283757893275

356 Barry’s Advanced Construction of Buildings
4d
Radius 2d
Radius 2d
4d
d
d
Figure 6.2 Hooked ends for reinforcing bars.
Rolled ribbed bar
Twisted ribbed bar
Twisted square bar
Figure 6.3 Deformed reinforcing bars.
its twisted surface presents some resistance to slip. The round section, ribbed bar and the
twisted, ribbed bars provide resistance to slip in concrete by the many projecting ribs
illustrated in Figure 6.3. Deformed bars, which are more expensive than plain round bars,
are used for heavily loaded structural concrete.
Shear
Beams are subjected to shear stresses due to the shearing action of the supports, and the
self-weight and imposed loads of beams. Shear stress is greatest at the points of support
and zero at mid-span in uniformly loaded beams. Shear failure occurs at an angle of 45°,
as illustrated in Figure 6.4. Due to its poor tensile strength, concrete does not have great
shear resistance and it is usual to introduce steel shear reinforcement in most beams of
over, say, 2.5 m span.
To maintain the main reinforcing bars in place while concrete is being placed and until
it has hardened, it is usual practice to use a system of stirrups or links, which are formed
from light section reinforcing bars. These rectangular stirrups are attached by binding wire
to the main reinforcement. To provide shear reinforcement at points of support in beams,
the stirrups are more closely spaced, as illustrated in Figure 6.4.
Fixed end support
A beam with pin-jointed end support will suffer simple bending under load, whereas a
beam with fixed end support is restrained from simple bending by the fixed ends, as illustrated
in Figure 6.5. Because of the upward, negative bending close to the fixed ends, the