Civil Engineering Reference
In-Depth Information
Figure 1.2
CIRIA Guide 2—meanings of symbols
c
1
, c
2
, h, l
and
l
o
The CIRIA Guide considers that the active height
h
a
of a deep beam is
limited to a depth equal to the span; that part of the beam above this height
is taken merely as a load-bearing wall between supports.
1.4.1
CIRIA Guide 'Simple Rules'
CIRIA's 'Simple Rules'
are intended primarily for uniformly loaded deep
beams. They can be applied to both single-span and continuous beams.
1.4.1.1
Flexural strength
Step 1:
Calculate the capacity of the concrete section.
(1.3)
where
f
cu
is the concrete characteristic strength and
b
the beam
thickness.
Step 2
: If
l/h
a
.5 go to step 3. If
l/h
a
>
1.5 check that the applied moment
M
does not exceed
M
u
of Eqn (1.3)
Step 3:
Calculate the area
A
s
of the main longitudinal reinforcement:
A
s
>M/0.87
f
y
z
(1.4)
where
M
is the applied moment,
f
y
the steel characteristic strength
and z the lever arm, which is to be taken as follows:
z
=0.2
l
+0.4
h
a
for single-span beams
(1.5)
z
=0.2
l
+0.3
h
a
for continuous beams
(1.6)
Step 4:
Distribute the reinforcement
A
s
(Eqn (1.4)) over a depth of 0.2
h
a
.
Anchor the reinforcement bars to develop at least 80% of the
maximum ultimate force beyond the face of the support. A proper
