Environmental Engineering Reference
In-Depth Information
Fig. 3.7 Bending moment-curvature relationship for rectangular prestressed concrete cross-
sections (simpli
ed)
The progression of the M-
k
relationship after exceeding M
I,II
differs according to the
type of prestress:
- Pretensioned and grouted post-tensioned tendons: The M-
relationship in the
cracked state (II) is generally flatter than for the non-prestressed reinforced concrete
cross-section, depending on the cross-sectional area of the prestressing steel.
The prestressing steel contributes to carrying the external action effects up until
the 0.1%proportionality limit is reached (f
p0.1
;(1/r)
p0.1
). Its reserves of loadbearing
capacity depend on the effective prestress
s
ð
0
P
at the ultimate limit state taking into
account all losses of prestress at the point in time being considered (t
0
t
k
<1
), see
Figures 3.4 and 3.5:
Ds
ptd
¼
f
p0
:
1d
s
ð
0
Þ
ptd
¼
f
p0
:
1k
=g
S
g
P
s
ð
0
Þ
Pmt
- Internal or external unbonded tendons: The cross-section of the prestressing steel
only contributes to carrying the external action effects via the internal statically
indeterminate coupling with the reinforced concrete cross-section. If this is neglec-
ted, the cross-section behaves like a reinforced concrete cross-section with an
additional eccentric or concentric compressive force.
