Civil Engineering Reference
In-Depth Information
Figure 12.2
Bridge cross-sections considered in Examples 12.1 to 12.3: (a) closed section;
(b) open section.
prestressing force
P
m
and due to the sustained load
q
, respectively. The
permanent stress at any
fi
bre due to
P
m
and
q
combined is:
M
q
y
P
m
A
σ
perm
=
I
(1
−
β
D
)
−
(12.7)
where
A
and
I
are the area and the second moment of area about centroidal
axis of the gross concrete section;
y
is the coordinate of the
bre considered,
measured downward from the centroidal axis (Fig. 12.2). Substituting Equa-
tion (12.5) to (12.7) in Equation (12.2) and solving for the balanced de
fi
fl
ection
factor gives:
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