Prestressed Concrete Structures Multiple Choice Questions on “Design of Shear Reinforcement”.

1. The ultimate shear resistance for any given section, vc should be least of values __________

a) v_{cw} and v_{cf}

b) v_{ew} and v_{ef}

c) v_{rw} and v_{rf}

d) v_{dw} and v_{df}

Answer: a

Clarification: At any given section, the ultimate shear resistance, v_{c} should be the least of values v_{cw} and v_{cf} where, v_{cw = ultimate shear resistance of section cracked in web, vcf = ultimate shear resistance of section cracked in flange.}

2. What should be provided if the shear force due to ultimate load is less than the shear force of the concrete?

a) Tensile reinforcement

b) Shear reinforcement

c) Principle reinforcement

d) Compressive reinforcement

Answer: b

Clarification: When V the shear force due to ultimate loads is less than the shear force of the concrete v_{c}, the shear force which can be carried by the concrete, a minimum shear reinforcement should be provided in the form of stirrups with spacing.

3. The spacing provided for shear reinforcement is given as __________

a) S_{v} = (A_{sv}0.87f_{y}/0.4b)

b) (A_{sv}0.91f_{y}/0.4b)

c) (A_{sv}0.12f_{y}/0.4b)

d) (A_{sv}0.23f_{y}/0.4b)

Answer: a

Clarification: The spacing provided for shear reinforcement S_{v} = (A_{sv}0.87f_{y}/0.4b), S_{v} = spacing of stirrups along the length of member, A_{sv} = cross sectional area of stirrup legs effective in shear, b = breadth (for T,I,L beams it is taken as breadth of rib, b_{w}).

4. When the shear force due to ultimate loads is less than 0.5 times shear force of concrete then shear reinforcement is?

a) Provided

b) Not provided

c) Made equal

d) Made zero

Answer: b

Clarification: When the shear force due to ultimate loads V is less than 0.5 times the shear force of concrete: (v < 0.5v_{c})

Then no shear reinforcement is provided in the members of low importance.

5. When v > v_{c} condition exits, then the shear reinforcement provided includes which extra terms than actual spacing equation?

a) f_{y}, d_{t}, v, v_{c}

b) f_{t}, d_{t}, v, v_{c}

c) d_{t}, v, v_{c}

d) f_{e}, d_{t}, v, v_{c}

Answer: a

Clarification: When V exceeds V_{c} shear reinforcement is required conforming to the relation (V > V_{c})

The extra terms used are f_{y} , d_{t}, v, v_{c} these are included in the spacing equation S_{v}

S_{v} = (A_{sv}0.87f_{y}dt / V-V_{c}).

6. The term dt in the spacing equation is termed as __________

a) Lowest value of depth

b) Neutral value of depth

c) Highest value of depth

d) Peak value of depth

Answer: c

Clarification: When v > v_{c}, the spacing provided in that:

d_{t} is the highest value of depth from the extreme compression fiber to longitudinal bars and depth from extreme compression fiber to centroid of tendons.

7. The spacing of stirrups for maximum shear stress is __________

a) 0.9d_{t}

b) 0.10d_{t}

c) 0.12d_{t}

d) 0.7d_{t}

Answer: d

Clarification: The spacing of stirrups should exceed neither 0.75d_{t} nor 4 times the web thickness of flanged members, for maximum shear stress the spacing of stirrups:

S_{v} > 0.75d_{t} = > x web thickness.

8. The maximum spacing (S_{v})_{max} is provided for the condition is?

a) V > 1.8V_{c}

b) V > 1.5V_{c}

c) V > 2.0V_{c}

d) V > 3.5V_{c}

Answer: a

Clarification: When V exceeds 1.8V_{c}, the maximum spacing should be reduced to 0.5d_{t}, the lateral spacing of the individual legs of the stirrups provided at a cross section should not exceed 0.75d_{t}, if V > 1.8V_{c}, the maximum spacing is:

(S_{v}) max = 0.5 d_{t}.

9. The maximum shear stress value for M_{35} and M_{50} is?

a) 3.5 and 4.0

b) 3.7 and 4.6

c) 3.8 and 6.0

d) 4.2 and 4.0

Answer: b

Clarification: The maximum shear stress value for M_{35} grade concrete is 3.7n/mm^{2}, the maximum shear stress value for M_{50} grade concrete is 4.6n/mm^{2}, M_{30} grade concrete is 3.5n/mm^{2}, M_{40} grade concrete is 4.0n/mm^{2}, M_{45} grade concrete is 4.3, M_{55} grade concrete is 4.8n/mm^{2}.

10. The section should be redesigned if the nominal shear stresses __________

a) Exceeds the given values

b) Equal

c) Zero

d) Constant

Answer: a

Clarification: When the nominal shear stress, v/bd exceeds the maximum permissible shear stress values for the particular grades of concrete like M-30, M-35, M-40, M-45, M-50, M-55 and above then the section should be redesigned (this is according to table of maximum shear stress(n/mm^{2}) (IS: 1343-1980).