Civil Engineering Reference
In-Depth Information
Tendon
P
Central axis
(a)
(b)
Central axis
(c)
Figure 5.8
Equivalent load through discretization of the tendon force. (a) Tendon as
external force of an element. (b) Equivalent tendon force of an element.
(c) Equivalent tendon forces along the central axis of the beam.
additional moments called
secondary moments
. A common approach to
evaluate secondary moments due to post-tensioning is to model the effect
of the post-tensioning tendon as a series of equivalent uniformly distributed
loads. Figure 5.9 shows the required equations for the calculation of the
equivalent loads for a typical end span of a post-tensioned beam.
Central line of
pier
c
4
P
c
1
C.G.C
c
3
e
2
c
2
e
4
y
ti
e
3
e
1
0.4
L
0.5
L
0.1
L
L
(a)
w
eq
3
M
4
M
1
p
P
w
eq
1
w
eq
2
e
1
=
y
ti
−
c
1
e
4
=
y
t
1
−
c
4
c
3
= (
c
2
− 5
c
4
)/6
w
eq
3
= 2
P
(
e
4
−
e
3
)/(0.1
L
)
2
e
2
=
c
2
−
y
t
1
M
4
=
Pe
4
w
eq
1
= 2
P
(
e
1
+
e
2
)/(0.4
L
)
2
e
4
=
y
t
1
−
c
3
w
eq
2
= 2
P
(
e
2
+
e
3
)/(0.5
L
)
2
(b)
M
1
=
Pe
1
Figure 5.9
(a) and (b) Post-tensioning equivalent loads for two-span continuous bridge.
(Data from Precast/Prestressed Concrete Institute,
Precast Prestressed Concrete
Bridge Design Manual
, 3rd Edition, 2011.)
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