This document presents an overview of the working stress design (WSD) method for designing rectangular reinforced concrete beams. It defines singly and doubly reinforced beams, and explains that WSD is based on elastic theory, with concrete and steel assumed to respond elastically up to 50% of their compressive strength and yield strength, respectively. The key aspects of WSD covered include design conditions for cracked and uncracked sections, strain compatibility, and calculation of resisting moments for singly and doubly reinforced beams. Advantages of WSD include its compatibility with elastic analysis and familiarity to experienced engineers, while disadvantages are its inability to directly predict failure modes or compare to experimental collapse tests.

2. Presentation on
Rectangular beam design :
singly and doubly reinforced
beam by WSD

3. What is a 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, but when steel is provided in
tension zone as well as compression zone is called doubly
reinforced beam.

4. Necessity of reinforcement in
beam:
longitudinal reinforcement is placed
closed to the bottom side of the beam
Concrete is good in compression and bad in tension.
Tensile strength of concrete is about 1/10 of f’c.

5. Behaviour of a beam under loads

6. RCC design methods:
RCC design
method
USD
method
WSD
method

8. Working stress design method
(WSD)
 This design concept is based on elastic theory, assuming a straight line
stress distribution along the depth of the concrete. Concrete response
elastically upto compressive strength not exceeding about ½ of its strength,
while steel remains elastic practically upto yield strength. So, in practically,
allowable stresses are set at about ½ the concrete compressive strength
and ½ the yield stress of steel.
 The concrete remain elastic at ½×f’c which range to strain of about 0.0005
and the steel is elastic near to it’s yield point or strain of 0.002.
 According to ACI code the value is equal to 0.45× f’c .
Assumptions:
1) Section remains plane
2) Stress proportioned to Strain
3) Concrete not take tension
4) No concrete-steel slip

9. Fig: Steel stress-strain curveFig: Concrete stress-strain curve
Both of the material’s stress is proportional to strain

10. Design Conditions:
1) Stress elastic and sections uncracked:
Tensile strength of concrete fct <Modulus of rupture fr
Compressive stress of concrete fc << ½ f’c
Tensile stress in steel fs < fy yield strength of steel
2) Stress elastic and section cracked:
Tensile strength of concrete fct > Modulus of rupture fr
Compressive stress of concrete fc < ½ f’c
Tensile stress in steel fs < fy yield strength of steel

11. Singly reinforced beam :

13. Strain compatibility:

15. Doubly reinforced beam :
If concrete section cannot develop the required compressive force to resist the
maximum bending moment then additional reinforcement is added in the
compression.

16. Resisting Moment:

17. Strain compatibility :
ACI recommended that f’s be
equal to twice this value

18. Following are some advantages of Allowable stress design method
• Elastic analysis for loads become
compatible for design.
• Old famous books are according to this
method.
• Experienced engineers are used to this
method.
• In past it was the only method for design
purposes.
• This method is included in AISC-05
specifications as an alternate method.
Advantages of Using WSD
method

19. • Latest research and literature is very
limited.
• Same factor of safety is used for
different loads.
• Failure mode is not directly predicted.
• With some overloading, the material
stresses increase but do not go to
collapse.
• The failure mode can not be observed.
• The warning before failure cannot be
studied precisely.
• Results cannot be compared with
experimental tests up to collapse.
Disadvantages of Using WSD
method