5. Singly Rectangular Beam
A Beam is any structural member
which resists load mainly by bending.
Therefore it is also called flexural
member. Beam may be singly
reinforced or doubly reinforced. When
steel is provided only in tensile zone
(i.e. below neutral axis) is called
singly reinforced beam.
6. Assumptions for
DesignofMembers by Working
Stress Method
Plane sections before bending remain
plane after bending.
Normally, concrete is not considered for
taking the tensile stresses except
otherwise specifically permitted.
Therefore, all tensile stresses are taken
up by reinforcement only.
The stress-strain relationship of steel
and concrete is a straight line under
working loads.
13. Doubly Reinforcement
beam
If a beam cross section is limited
because of architectural or other
considerations, it may happen that the
concrete can not develop the
compression force required to resist
the given bending moment, in this
case ,reinforcement is added in the
compression zone, resulting in so
called Doubly reinforced beam
.i.e., one with compression as well as
tension reinforcement.
14. Why Doubly reinforcement
used
If concrete can not develop the
required compressive force to resist
the maximum bending moment, then
additional reinforcement is provide in
the compression zone.
Reinforcement is provided in both
compression and tension zone.
16. Development of moment
In stress distibution,the design
moment is more than the balanced
moment of resistance of the section,
M = M1 + M2
The additional moment M2 is resisted
by providing compression
reinforcement As’
and additional tensile reinforcement
As2
18. Reinforcement in Beam
The total tensile reinforcement Ast
has two components As1+As2 for M1
and M2
The equation of Ast,
Ast=As1+As2
Where, As1=
(bd/100)
And
As2 = M2/[Ó (d-d’)]
compressive
reinforcement,
19. Clear cover for design
Not less than 1.5 in. when there is
no exposure to weather or contact
with the ground
For exposure to aggressive weather
2 in.