# Design of RC Structures Questions and Answers – Working Stress Method

This set of Design of RC Structures Multiple Choice Questions & Answers (MCQs) focuses on “Working Stress Method”.

1. Working stress design method is a method for plain concrete where concrete is assumed to be non-elastic.
a) True
b) False

Explanation: The Working Stress Method is a traditional method of design used for reinforced concrete design where it is assumed that concrete is elastic; steel and concrete acts together elastically. The relationship between loads and stresses is linear up to the collapse of the structure. The basis of the method is that the permissible stress for concrete and steel are not exceeded in the structure anywhere when it is subjected to the worst combination of loads.

2. Which of the following is not an assumption for working stress design method?
a) Tensile strength of concrete is considered
b) Bond between steel and concrete is perfect within the elastic limit of steel
c) Concrete is elastic
d) A section which is plane before bending remains plane after bending

Explanation: The working stress method is based on the following assumptions:
i. A section which is plane before bending remains plane after bending,
ii. Bond between steel and concrete is perfect within the elastic limit of steel,
iii. Tensile strength of concrete is ignored,
iv. Concrete is elastic,
v. The modular ratio has value of (280 / 3 σcb).

3. Which of the following IS Code has described about working stress design method?
a) IS 10626
b) IS 456
c) IS 4031
d) IS 800

Explanation: The Indian Code IS 456 has given working stress method in Annex B give greater emphasis to limit state design. This code uses a factor of safety equal to 3 on the 28-days cube strength to obtain the permissible compressive stress in bending in concrete. And equal to 1.78 on yield strength of steel in tension to obtain the permissible tensile stress in reinforcement. So for properly designed structural elements, the stresses computed under action of working loads will be within the elastic range.

4. Which of the following equation expresses the working stress method for reinforced concrete?
a) μR > 4L
b) μR > (L / 2)
c) μR > 2L
d) μR > L

Explanation: The working stress method can be expressed by the equation as:
μR > L
Here,
μ = inverse of factor of safety which is less than unity,
R = resistance of the structural elements and
L = working loads on the structural elements.

5. Working stress method is a simple method only for the design of simple structures.
a) True
b) False

Explanation: Working stress method is a simple method both in concept as well as in application. The simplicity of this method is its advantage. Due to this reason, it is still used for design of some complex structures such as overhead water tanks. It is a reliable method.

6. Working stress method knowledge is essential for Limit state method.
a) True
b) False

Explanation: It is essential to have knowledge of WSM, since it forms a part of Limit state method. The Indian standard 456-2000 has both the methods incorporated in it. But the concept of WSM is retained for checking serviceability states of deflection and cracking. The design usually results in large sections of structural members as compared to LSM. Due to this, structure design by WSM gives better serviceability performance.

Sanfoundry Global Education & Learning Series – Design of RC Structures