Prestressed Concrete Structures Questions and Answers – Strain Compatibility Method

This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “Strain Compatibility Method”.

1. The estimation based on compatibility of the strain of prestressed concrete involves __________
a) Flexural strength
b) Tensile strength
c) Compressive strength
d) Bulking strength

Explanation: The method by which the flexural strength of prestressed concrete is estimated based on the compatibility of strains and equilibrium of forces acting on the section at the stage of failure is known as strain compatibility method.

2. The distribution of concrete in the strain compatibility method is?
a) Aligned
b) Curved
c) Linear
d) Bent

Explanation: The distribution of concrete strain is linear (plane section normal to axis remains plane even after bending), the basic theory is applicable to all structural concrete sections whether reinforced or prestressed and some assumptions are made.

3. The resistance of concrete is neglected at __________
a) Tension
b) Compression
c) Shear
d) Breakage

Explanation: The resistance of concrete in tension is neglected in strain compatibility method at the end of the section, the maximum compressive strain in concrete at failure reaches a particular value are the assumptions made in strain compatibility method.

4. The stress distribution in the compression zone of concrete can be defined by means of __________
a) Specific gravity
b) Coefficient
c) Modulus of elasticity
d) Span moment

Explanation: The stress distribution in the compression zone of concrete can be defined by means of coefficients applied to the characteristic compressive strength and the average compressive stress and the position can be assumed.

5. The flexural compression stress in the compressive zone follows the __________
a) Block curve
b) Anchorage curve
c) Mid span
d) Stress strain curve

Explanation: The flexural compressive stress in the compressive zone closely follows the stress strain curve of concrete and the properties of the concrete stress block can be expressed in terms of the characteristic ratios of k1 & k2.
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6. The stress-strain characteristics of steel used as prestressing tendons are necessary for __________
a) Principal computation
b) Stress computation
c) Flexural computation
d) Strain computation

Explanation: Knowledge of the stress-strain characteristics of steel that is used as prestressing tendons is necessary for flexural strength computations by the strain compatibility method and a typical short- term design stress-strain curve for concrete recommended in the British & Indian standard codes.

7. The number of steps to be followed in the strain compatibility method is?
a) 4
b) 7
c) 10
d) 6

Explanation: The major steps to be followed in the strain compatibility method are summarized below compute the effective strain, assume a trail value for the neutral axis, using the stress-strain curve for steel compute the total compression Lu & tension Tu, if the compressive and tensile forces are equal, evaluate the ultimate moment Mu.

8. Who suggested a graphical version compatibility method?
a) Cornd
b) Morsch
c) Lin
d) Musy

Explanation: Morsch has suggested a graphical version of the strain compatibility method in which the failure of the compressive zone is assumed when the extreme compressive fiber reaches a strain limit of 0.2%, many codes have recommended simplified procedures for calculating the flexural strength of concrete sections which are reinforced with high tensile steel in the tension zone.

9. How much percentage of tensile strain is assumed at the failure of under reinforced sections?
a) 0.7%
b) 0.5%
c) 0.4%
d) 0.2%

Explanation: For under reinforced sections, the failure of the prestressing steel is assumed to take place at a maximum tensile strain of 0.5% however the method can be considerably simplified under reinforced sections, in which the stress in tensile stress at the collapse stage is more or less equal to the characteristic tensile strength of tendons.

10. The strain compatibility method is generally applicable for __________
a) Under & over reinforcement sections
b) Partially prestressed sections
c) Mid span sections
d) Fully prestressed sections

Explanation: Many codes have recommended simplified procedures for calculating the flexural strength of concrete sections which are reinforced with high tensile steel in the tension zone; the use of the strain compatibility method, generally applicable for both under & over reinforced sections is illustrated.

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