This document provides information on the design of a concrete beam, including: 1) Key principles in beam design such as determining the effective depth ratio and performing deflection checks. 2) Details on flanged beam design including how the location of the neutral axis affects the process. 3) Procedures for continuous beam design including determining load cases, calculating fixed end moments, and using moment distribution.

1. Building Project (SPC1)
Design of Concrete Beam
Done by: Eng.S.Kartheepan (M.Sc, B.Eng, AMIESL, AMIIESL)
Department of Civil Engineering
IET, Katunayake
E-mail: karthee2087@gmail.com

2. Principle in beam design
• Normally in beam design, the effective depth of beam is
determined the ratio between span/effective depth is less or
equal to 15. (l/d <=15)
• This should be performed in the initial stage of design after that
design calculation for beam will be executed and finally the
deflection check will be carried out to make sure the particular
effective depth.
• Normally in continuous beam design, load cases are going to do
for finding the critical bending moment and critical shear force.

3. Flanged Beam
• The depth of neutral axis in relation to the depth of the
flange will influence the design process.
• The neutral axis of the beam is given below
• When the neutral axis lies within the flange (hf), the
breadth of the beam at mid- span is equal to the effective
flange width (bf).
x<hf – Flanged beam action
• If x>hf then the breadth is taken as the actual width of
the beam (bw)
Effective span – for continuous beam the effective span should
normally taken as the distance between the centres of supports

4. Effective Flange width
Effective width of flanged beam ?
(BS8110-1997-Part – 01)

5. Effective Flange width
Effective width of flanged beam?
• The In the absence of any more accurate determination this
should be taken as:
a) for T-beams:web width + lz/5 or actual flange width
b) for L-beams:web width + lz/10 or actual flange width
Where:
• lz - is the distance between points of zero moment (which, for
a continuous beam, may be taken as 0.7 times the effective
span)

6. Load distributions and moments

7. Load distributions and moments

8. Load distributions and moments

9. Fixed End Moments
Example

10. Fixed End Moments
Example

11. Fixed End Moments

12. Fixed End Moments

13. Fixed End Moments

14. Fixed End Moments

15. Continuous beam design
• After the finding the fixed end moments in each span of the
beam, moment distribution will be carried out to finding the
final bending moments in each cases.
• Load cases are very important to finding the final design
bending moment from all cases and also critical bending
moments and shear forces can be found.
• Moment distribution is already discussed in slab design and
follow the same approach.

16. Principle in beam design
• If the number of span is two then there are three cases will
be taken in analysis.
• How ever, if the number of span is more than three, those
cases also three cases will be selected.
Example:
1. Load case – 01: all spans loaded with 1.4Gk+1.6Qk
2. Load case – 02: alternate spans loaded with1.4Gk+1.6Qk
3. Load case – 03: alternate spans loaded with 1.4Gk+ 1.6Qk

17. Principle in beam design

18. Principle in beam design
Example

19. Principle in beam design
Case No: 01

20. Principle in beam design
Case No: 02

21. Principle in beam design
Case No: 03

22. Shear Force Diagram

23. Bending Moment Diagram

24. Classification of exposure conditions (Table 3.2,
BS8110, 1997, Part - 01)

25. Nominal cover to all reinforcement (including links)
to meet durability requirements (Table 3.3, BS 8110,
1997)

26. Nominal cover to all reinforcement (including links) to
meet specified periods of fire resistance (Table 3.4, BS
8110, 1997)

27. Design formula

28. Reynold’s Hand book

29. Minimum Reinforcement

30. Bar Spacing in Beam

31. Shear check in Beam

32. Shear check in Beam

33. Design Concrete Shear Stress

34. Bent-up bar

35. Deflection check in beam

36. Deflection check in beam

37. Deflection check in beam

38. Crack control in beam

39. Curtailment detailing in reinforcement work
Curtailment is a way of reducing the area of tensile reinforcement
at points/areas (either on a beam/slab) where bending moment is
minimum or zero for the purpose of achieving an economic
design.
Simplified rules for beam
Curtailment of Reinforcement in Beams: Reinforcements are
curtailed along its length in beams depending on the bending
moment at the section. Anchorage or development length
required at support is provided during curtailment of
reinforcement.

40. Curtailment detailing in reinforcement work
BS8110 – 1997 – Part – 01 , Clause 3.12.10.2 in Figure 3.24 as
well as BS8110 – 1985 – Part – 01 , Clause 3.12.9 detailed the
rules.

41. Curtailment detailing in reinforcement work
Simplified rules for beam
a) Simply support beam
In the simply supported beam since the moment is nearly zero at
the ends and the tension stresses also reduces so the tension
bars are curtailed.

42. Curtailment detailing in reinforcement work
Simplified rules for beam
b) Continuous beam
In the continuous beam there is negative moment at the
intermediate support so 100% bars are provided at the top but as
negative moment decreases so 60% steel is used.

43. Curtailment detailing in reinforcement work
b) Continuous beam

44. b) Continuous beam

45. Curtailment detailing in reinforcement work
C) Cantilever beam

46. C) Cantilever beam

47. Lap Length in Beam
In case of beam we generally use 24d for compression zone and 45d for
tensile/tension zone
• Lapping (24d) in top bars avoided L/3 distance from both end. For top bar
lapping should be at mid span.
• Lapping (45d) in bottom bars lap should be provided at column junction or
L/4 distance from column face but should not be in mid span of beam.
• Stirrups should be closely spaced near the columns and lose/normal at mid
span.
• Lapping of bars should be alternately provided

48. Lap position in Beam, Column and Slab
Laps:
- between bars should normally be staggered and not located in
areas of high moments