Civil Engineering Reference
In-Depth Information
The Lever Arm Distance from
T
to
C
30.00
3.34
26.66 in.
z
Calculating
a
,
c
,
and
t
a
4
4.19
8.19 in.
c
a
1
8.19
0.85
9.64 in.
t
d
c
30
9.64
9.64
(0.003)
(0.003)
0.00634
c
0.005
Section is ductile and
0.90
Calculating
M
n
M
n
Tz
(0.90)(607.2)(26.66)
14,569 in.- k
1214 ft- k
5.3
ANOTHER METHOD FOR ANALYZING T BEAMS
The preceding section presented a very important method of analyzing reinforced con-
crete beams. It is a general method that is applicable to tensilely reinforced beams of any
cross section, including T beams. T beams are so very common, however, that many de-
signers prefer another method that is specifically designed for T beams.
First, the value of
a
is determined as previously described in this chapter. Should it be
less than the flange thickness
h
f
, we will have a rectangular beam and the rectangular
beam formulas will apply. Should it be greater than the flange thickness
h
f
(as was the
case for Example 5.2), the special method to be described here will be very useful.
The beam is divided into a set of rectangular parts consisting of the overhanging parts
of the flange and the compression part of the web (see Figure 5.7).
The total compression
C
w
in the web rectangle and the total compression in the over-
hanging flange
C
f
are computed:
c
ab
w
C
w
0.85
f
c
(
b
b
w
)(
h
f
)
C
f
0.85
f
but if
a
h
f
, replace
h
f
with
a
.
Figure 5.7
Separation of T beam into rectangular parts.
