2. BEAM - INTRODUCTION
► A beam is a structural element that primarily resists loads
applied laterally to the beam’s axis.
► Its mode of deflection is primarily by bending. The loads
applied to the beam result in reaction forces at the
beam’s support points.
► The total effect of all the forces acting on the beam is to
produce shear forces and bending moments within the
beam, that in turn induce internal stresses, strains and
deflections of the beam
3. TYPES OF BEAMS: ACCORDING TO END
SUPPORT
1. Simply supported beam
2. Continuous beam
3. Over hanging beam
4. Cantilever beam
5. Fixed beam
6. Trussed beam
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16. CANTILEVER BEAM
► A cantilever beam is a rigid structural element supported at one
end and free at the other, as shown in figure. The cantilever
beam can be either made of concrete or steel whose one end is
cast or anchored to a vertical support. It is a horizontal beam
structure whose free end is exposed to vertical loads.
17. ► In a building, a cantilever is constructed as an extension of a
continuous beam, and in bridges, it is a segment of a cantilever
girder. It can be constructed either cast-in-situ or by segmental
construction by pre-stressing methods.
► Cantilever construction allows overhanging structures without
additional supports and bracing. This structural element is widely used
in the construction of bridges, towers, and buildings, and can add a
unique beauty to the structure.
► This beam carry load over the span which undergoes both shear stress
and bending moment.
18. Structural Behaviour of Cantilever
Beam
► A cantilever beam bends downwards when it is subjected to
vertical loads,A cantilever beam can be subjected to point
load, uniform load, or varying load.
► Cantilever Beam Bending Downwards Due to a Load at free
end.
► Irrespective of the type of load, it bends downwards by
creating a convexity upwards. This bending creates tension
in the upper fiber and compression in the lower fibers.
Hence main reinforcement is provided to the upper fiber of
the concrete beam, as there is high tensile stress as shown
in Figure
23. SHEAR FORCE
► The shear force at any section of a cantilever
beam is the sum of loads between the section
and the free end
BENDING MOMENT
► The bending moment at a given section of a
cantilever beam is the sum of moments about the
section of all the loads acting between the
section and the free end.
24. Advantages of Cantilever Beams
► Cantilever beams do not require support on the
opposite side.
► The negative bending moment created in cantilever
beams helps to counteract the positive bending
moments created.
► Cantilever beams can be easily constructed.
25. The disadvantages of cantilever beams
are:
► Cantilever beams are subjected to large
deflections.
► Cantilever beams are subjected to larger moments.
► A strong fixed support or a backspan is necessary
to keep the structure stable.
37. Application of Cantilever beam
► Cantilever bridges.
► Overhanging elements and projections.
► Balconies.
► Machinery and plant such as cranes.
► Overhanging roofs such as stadium roofs, and shelters.
► Shelving.
► Furniture.
