RCC Sheet 24

1) Question.

The moment of resistance of a T-beam when the netural axis falls in the web is equal to
Answer.
- 1
  
  $σ_{c b} x b_{F} x d_{F} (d - y)$
- 2
  
  $σ_{c b} x b_{F} x d_{F} (d + y)$
- 3
  
  $σ_{c b} x b_{F} x d_{F} (0.5 d - y)$
- 4
  
  $σ_{c b} x b_{F} x d_{F} (0.5 d + y)$
Answer: 1

Explanation:
2) Question.

In the previous question, the depth of the net compression $(y)$ below the top of a beam is ny
Answer.
- 1
  
  $y = \frac{2 n - d_{F}}{n - d_{F}} x \frac{d_{F}}{3}$
- 2
  
  $y = \frac{3 n - 2 d_{F}}{2 n - d_{F}} x \frac{d_{F}}{3}$
- 3
  
  $y = \frac{n - d_{F}}{2 n - d_{F}} x \frac{d_{F}}{3}$
- 4
  
  $y = \frac{2 n - d_{F}}{3 n - 2 d_{F}} x \frac{d_{F}}{3}$
Answer: 2

Explanation:
3) Question.

When the neutral axis of a T-beam falls outside the flange (below the slab), then
Answer.
- 1
  
  $b_{F} x d_{F} (n + 0.5 d_{F}) = m A_{s t} (d + n)$
- 2
  
  $b_{F} x d_{F} (n - 0.5 d_{F}) = m A_{s t} (d - n)$
- 3
  
  $b_{F} x d_{F} (n + d_{F}) = m A_{s t} (d + n)$
- 4
  
  $b_{F} x d_{F} (n - d_{F}) = m A_{s t} (d - n)$
Answer: 2

Explanation:
Where $b_{F}$ = Width of flange

$d_{F}$ = Depth of Flange or slab,

d = Effective depth or vertical distance between the top of the flange and the centre of tensile reinforcement

n = Depth of neutral axis below the top of the beam

$A_{s t}$ = Gross area of tensile steel, and

m = Modular ratio
4) Question.

If the effective depth of a doubly reinforced concrete beam is d, and maximum stress in steel and concrete is $σ_{s t}$ and $σ_{c b}$ respectively, then the neutral axis depth factor (k) is given by
Answer.
- 1
  
  $k = \frac{m σ_{c b} + σ_{s t}}{m σ_{c b}}$
- 2
  
  $k = \frac{m σ_{c b}}{m σ_{c b} + σ_{s t}}$
- 3
  
  $k = \frac{m σ_{c b} - σ_{s t}}{m σ_{c b}}$
- 4
  
  $k = \frac{m σ_{c b}}{m σ_{c b} - σ_{s t}}$
Answer: 2

Explanation:
5) Question.

Which of the following statement below is correct
Answer.
- 1
  
  The anchorage value of a hook is assumedsixteen times the diameter of the round bar if the angle of the bend is $45^{o}$
- 2
  
  steel bar are generally connected together to get greater length than the standerd lengths by providing hooked splice
- 3
  
  for plain mild steel reinforcing bars, when hooks are used, they should be of U-type
- 4
  
  all of the above
Answer: 4

Explanation:
6) Question.

The length of lap for reinforcement bar in compression shall not be less than
Answer.
- 1
  
  $\frac{ϕ σ_{s}}{2 τ_{b d}}$ or 24 $ϕ$ whichever is smaller
- 2
  
  $\frac{ϕ σ_{s}}{4 τ_{b d}}$ or 24 $ϕ$ whichever is greater
- 3
  
  $\frac{ϕ σ_{s}}{2 τ_{b d}}$ or 30 $ϕ$ whichever is smaller
- 4
  
  $\frac{ϕ σ_{s}}{4 τ_{b d}}$ or 30 $ϕ$ whichever is greater
Answer: 2

Explanation:
where $σ_{s}$ = Actual compressive stress in bar
7) Question.

The length of lap for reinforcement bars in tension shall not be less than
Answer.
- 1
  
  $\frac{ϕ σ_{s}}{2 τ_{b d}}$ or 24 $ϕ$ whichever is smaller
- 2
  
  $\frac{ϕ σ_{s}}{4 τ_{b d}}$ or 24 $ϕ$ whichever is greater
- 3
  
  $\frac{ϕ σ_{s}}{2 τ_{b d}}$ or 30 $ϕ$ whichever is smaller
- 4
  
  $\frac{ϕ σ_{s}}{4 τ_{b d}}$ or 30 $ϕ$ whichever is greater
Answer: 4

Explanation:
where $ϕ$ = Bar diameter,

$σ_{s}$ = Actual tensile stress in bar, and

$τ_{b d}$ = Permissible average bond stress
8) Question.

Which of the folling statement below is correct ?
Answer.
- 1
  
  Diagonal tension is caused by the combined action of longitudinal tension and the transverse shearing stresses
- 2
  
  Shear reinforcement in the form of vertical bars is known as stirrups
- 3
  
  According to IS : 456 - 1978, if the shear stress is less than one -tenth of compressive stress $(σ_{c b})$ in concrete at extreme fibe, no shear reinforcement is necessary
- 4
  
  all of the above
Answer: 4

Explanation:
9) Question.

If modular ratio is m, effective depth is d and stress ratio is $τ = σ_{s t} / σ_{c b}$ then the depth of neutral axis $(n_{c})$ of a balanced section is
Answer.
- 1
  
  $\frac{m}{m - τ} x d$
- 2
  
  $\frac{m}{m + τ} x d$
- 3
  
  $\frac{m + τ}{m} x d$
- 4
  
  $\frac{m}{τ} x d$
Answer: 2

Explanation:
10) Question.

The maximum shear stress $(τ_{m a x})$ in a reinfoeced concrete beam of width (b) and subjected to a shear force (F) is equal to
Answer.
- 1
  
  $\frac{F}{b (3 d - n)}$
- 2
  
  $\frac{2 F}{b (3 d - n)}$
- 3
  
  $\frac{3 F}{b (3 d - n)}$
- 4
  
  $\frac{4 F}{b (3 d - n)}$
Answer: 3

Explanation:

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