Civil Engineering Reference
In-Depth Information
Figure 6.22
Non-zero stress limits
Similarly, if the stress limit on the top fi bre at section 2.0 is -1 MPa instead of zero,
under the minimum moment (greatest hogging moment) the centre of pressure may
move down from the prestress tendon centroid to the limit of the augmented bottom
of the kern,
a
b
1
. Using the same assumptions as above,
a
b
1
=
a
b
×(4 + 1)/4 = 1.25
a
b
= 1.25 × 0.768 = 0.96 m.
Consequently, the new prestress lever arm
l
a
= 0.875 - 0.2 + 0.96 = 1.635 m,
increased from 1.443 m.
