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358 Barry’s Advanced Construction of Buildings
Negative bending over supports
Positive bending between supports
Pairs of bars cranked
over support
Stirrup
Figure 6.6 Reinforced concrete beam to span continuously over supports.
Stretching of top
surface indicates
tensile stress
Main reinforcement on
top of the cantilever slab
Compression of lower
surface indicates
compressive stress
Slab projects as
cantilever from wall or
frame
Figure 6.7 Cantilever slab.
Because of the fixed end support, the upward negative bending at supports will cause
some appreciable deformation bending of columns around the connection of beam to
column. Where a beam is designed to span continuously over several supports, as illustrated
in Figure 6.6, it will suffer negative, upward bending over the supports. At these
points, the top of the beam will suffer tensile stress and additional top reinforcement will
be necessary. Here additional top reinforcement is used against tensile stress, and the
bottom reinforcement is cranked up over the support to provide shear reinforcement, as
illustrated in Figure 6.6.
Cantilever beams
A cantilever beam projects from a wall or structural frame. The cantilever illustrated in
Figure 6.7 may take the form of a reinforced concrete slab projecting from a building as a
balcony or as several projecting cantilever beams projecting from a structural frame to
support a reinforced concrete slab. As a simple explanation of the stress in a fixed end