Civil Engineering Reference
In-Depth Information
Design torque for this spandrel
beam may be reduced because
moment redistribution is possible
Figure 15.7
Compatibility torsion.
c
tension-compression. This cracking value is taken to be
4
f
and thus the torque at
cracking,
T
cr
, is
A
cp
p
cp
c
T
cr
4
f
When reinforced concrete members are subjected to axial tensile or compressive
forces,
T
cr
is to be computed with the expression to follow in which
N
u
is the factored
axial force taken as positive if the force is compres
sive and n
egative if it is tensile.
A
cp
p
cp
f
pc
c
T
cr
4
f
1
c
4
f
After cracking occurs, the torsional moments in the spandrel beam shown in Figure
15.7 are reduced as a result of the redistribution of the internal forces. Consequently, the
torsional moment used for design in the spandrel beam can be reduced.
15.4
TORSIONAL STRESSES
As previously mentioned, the torsional stresses add to the shear stresses on one side of a
member and subtract from them on the other. This situation is illustrated for a hollow
beam in Figure 15.8.
Figure 15.8
Torsion and shear stresses in a hollow
beam.
(a) torsional stresses
(b) shear stresses
