Prestressed Concrete Structures Multiple Choice Questions on “Principles of Dimensioning”.

1. The design values of the resistance must equal or exceed the sum of ____________

a) Design deflection

b) Design loads

c) Design bars

d) Design cross section

Answer: b

Clarification: In the design of prestressed concrete member, the minimum required resistance is predetermined for certain limit states such as collapse, deflection and cracking for each of these, the design values of the resistance must equal or exceed the sum of the design loads obtained by multiplying the specified characteristic loads by the appropriate partial safety factors.

2. The design strength of the material being known, the problem generally reduces to the determination of ____________

a) Dimensions

b) Displacements

c) Parameters

d) Length

Answer: a

Clarification: The design strength of the material being known, the problem generally reduces to the determination of suitable dimensions for the member, that is the cross sectional details followed by the design of prestress required and the corresponding eccentricity and area of reinforcement for the section.

3. The trial and error method of assuming a certain section and checking its resistance is often ____________

a) Easy method

b) Time consuming

c) Reverse method

d) Direct method

Answer: b

Clarification: The trial and error method of assuming a certain section and checking its resistance using the appropriate design formula is often time consuming since a section satisfying the requirements at the serviceability limits may be deficient at the limit state of collapse.

4. A direct method for computing the leading dimensions of a section is often feasible as in the case of ____________

a) Pure flexure

b) Partial flexure

c) Total flexure

d) Unpure flexure

Answer: a

Clarification: The direct method for computing the leading dimensions of a section is feasible in case of pure flexure where the necessary effective depth and breadth of the compression face are controlled mainly by the collapse limit states.

5. In the case of flanged member on the basis of collapse the width and depth of the compression flange is?

a) Constant

b) Zero

c) Fixed

d) Increased

Answer: c

Clarification: In the case of flanged member on the basis of collapse the width and depth of the compression flange is, while the thickness of the web is based on ultimate shear or a practical consideration of having curved cables with minimum cover requirements.

6. The minimum prestressing force required and the corresponding eccentricity are controlled by the serviceability limit states at which the stresses are not to exceed the ____________

a) Permissible values

b) Constant

c) Zero

d) Limited values

Answer: a

Clarification: The minimum prestressing force required and the corresponding eccentricity are controlled by the serviceability limit states at which the stresses are not to exceed the Permissible values are these values are permitted or limited to a certain extent.

7. The limit states of deflection rarely influence the design of prestressed members?

a) Class 4

b) Class 3

c) Class 1 and 2

d) Class 5

Answer: c

Clarification: The limit states of deflection rarely influence the design of prestressed members Class 1 and 2 since the members will be normally uncracked at service loads and in addition a pre camber will be provided by the initial upward deflection due to the prestress.

8. In case of member subjected to axial tension, the concrete section and the minimum prestress are mainly controlled by?

a) Permissible stress

b) Transverse stress

c) Strain

d) Principle stress

Answer: a

Clarification: In case of member subjected to axial tension, the concrete section and the minimum prestress are mainly controlled by Permissible stress at the service loads and in some cases (walls of tanks) by practical considerations.

9. The dimensioning of prestressed members subjected to axial load and bending is governed by ____________

a) Permissible stresses

b) Neglected stresses

c) Allowable stresses

d) Ranged stresses

Answer: c

Clarification: The dimensioning of prestressed members subjected to axial load and bending is governed by stress condition equations formulated for the opposite extreme faces of the section or by the aid of design charts for the different cases of members with uniform or non uniform prestress.

10. The required cross sectional dimensions and the prestress may be determined by solving ____________

a) Stress conditions equations

b) Multiple equations

c) Single equations

d) Unique equations

Answer: a

Clarification: Stress condition equations formulated for the opposite extreme faces of the section or by the aid of design uniform or non uniform prestress are solved for determining required cross sectional dimensions and the prestress.