BASICS STEP FOR DESIGN AND IS CODES

1. DESIGN OF RC BEAMS
PRESENTED BY
AGALIYA B V
BASINENI UDAY KUMAR

2. Basic Steps To Design A Beam
 Assume the section size, grade of steel and concrete according to
the structure to be built,
 Calculate the total UDL, point load and other loads if applicable,
 Calculate the factored moment,
 Revise the size and grade of materials if required,
 Calculate the area of steel required,
 Provide the reinforcement detail.
Before going to start the design of beam, let's understand the
following three concepts which are useful for design calculation.

3. BEAMS
 Beam is a horizontal structure member used to carry vertical load, shear
load and sometime horizontal load.
Beam type
 There are two types of RCC beam, Singly reinforced beam and doubly
reinforced beam.
Singly reinforced beam
 If the factored moment (Mu) is less than the limiting moment
( Mulim ) then the beam is designed as a singly reinforced beam.
( Mu<Mulim )
 We mostly use the singly reinforced beam in the building if the stresses
are less.
 The bottom reinforcements are designed to resist the tensile load.
 Top reinforcements are also provided in a singly reinforced beam but it
is designed to hold the stirrups in position and not designed to be
carried the compression load.

4. Doubly reinforced beam
 When the factored moment (Mu) is greater than the limiting
moment (Mulim) then the beam is designed as a doubly reinforced beam.
(Mu > Mulim)
 The bottom reinforcements are designed to resist the tensile load and top
reinforcements are designed to resist the compressive load.
 The doubly reinforced beam is most suitable where there is a higher
chance of earthquake or stress reversal. also, if an increase in depth is
limited for the beam.

5. Neutral axis
 Neutral axis separates the compression and tension zones in the beam. it
is denoted by xu. formula to find xu is following,
 xu=0.87⋅fy⋅Ast0.36⋅fck⋅bxu=0.87⋅fy⋅Ast0.36⋅fck⋅b
 To avoid the brittle failure of concrete, keep the maximum depth of
the neutral axis (xumax) always less than the neutral axis (xu).
xu ⊁ xumax
 The value of xumax for different grade of steel can be obtained from
 IS 456, p- 70 or SP. 16, p-9.

6. TYPES OF BEAM SECTION
Types of beam section
There are three types of beam section,
Balanced section
In the balanced section,
xu = xumax
Mu = Mulim
The strain in concrete and steel will reach their limiting values
simultaneously.

7. Under reinforced section
 The steel will fail first with showing the warning if under reinforced
section is used in the beam. the failure called ductile failure.
 Every designer prefers to design the section according to the under the
reinforced section.
xu < xumax
Mu < Mulim
Over reinforced section
 The concrete will fail first without showing any sign. the sudden
failure will occur if the over reinforced section is used. the failure will
be called brittle failure.
xu > xumax
Mu > Mulim

8. DETAILS PROCEDURE OF DESIGN OF
BEAM
Step 1: In the first step, calculate the intensity of the load which is
expected to act on the beam. This can be found out by adding the
transferrable loads from the slab to the beam, and the self-weight of the
beam. Also find out the clear span of the beam to be designed, from the
provided drawings.
Step 2: In the next step, find out the effective span of the beam (pg 34 of
IS456). In case of a simply supported beam, the effective span is found
out, should be the least of the following two values-
 Clear span plus effective depth
 Centre to center distance of the support.

10.  In the case of Cantilever Beam, the clear span(overhang portion) is mostly
adopted as the effective span to be used for the purpose of Design. After
finding out the effective span of the beam, find out the bending moment
and shear force, from the loads obtained through step 1.
Step 3: In this step, find out the trial dimensions of the beam. In the case of a
simply supported beam, the trial depth is taken as l/12 to l/15, where l is the
effective span of the beam. The breadth of the beam taken as is half the depth
of the beam.
Step 4: Perform the Depth check step. The depth check formulae provide the
minimum required depth of that beam and can be found out from any Design
book. The provided depth should always be equal to or greater than minimum
depth obtained. If not, the section should be redesigned by using different
span to depth ratios.

11. Step 5: Calculate the amount of reinforcement required. As the section
Designed should be an under reinforced one, so that formulae required for
under reinforced section should be adopted. After putting the required
value in the formulae, a quadratic equation is going to be formed, which
when solved, provides the amount of reinforcement used, depending upon
the bending moment and the dimensions of the beam.
After finding out the amount of reinforcement used, it is then checked
against the minimum reinforcement required for the section. It is also
checked against the maximum reinforcement that should be used, which is
generally 4% of the total cross-sectional area of the beam. If it does satisfy
against this two of it, the section should be redesigned.
Step 6: In the next step, calculate the cross-sectional area of a single steel
bar, that is going to be provided in the beam as per their diameter. Then by
dividing the amount of reinforcement used obtained in the previous step,
by the cross-sectional area of a single bar, the number of the bars required
for bending can be found out easily. The design for bending is completed

15. Step 7: The shear design starts. At the beginning of this step, find out the
nominal shear stress and permissible shear strength depending upon the
dimensions, and the percentage of tensile reinforcement. If the nominal
shear strength exceeds the permissible shear stress, shear reinforcement is
to be designed. It is also verified that the nominal shear stress should not
exceed the maximum shear strength, either the section is redesigned.
Step 8: As per shear reinforcement formulae, the spacing of shear
reinforcement is found out. The obtained spacing should not be more
than—
 0.75d, where “d” is the depth of the section
 300mm.
 It is also checked against the minimum spacing required.

16. Step 9: The Serviceability check is done. The Serviceability check
includes, check for deflection and cracking (pg 37 of IS 456). The
development length (pg 42 of IS4546) is also found out from the given
formulae.
Step 10: This is the last step of the Complete Design process, in which,
detailed design data are provided and a cross-section of the beam showing
the reinforcement detailing is also provided.

17. THANK YOU