Design value of strength For concrete
where, ymc = Partial factor of safety for concrete = 1.5
fd = design value of strength
For steel
fd = fy / 1.15 = 0.87fy
Singly Reinforced Beam
Here d = effective depth of the beam
Some special cases
Doubly Reinforced Section
where fSC = stress in compression steel and it is calculated by strain at the location of compression steel (fSC)
Singly reinforced T-Beam
Case-1: When NA is in the flange area
i.e., Xu < Df
(i) for Xu
(ii) Ultimate moment of resistance
Mu = 0.36fckbfXu(d - 0.42Xu)
or Mu = 0.87 fyAst(d - 0.42Xu)
Case-2: When NA is in the web area (Xu > Df)
Case (a) when Xu > Df and
i.e., depth of flange in less than the depth of the rectangular portion of the stress diagram.
Special Case (2): When Xu > Df and
i.e., the depth of the flange is more than the depth of the rectangular portion of the stress diagram.
As per IS 456 : 2000
(bf – bw) Df portion of the flange is converted into (bf – bw)yf section for which stress is taken constantly throughout the section is 0.45 fck.
As per IS 456 : 2000
yf = 0.15Xu + 0.65Df < Df
For actual depth of neutral axis
0.36fekbwXu + 0.45fek(bf - bw) yf = 0.87fyAst1 + 0.87fyAst2
or 0.36fckbwXu + 0.45fck(bf - bw)yf = 0.87fyAst
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1. What is the purpose of beam design in civil engineering? |
2. What are the key factors considered in beam design? |
3. What are the different types of beams used in civil engineering? |
4. How is beam design affected by different load types? |
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