Civil Engineering Reference
In-Depth Information
upper portion of the beam; this is in addition to the orthogonal web
reinforcement.
1.6
ACI Building Code 318-83 (revised 1986)
1.6.1
Flexural strength
For flexural design, ACI Code 318-83 (revised 1986) defines a deep beam
as a beam in which the ratio of the clear span
l
o
to the overall depth
h
is
less than the limits in Eqn (1.18):
simple spans:
l
o
/h
<1.25
(1.18a)
continuous spans:
l
o
/h<
2.5
(1.18b)
1.6.1.1
Minimum tension reinforcement
The main steel ratio ρ shall not be
less than ρ
min
of Eqn (1.19)
ρ
min
=200
/f
y
(1.19)
where ρ
min
=
A
s
/bd, A
s
is the main tension reinforcement,
b
is the beam width,
d
is the effective depth and
f
y
is the steel strength (lb/in
2
). For
f
y
=460N/mm
2
(about 66500 (lb/in
2
)), ρ
min
is about 0.3%.
1.6.1.2
Web reinforcement
An orthogonal mesh of web reinforcement is
required. The minimum areas of the vertical and horizontal bars shall satisfy
Eqn (1.20).
A
v
/
bs
v
≥0.15%
A
h
/bs
h
≥0.25%
(1.20a)
(1.20b)
where
A
v
is the area of the vertical bars within the spacing
s
v
and
A
h
is the
area of the horizontal bars within the spacing
s
h
.
1.6.1.3
Flexural design
Apart from the above requirements, the ACI Code
does not give further detailed guidelines. It merely states that account shall
be taken of the nonlinear distribution of strain and lateral buckling.
1.6.2
Shear strength
The shear provisions of ACI Code 318-83 (revised 1986) apply to top-
loaded simple or continuous beams having a (clear span)/(effective depth)
ratio
l
o
/d
less than 5.
1.6.2.1
Shear strength: simply supported deep beams
Calculations are
carried out for the
critical section
defined as follows. For uniformly
