Civil Engineering Reference
In-Depth Information
Figure 6.1
The principle of parasitic moments
but of opposite sign, must be applied at each internal support Figure 6.1 (i). These
continuity moments are called the 'parasitic moments' or
M
p
. The prestress moment
at any point in a continuous beam is then
Pe
+
M
p
, Figure 6.1 (j). Although these
continuity moments due to prestress are of exactly the same nature as the continuity
moments due to external loads, engineers and students appear to be baffl ed by them.
However, whereas the free bending moments and the continuity moments due
to external loads are linked by the laws of statics and are consequently considered
together as 'the bending moment', it is convenient to consider
Pe
and
M
p
separately.
The eccentricity of the prestress is under the control of the designer, who may thus
vary the resulting
M
p
between certain limits, as explained in
6.8
.
