# Prestressed Concrete Structures Questions and Answers – Flexural and Shear Strength

This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “Flexural and Shear Strength”.

1. In the case of composite sections, the percentage of tensioned reinforcement is less than?
a) Simple beams
b) Complex beams
c) Tee beams
d) Edge beams

Explanation: In case of composite sections the percentage of tensioned reinforcement is less than that in most simple beams so that the section is invariably under reinforced and the compression zone generally consists entirely of insitu concrete of lower compressive strength, and the value of the cube strength of concrete to be used in flexural strength equations will obviously be that of insitu cast concrete.

2. If the compression zone contains part of precast element, the computation is done by considering?
a) Grades of concrete
b) Cross section
c) Durability
d) Strength characteristics

Explanation: If the compression zone contains a part of precast element, the average compressive strength computed by considering the cross sectional area of insitu and precast concrete is used in the computation of compressive force.

3. The effective bonding between the two parts of composite beams is developed by _______________
a) Smoothing
b) Roughening
c) Painting
d) Detacahing

Explanation: Effective bending between the two parts of a composite beam may be developed by providing castellation in the precast unit or by roughening the contact surface of the precast unit before placing the insitu concrete or by projecting reinforcements from the precast unit which serve as ahead connectors.

4. The design of shear connections depends upon the strength of ____________
a) Ex situ cast concrete
b) In situ cast concrete
c) Tampered concrete
d) Prestressed concrete

Explanation: In the design of shear connection it is generally assumed that the natural bond at the interface contributes a part of the required shear resistance depending upon the strength of the insitu cast concrete and the roughness of the precast element and any extra shear resistance over and above this should be provided by shear connectors.

5. When ties are not provided the permissible values of the horizontal shear stress is?
a) 0.6n/mm2
b) 4.6n/mm2
c) 1.6n/mm2
d) 8.6n/mm2

Explanation: The permissible values of the horizontal shear stress for different types of contact surfaces is specified as: 0.6n/mm2 when ties are not provided and the contact surface of the precast element is free of laitance and intentionally roughened to an amplitude of 5mm and 25n/mm2 when minimum vertical ties are provided and the contact surface is roughened to an amplitude of 5mm.
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6. The ties consisting of single bars and multiple leg stirrups should have a spacing not exceeding ____________
a) 600mm
b) 400mm
c) 1100mm
d) 900mm

Explanation: The ties consisting single bars, multiple leg stirrups or vertical legs of welded face fabric should not have a spacing not exceeding four times the least dimension of the supported element nor 600mm whichever is less the Indian standard code IS: 1343 does not make any specific recommendations regarding the shear stresses in composite sections.

7. If the surface is rough tamped and without links to withstand a horizontal shear stress of 0.6n/mm2 and assuming the moduli of elasticity of precast and insitu cast concrete to be equal the centroid of the composite section is located 110mm from the top of the slab, second moment area of composite section is 2487×105mm4, calculate ultimate shearing resistance?
a) 14
b) 12
c) 18
d) 21

Explanation: vu = ultimate shearing force, τ = vus/ln, s= (350x30x95)mm3, b = 80mm, τ = 0.6n/mm2, vu = (0.6x2487x105x80/350x30x95) = 12000n = 12kn.

8. Design ultimate horizontal shear stress with nominal links and the contact surface are as cast (assume τ = 1.2n/mm2)?
a) 15kn
b) 23kn
c) 12kn
d) 24kn

Explanation: The ultimate shear resistance is expressed as vu = (τlb/s) = (1.2x2487x105x80/350x30x95) = 24000n = 24kn, τ = 1.2n/mm2.

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