Civil Engineering Reference
In-Depth Information
This value exceeds 4 but is well below 8. The conclusion is that con-
tinuous pedestrian traffic might result in adverse comment, but the level
of movement typical of an open-plan office would not do so.
3.11.4
Composite beam - fire design
The method used below is explained in Sections 3.3.7 and 3.10.
From Equations 3.118 the characteristic loads per unit length of beam
are:
g
k
=
17.6 kN/m
q
k
=
24.8 kN/m
so
q
k
/
g
k
=
1.41
From Equation 3.31,
1071 1
135
. .
. .
+×
+×
η
fi
=
.
.
=
057
15
141
The beam will be designed to have a bending resistance at mid-span in
fire resistance class R60. The design bending moment at mid-span for cold
design is 563 kN m, from Equation 3.108 and the resistance is 709 kN m,
from Equation 3.115. The resistance ratio (Equation 3.32) is
η
fi,t
=
0.57(563/709)
=
0.45
Fire protection is provided by encasing the web in normal-density con-
crete, as shown in Fig. 3.31, and by filling the voids above the steel top
Figure 3.31
Detail of concrete-encased web
