# Design of RC Structures Questions and Answers – Limit State Method

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

1. Which of the following method takes into account the serviceability requirements?
a) Working Stress method
c) Limit State method

Explanation: The Ultimate load method accounts for safety but not satisfactory serviceability requirements at service loads. The limit state design method is an ideal method and accounts not only for ultimate strength of structure but also the serviceability and durability requirements. This method avoids the demerits of other methods.

2. Limit state is the limit of safety requirements before failure occurs.
a) True
b) False

Explanation: In the method of limit state of design the limit state is the acceptable limit of safety and serviceability requirements. This limit is before the failure of the structure occurs. There are two prominent types of limit state considered in design namely Limit state of collapse and Limit state of serviceability.

3. Which of the following is not a limit state of collapse?
a) Premature cracking
b) Limit state in shear
c) Limit state in flexure
d) Limit state in torsion

Explanation: The limit state of a structure can be assessed from rupture and from buckling due to elastic or plastic instability or overturning. The limit states of collapse considered in design are: Limit state of collapse in flexure, shear, compression and torsion.

4. The resistance to axial load should be less than combination of loads on the structure.
a) True
b) False

Explanation: The resistance to bending, shear, torsion and axial loads at every section should not be less than the appropriate value of loads at that section. This value is produced by the most unfavorable combination of loads on the structure using the appropriate partial factors.

5. Which of the following is not considered in limit state of serviceability?
a) Excessive cracking
b) Excessive deflection
c) Excessive compression
d) Excessive vibrations

Explanation: The limit state of serviceability includes: excessive deflection, excessive cracking and excessive vibrations. Out of these, the important limit states of serviceability are excessive deflection and excessive cracking.

6. Cracking of concrete adversely affects the appearance of the structure.
a) True
b) False

Explanation: The deflection of structure does not adversely affect the appearance or efficiency of the structure or finishes or partitions. Also cracking does not affect the appearance or durability of the structure. The limit state of excessive deflection and cracking is applicable only at service loads. It is estimated by elastic analysis.

7. Which of the following is used to denote the characteristic strength of concrete?
a) fy
b) fck
c) fx
d) fc

Explanation: The characteristic strength is the strength used for design of concrete it is that value of strength of material below which not more than 5% of the results are expected to fall. It is expressed by symbol (fck) and measured in (N/mm2). The value of this strength is different for different grades of concrete.

8. Which of the following is design strength of the material?
a) (f / γm)
b) (f / 2γm)
c) (f / 1.15γm)
d) (f / 1.5γm)

Explanation: The design strength of the material (Fd) is given by:
(Fd) = (f / γm)
Here (f) is the characteristic strength of material that is (fck) for concrete and (fy) for steel.
m) is the partial safety factor for the material and according to the limit state.

9. What is the value of partial safety factor for steel in assessing the strength of a structure?
a) 1
b) 1.50
c) 1.15
d) 1.2

Explanation: When assessing the strength of a structure or structural member for limit state of collapse, the value of partial safety factor (γm) is taken as:
mc) = 1.5 for concrete and
ms) = 1.15 for steel.

10. Characteristic load is that value of load which has a 96% probability of exceeding in the lifetime.
a) False
b) True

Explanation: The characteristic load is that value of load which has a 95% probability of not being exceeded during the lifetime of the structure. Since the sufficient data is not available to express the loads in statistical terms, loads given in various codes are assumed as the characteristic loads.

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