information
Figure 4.9
Continuous precast bridge of Example 4.6: (a) three-span bridge: (b)
cross-section of one beam at mid-span; (c) joint of precast beams at
supports B and C; (d) typical prestress tendon profiles in precast beams.
tinuous. Again, for the sake of simplicity, we shall consider that the
superimposed load is applied at
t
0
on the continuous structure.
The prestress in each beam is achieved by straight tendons A and
parabolic tendons B and C. The prestressing of A and B is applied to
simple beams, while C is inserted after placing the beams in position
and the cable runs continuous over the whole length of the bridge.
Further, we shall consider that cables B and C have identical pro
les
(Fig. 4.9(d) ). The cross-section areas of prestress steel
A
ps
are 430, 1000
and 1000 mm
2
(0.67, 1.55, 1.55 in
2
) for tendons A, B and C, respectively;
the initial prestress forces are: 500, 1160 and 1160 kN (112, 260 and
260 kip). Consider that these forces exclude friction loss and that the
prestress force is constant over the full length of a tendon.
Non-prestressed steel of total area,
A
ns
fi
3750 mm
2
(5.81 in
2
) is dis-
tributed over all surfaces of the cross-section; thus, we here assume that
A
ns
has the same centroid as
A
c
(point O in Fig. 4.9(b) ) and that the
=
Search WWH ::
Custom Search