Aksis Giriş Ders

Beam
• A beam is a structural element that primarily resists loads
applied laterally to its axis
• Its primary mode of deflection is bending
Types of beams
• Simply Supported Beam

• Fixed beam
Types of beams
• Overhanging Beam

• Cantilever beam
Continuous Beam
• Beams are made continuous over supports to increase the
structural integrity
• In regions with high seismic risk , continuous beams and
frames are preferred in buildings and bridges
• It is a statically indeterminate structure
Design Steps
1. Depth of beam
 As specified in IS:456-2000, Vertical deflection should not be
more than [Span/350 or 20 mm].
 Above condition is satisfied if Span/Depth ratio is kept not
more than 26
 Generally continuous beams carry very heavy DL and LL so in
practical Span/Depth ratio is kept 10 to 15
 If a higher Span/Depth ratio is used, it will give a shallow
depth requiring high percentage of steel
2. Effective Span
 According to IS:456-2000
 For support width less than 1/12th of clear span:
Effective span= Clear span + Eff. depth of beam
or Whichever
is less
Distance between centre of
supports

 For support width > 1/12th of clear span

or Whichever
is less
600 mm
a. For end span having one end fixed and other continuous
or
For intermediate span

Effective span= Clear span between supports

b. For end span having one end free and other continuous

1
Effective span= Clear span + 2
Effective depth
or
1 Whichever
Clear span+ Width of discontinuous is less
2
support
 For continuous monolithic frames :
Effective span= Center line distance between members
3. Load Calculation
• DL on beam has to be calculated due to self wt. of slab and
floor finish
• Factored values of DL and LL are calculated

4. Bending Moment and Shear Force

• For getting the maximum positive BM near the mid span, LL
is placed over span under consideration and alternate spans
• For maximum negative values of BM at support and maximum
shear force, adjacent spans on both sides of support under
consideration are loaded and also the spans alternate to
these.
• The following empirical coefficients may be used for BM and
SF calculation for continuous beams having approximately
equal spans with UDL resting on supports and not monolithic
with them
5. Redistribution of moments
• The design maximum moment is obtained by decreasing the
negative moment by a particular value and increasing the
positive moment by same value
• According to IS:456-1978 readjustment of moments should not
be more than 15 %

6. Determination of Moment of Resistance

• Moment of resistance is determined using LSM or WSM

7. Determination of Main Reinforcement

• In LSM
8. Shear Reinforcement
9. Detailing
Q. 1. Design a continuous beam of two spans supported on
masonry walls using LSM and allowing for 15% redistribution
of moments. The following data may be used.

Clear span between supports= 6m

width of masonry supports= 300mm
Thickness of reinforced concrete slab= 150mm
Spacing of continuous beams= 3m c/c
Self wt. of floor finish= 0.4 kN/m2
Live load on office floor= 4 kN/m2
Characteristic strength of concrete= fck= 15N/mm2
Characteristic strength of steel= fy = 415 N/mm2
Q. 2. A reinforced concrete continuous beam of three equal
spans AB=BC=CD= 7m, is simply supported at the ends A and
D. If the beam supports a Uniformly distributed LL of 20
kN/m. Design a suitable rectangular section for the beam and
sketch the details of reinforcements. Adopt M-15 grade
concrete and Fe-415 steel.